LOL my ball is bouncing all over the place!

No only on the old modules which allowed me to have the engine running.

No the reading signal from the ECM to the Ignition Control Module (trigger 5 v peak to peak) went flat. Yes it was still running when that happened.

The signal from the ignition control module to the coil was still present.

Does that help?

 

And that sounds like the problem. The ECM is losing focus. A new computer should fix it.

 

So you saw the whole signal set to 5VDC it should have been set to 10VDC you never want to scope something at the edge of the signal amplitude.

The signal dissapearing has me baffled.How did the car run then?Any difference?Mabey it was not the right signal? Mabey the ground?What did he ground it to?The engine? If so check your engine ground.

It would have only taken a couple of cranks to get the signal from the ECM with the new one all you needed to see it would have been a couple of cycles.Oh well too late now I guess.Gonna have to wait for the new ECM.But I would be checking grounds in the mean time.

 

So when the new computer arrives tomorrow and I install these new components and it works. I guess I owe you either donuts or a dollar.

 

Please explain to me how an ECM "loses focus" and the car still runs?

 

See I wouldn't have known any better.

Well when its running it has a roughness almost like a mis firing. Significant enough to feel it through the body, and steering wheel. You can tell it is not well. I'm comparing this to the previous 5 yrs. I detected it right away late last week which is why I replaced the plugs over the weekend. Of course we it reaches the point when it goes nuts, its barely running spits sputters acts like its going to explode and then dies. It sounds and feels horrible when it reaches that point.

I asked about whether it needed a ground or not, he said that adding the ground only cleans up some of the noise. That its not really necessary. He sits next to me at work, and when I first asked him about all this earlier today, he has a PCB back plane and power supply with a controller connected. He was showing me what you all were talking about by probing a component on the controller. He made a mention of it at that time too that you can ground the connection but its not necessary.

I still have the scope here but not sure if I could set it up to do all that by myself. I was going to take it back to the office in a few minutes since the storm has passed and get those images off the disc so I can post them.

 

This is getting to be one of the most interesting and enlighten post I've seen in a while. I sure am learning a lot.

EDIT:

I just checked the leads are not long enough for me to probe the wires and place the unit in the passenger seat so that while I would be cranking the engine I could get an image. Sorry.

 

It is interesting that you say the signal from the ECM to the ignition control module went flat. But, without that signal, the ignition control module would not fire the coil and the engine would not run.
So, I'm guessing that some of the input signals were missiing, not all of them. It is just that the oscilloscope was not sweeping the face of the screen at the correct time to see the existing pulses -- during retrace of the screen, it is blanked out.
If this is true, it is interesting and sounds like an ECM problem when it heats up.
But, this does not explain why a new/replacement ignition control module will not run the engine.

Tom Piper

 

You mentioned on one of your test drives, the tach started to act up and the engine started to run ruff.

Have you tried disconnecting the input lead to the Tach. Filter from the circuit?

On the Ignition coil there are two connectors. A two pin Black connector and a two pin Gray connector plug. On the Gray connector Pin B is a Pink/Black wire (10 amp coil fuse) and Pin A goes to the input of the Tach. Filter.

If one of the capacitors in the Tach. Filter circuit is shorting out, it could cause problems on the Primary circuit of the Ignition Coil.

 

The problem with the ground is on a PCB board there are no devices nearby that are generating a signal so you can leave it off.In your car there are a lot of signals being generated(ever hear static on a radio from a car) so it would be better to ground it.Some of those might mask your signal.I am not saying that is what happened here just some food for thought.It does seem to lean towards a heat/electrical issue with the ECM right now based on your description of it getting worse as it heats up but like Tom I still do not see why the new module would not at least fire the car.Wish you had the scope on the new module to see if the signal got grounded out.I just have a gut feeling that a ground is involved here.

 

You know that went through my head to just did not think to disconnect it.Worth a shot. Did you notice any tach problems while you had the scope on it?

 

Here's the image of the scope capture:

 

When the signal dies on CH1 does the signal on CH2 die with it?

 

I'm sorry I didn't mean to be misleading. Ever since Monday morning on the way to work when it started misbehaving and I limped it back to the house, each time it reaches the point where it starts to spit, sputter and die, the tach starts jumping wildly.

Preceeding that sometime around mid week last week, I detected this roughness, difficult to describe but you know when your engine is not running the way it should and with a V8 it shows up. At first I thought it was a plug fouling. Thursday last week I took it out on the interstate to run it a bit since I do a lot of short driving during the week (I only live a few miles from work.) I ran it hard for about 15 miles each way down and back and at my halfway point when I got off the interstate to return home it was still missing. It didn't do what its doing now, that must have been the prelude to what was to come. Anyway not knowing, I thought it was plugs and replaced them over the weekend (I've been running NGK Iridiums and replaced them with the same). On Monday, I had to stop by the bank on the way to work again this is only a couple miles from home. I stopped got some money and when I started up to leave it was really missing badly I didn't make it out of the parking lot. When I came to a stop at the exit it spit and sputtered, then I got an SES lamp, a Service ASR and the AC went from cold to max heat. It had done this part before a few times but not the missing or dying. Usually when I got the SES/ASR and max AC to heat, I could pull over stop and restart and the condition cleared. This time when it happened I started and restarted it several times and the condition would clear, on the third restart it cleared and I headed straight to the house. I pulled the codes which drove me to the ignition control module and found the ground wire to the engine wasn't tight. So I removed the bolt cleaned the surface and the wire end and re-installed it making sure it was tight now.

So I took it for a test ride around my subdivision and it seemed fine. I had no idea what was to come. So I got ready to go to work and wanted to stop by a auto parts store to pickup a tool to release the fuel line as I want to replace the fuel filter and that is when hell broke loose. It was about a 6-8 miles from my home and just as I pulled in to park the engine stumbled the tach jumped briefly and it died before I had shut it off. So I picked up my tool, and came out to start up and leave. The engine was probably running about 210 degrees and it didn't start the first couple times I tried it. I tried again and it started so I took off out of the parking lot and didn't make it out when it died on me. I tried to restart but it would fire over. I waited a few minutes tried a few times no start. Waiting a few more minutes and it fired so I left the parking lot got about two blocks down the street and it died again. I pulled over to the side of the road, and after about 30 minutes of sitting there making a few calls to let people know what was up and calling the dealer to find out about having it towed I tried one more time and it fired. So I took off and got about a mile or so down the road it started bucking and sputtering and I was focused on getting it into a parking lot off the street. At this point I realized that by letting it cool down 10-20 degrees it would refire. So I waited there for about 45 minutes or so, and tried again, traffic was heavy I got stopped at a light turned onto another road leading to my house and got stuck at a train crossing. It died again by stumbling sputtering and tach jumping wildly. After several attempts I got it started and went about a block or so it started to die again and got it off the road. (Which btw four corvettes passed me by with my hood up and not one stopped. Although one jerk drove by and yelled you should have bought a VW.) Ha ha. So I waiting about an hour and it restart and made it the rest of the way home before it would get in the mode, I was real lucky on the last leg.

Ok so now, I pull codes and run through the diagnostics and it pointed to a faulty ignition coil module connection or fault ignition coil module. Figuring that was the problem and it was rather late now, I waited until the next morning to get someone from work to come get me and take me to the chevy dealer to end up paying full list for a new module. I installed it and all it would do is crank it would not fire. At that point I pm'd Bogus several times and finally called him in which we walked through the diagnostics. Before we stepped through it together he had me pull the ECM and check the wires and check continuity of the wire from the ICM to the ECM the ground and the two wires to the coil from the ICM connector. All checked good. So he suggested to me to just plug the old module in. I touched the starter and it fired right away. The natural assumption was a defective module. So Chevy only had the one I got so they ordered a new one. I picked up the next morning and installed it. Same thing it would not fire. Plug the old one in it fires. So after several more conversations with Bogus I took the two modules down to NAPA to have them tested old and new. Although they didn't have the right connector they did have a setup where they could connect leads to the pins of the module and test them. Both checked good. More conversations with Bogus and we are both scratching our heads. That evening when I got home from work and on a suggestion from Bogus I verified the codes were cleared and started it up with the old module to see what codes it would throw when it failed. After twenty some minutes of running it in the garage I couldn't get it to fail. Temps reach 230 fans kicked on (AC was off) temps dropped some but it wouldn't fail. So I took a break ate dinner and came out deciding to drive just on my street to see if I could make it fail. After about 10-15 trips up and down my streets it finally at about 219 degrees started missing real bad more than it normally was doing and then started bucking just before it started doing that the tach started jumping. I made a three point turn to get back to the house and it really started bucking and the tach jumping wildly as I pulled into my garage I put it in park and rev'd the engine up to about 1500 rpm where it bucked spit sputtered the tach was jumping all over from 0 to redline and then it died. I restarted it brought the rpms up to about 1100 and it was missing and bucking and sounded horrible tach was going nuts and it died. I tried to restart it two more times but it would not start. I never got an SES lamp. So I checked the codes anyway and I get a 4.0 test showing an H41. This is the ignition control circuit open or shorted circuit DTC.

At this point it was late last night I've reached maximum frustration level and just put it to bed. Today you can see the trail of events that have happened in this post.

Sorry this was so long but I want to ensure the story and events are intact so there is less guessing as to what exactly is happening.

As long as it is cooled down some and with the old ICM it fires instantly, I plug in the new module it just cranks no indication of every firing.

So this is where I'm at. I have a new ECM, new ICM module and new coil being overnighted to me.

At the suggestions of some I was able to get a scope on it this evening see previous post with the picture.

During the diagnostics tests, the latter stages is to test for voltage on the two leads from the ICM connector to the coil that is the pink/black and white wires I believe them to be terminal A and D. Both of those show 12 volts with the ignition on. I get .5 volts on terminal B to ground with ignition On. On the same terminal and ground switching the DVM to A/C mode and cranking the engine I get 1.96-2.02 volts which right in the middle of the 1-4 volts the test is looking for.

I'm saving my call to Gordon until after I get the parts tomorrow and find out what happens after they are installed. So that is where I'm at with this beast now. Your thoughts and suggestions are so greatly appreciated. Thx.

 

I know as soon as you mentioned that I felt like a total *** for not doing that.

 

No but then other than the normal roughness I had been experience prior to it freaking out, it ran perfect for during the time we were scoping. As I told my friend, its no problem as it will start and we can go for probably 20-30 minutes before its going to go nuts on us. He did make a comment that the exhaust does smell a little rich. Can't say for sure, but I haven't noticed any unusual carbon build up on the corsa exhaust tips. I suppose over the last few days I've become use to it. And when I changed the plugs you couldn't ask for a better example of a perfect plug after 40K on them.

 

Nope we just lost that one signal, the yellow signal in the image it went flat.

 

Interesting, the Chevy dealer here puts a lifetime warranty on any ACDelco parts they install, whether they furnished the part or not. Granted, their labor isn't cheap but from long experience with vettes if it isn't something I can quickly fix I take it in. Like you, I have to get a rental car and I'm money ahead getting it fixed as quickly as possible. And I've had one water pump replaced under warranty, I had to pay labor but no parts cost. You would think GM would hold the dealers to a single, high standard but I guess not.

Something that may help someone later, Enterprise car rental has pretty good rates if the reason you are renting is that your primary vehicle is down. I have gotten $27 a day rate in the past, my latest was $32.

Wish I could help with your problem, but it's sort of like fixing computers over the telephone, tricky at best.
Good luck, I hope you find the problem ASAP.

 

Thanks. I called the Chevy dealer that I usually let work on it when it first died on me leaving the parts store. But the Corvette service advisor kept saying its your opti, and I kept telling him that is not the codes I'm getting, it runs fine until it gets hot then throws the DTC 41. He wouldn't budge off that and I reminded him that 3 yrs ago they replaced both the water pump and opti. He said well too bad its your opti and it will be 900-1000. Then gave me a number for a tow truck.
No matter what I tried to tell him as to what has been down and exactly what it was doing he wasn't going to listen. He sounded like a broken record it's your opti. So with that attituide I decided not to let them handle this repair.

On electrical parts they say no warranty. They will exchange one time but that is it. No warranty on the work they did either water pump or opti. Which really bothered me because at the time that was one of my deciding factors to let them do it. He says well things have changed here now, no warranty it will be about 1000.

Yeah I'm using Enterprise now. Except its like 40. a day 250. a week.

 

Things have changed? If the damned install has a warrantee, they cannot void it. They still have to honour any written warrantees at the time they are created.

I don't feel it's the opti...

After reading this thread, I need to get a cheap scope!!!