89vette

This is a follow up to this post
http://www.corvetteforum.cc/ubb/Foru...ML/010059.html

Well its not looking good. I swapped in another ECM and I get the same thing. Car will not start. I disabled VATS no go. While watching Diacom while cranking, I get no injector pulses and my timing reads zero. I loosened the distributor and and twisted it and the fuel pump energized. This tells me the ECM is seeing a a pulse. For the heck of it, I ohmed the pickup coil per the service manual and it checks out ok. I also used my volt meter and checked all grounds against the three power feeds into the ECM. All checked out good. So I have power,and good grounds. I smell nothing burned.
At this point, I have no idea where to turn next. Something is causing the ECM not to command fuel and spark. But what? This makes no sense to me. For what its worth, everything in the car works like all the lights, radio, blower, etc.

Anyone have any idea, I'm all ears.

Thank you,
Jason

JohnGuc

I popped a dash fuse that gave the same signs you are seeing.

Aggravated4life

Dont have a clue but will try and throw ideas around to double check.
I guess just for the heck of it, check every single fuse in the box and make sure theyre all ok.

You smelled something burning the first time you posted...

then you mention you twisted the distributor and the pump energized...sounds like some wiring issue somewhere.

Im starting to think the wires that come through the junction back at the firewall and into the car need to be checked out.

You may have to take your dash pieces off and look inside there for any chafing of wires or brokens or shorts.

Did you unplug the harness wires at the distibutor and check for broken terminals and power?

How about the large plug connector that comes off the dist. and connects at the back of the engine?
Is that broke off or loose?
(im asking since you said you had no spark)

If you checked for spark and found none, go probe the negative side of the ignition coil with a test light.

If youre not sure which is the negative, one side will have a steady supply of power and the other side will flash the test light on and off while cranking the engine over.get someone to crank the engine over while you test them.

If neither side has power, theres an open wire in the voltage supply to the coil.
If both sides have steady power,then the problem is primary ignitions control of the coil.

Did you check the pick up coil?
With the engine cranking it should show at least 0.5 volts measured with a AC Voltmeter.

try to fix the spark problem first before tackling the injector pulse issue...however theres a good way to test if the injectors are in fact working by using a stethoscope and listening for them click open and closing when the engine is cranked.

Did you check the power at the wires directly at the ECM itself where they plug in?

Is your ECM located under the passenger dash panel like on the 86?
or is it mounted in the engine bay above the battery?
Cant rem what year GM moved it.
Think it was 90 maybe...

Anyways I checked the passenger side kick panel under the ECM..that damn light bulb was burning some wires near the ECM under the dash on my car so I removed the light bulb piece out of there.

Thats all I can come up with now..hope you find the fix real soon.
When your car died I thought maybe you blew the timing chain but your testing has shown
you werent getting power to spark and pulse widths.

Keep us posted...and hope David Fulcher will catch this post..if not Page him here on a post and hopefuly he can help.
If youre not sure who he is, hes the top guy to talk to about anything on Vettes.

89vette

My car runs a 1227730 ECM which is speed density. I converted it over about 6 weeks ago. When you twist the distributor, the fuel pump energizes for two seconds. This is a normal reaction and tells me the ECM is seeing a reference pulse from the dist so I assume. Now, the one thing that would cause my problem is the lack of a distributor reference pulse. The ECM does not know the engine is cranking. A bad pick up coil will cause a lack of a reference pulse. My pick up coil ohms out OK per the service manual test. Regardless, I still need to replace it. The thing that worries me is that I'm pretty sure the fact that by twisting the distributor and causing the fuel pump to energize, the ECM is seeing a reference pulse. This is only a logical assumption though based upon reviewing wiring diagrams.

Thanks,
Jason

-=Jeff=-

Jason,

You did not mention it but did you:

- Check voltage at all fuses?
- Check for a bad Fusible link?
- Are you able to swap the 165 back in by just plugging it in again and testing it?

- just as a precaution, ohm out all your injectors to be sure they are not shorted..


That is all I can think of...

89vette

Jeff,

I verified the fusable links. I verified all power and grounds to the ECM. I did not verify voltage to all fuses. I did not check injector resistance. Really that should matter since the ECM is not telling them to fire. There is power to the injector harness with the key on. All else electrical is in working order. All signs now are pointing to the PU coil but like I said I wish I knew what was energizing the FP whe I twist the dist.

Jason

Goody

Just an idea, but would the neutral safety switch matter in any of this??

-=Jeff=-

Nope he is running a 6spd.. and the car is cranking so that eliminates the CLutch safety switch.

Jason,

I gotcha.. at least you know there is voltage at the injectors.. As Bill said.. sounds like wiring .. I would sart ohming out all the injector and Distrib wires going back to the ECM.

Jeff

89vette

Yea I guess that would be a good idea. I'm trying the PU coil tonight but I'm not holding my breath.

Jason

Red91C4

Ok, this may sound stupid simple and you may have checked it, but have you verified that the distributor does indeed turn when you crank the engine? If the ditributor gear or the timing chain took a dump then the ditributor shaft will not turn and you will have no spark and no reference pulse. Just a thought.

89vette

Red91, Its a good thought. I did not watch the shaft turn but I have oil pressure while cranking so I know its turning.

Thanks for the reply.
Jason

HighHopes85

Jason, This might not be of interest, but when I did the 730 swap, I made sure the injector ground outs from the ECM went direct to ground...not to the TPS, IAC, etc reference ground.

What does your tach read while cranking? -Matt-

89vette

The tach reads zero also I'm pretty sure. What drives the tach in the ECM? Is it the reference pulses?

Jason

HighHopes85

Here is why I was asking. The tach signal comes directly from the Tach terminal on the cap (well, you have the tach filter in there). Back in the day, in my Chevelle, I had hooked up an Ignition coil backwards BUT the tach still read correctly. In other words, the battery was going in where the tach was supposed to be and vice versa. SO does this mean anything? Well, maybe...

The way the coil works, the secondary which fires through the bottom button and goes to the rotor doesn't care which lead of the primary it gets hit with. Try to disconnect the tach wire and see if it fires. Also, disconnect the 4 pin distributor connector and see if it fires (it should not fire with the 4 pin connector disconnected, but if it does, it is DEFINITELY the pickup coil). I am trying to think of how I went about testing my prob but can't quite remember and well start off with those 2 things. -Matt-

89vette

Thanks for all the help guys. The coil ended up being the problem. It seems with all the tools I have I over studied the problems not bothering with the simple things. At any rate, once I heard that 396 come to life again, I fell in love all over.

Jason

-=Jeff=-

WOOHOO!!!!

That is GREAT News!!!

Juliet

That's neat. Thanks for posting the solution too. That really helps to learn about these voodoo black box C4s (compared with my carbureated C3).