hypno92

1995 trans am lt1 with auto 102k miles rebuild trans
what's new
optispark,plugs wires,fuel rail,fuel pressure regulator,180 thermostat

my car cranks and sometimes starts when it dose start it runs fairly nice but stalls randomly and is really hard to restart the car just cranks.somtimes fires up but runs really bad!
I have no scanner for the obd1 system and belive it the car dose not throw any codes, the only time it throws a code is when the car is idleing after heating up the rpms drop to 600 and the check engine light comes on with my radiator fans but when I drive the car the light gose away almost instantly I have a mechanical gauge reading in my car so I know its not overheating
these problems are annoying and I just want to drive my car help me
while my engine is running I noticed a hissing noise under the hood but I can't find a suspected vacuum leak

hypno92

Now rpms don't even wiggle when I crank car doesn't start at all

Jr.Samples

Start with the basics. You car is an air pump and needs three basic things to run.

Air
Fuel
Spark at the right time

Pull a couple plugs

Do they look wet?
Check for spark.
If spark
Look at fuel pressure. You will need a gauge at the end of the fuel rail.

This should get you started.

hrcslam

Yep, check for spark when the issue arises (sounds intermittent). Have you had the ICM checked?

hypno92

How can I cheak the icm, also these are the symptoms it was having before I bought it I think I may need to try another opti

hypno92

How do I check for air and spark

hrcslam

Check for spark by removing the spark plug wire and creating a spot for it to arc to a ground. This is kind of dangerous so wear gloves and keep clear. If it does shock you it'll only last for a milli-second though. I normally put a phillips screwdriver into the sparkplug end of the spark plug wire, then place the metal part of the screwdriver close to something metal on the engine. Then I'll have someone crank the motor over (pull the fuel fuse so the car doesn't start). If it sparks you have spark, if not you don't.

There are other safer ways to do this, they even make tools specifically for this. If someone you know has a timing gun it'll work perfect for this check.

to check your ICM I think AutoZone or O'reilly's checks them, but they check them only when they are cold. Ours tend to go bad when they heat up (it's mounted to the front side of the drivers side head). Good luck.

nitrous2fast

iTrader: (2)

If/when you have the ICM checked, have them run it four times. If it fails at least once get a new one.

hypno92

Well today I cranked the car and it wants to start it cranks and sputters but won't turn over rpms are wiggling now on the TAC, so I'm going to assume I have spark can I take the icm off and have it tested

nitrous2fast

iTrader: (2)

Yes you can take it off. on the drivers side head behind the coil.

hypno92

Ok I'm going to give the icm a test, I hear the fuel pump priming when I turn the key, my fuel filter could be clogged but idk let me find out what the icm is doing first

hypno92

Got the Icm tested twice and it failed both times

hrcslam

So you replaced it and it runs good now?

hypno92

No I replace both that and the coil and still no start no spark at coil or plugs on the block still just cranks, checked all fuses harnesses icm gets power coil gets power to the harness maybe my opti failed already?

hrcslam

Did you check to make sure the opti is getting power? The plug runs behind the water pump under the throttle body on the passenger side (opposite of the coil wire).

If you disconnect the wire from the coil and try to start the car does the coil spark?

hypno92

The harness to the opti was shot when I looked at it the plastic piece that is supposed to clip in is broken but the wires are still good and intact and no spark at the coil at all and I guess I wouldn't if the opti failed? The opti sends a remote signal out the the pcm as the cam spins it then the pcm sends the ignition read signal to the icm then to coil then sparks to opti

hypno92

I hate to answer my own questions but I think my problem may lay at my opti or my opti harness

hypno92

Everyone I know keeps telling me to cut my losses and sell the car,its not worth it, every mechanic I have look at it can't figure it out they just say gms are a headace
I just want to prove everybody wrong and fix this dam car and next year I start building it up

hrcslam

Follow these directions <- link to optispark diagnostic instructions.

If your opti doesn't get 12VDC with ignition on fix that issue. If it's got 12VDC check the ground wire for continuity. If that's good check output signal for 1-4VDC. If that checks out then you need to trace the wires from the ICM to the PCM for continuity and signal.

hypno92

I will check this tomorrow I just bought a multimeter and a little test light