94 LT dies will start latter
10-13-2011, 08:12 PM
#1
3rd Gear
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94 LT dies will start latter
I have a 94LT! Runs perfect. but sometimes dies driving down the rosd or just sitting at idle. also can be running turn it off come back and it won't start. engine turns over but there is no fire from disributor. You can wait about 5 min. It starts and runs fine again. there is no warning went this will happen. does not miss fire or anything its just like you turned the key off. i replaced the distributor car ran fine for about 1and a half months. i replaced the control mod, the coil, the cap and rotor.made no difference. HELP! Should I do the disributor agian?
10-13-2011, 08:29 PM
#2
are you certain there is no spark?
has anyone checked the fuel pressure and replaced the filter? This sounds alot like a filter that plugs up, stalls the motor then after pressure drops will allow gas to flow again.
If fuel is not the issue, then it sounds like heat might be....something getting hot or part of the harness moving around and shorting. Try idling it and wiggling sections of the wire harness under the hood...see if that makes it stall.
I forget....does that yr model have the ECM under the hood? Heat does weird things to electrical parts.
Should go without saying...but DO check the harness grounds. NOT the battery grounds...the harness grounds. The bundle by the oil filter especially. If they are loose that will break the control circuit and kill the engine.
has anyone checked the fuel pressure and replaced the filter? This sounds alot like a filter that plugs up, stalls the motor then after pressure drops will allow gas to flow again.
If fuel is not the issue, then it sounds like heat might be....something getting hot or part of the harness moving around and shorting. Try idling it and wiggling sections of the wire harness under the hood...see if that makes it stall.
I forget....does that yr model have the ECM under the hood? Heat does weird things to electrical parts.
Should go without saying...but DO check the harness grounds. NOT the battery grounds...the harness grounds. The bundle by the oil filter especially. If they are loose that will break the control circuit and kill the engine.
10-13-2011, 08:38 PM
#3
Instructor
that is the exact symptom I had, mine was related to clogged cats. If you are driving and it dies, pop the hood and see if the manifolds are red, if they are, your cats are clogged.
10-13-2011, 08:44 PM
#4
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Tkx for the reply. Yes for sure no srark. had it tested and put in shop. thats why I replaced the distributor, witch fixed the prob but started doing the same thing mon1/2 latter.doesn't really seem to mater if engine is heated up . some times pull up go in some where for 2 or 3 hours come out won't start. jus never know when.some times starts back up after waiting 3 min. some times won't start for 2 hours.
10-13-2011, 09:11 PM
#5
Drifting
Are you handy with a meter? There is a procedure where you check for the pulses to the PCM from the opti. That pretty much tells if the problem is Opti related. You didn't mention if the car is displaying any codes. That would be a big help.
10-13-2011, 09:17 PM
#6
Instructor
this guy is great to show you how to test the opti...
http://shbox.com/1/4th_gen_tech2.html
here's the extract...
OPTI and Spark Test
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 modern digital meter with at least 10 megohm impedance to protect the PCM (in case you measure anything in that direction).
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).
If you don't see the proper ac voltage the problem could be the optispark, the harness to the optispark, the PCM (not common) or any of the wiring in between. Visually inspect all the connections you can get to for poor contact or corrosion.
At the end of the optispark harness (disconnected from the opti) with the key ON, you should see:
A = ~5vdc
B = ~5vdc
C = 12vdc or system voltage
D = ~0 - 0.2 ohms ground
http://shbox.com/1/4th_gen_tech2.html
here's the extract...
OPTI and Spark Test
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 modern digital meter with at least 10 megohm impedance to protect the PCM (in case you measure anything in that direction).
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).
If you don't see the proper ac voltage the problem could be the optispark, the harness to the optispark, the PCM (not common) or any of the wiring in between. Visually inspect all the connections you can get to for poor contact or corrosion.
At the end of the optispark harness (disconnected from the opti) with the key ON, you should see:
A = ~5vdc
B = ~5vdc
C = 12vdc or system voltage
D = ~0 - 0.2 ohms ground
10-25-2011, 03:29 AM
#8
Cruising
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Do your sys and security light flash while driving. If so it is your ECM that is the problem. I just had to replace mine on my 1993. This may sound crazy but I got this on another forum. Next time it just turn won't fire raise the hood and take the palm of your hand and slap the top of the ECM 5 to 6 times and get back in and start it up and go on with your business. If this work then your ECM is bad. Sounds crazy but I thought so as well but I did it and I no longer had to wait 10 to 15 min for it to start because it fired up every time I did this without a delay.
