95 Z28

Car was running fine. I was on my way to church Sunday so my karma should have been good. I took off from a stop somewhat lively but didn't break the tires loose, and in just a minute or less the engine stopped running, no noise, no error lights, no new leaks. When I crank it, it turns over great but it never tries to start.

Opti was replaced about 5 years ago. I know that doesn't mean it's good but it isn't the original and it has been working with no erratic or intermittment problems.

No error codes in Freescan or Datamaster.

I thought it was a fuel problem, yes I have almost a full tank. I can hear the fuel pump relay energize and the fuel pump operate. I depressed the fuel schrader valve and gas sprayed out so I'm pretty sure I'm getting some fuel to the injectors.

Turned attention to the ignition circuit
Test coil wire - good (measured resistance)
Test Ignition Coil - good (measured resistance of primary and secondary)
Test ICM - good (voltage on A & D, C has 0 resistance to ground and B voltage pulsates)

All above as per the sticky on testing the Opti in this forum, Shoebox's site, and the Haynes manual by the way.

I hooked a timing light to the coil wire and battery, put a zip tie around the trigger, and cranked the engine. I get no light which I'm thinking indicates no spark at the coil. However, when I get some extra hands this evening I'm going to check for actual spark at the coil.

What would one do at the coil to collapse the field thus exciting the coil to generate a spark. Do you ground one side of the primary or open the connection or does that work?

I'm open to suggestions. Meanwhile I'll wait until my extra hands arrive.

 

Just because fuel is coming out of the shroeder valve does not mean it has enough fuel pressure to start. Put a gauge on it and test the fuel pressure in the run position and while cranking. Should be around 40 psi.

 

Yeah, I'll need to do that.

Tonight when I could check whether I'm getting spark from the coil with someone else cranking the car, I didn't see any spark at all through the coil wire.

 

I know it still doesn't make sense, but mine wouldn't fire last Friday until after I disconnected the battery for a few seconds. Have you tried that? Also, today I found that all three ground wires that attach to the block near the ICM and coil had frays and cracked insulation near the terminals. I cut the ends off of the three, crimped them all together into one ring terminal, and replaced the ground strap to the frame. The car now fires faster than it ever has since I have owned it. Maybe you have the same problem?

 

I just took the battery loose this evening to see if it resets something in the PCM. I'll put it back on in the morning.

I just remember seeing 1 braided ground "wire" going to the ICM bolt and I think it's in good shape. I'll look closer at that in the morning. For kicks do you remember where the three connect to the frame? In different places or all the same place?

Since you've "reset" your PCM has it acted up again? and if not how long has it gone?

 

The three wires connect to the block, not the frame. They attach to the same post that the braided ground strap does on the block. The other side of the ground strap attaches to the frame along with one other ground just above the driver side sway bar mount.

Since I reset the ECM, I have not had the problem again. I tried to make it happen again after I got it home last Friday. 10 times restarting in the driveway didn't make it happen. I have driven it a few times since with no trouble. Tonight I started it about 7 or 8 times after fixing the grounds with no troubles.

 

The one I remember runs from the block at the ICM to the frame on the drivers side back about 6 inches from the radiator. I check on others I may not be remembering.

 

update

Fuel pressure gauge shows 40 psi with the ignition on. Can't test running pressure as car won't run.

Grounds bolted on at ICM/Coil look good.

Taking ICM to AutoZone for test.

 

For those who care it was the ICM. I took it to AutoZone and it failed miserably. New one in and the car fires right up.

 

My '96 Z28 has random times where it cranks way longer to start than the usual 2-3 seconds. Whats up with the ICM ? Where is it located ? I just put some killer new battery cables on and my Check Engine light is on, so I was going to disconnect the battery to reset it and see what happens.

 

Excellent...

 

The ICM is on the front of the drivers side cylinder head. Here's a pic from Shoebox's site: http://shbox.com/1/coil_loc.jpg

Replacing the battery should have nothing nto do with any check engine light. Take the car to Autozone and get the codes pulled. DOn't believe what they tell you the codes mean...come here for the F-Body specific codes.

What are 'killer battery cables'?

 

My car's engine seems to be running smoother and more powerfully. It's very likely tha ICM has been failing for some time. I hope that's your problem and not the Optispark distributor which can also act like you're describing.

If you let the guys at AutoZone look up the code on their computer, you can ask them for a printout. Then you'll have that to bring home and check codes here.

If you remove the ICM they have a test rig that will specifically test it.

 

I was looking for a link on the battery cables, sorry. They are made by innovative wiring and are very heavy duty pieces. The cables on my car previously were worthless and weak, especially the positive line to the passenger inner fender juction box.
But, like I stated, I'm still having issues, like longer cranking, at times. Is the ICM an all or nothing deal ? If it is on it's way out can it fail intermittantly ?