Bonneville no start condition

I'm just starting a new thread re: my own problem instead of tagging onto another. I've had a terrible time diagnosing this issue. The symptom is extended crank, no cylinders firing. -At Times- it will fire up and run perfectly, but particularly in the cold ambient temperature, nothing.

1991 Bonneville (LE or SE) with 3.8l engine. 196,000 miles.

I've checked for spark and injector firing (with a noid) and both appear OK.

I've thrown lots of parts at it (foolishly) and used a scan tool, which set no codes and gave no clues with sensor values.

I've tried heating the ECM and ignition module with a hair dryer to test for thermal influence. Below I'm pasting more details:

I've checked and/or replaced:
O2 sensor
CTS (coolant temp sender)
Crankshaft sensor
Camshaft sensor
Fuel pump
Fuel sender
Fuel filter
plugs
Cleaned all ground points
Neutral safety switch
Dome light
Fuel pressure
Ignition module tested by a parts store many times in succession (to warm it up).


Of interest:
*I used a good scan tool for some time while trying to diagnose the problem (after most of the new parts were installed). NO codes were ever set, and all values appeared to be "in range." Unfortunately, it never failed to start while I had the scanner!

*WHEN it runs, it runs very well, and will start right back up if I shut it off. The problem occurs only after sitting many hours, at which time it cranks fine but doesn't kick in.

*Another problem which may/may not be related: sometimes the cruise control spontaneously quits on the highway, but that is quite infrequent.

*I discovered my ECM (engine control module) was not properly seated in its' plastic mounting bracket. The connections were all fine, but the unit was loose enough to lean forward and contact ground points. It is important that the ECM case not be grounded, since many sensors provide their readings by transmitting a ground signal to the ECM.

*This car was stolen once and hot-wired, if that is relevant.

*I have the actual OEM service manual and up-to-date Technical Service Bulletins (TSBs), which I've scoured many times. I would reproduce the recommended diagnostics for you, but it is dozens of pages. If there is interest expressed, I might scan some of it for you.

Possible fixes I plan to explore further:
1) Learn to use a "noid" to determine if the injectors are firing.
2) Use the spark tester (purchased yesterday) to see if there is spark.
3) Replace the air filter (it is dirty, but doesn't look that bad)
4) Check for exhaust back-pressure using a vacuum gauge on the intake. (I've read this suggestion elsewhere).

Suggestions for others with this problem (now that I'm a little bit wiser):
***Note that most of these are free or cheap!***
1) Check for actual spark. I'll assume you've already inspected the wires and plugs. (I believe I should have checked for spark FIRST rather than last... I've just never done it, and did what was familiar first).
2) Check for fuel pressure. Use common sense, but the simplest test for pressure is to turn the key to the run position (engine off) for two seconds, then turn it off. Unscrew the valve cap on the top of the engine (NOT THE A/C LINE elsewhere). Use a rag and shield your face, then briefly press the valve stem. Fuel should squirt (not dribble). If you are the least bit hesitant, fuel pressure testers are not that expensive, clearly safer, and give you an actual reading (should be about 42 psi).
3) Check to see if the injectors are being told to fire. Like in #1 above, I should have done this at the beginning, I've just never used a noid light.
4) Check your ground points! a)The main engine ground is right underneath the ignition module/coil pack. It is a little hard to get to, but worth cleaning up. b)The ignition module grounds to the mounting bracket. The factory manual instructs you to use dielectric grease when installing, to protect the ground. c) Smaller grounds are located around the engine compartment, just look for the wires that are screwed to the sheet metal. d)In the trunk (mine was VERY bad) under the carpet on the passenger side floor just forward of the antenna.
5) I don't know about you, but I seem to skip checking the condition of wires too often. Example, when I changed the O2 sensor, I realized that the insulation had been worn through to bare copper several places! Take the time to follow all those wires around with your fingers and make sure they are intact. Check the connectors for corrosion.
6) Many parts stores will now test many components for free. I suggest having them test your ignition module (label all those wires when you take 'em off). Ask them to run the test about 10 times in a row, until the module feels quite warm. That can help diagnose temperature-related problems. Since our problems are with cold, I may yet put my module in the freezer and keep it iced down until they test it. (Do I have to tell you... keep it dry!)
7) Scan Tool: I'm fortunate to have a store that gives out $300 scan tools on loan! Of course, you pay up front, but get a refund when you return it. If you are not so lucky, most parts stores will now scan your computer for you. Remember that NOT ALL malfunction codes cause the "check engine" light to come on. See what there is to see, but remember that scan tools may list a problem with a component that is actually good. i.e., poor air/fuel mixture can result in an O2 sensor code being set. The sensor isn't bad, the fuel mixture is what needs fixing!

Hopefully this tome has given you some ideas... I'll look forward to your iideas for my situation!

I have been battling the same problem. I just sorta figured out a half-ass solution. I disconnected the CTS wire, I think its a green with blk stripe. This, for me fixed my problem, the only thing is that the temp guage doesnt work. I might add that in the past I had replaced the CTS 2 times, along with everything else you mentioned above. Like I said, I've been battling this with my car since Sept 2003 (look in the archives). Let me know how this turns out.

Update-
Wouldn't you know it! After it sat "dead" for several weeks, I reached in the door and turned the ignition key to see if it would work. Of course it did!

Unfortunately, I still have no idea WHY, or WHEN the problem will reoccur.

P.S. the ambient temp DID get up to a balmy 40 degrees F today....

Update-
Wouldn't you know it! After it sat "dead" for several weeks, I reached in the door and turned the ignition key to see if it would work. Of course it did!

Unfortunately, I still have no idea WHY, or WHEN the problem will reoccur.

P.S. the ambient temp DID get up to a balmy 40 degrees F today....

I'm still baffled... it started for me again this AM, but I don't dare rely on it not to leave me stranded with my 3-year-old.

I don't see where the temperature changed enough to be a significant factor. As for intermittent grounds or other wiring faults, I barely moved anything enough to think it might have jostled a connection... I literally opened the door, reached over the steering wheel, and turned the key. It fired right up, and ran smoothly. Any ideas? I don't trust the car enough to shut it off anywhere but home!

Down to 21 deg F this AM and she was coated in frost. Started with a bit of a hiccup, but then appeared to run fine.

That pretty much convinces me that thermal cycling is not the issue.

I've looked for underseat grounding points as others have posted in various threads, but don't see where there might be one. Obviously it is hard to see through the carpet... Can anyone give me a clue where to look, or do I just need to pull the seats, carpet? I sorta hate to do all that without knowing for sure there is a ground point to be found there!
Thanks!

dmccr, I had a similar problem. You can tell especially if you are driving with the headlights on. They will blink and the car will jolt roughly. This had me stumped! I found out that it was the ground wire that goes near the alternator housing. The connection was really bad and would cause the car to loose ground. Good luck!

I wish I had a clue!

I drove it to work, and on errands yesterday. It started fine each time. This morning, craaaaannnnnkkkkk. No start. Sounded like perhaps blowing back into the intake as I let off the crank.

I intend to post pictures of the wiring at the floor between the driver seat and door for general edification.

The next time it doesnt start, check to see if your power windows and seats are working. If not check the 30 Amp relay in the fuse box controlling the seats. It ties in with the fuel pump and windows. Mine was an intermittent problem like yours and after I cleaned the relay contacts, no more problems. Good luck.

Thanks for the idea... as much time as I've put in to this, I'll clean all the contacts, just because it is easy and might solve something!

Thanks for the idea... as much time as I've put in to this, I'll clean all the contacts, just because it is easy and might solve something!

Sorry, that will be a 25 Amp, not 30 Amp you'll be looking for.