A few weeks ago I had a code 18 pop up on my 93 Buick Regal 3800. As the problem progressed, it would run ok when cold then start to stumble after about 10 minutes. Now it starts giving me problems sooner.

At first I took it to a mechanic and he looked at the shop manuals and decided to try swapping out the crankshaft sensor, but it didn't make a difference. I didn't want to spend more money on it so he recommended checking the wires and if they were fine change the the ECM. I checked the wires with an ohmeter and the seemed to check out so I replaced the ECM and it did nothing.

After a lot of research it seems code 18'* can pop up from non-cam/crank issues. Hoping for some suggestions of tests to do.

Here are some things I've done/checked:
Turned drive shaft by hand when cold and cms and cks gave signals
Checked icm and coils at autozone and they checked out
Checked spark using spark tester. They work
Used stethoscope on fuel injectors and they're doing their thing
Checked fuel pressure (40 psi which should be fine)
Changed fuel filter which helped idling but I feel this is electrical

I haven't tried replacing the cam sensor but it seemed to give a signal (magnets there). Any suggestions of things to try or retest would be much appreciated. Thanks.

As I understand it, the camshaft sensor signal is only used to determine when cylinder 1 is firing, and uses the crank sensor for everything else. If the cam signal fails, than the computer should still be using the crank sensor, but there is a 1 in 6 chance the injector timing will be correct.

What this means for you is that the car should either run right, or not be right, and it would seem to be intermittent.

I would suspect something is to blame on the crank position side of things, or it could also be wiring too.

The problem is consistent, its generally a matter of how quickly it happens. It started out intermittent when I was accelerating hard but now it happens either within 30 seconds or once the car runs a bit, so like a couple minutes.

Once the code 18 sets, it either accelerates slowly or will stumble and almost seem lost and not get past around 1800 RPM and will continue till I shut off the car or go to idle. I used a spark tester and it seems to be getting spark when it stumbles.

This problem seems heat related and electrical related. Could it be possible that the cam sensor overheats and stops working? Or can wires/connectors short out? I'm a bit skeptical to say its the crank sensor because my mechanic replaced it and he said it ran "worse".

To be honest, I really don't think it is related to the cam side of it. If it was, as I understand things it would simply set a SES light, but run fine until you shut it off, because it is using the crank sensor to run the car. It just uses the cam sensor to see when cylinder 1 passes by.

Just as an update, I tried running it with the cam sensor unplugged and it immediately ran bad and set a code 41 (cam circuit). When I tried plugging it back in, it now immediately sets off a code 18 and runs like crap (high idle, occasional stutter, little to no acceleration)

I tried putting in a new cam sensor, but when I opened the box there was a seal from the connector (returned) and possibly broken. Swapped the sensor and it ran the same but I'm going to try another one to be 100% sure.

Do you have any tips for checking wires for shorts, signals, and such? I pretty much just put an ohmeter on each side to check for continuity and opened up some of the wiring for a visual check.

On a side note but possibly related, I have some white smoke coming from the back of the engine. I'm not sure if its coolant that spilled on the exhaust that hasn't burned off, smoke from the exhaust (car has really bad exhaust leak), or a sign of something else?

Is there a remote possibility it could be the TPS (throttle position sensor)? I replaced it about a year ago with a cheap aftermarket and it hasn't been 100% since and the connector also broke while changing it. It could be a red flag for other stuff, but could it cause a code 18 timing signal issue?

I tried replacing the cam sensor and it didn't work and I now get a code 18 almost instantly after starting the car. It still runs (not very driveable) but almost no acceleration.

I checked the MAF sensor and the wires looked fine.

You should read my post on my Code 18. I had a shop manual with the troubleshooting and I followed every step. Even did register checks on wiring etc. My code 18 was caused by a bad coil. My car was a 1993 Buick LeSabre with the 3.8 litre engine. When I got the coil replaced the code 18 went away. A few days later I got code 19. I checked under the hood in the dark and saw a bad ignition wire; got a mid grade set of wires and the code 19 went away. Code 18 and 19 can be caused by ignition coils and wires outside of what the bleeding shop manual states, at least for my 93 LeSabre.

Dad told me once that if you want to check for arching in coils or ignition wires is to look under the hood when it is dark; arcing shows up better. HOWEVER, please be very careful and don't put your hands into the engine compartment as you can not see the belts etc.

Here is the post on my code 18 issue, I even opened her up to check the timing chain; which could have went for many more miles LOL. Ugh. So to recap, Code 18, bad coil, code 19, bad ignition wire. Car has been running fine ever since.

https://www.gmforum.com/buick-172/19...epairs-301438/

OK, saw where you had your coils checked; how did they check them? I suggest buying a new set of coils; here is a guy on ebay selling all three; AC Delco brand, for $53.50 and free shipping; if you search you can find cheaper Chinese ones.

New ACDelco Ignition Coil Set 3 D555 C1235 DR39 | eBay

Definitely read your thread all the way through early on. The way I checked the coils was used an ohmeter across the terminals (I guess thats the term) for each coil and they were consistently around 5.67 kOhms (The secondary resistance). I had autozone check them as well and he checked only one of the primary resistances. I don't remember what he said but he said the primary was fine but complained about the secondary resistance being too low. I'm not sure what exactly its suppose to be but doesn't seem out of whack.

I did replace the wires and plugs last year. I hooked up a inline spark tester on the coil side and they seemed to all fire correctly.

So to check for arching do you just unplug the under-hood light and look closely while its running?

I'll try taking a video maybe tomorrow to see if it helps diagnose it. To be honest I'm about ready to dump unfortunately, which is hard because its my first car and I've had it for like 7 years now.

Thanks for the help. If anyone is going to be able to help me at this point its probably going to be you because this problem seems kinda rare.