Jason Cromer: 800-498-2301 Sam Taylor Buick/Cadillac, Ft. Walton Beach, FL
The sensor resides on the RH side (passenger) of the engine block, in the coolant drain location. The F-body uses only one sensor. Other body platforms may use two sensors on their LT1 applications.
On the 1994-1997 LT1 F-body PCM, there is a replaceable module that receives the knock signal. 1993 ECM's have the receiver circuitry built-in to the computer and have no replaceable module.
You may have heard about an LT4 knock module. This module came from the 1996 LT4 Corvette, that had roller rockers as standard equipment. The LT4 module is tuned to allow for the noise the rockers make (not perceiving it as knock). If you have similar valvetrain modifications on your LT1, it may be a good idea to swap to the LT4 module to reduce the chance of "false knock" (knock not related to detonation).
The LT4 module can be used on 1994-1997 engines (OBD-I and II) and no change of the knock sensor is needed (even though the sensors changed in 1996). There is no specific LT4 knock sensor. However, there are differences in the impedance of the sensors between OBD-I and II as listed in the testing section below. You must use the sensor that is matched to your OBD type (or have a wiring modification as frequently done in an OBD type swap situation).
Key OFF. Connector off at the knock sensor. Measure the resistance between the KS terminal and ground. Resistance should be between 3300-4500 ohms (OBD-I) or 93k-107k ohms (OBD-II). If it is not, the sensor is faulty or the sensor is not making good contact with the block. Try another resistance reading from the sensor terminal to the outside metal of the sensor body.
If all that is good, it might be a faultly knock module (in case of 94-97) or a problem with the computer, itself.
OBD-I (1993-1995) knock sensor GM PART # 10456126 ACDelco #213-96
OBD-II (1996-1997) knock sensor GM PART # 10456287 ACDelco #213-325
Note: It is possible that the LOW COOLANT lamp may come on after this procedure. It should go out after the engine has gone through several heat and cool cycles. Make sure that the remote reservoir is kept at the proper level. If the light seems to come and go, make sure the level in the remote reservoir is proper. Normal operation of the cooling system often causes coolant from the radiator to overflow into the remote reservoir. As the engine cools down, the radiator creates a vacuum and pulls this coolant back into the radiator. The piping from the neck of the radiator to the reservoir must be air tight for this to occur. Since these cars are getting older, it is not uncommon to get a small leak in the pipe that goes under the battery. Acid wears away at the pipe until it makes a hole. Even a small hole is enough to cause problems. A telltale sign is a small amount of coolant under the right front of the car after it is parked a while. Usually, only taking out the battery will reveal where it is coming from, because it slowly drips on the splash panel underneath and may travel along to another area to drip off.
If the lamp is coming on for no apparent reason (you have verified coolant level is fine-that is, checked the level in a cold radiator and verified you have the proper level in the remote reservoir), you have just a few choices: The thermostat only has control of opening temp to allow coolant flow, after that it does nothing but cause a predetermined amount of restriction in the flow. To make the most of the lower temperature thermostat, it should be accompanied by reprogramming of the fans, so that they will come on at a lower temperature. This will help to maintain a lower overall temperature in all driving conditions (especially when stopped in traffic). It is not mandatory that you do this and a 160?can be installed by itself with no other modification. The hydraulic lifter has an internal plunger that has a specific amount of travel. On stock engines, the purpose of preload is to compress the plunger so the pushrod will be riding on a "cushion" (acts like a shock absorber). With stock lifters, turning the rocker nut another ?to ?turn, will normally put you in the ballpark for quiet operation without being too tight and the adjustment should last a long time. Specific lifters like the Comp Cams "Comp R's", have less internal travel. ?turn preload is more than plenty, with 1/8 or just barely any preload being better for high revving engines. Comp actually recommends .002-.004 preload on a warm engine. There are several methods for setting the lash with the engine not running and are listed below. Read through them all. You might prefer one method over another. They all accomplish the same thing. When the arrow is at 12 o'clock you will be at either #1 or #6 TDC. You might have trouble identifying whether #1 or #6 is at TDC when the crank arrow is at 12 o'clock. Probably the easiest way is to look over the other valves or lifter positions. Compare them to the charts below, showing which can be adjusted. Any valve that can be adjusted should be UP (closed) and the lifter/pushrod should be down. Valves that are not to be adjusted will be in varying degrees of being open or DOWN (lifters/pushrods UP). I used to recommend looking at the valves on the #1 and #6 cylinders, but sometimes it can be difficult to tell by those cylinders only. After looking at the charts below and your valves or lifters/pushrods, you should have it figured out rather quickly.
Continue the above procedure for each cylinder until all valves are adjusted to the same amount of preload. This procedure will work for any hydraulic lifter cam with adjustable rocker arms. Refer to this diagram posted above if you need visual reference. If you don't see the proper ac voltage the problem could be the optispark, the harness to the optispark, the PCM or any of the wiring in between. Visually inspect all the connections you can get to for poor contact or corrosion.
edited 5/16/2004
Normal pressure when the engine is not running and lines have been pressurized is 41-47 psi. This same pressure should be observed at wide open throttle (WOT). WOT can be simulated by removing the vacuum hose to the regulator at idle. At idle (because of the effect of the vacuum to the regulator) pressure will be less than what you observe with the vacuum line off. There may be anything from a 3 to 10 psi difference. Note: any indication of fuel in the vacuum line to the regulator, means the regulator is leaking and should be replaced. Check the line for fuel or the smell of fuel.
To fully determine that you don't have a pressure drop off during actual WOT situations, you should tape the gauge to your windshield and take it for a test run. This will tell you if the pump can meet actual fuel flow demands at pressure and not just at a simulated WOT condition (as when removing the vacuum to the regulator).
When you have a gauge connected and the pressure looks initially good and then bleeds off quickly when you shut the engine off, you can do a couple of tests to help you figure out where the pressure loss is.
What the factory manual says to temporarily install, is a set of "fuel line shut off adapters" (probably something the normal guy is not going to have available). You remove the fuel lines from the rail and connect these valves in between. This lets you shut off either side of the lines for testing.
You can do the same thing by pinching the flexible lines to shut them off, but risk breaking them. You might be able to do it (your risk) by using a needle nose vise grips and putting some scrap hose as cushions on the jaws. Then use that to clamp off the line just enough to seal it. Obviously, this is not the best way to shut off the lines and could result in breakage. Heat and age can make the hoses brittle. If you don't want to risk it, don't. It's just a suggestion.
You can use the fuel pump prime connector for pressurizing the system (jumper 12v to it to run the pump).
Watch your gauge as you jumper the prime connector. When you have good pressure remove the jumper and clamp off (or use shut off valve) the fuel supply line (3/8 pipe). If pressure holds, you have a leak on the feed line somewhere before it gets to the clamp (or shut off valve) or at the check ball in the pump. If it still goes down, release your clamp (or open shut off valve). Pressurize the system again, then remove the jumper and this time clamp (or shut off) the return line (5/16 line). If pressure holds, then the regulator is faulty. If pressure does not hold, you need to locate leaky injector(s).
If you can't tell a leaky injector from reading the plugs, you can look and see if injectors are leaking by removing the fuel rail screws and pull the rail and all the injectors up, so you can see under them. Leave them over the injector ports. Pressurized the system and look under the injectors to see if any are dripping. Typically, when the gauge reads: Avoid running your car out of fuel! The fuel also acts to keep the pump cool. Running out of fuel can trigger a pump failure.
If you are having a problem not related to the "normal" way the gauge acts as stated above, there are some things you can check. approximate: To test back to the gauge, ground the purple wire on the body side of the connector back toward the gauge (key ON). The gauge should read empty. With the connector unplugged and no ground applied, the gauge should read full. It is NOT recommended to to push or pull on the pintle of an IAC that has been in service. The force required can damage the threads on the worm drive. Also, do not soak the IAC in any liquid cleaner or solvent, as damage may result. When installing a new IAC, you may move the pintle to match the measurement of the old one. The force required to move a NEW valve will not cause damage to it. Use engine oil to lubricate the o-ring. Tighten attaching screws to 27 lb. in. An easy way to tell what part of the system may have trouble is to go to the vacuum check valve and test the lines back to the mode selector, intake manifold and to the vacuum tank. The check valve often cracks and is the source of a leak, so be sure to inspect and/or test it.
A hand held vacuum pump (like a Mityvac), makes testing pretty easy (your lungs can be used as an alternate vacuum source ;-) ). At the check valve, remove the hoses one at a time and apply vacuum to each and see if it holds. The line to the intake manifold will have to be removed at the manifold and plugged back toward the check valve for you to test the line for leaks. If you find a leak on a particular hose, you will have to trace out the cause on that section.
1996-1997 f-body cars have two cats.
1993-1995 LT1 f-body cars are all OBD-I (regardless of how many cats they have).
1993 LT1 f-body cars can flash trouble codes by shorting 2 pins in the DLC and observing the Service Engine Soon lamp (like most earlier model GMs). 1994 and later must use a scan tool. The computers changed from ECM (Engine Control Module) in 1993 to PCM (Powertrain Control Module) in 1994 and later (adding electronic transmission control). Though 1993 and 1994 were both OBD-I, they used different computers. 1993s used the replaceable chip type (PROM), while 1994 and up used flash memory for storing the program (EEPROM).
1996-1997 LT1 f-body cars are OBD-II.
1993 LT1 f-body cars have two 1 wire, non-heated O2 sensors. 1994-1997 have two 4 wire, heated O2 sensors (with 1996-97 cars having two additional rear (post cat) O2s to comply with OBD-II). On the f-body, front O2s use a flat connector. When rear O2s are present, they use a square connector.
The only 1995 f-body engine that is OBD-II is the 3.8L V6 that came out during the model year (replacing the 3.4L V6 that was OBD-I).
RPO NA5 = Federal Emissions System
RPO NB6 = California Emissions System
Wholesale prices and no rip-off shipping.
Dal Slabaugh: retired as of 12/1/2007
Best wishes and thanks for all the years of service to the GM community!
The Keyless Entry Receiver is capable of accepting Vehicle Access Code (VAC) programming from any two random Transmitters. One or two Transmitters can be programmed. When two Transmitters are programmed, they must be programmed during the same program sequence, one after the other but not simultaneously. The Transmitter is manufactured with a permanent VAC combination (one of over 4 billion combinations) that cannot be changed for the life of the Transmitter. The Receiver can only be programmed by the Transmitter when it is powered at the Battery input at connector C2 terminal "F" and the program input line is grounded to connector C1 terminal "A".
Programming procedure:
Important
NOTE: Always program both transmitters when replacing a lost or damaged transmitter. The first transmitter code programmed will always be in both memories until a second transmitter is programmed within the same sequence.
Action
Normal Results
The BCM can display a series of DTCs, when it is placed in the diagnostic mode. These DTCs are displayed as flash codes through the "Security" indicator lamp on the instrument cluster (much like the 1993 and earlier OBD-I codes are flashed on the SES lamp). During normal operation, if the BCM detects a fault on a monitored circuit, there will be no flashing or any indication that a fault has occurred, though you might detect a system malfunction. The system faults will be recorded as "Current" or "History". A "Current" DTC means that the condition was present when the diagnostic mode was entered. A "History" DTC means the condition has occurred since the BCM was installed in the vehicle, but may not be present currently. If a "Current" DTC is present, the associated "History" DTC will always be present. When you work on systems associated with the BCM, you should always check for DTCs.
Diagnostics is entered by performing the following steps:
The BCM will begin to flash DTCs 4 seconds after entering the diagnostic mode, from the programming mode. Each flash of the "Security" indicator lamp on the I/P represents a number. For example, one flash followed by two quick flashes represents a code 12. Each code is displayed 3 times before the next code is displayed. Any DTCs present are displayed in numerical order. Once the last code is displayed, the list begins over again with the first code. The display continues until the diagnostic mode is exited.
History DTCs are those indicating that the BCM previously detected a fault with later disappeared. Any DTC that has a 3 as its first digit is a History DTC. The reason could be that the fault is a true intermittent only happening occasionally or that the system which the DTC monitors is not currently being operated.
If a visual physical check does not find the cause of the concern, the vehicle can be driven with a DVM connected to the suspected circuit. An abnormal voltage or resistance reading when the concern occurs indicates the concern may be in that circuit.
"Current" DTCs (21-25) will remain stored and display as long as the BCM detects the fault criteria. "History" DTCs (31-35) can be cleared by pressing the door lock switch for a period of 4 seconds while the BCM is in the diagnostic mode. The chime will sound 3 times at the end of the 4 second period as a confirmation that the DTC(s) have cleared.
BCM Schematic for 1996 (1997 probably the same).
BCM DTC
DESCRIPTION
12
Begin Diagnostic Display
21/31
Courtesy Lamps Feed (Circuit Shorted to Ground)
22/32
Courtesy Lamps Return (Circuit Shorted to Battery +)
23/33
Retained Accesory Power (Circuit Shorted to Ground or Battery +)
24/34
Fasten Seatbelt Indicator Lamp (Circuit Shorted to Ground or Battery +)
25/35
Security LED present (with AU6 only)
41
Last Transmitter Message Received Valid (with AU0 only)
42
Last Transmitter Message Received had Invalid ID (with AU0 only)
43
Last Transmitter Message Received had Sumcheck Error (with AU0 only)
44
Last Transmitter Message Received had Encryption Error (with AU0 only)
45
Receiver Processing Currently in 20 Second Lockout (with AU0 only)
55
Begin Configuration Display
-## Hardware Configuration
-## Software Configuration
Flush procedure:
Bleed procedure:
edited 10/10/2004
튏
튔
Ohms
100
212
177
90
194
241
80
176
332
70
158
467
60
140
667
50
122
973
45
113
1188
40
104
1459
35
95
1802
30
86
2238
25
77
2796
20
68
3520
15
59
4450
10
50
5670
5
41
7280
0
32
9420
-5
23
12300
-10
14
16180
-15
5
21450
-20
-4
28680
-30
-22
52700
-40
-40
100700
Use a Digital Volt Meter (DVM) set to ohms to measure resistance. Note: Use a high impedance meter (at least 10 megohm) when dealing with the PCM. Most modern DVMs will do, but your old analog meter can damage the PCM. It is also a good idea to get a " reference" from the meter you are working with. With the DVM on the ohms scale, touch the two meter leads together and note the ohm reading. It may not always be perfectly zero, but may be within a tenth or two. Now when you take an ohm reading, you will know what the meter will show when there is really no resistance.
If the sensor seems to be ok, you may also need to test at the harness connector for proper lead conditions. Use your test meter set on the dc voltage scale to do this. You will need the key in the RUN position, but don't have to start the car.
Footnote: If you ever have to test the IAT, it operates the same as the two lead coolant sensor. The same temp vs. resistance table above is applicable to the IAT, as well as the +5vdc lead and ground wire at the harness connector.
edited 1/03/2005
The knock sensor system is used for the detection of detonation. The computer retards spark advance based on the amount of knock received. The knock sensor produces an ac voltage according to the amout of knock. The computer receives the signal and it's programming determines how the computer will change the spark advance.
With the connector off the knock sensor, check for 5v on the harness terminal with key ON. Continue if that is good. If not good, check at pin C8 (1993), D22 (94-97) on back of computer. If voltage is ok at the back of the computer, repair the wire from the computer to the sensor.
edited 7/29/2005
Drain
It is always a good idea to keep coolant away from the distributor (optispark) to avoid any potential problems when doing any of this work.
Refill
If, after doing work, you want to verify the coolant level for a few days, check that the level is to the top of the radiator neck when the engine is cold. Add coolant to top it off, if needed. Then, also make sure that the level is correct in the remote reservoir.
edited 3/16/2008
Electric cooling fans attached to the radiator keep the LT1 from overheating when there is little or no air passing through the radiator core (car going very slow or stopped and engine running). It is normal for the temps on the gauge to go up to the middle or past middle of the gauge before the fans kick on. The middle of the gauge is in the range of 210?- 220? With factory programming, the PCM will command low speed fans (or primary fan) "ON" at 226?and "OFF" at 221?and high speed fans (or secondary fan) "ON" at 235?and "OFF" at 230? The fans should come on before it gets to any part of the red zone. (see "dual fan configuration" below about primary and secondary fans)
The f-body LT1 uses a 180?thermostat as stock.
The PCM gets it's temp readings from a sensor that is in the water pump. If the reading the PCM receives is inaccurate, the fans may not come on at the correct time. The PCM also uses this temperature for lookup in fuel calculation tables. If there is a problem that causes the reading to be always low (cold), the PCM will add extra fuel. This can cause hard starting when warm and an overly rich condition when running.
The gauge gets it's information from a sensor that is in the driver's side head. Inaccurate gauge readings can be from this sensor or it's wiring (the wire burned on a header pipe is common). The temp that the PCM sees can be monitored with a scan tool and compared to the gauge reading. They should be close, but don't expect them to be "perfectly" synchronized.
The fans are programmed to come on when the a/c is turned on. A/c Pressure monitoring sensors feed the PCM info and depending on the situation, the PCM may command the fans off for brief periods. Also, when the car reaches sustained higher speeds, the fans may be commanded off so incoming air can flow through the radiator unimpeded and provide the cooling needed.
Fans will also come on when the SES lamp comes on. The PCM does this when certain (most) DTCs are detected to protect the engine from a situation where it may overheat.
There are two versions of the dual fan configuration:
These fans use a two relay architecture that can be seen in the fuse/relay panel that is under the hood.
2 Relay System
PCM Commanded Fan Operation
PCM Wire Color Grounded
Fan Operation
Relay Operated
#1
#2
#3
Primary@226?
Drk Grn @A11
Primary (LH) fan full speed
X
-
n/a
Secondary@235?
Drk Blu @A10
Secondary (RH) fan full speed
X
X
n/a
3 Relay System
Low Speed@226?
Drk Grn @A11
Low Speed (both fans)
X
-
-
High Speed@235?
Drk Blu @A10
High Speed (both fans)
X
X
X
For both fans to operate in either system, both relay leads must be grounded. Grounding only the Drk Blu wire will result in only the RH fan operating at high speed.
Here are some fairly simple things to check for various complaints:
Other cooling issues
The low coolant sensor is a most common cause of complaint. If it gets dirty, it may cause the lamp to come on when the coolant level is actually ok. Sometimes it fails and no amount of cleaning will fix it. The sensor is only connected to the lamp on the dash. It does not report to the PCM and no DTC's will be set. Because of this, some people choose to simply unplug the sensor to get rid of the annoyance without having to fix it. Unplugging it will make the lamp go out, but you will have to monitor the coolant level yourself. As critical as the coolant is to the LT1, having it working makes sense.
Thermostats and cooling
The temp rating of the thermostat is merely at what temp it will begin to open and allow coolant flow. It is purely a mechanical, temperature reactive device and has no external control or monitoring. A frequent reason behind a lower temp thermostat is to be able to make use of more aggressive spark advance without the engine having any spark knock (detonation or pinging). Excessive spark knock is detrimental to the engine. Spark knock is also monitored by the computer and timing advance is pulled (retarded) by the computer. When timing is retarded, performance and power will decline.
There is a fine line between between enough spark advance for high performance and the penalties for too much. The engine temperature plays a role in that the coolant wicks away heat from the combustion chambers in the head. Higher overall engine temperature results in higher overal combustion chamber temperatures. Installing a lower temperature thermostat alone may actually decrease performance because a certain amount of heat is needed to burn the air/fuel mixture efficiently. If you see a decrease in gas mileage with a lower thermostat, alone, this may be the reason. The trick is to lower the temperatures but add enough timing to increase performance over what it was originally.
An often asked question is "Will my engine stay cooler with just a 160?thermostat?". The answer is yes, as long as there is good air flow across the radiator and the cooling system is working efficiently. Note that engine temps will still climb as they did before when you are stopped (as in traffic). However they may not rise as much, since you are starting out at a lower temperature than before. When you are moving again, it will be possible for the temps to lower more than what the 180?thermostat would previously allow. Cruising down the road, your engine should definitely stay cooler than before. Remember that the rated temperature of a thermostat is the temperature that it begins to open. While crusing on a moderate temperature day, an LT1 will generally run 10?20?warmer than the thermostat temp rating. Make sure you use the correct, long LT1 thermostat as described in the troubleshooting section above.
Something else to consider, is that when the engine gets to ~220?(even before the stock fan ON temp of~226? and you are at MAP loads of 70Kpa or more, the PCM begins to retard the timing. That is one reason why people feel their cars don't run well when they are hot. The GM folks built the retard into the spark tables because when the engine is hotter, there is more chance for spark knock. If you can keep the temperatures from getting up into that range, then you might feel more power when you need it.
Altering the fan ON temps can be done through reprogramming the computer or an aftermarket "fan switch" such as sold by SLP and JET . Manual fan switches can also be wired up to operate the fan relays so that the fans can be operated at any given time the driver wants (like in staging lanes). There are explanations on how to wire the manual switch up on the 'net and there are even a couple of wiring diagrams on my main Tech Page. If you look at the fan schematics, you can probably see that there can be several solutions to operating the fans manually, either by controlling the relays (my preference) or powering the fans directly with 12v and a switch.
edited 9/06/2007
Do this when the engine is cool (like after sitting overnight or for several hours where there is no residual pressure in the system). This way there will be no need to drain any extra coolant from the system.
8/05/2005
T56 Service Manual (pdf format)
Right click if you want to download and save
Left click to view online
Zero lash is when you go from having slack between the lifter, pushrod and rocker arm, to the exact point of no slack. The lifter needs to be on the base of the lobe when setting valve lash. When a cylinder is at TDC, both lifters should be at the bottom of their travel (base of the cam lobe).
Gauging zero lash by hand is not an exact science. When setting the valve lash with the engine not running, you can get close enough by doing the "spin the pushrod" method. Loosen the rocker arm until you can feel slack in the pushrod to rocker arm. Spin the pushrod with your fingers while tighening the rocker arm back down. When you BEGIN to feel drag while spinning the pushrod, you are at zero lash. Once zero lash is reached, stop and add your preload. DO NOT go back and try to feel the adjustment. The lifter will immediately begin to bleed down a little. Tension on the pushrod will relax and this will make it seem like your adjustment did not work. If you want to recheck zero lash, you must loosen the rocker arm nut and tighten it down again while spinning the pushrod as before. At that point you want to set the preload and LEAVE IT ALONE.
For reference:
3/8" stud: ?flat = .003472"
7/16" stud: ?flat = .00416"
Rotating the nut 1/6 of a turn (until the next flat side is in the same position as the previous flat side) is a "flat".
Consequences of improper adjustment:
Too tight - the valves will not completely close and you will lose compression. The engine will run rough, if it will run at all.
Too loose - the rocker arms will make noise from the slack and pushrods could be dislodged. Possible damage could occur from either extreme.
Some like to adjust the rockers while the car is idling. If you wish to do this, loosen one rocker at a time until you can hear it click. Tighten the nut, but don't exert downward pressure on the rocker arm with your socket. At the point when audible clicking is gone, tighten the nut another 1/4 turn for your preload (Comp R lifters, less as noted above).
If you have never had the crank hub off (or know for sure that it's orientation is correct), you can use the arrow that is on the balancer to tell you where you are. You don't have to spin the crank every 90?with this method.
When at #1 TDC you can adjust the following valves:
Intake: 1, 2, 5, 7
Exhaust: 1, 3, 4, 8
Rotate the crank one revolution until the pointer is again at 12 o'clock. This will let you adjust the remainder of the valves. If you did #1 the previous time, you should be now at #6 TDC.
When at #6 TDC you can adjust the following valves:
Intake: 3, 4, 6, 8
Exhaust: 2, 5, 6, 7
If you want to set the lash by bringing each cylinder to TDC, watch the valves and the pointer on the balancer and follow the Firing order:
1-8-4-3
6-5-7-2
Adjust both intake and exhaust of the cylinder that is at TDC. You will have to make 2 revolutions of the crank, stopping at 1/4 (90? turn intervals for each cylinder.
Another cylinder by cylinder method that does not require looking at the balancer position, follows:
(A remote starter switch is quite helpful)
Here is something additional for those that use "poly locks" (typically used with roller rockers).
Since the poly lock is not a prevailing torque fastener like the nut used with the stock rocker and ball arrangement, it spins freely on the rocker stud. This gives you an advantage to finding zero lash. With the allen lock backed off, spin down the nut until it just stops. This is very close, if not right on zero lash in most cases. Check your pushrod for proper movement and play with it to get a feeling just how snug or loose the nut should be to obtain zero lash. Once you do that, you can just use the nut to reach zero lash and not have to worry about messing with the troublesome pushrod. This will speed up your valve adjustment.
Another aide is to make a mark on the top of the nut so that you can easily see how far you have turned the nut. I always found it a little difficult to obtain the exact amount of rotation on the nuts under the cowl, because of there being less room to swing a ratchet or other tool handle. I used a little dab of white paint on the top and was easily able to tell when I made a half turn or whatever was needed. Now, I can just use a wrench to tighten the nuts, then throw the allen wrench on it and snug the set screw down (while holding the nut).
Some like to run the allen set screw down and then tighten it and the nut together. If you overdo it this way, you may break the nut. I always have good luck with setting the nut and then the set screw. With all the variables in making adjustments to hydraulic lifters like the number of turns for preload, methods of finding zero lash and trying to see what you are doing under the cowl, slight errors are common. Just try to be as consistent as possible and use the method that works best for you.
edited 1/6/2008
The opti has two functions in the spark process. The first thing that happens is as the cam turns, the optical section of the optispark picks up the signals by the rotation of the shutter wheel. The pulses are sent to the PCM via the optispark electrical harness. The PCM processes the signals along with other sensor input and determines the proper time for the coil to fire. The PCM sends a signal to the Ignition Control Module (ICM) and it, in turn, causes the coil to fire. The spark from the coil travels through the coil wire back to the secondary ignition section of the optispark (cap and rotor), to be distributed to the proper cylinder.
If the opti is never sending the signal to the PCM, the PCM will never send a signal to fire the coil.
Here is some testing you can do. Refer to this diagram.
Disconnect the ICM connector. Leave coil connected.
Turn key to ON.
Check for dc voltage with a digital meter at harness terminal "A" to ground and and also "D" to ground. Note: Use a high impedance meter (at least 10 megohm) when dealing with the PCM.
Result should be 10v dc or more on both terminals. If you get no voltage, use the diagram and chase back toward the coil and the ignition fuse. Power for the ICM comes from the ignition fuse and through the coil, so any of that could be bad.
If you have good voltage, switch the meter to ac scale and connect test leads to terminal "B" and to ground. Observe meter while cranking the engine. You should see between 1 and 4 volts ac (those are the pulses that trigger the coil to fire).
Pellet Code
Key Resistance in Ohms
Nominal
Low
High
1
402
386
438
2
523
502
564
3
681
654
728
4
887
852
942
5
1130
1085
1195
6
1470
1411
1549
7
1870
1795
1965
8
2370
2275
2485
9
3010
2890
3150
10
3740
3590
3910
11
4750
4560
4960
12
6040
5798
6302
13
7500
7200
7820
14
9530
9149
9931
15
11800
11328
12292
Use a multimeter to check the resistance of the pellet in the key and compare to the table above. Touch the meter leads to each side of the pellet on the metal bar. The nominal reading is the ideal reading. It most likely will be in the range delimited by "low" and "high". There are 15 different key pellets used. Use this information when you need to get a new key made or for finding a resistor if you wish to bypass the system.
edited 1/24/2005
Some people have reported ignition problems that seem to be heat related. One item that can be relieved of some heat stress is the Ignition Control Module (ICM). Merely spacing the coil and ICM bracket away from the cylinder head has solved miss problems in some cases. Any time you can reduce the amount of heat in an electronic component, it will normally prolong it's life and allow for more stable operation.
Getting to the coil and coil replacement is covered elsewhere in my Tech Pages, so I am not going to step through that procedure.
On my 1995 Z, I used a very simple approach to creating some space between the coil bracket and the head. I used some common 3/8" flat washers that I already had laying around. After removing the coil and studs, I put 2 washers between the "stud nut" and the cylinder head on the inboard stud. There is also a bracket for the EVAP hose that goes on this stud to take up some room. I used 3 washers on the outboard stud. With the thickness of the washers I had, this made the distance on each stud approximately the same (approximately 3/16").
The washers are used, because without the coil bracket sandwiched on the stud, the threads would bottom out in the head. This just gives a little extra space, which is not a problem.
Once the washers are in place and the studs screwed back in, you can mount the coil on the outside of the stud nut, instead of the inside where it was before. Torque value for both the stud to head and the nut is 18 lb. ft.
The total gap came out to about 1/2". Note that one of the studs has more threads on the outside portion of the stud nut. This is the stud that goes in the outboard head hole and is longer to accomodate the ground straps attached to it.
Another note: 1993 owners may have a bolt instead of a stud on the inboard side and others may have identical studs on both sides. It really does not matter. The intent is to create an air space between the head and the coil bracket. A little ingenuity and a couple of additional fasteners may be needed.
Tighten up the fasteners and reconnect electrical harnesses and you are done. I don't have any dyno runs or temperature comparisons for before and after, but for next to nothing in cost, this mod can't hurt.
I am not the first one to do this and it could be done using other methods and materials (perhaps, even more effectively). This just happens to be the way I did mine.
Update: At least one person monitored the temperature of the ICM and the head after the mod. With the engine running, the ICM stayed cooler, but when the engine was turned off, the ICM did not dissipate heat as fast as the head did. I did not get any info on how long the ICM stayed hotter. I am just providing that for your information and you can draw your own conclusions.
5/10/2003
If you have issues you need to track further, a leakdown test will be able to tell you whether rings, valves or head gasket might be leaking.
edited 5/10/2003
A fuel pressure test gauge can be bought at your local auto supply for ~$35. Attach it to the schrader valve that is on the fuel rail. Schrader valve location on 1994-1997
edited 2/05/2007
Most people notice that the fuel gauge does not read in a linear fashion. It will stay on the full side for a long time and then once it starts moving, it will drop rapidly. This is due to the shape of the tank and the placement of the float assembly/gauge sender unit. The tank has a bit of a wedge shape to it, that causes there to be more volume in the upper part of the tank than in the lower. The float only reacts to an up and down level and does not compensate for the tank shape.
Locate the pump electrical connector on the rear of the floor pan under the car (above the LH axle tube). It has purple, gray and black wires going toward the fuel tank. Unplug the connector. With a meter set to ohms, read resistance between the black and purple wires going to the tank.
The readings should correspond to your gauge. If the reading(s) seem accurate to what you have in the tank, the sender is ok. If they don't, the sender or wiring from that connector to the sender has a problem.
edited 2/22/2005
Note that the 1993 IAC has a square electrical connector and the valve screws into the throttle body, instead of being held on by screws like those of later years.
edited 4/15/04
This is a common fix for when the air no longer blows out the vents. When there is not enough vacuum to operate the actuators, they will only direct air to the floor and defrost ducts by default. Diagram of HVAC system.
edited 4/13/2004
Late model 1998 and up axles used a smaller hub center on the rear axles. Therefore the wheels were made with a smaller hub opening on the back. When you try to swap these wheels onto an earlier model 4th gen, the center of the wheel won't fit over the rear axle hub. The wheel has to be relieved a small amount to allow it to slip on. You can dry fit the wheel to "mark" where the interference is, then you will be able to see the area that needs attention. Use a Dremel, sandpaper or even a half-round file to take of the little bit that is required. It does not have to be perfect, as the wheels are centered by the conical lug nuts, not the hub and that part of the wheel is never visible. Just relieve it enough to get the wheel on/off easily. If you ever intend to rotate your tires, you will want to do this to all four wheels (The fronts will fit without any modification. There are no clearance issues with them). Don't ever try to force the wheel on with the lug nuts. You can strip lug studs and/or get the wheel stuck.
and is it OBD-I or OBD-II?
1993-1995 LT1 f-body cars have one cat, with the exception being California Emissions (RPO NB6) A4 cars having two. All 1995 M6 cars have one cat.
edited 10/10/2008