Diagnostic help needed

[ChrisCairns]

I have a no spark intermittent problem

Car is now full S2 with FAST.

It first manifested itself at Woodburn, Oregon last year. The engine simply stopped on return road. I had it towed back to the pit and changed to a spare coil pak/module WITHOUT the Buick adapter for the MSD ignition box. It started right up.

I then returned the MSD box and they shipped me a new one, admitting they had found a problem. I had no more engine suddenly stopping. I went to Vegas....never had that problem. I then put the MSD box and adapter back in. Started fine until I removed the engine for a refresh.

I got the engine back and I put it in. It wouldn't start. I checked lots of stuff and it finally started .... after I found the plug which you insert into the adapter to isolate the MSD box was not plugged in all the way. I thought I had found the problem AGAIN.

Then it stopped suddenly a few days later. I switched out the coil pak/module and put another one in without the adapter and it started. It ran right up to last Saturday at the track without the MSD box and Adapter where after the 3rd pass it stopped again on return road. And all three passes had been horrible with outrageous missing. I put in a new crank sensor once home...still no spark.

Yesterday I found the cam sensor reluctor was loose. Lil screw had backed out. Tightened it up and the engine started immediatedly and ran "right".

Today some friends came over and I started it up for them, after running it earlier for 20 minutes.... and within 3 minutes, after idling and reving up perfectly, it stopped. Won't restart. No spark.

I've checked many connections, including to the FAST box, to the old ECM connectors, coil connector, crank sensor connector, cam sensor connector and ran my finger over many more wires and connectors. Nada.

I need to find this problem before the Woodburn Buick meet in two weeks. We don't have a lot of Buick stuff out West here so this meet will be cool IF I can find the gremlin.

All suggestions are very welcome.

Thanks, Chris

 

[turbodave231]

I think you are loosing your crank signal to the module. I would have told you to replace the crank sensor, but you have done that. I would check the pin tension on the terminals at the crank sensor and the module. It sounds like you either have loose terminals or a break in the wiring.

Check to see that the module power and ground terminals are good too. If the module is loosing power or ground, the same effect will happen.

If you have the problem occurring, you should verify cam and crank signals with a DVOM. Backprobe the cam and crank signal wires at the module. Pins J and K, I beleive. A straight pin works good for this.

With the key in the run position, turn the engine by HAND and watch the crank signal voltage. The voltage should be 7-8 volts and drop 3 times to .5 volts per revolution of the crank. Don't try to crank the engine while doing this test unless you have a lab scope to watch this circuit.

The cam signal works the same way but drops voltage only once every 2 revs of the crank.

One of these two signals is missing, or you don't have power to the module.

Good luck,
Dave

 

[ChrisCairns]

Thanks for the help Dave.

I have the flu and didn't give as much info as I could have yesterday due to what I thought was my imminent death.

Previously I'd brought up the FAST sensor screen while cranking the engine in it's no-start condition and it showed NO rpm signal....hence just what you said....crank sensor not giving a signal.

And I have 3 different coil pak/modules set up. Two with the Buick adapter for the MSD and one without. Each time I put the coil/mod without the adapter back onto the engine it starts. I did that this morning and it started right away. So I don't know if I have 2 bad coils/mods and one good one or if there is a wire terminal problem by the coil/mod and each time I change it I inadvertently "wiggle" the loose wire. I've checked the module plug-in millions of times...and can't see any looseness or bad terminals.

The ground connections are good. (I'm big on good grounds).

I would like to be able to do the back probe if (when) the engine goes back into it's no-start condition, as I'm sure it will since I haven't definitively found the problem. Educate me here please. Does the "hot" crank sensor wire come from the ECM (FAST) and to the crank sensor, then the signal goes back to the coil/module? Or does the signal go to the FAST box, which then sends a signal to the module? I'm asking this because I think I'm going to have to tear into the mess of wires in the loom and follow each one from/to the crank sensor.


***One of these two signals is missing, or you don't have power to the module.***

I agree. Where does the power for the module (I assume you mean module under the coil pak) come from? Is it the FAST box??

Thanks again for your help.

Chris

 

[TurboTR]

The signals come from the crank and cam sensors, to the coil module, which then passes them on to the ecu. The only problem you might see when you try and backprobe is, the sensor output signal is "pulled up" by the module. If you disconnect the 3 prong weatherpack at the crank sensor and try to probe the crank sensor output directly for example, you will see no activity on the sensor output 'cause the pullup is missing. You can attach your own, external pullup however and probe just the sensor, with it detached from the coil module. Like a 10k resistor from the signal out to the power wire will work fine. Of course you'll have to also provide power and ground. Alligator jumper wires work great for this.

Your batch fire ecu should not need the cam signal to run. The coil module will still need it however. It needs it to be able to sync up to the cylinder count.

We are taught that in general, wiring and connections (including fuses) are like ~ 2 orders of magnitide less reliable than the rest of an electronic system. Thus that's almost always the 1st place to start suspecting and looking...

It sounds to me like a connector/wiring problem at the coil module, since each time you disturb it there it works briefly. The pins/cavities may be worn out. No rpm at the ecu says the crank signal (ref pulse) is not making it to there. PS the CCCI module is powered from the vehicle wiring harness, not the ecu.

Hope that helps some... And good luck at Turbo Thunder! Hope the rain holds off...

TurboTR

 

[EightSecV6]

Chris,
The cam sensor signal will indicate no RPM on the FAST screen as well, you have to have this signal to run with the factory ignition and the FAST..... I have been down the road with the cam sensor/solid roller problem many times. If it was loose when you checked it, you can bet it is loose or has slipped on the shaft right now.Check it out, if it has slipped, overnight it to me next week, I'll modify it the same day and send it back.I thought I remember you telling me you had an extra you were going to send anyway? maybe not? Dont hesitate to call.
Bill

 

[ChrisCairns]

TurboTR....good information...thanks. And I have the sequential FAST...dunno if that would make a difference with diagnosing this problem.

However, I'm leaning the same way you are....that there's some bad connection somewhere by the coil/mod. I just came in from the shop....I've been out there scientifically wiggling all wires by the coil, trying to get it to stop running. Nope, just keeps ticking.

Bill....yes, you did tell me to send it back for the modification. I was just being lazy or stupid or a bit of both.

After I found the loose ring I loctited the screw in and then after the latest quit-and-no-start condition yesterday, it was the first thing I checked and it was still solid. Then as I mentioned I put the coil/mod without the adapter back in and it starts and runs now. But for how long.

I do appreciate all the help you guys have given, but I have a feeling this is going to be one of the those labor intensive try-to-find-the-bad-connection thingies.

 

[ChrisCairns]

As a follow-up.....

I told a friend who's a mechanic in a small town not far from me, about this problem I was having and my belief that it has to do with a poor connection around the coilpak/module. He told me that he'd replaced in the past 3 years about 10 of the push in connection thingies that go into the module on various GM vehicles due to bad connections.

I think next week I'm going to buy that connector piece, wire it in, and see if it fixes my problem.