Hi all.. I've lurked here a while, but newly registered, hoping you all can help me with a weird problem I'm having.

My '98 Olds Silhouette started acting up a couple days ago. No previous signs of trouble, then it started cutting out randomly as I was climbing a twisty mountain road. I pulled over into a parking turnout and it stalled. It cranked an unusually long time before restarting, then ran long enough to get me back down to a gas station at the bottom of the mountain, but it did stall a couple of times en route. When it dies, it does so quickly, as if you shut the key off. No sputtering, no coughing or anything, just a quick shutoff.

I towed it back home, hooked my scanner up and found a pending code - 1374 - Crankshaft Position High/Low Resolution Frequency Correlation.

By the time I got home, it had cooled off quite a bit, and it restarted immediately, as normal. It ran for several minutes until it reached operating temperature, then died again. This is when I started my real diagnosis. I found that it loses spark when it dies, and but always has injector pulse. I verified proper function of both crankshaft position sensors, via oscilliscope, and AC voltage reading of the 7X sensor. I was becoming convinced that I had a bad ignition module, but wanted to be sure, so I removed the coil pack/module assembly and carefully inspected it. All three coils tested perfectly within specs on both primary and secondary, with no signs of cracking or other damage.

Another interesting thing to note: With my scanner hooked up and the engine running, Ignition Advance shows 0.0 degrees. No change with any throttle input or whether it'* in gear or not. That is obviously not correct. With the key on, engine off, it reads 24.0 degrees, but goes to 0.0 as soon as it starts. I tested my scanner on two other different vehicles, and observed what I would normally expect to see - timing hovering around 10 degrees at idle, and changed predictably with application of throttle. Thus, my scanner is working correctly, but for whatever reason, the computer is either not reporting timing accurately or at all, or the timing itself is completely wrong. It just occurred to me that I should check the timing with a timing light to see what it'* actually doing, but as the engine runs no differently than it always has, I'm assuming the timing is being controlled as normal, but the computer is simply not reporting it accurately or at all.

When the engine runs, it seems to run fine. Does not seem to run any different than it has run for many thousands of miles before this. No other codes in the computer, stored or pending.

I have gone through several warmup cycles with it, and like clockwork, it always dies when it reaches operating temp or shortly thereafter. I was thinking about having the module tested before replacing it, but as it only dies when fully warmed up, I figured they would not be able to duplicate the problem with their machine. So, I replaced the module and erased the code, fired it up, and...

No change.

Starts up and runs fine when cold, shuts off when fully warmed up. The same 1374 code came back very quickly, before it even died the first time. Same 0.0 Ignition Advance reading while running.

Now I am at a loss. Sorry for the rambling post, but I now come to you fine folks for help. What direction should I go from here to diagnose this?

Thanks all..

Which module did you change? The 3800 ignition modules were known to cause issues when they got hot, but would work fine when cold.

Mike he has a 3.4L engine....

He has two crank sensors, I would be leaning towards the one in the block, which I think is the 7x, but he says he is getting a good signal on his oscilliscope(wow, how many techs have one of these?).....

When it won't start, there is no spark?

Hi.. Yes, sorry, I forgot to mention the engine! I know these only came with the 3.4L, so I guess I kinda forgot that not everyone knows that!

Yep, the 7X sensor passed both an oscilliscope and AC voltage test when cranking. I tested it multiple times, at the ignition module connector, as I wanted to confirm the condition of the wiring to it as well. Even when the engine won't start, it still tests good. And yes, I lose spark when it fails to start.

I had an issue just last week with a bad ignition module in the distributor of a GMC Jimmy.. replaced it with a new BWD from O'reilly, but still wouldn't start. I spent a bunch of time eliminating everything else to re-confirm my diagnosis, and came to the same conclusion - bad module. I took it back to O'reilly and had them test the new one, tested good, but they gave me another one to try just in case. It fired right up after installing the second new one. After having gone through that experience and wasted time, I can't help but wonder if I've run into that yet again??

When my van first died on me on the side of the road, I did all the basic tests I could with no tools to try and figure it out. I carry extra relays and fuses with me everywhere, so I swapped the fuel pump relay and checked all fuses, no change. Unplugged the MAF, as I know it can be an issue with these, but no change. My gut right off the bat went straight to a bad crank sensor or ignition module, especially when it restarted after cooldown, but I remain stumped. Very frustrating!

I've read stuff about loose connectors and wires on these, but in 20+ years of wrenching I've almost never encountered that. But I suppose it could be a possibility. I'm going to check all of the relevant connectors carefully and make they're tight, making good contact, and I will wiggle the wires around to see if that makes any difference, then report back.

Update: Ugh, problem still unsolved.

I reinstalled my original original ignition module, as the new one did not solve the problem. I erased the codes once again, and immediately upon startup the 1374 code came back pending. After three or four shutdown/startup cycles it came up current and set the service engine light.

However, this time the engine did not die upon full warmup. It ran and ran and ran, showing no sign of trouble. It was VERY hot here today, pushing 100° outside, and it was running in the sun with the A/C on, so I figured that if it was heat related, it would fail today if it ever would. Coolant temp was pretty stable around 197-199°, and I could definitely feel the heat coming off the engine. However, after two hours of idling, with the occasional rev, holding the throttle around 2000 rpm for a moment periodically, putting it in gear randomly, etc., it never died.. until I finally tried to take it out for a test drive on the road, and it died within seconds of leaving my driveway. To be precise, it died right when I hit the rumble strips in the middle of the road as I crossed the undivided highway near my house. So now I'm thinking that my issue is potentially a loose wire or connection somewhere, but where? Between the ignition module and PCM? Both crank position sensors consistently tested good through their wiring, so I'm not thinking there, but I am at a loss. I don't have access to a wiring schematic for this engine/vehicle, so I don't know which wires go where.

Any thoughts?

I tend to agree with you on this......if you have a good 7X signal when it won't start, and have tried a new ICM, then it could be a harness or connector.....

With the vehicle at normal operating temp, carefully grab the engine harness at various spots, and give a tug while the engine is running, to see if you can recreate the stall....it definitely sounds like a loss of signal from somewhere.....could be a broken wire inside the insulation, and when the engine flexes enough while driving, creates the problem....especially the harness coming from the 7X sensor to the ICM.....

Thanks for the input.. I'm going to be inspecting the harness and connections carefully today. Am I correct in assuming that the 24x sensor is not strictly necessary to run, but is mainly for idle refinement and general smoothness? So, if the 24x sensor is bad or a connection related to it is loose, it might run rougher, but should still run?

I've read many cases online of people saying they fixed the wiring related to the ICM or crank sensors, but no one has given clear specifics about what part of the actual harness they repaired. Am I most likely to find my issue at one of the connectors themselves? At a particular point in the harness where it is stressed or too close to the exhaust or something? Any input on that? Thanks for your help.

It will only start if you have a 7X signal......does not need 24X to start....

Ok, thanks.. Another question - What could be causing my faulty ignition timing reading on the scanner? Can bad input from either crank sensor cause that? Or my potential wiring issues? I haven't had a chance to look at it any further yet, but I'm doing so shortly.

Another very frustrating day... so, I did some snooping around under the hood, started pulling on harnesses and connectors and such, and ah HA! As soon as I touched the 7X connector at the ignition module, the engine died. Restarted, touched it again and it died. Restarted, let it idle for several minutes, then as soon as I touched it, it died. Ding ding ding, we have a winner! So I picked up two new pigtails, one for each end of this short harness, used new wire and made an all new connection between the sensor and the ICM. I ran the new harness well around the engine, away from the exhaust and anything else potentially dangerous. I also replaced the 7X sensor, as I figured that since it was a bit of a pain to get to and it was cheap, rather than possibly waste the labor doing it again later, I just replaced it with a new BWD.

I had double checked every other connection I could reach under the hood, and that was the only connection that responded to being finaggled. So, with renewed optimism that maybe I had finally solved it, I fired it up... and the 1374 code came back immediately.

Dangit.

It ran no different than before, and the ignition advance reading was still 0.0. I ran it through full warmup, tugging on and pushing connectors every which way, including both ends of the 7X, and it never died, despite running for nearly an hour... until I tried to pull it put of my driveway for a test drive, where it died almost immediately. By this time, I'm incredibly frustrated!

I did notice one slight change this time, however.. it had some trouble restarting right away, but once started, it would run fine at idle as long as I let it, but would always die after putting it in gear. Sometimes it would die the instant I moved the shifter, sometimes it would take a second or two, but it never ran long enough in gear to move the van more than a couple feet.

So I let it sit overnight, and of course this morning it starts up fine. Doesn't die in gear when cold, so I took it up and down the street a short distance, making sure to hit the rumble strips and a couple particular bumps along the way, and it ran fine for the first 8-10 minutes or so, until it was fully warmed up, then it predictably died. I ended up having to pull it back up the driveway, because it would not stay running in gear. And for reference, I've tried both drive and reverse, and it always dies right away.

Also, when it did run long enough to drive it this morning, it ran totally fine. Same power and everything as it has always had, no perceptible change that I'm aware of. It just dies when hot.

So.... should I start thinking about hiring an exorcist or what??? I am at my wit'* end!