Hi all! Longtime lurker, first-time poster. As the thread title says, I have a '91 LeSabre that has been making life exciting. 3.8L 3800 V6, A/T, ~220,000 miles. This is going to be a long post with a lot of information. Sorry in advance.

First, some history: I've owned the car for about a year and half. Before that, my dad had it for a few years. He purchased the car from a family friend (the original owner) who, from the way the car looks, drives, and runs most of the time, took pretty good care of it. Tons of maintenance history, parts receipts, the original manual, and even the original dealer window sticker came with the car. They also had these problems and tried a bunch of stuff, but never figured out the cause.

When I first took the car, it would start acting up and quickly get so bad that the car was undriveable. I tried to figure it out back then, but with little time and money to spend on it at the time, I gave up. The car sat parked in my driveway for over a year.

I finally decided that it'* time to either figure this out or sell the nightmare. A couple of weeks ago I replaced the battery (old one was long past dead) and suddenly it seems to be running a hell of a lot better than it was back then. When the problem does occur now, it'* not nearly as bad as it was back then, at least at first. It seems to be reliable enough now, and we really need a second car right now, so I went ahead and tagged/insured it.

Okay, into the madness... The primary issue is that the engine intermittently begins to stutter and/or miss and/or buck under load, this generally occurs after the car has been driven for a while. More on this further down.

A secondary issue, which I assume is related to the primary issue, is that it sometimes runs rough when cranked up. This can happen when the engine is cold or hot, doesn't seem to matter. Sometimes when this happens, it will sputter for a few seconds and then the idle will kick in and level it out. Sometimes the engine will die, I'll crank it back up, and it'* fine. Rarely, I'll crank it up for the second time and it'll sputter, and then the idle will shoot way up until I kill the engine (I am guessing 2000-3000+ RPM, no tach in this car.) And then I'll kill the engine, crank it back up for the second (or third time, depending) and it'll run just fine.

A tertiary issue is that sometimes the engine will stall when the car is going over a speed hump, usually if I'm doing more than 15mph over them. Like the previous issue, I assume this may be related to the primary issue. It doesn't usually kill the engine completely, but the SES light will light up for a second when this happens. Once or twice, the engine did totally die and I had to pull over and crank it back up. When this happens I generally hear a knock, but I'm not sure if it'* suspension making the noise, engine knock, alternator hitting the underside the hood, etc.

A quaternary issue is that the speedometer either doesn't work or the needle jumps around most of the time. The needle spends most of it'* time at either the zero point, at 45mph, or past 85mph on the speedo. Whether or not the vehicle is actually moving seems to have no effect on this. Could just be a bad cluster or VSS, or (according to some things I've read) could be related to the primary, secondary, and tertiary issues.

Now, let'* go back to the primary problem. The car will generally crank right up and run like a top after it'* been sitting for a while (30+ minutes.) The problem is intermittent and only starts after the car has been driven for a while, and only on some days it seems. On some days, I can drive the car around for most of the day and it'll be fine the entire time. On other days, it starts acting up after 30-45 minutes of cruising around. When this behavior does occur, the stuttering will begin subtly and get progressively worse, and the bucking more violent, the longer I drive the car. The 'fix' seems to be to turn the car off and let the engine cool down for 20-30 minutes. After that life is usually good again, at least for a while.

The sputtering/bucking is most violent and most noticeable at WOT with A/C running, but it does happen with less throttle applied (barely any throttle at all is needed to induce stuttering when the problem is really bad) and it is still noticeable without the A/C on. And of course, it gets progressively more violent and noticeable the longer I drive the car when this problem is occurring.

Running it at interstate speeds does seem to make the problem occur sooner rather than later, but that is also inconsistent. The other day I took a 30+ minute trip (each way) to Pull-A-Part in mixed interstate/city travel and had no problems. Yesterday, I took a trip of similar length in mixed interstate/city travel, problems began (but were barely noticeable) while heading to my destination and became progressively worse on the return trip. It was stuttering pretty bad by the time I got to my destination. Turned it off for 30 minutes, it cranked up and ran perfectly fine after. It is worth noting that the car was not running while I was in Pull-A-Part, but it was idling for 20 minutes while at my middle destination yesterday.

It probably goes without saying, but MPG has been absolutely awful. Based on the trip counter in the car (which is backed up with my phone'* GPS speedo app, which always runs when the car does) against gallons of gas pumped, I've calculated about 11 MPG average over the past couple of weeks. I've tried to drive it with a light foot except when getting on the interstate.

Also, the cruise control works. In my mind this means ECU/sensors are probably working, but I could be wrong. When the engine is running fine and the problem isn't occurring, it maintains normal speed and behavior while on cruise. When the sputtering/missing is occurring, cruise still works. but it loses small amounts of speed over time when it'* running on cruise.

I have a code check tool that plugs into the diagnostic connector under the dash, but it never throws a CEL/SES when the problem occurs. This has made it very difficult for me to diagnose.

Finally, here is a list of things I (or my dad) have done/checked/replaced (even if they may not be related) in order:

Last year:
*New plugs/wires
*Alternator replaced
*Water pump replaced
*Two motor/transaxle mounts replaced
*Checked for SES codes with diag tool repeatedly, no codes thrown

In the last two weeks:
*New battery
*New bolt for positive battery pole, original one wasn't tightening down well
*Checked fuses, none blown
*Checked with diag tool again, no codes thrown
*Checked that alternator is putting out 14+ volts at idle, and it is
*A/C recharged for summer
*New gas cap, old one didn't seem to be venting at all (long hissing sound when unscrewing it.)
*Rislone 4700 fuel system treatment added to a full tank
*Fuel filter replaced. A bit of brown liquid came out of the fuel line when I pulled the old filter off, but this could be removed gunk from the fuel system treatment.

Of course, none of these have fixed the problem. I was going to check the coils for resistance today, but it'* been pouring the rain so that may wait until tomorrow.

Here'* what I have to work with:

*Full mechanic'* toolset, SAE and metric
*Digital multimeter/voltage tester
*Jacks, jackstands

I can buy/rent more tools if needed, but if I can scrape by without that would be preferable. We've already dumped a bunch of money into this car.

If anyone has any ideas, please let me know. I am running in circles and don't know what to do next. Help me, Obi-Wan Kenobi, you're my only hope!

I forgot to mention in the original post: When the car cranks up and sputters to death with the rough idle, sometimes I can hear loud popping noises. It'* almost like a very loud hiccup.

What model of scanner are you using?

We had very similar issues when the Crankshaft position sensor failed on our Bonneville. It started with the car not restarting 20-30 minutes when warm, until it eventually started shutting the car down on the road. A code never set with this issue, and was resolved with the sensor replacement.

The ICM could also cause similar issues while warm.

You can also check MAF sensor, which could cause stalling issues with bumps and such, but it will usually set a code if that is the issue. You can confirm it is the issue by tapping it with the handle of a screwdriver.

Actron CP9001. Not a true code scanner in that it'* basically just a jumper for the diagnostic port pins.

See, that'* the thing. People say that with the crank position sensor being bad, not starting up is the usual symptom. The car has NEVER refused to start. I can crank it up, turn it off, crank it up, off, repeat, and it always fires up. Sometimes it just has the secondary rough idle issue I described, but simply turning the engine off and cranking it right back up again seems to 'fix' that.

Is there any way I can check that? I mean, it is a $125 part.

I also thought that could be the problem, but no SES light. I just asked my dad about it and he said that he replaced the MAF right before he gave me the car. So, once again, I'm stumped.

Last year I had a 3.8L that bucked and sputtered when under load, especially when accelerating after a full stop and after it had fully warmed up. Turns out it was one of the spark coils. After I replaced the 2/5 coil, the issue was gone.

Thanks for that info, I've actually been thinking the coils were to blame. It does feel like the car has dropped a cylinder or two when the missing happens, it seems to be fairly rhythmic. I know how to check the resistance between them with my ohmmeter but I don't know how I'd do that when the engine is hot and presenting the problem. Just have to be quick, I guess?

Still, I'd want to be sure. Replacing all three banks isn't cheap either.

Here'* what you can do to determine which one is at fault (if any).
Since all 3 are the same:
1) Purchase 1 replacement coil.
2) Replace one of the three coils (a simple and quick job)
3) See if issue persists.
4) IF issue persists, take out the new coil, put the old coil back.
5) Replace one of the remaining 2 with the new coil, see if issue persists.
6) IF it still persists, replace the third coil with the new, and put the old second one back.
7) If issue persists, you will know it is not a coil issue. Put the old 3rd coil back and return the new coil you purchased. You will have invested time, but if this is not the issue, then you can get your money back and no cash lost. If this resolves your issue, you will have spent the minimum funds necessary.

If the ICM hasn't been replaced, it'* likely still fitted with the Magnavox ignition system. This has the coils as 1 integrated unit, with plug wire posts down both sides. This system is prone to failure, and everyone generally encourages replacing this system with a delco ICM and coil packs (3 individual coils, all terminals on the same side). If the ICM has never been addressed, it would likely be best to do this swap out with salvaged parts to keep costs down. The series 1 system is typically a direct replacement, just be sure to get the brackets and such with it.

Also, does the Service Engine Soon light come on at all? It should come on with the key, and then go out when running. Also, when you check codes with the device that you have, you should always get a code 12, even if everything is working properly.

And if you believe the coils are suffering from a heat related failure, you can pull the coil pack, and check the resistances. Then stick the coil pack in a 150-170* oven, let it get nice and toasty, then check it again. If it is heat related, it should be apparent at that point. Just be sure not to set it to broil, because for some reason plastic doesn't like that.

Now, this is new information! Yeah, mine has the OEM-type with three posts on either side. I'll happily replace it if it'* that prone to failure, might as well give it a shot right?

I'm not too familiar with the lineage of the 3800 engine, I just know it'* said to be very reliable. What years/models have a Series I that I can salvage a complete Delco package from, exactly? Which exact parts do I need to grab? (I assume ICM bracket, ICM itself, and the three coils to mount above?) Also, how are the plug wires connected with the new post layout?

I'll head up to Pull-A-Part this coming week if they have any matching years/models on the yard and I can afford the parts.

Yep, the SES does come on during the pre-ignition test, and the scanner does cause the SES to flash a code 12 three times. I only meant that it never throws any trouble codes.

That'* a good idea, I may try that. Still, since it'* the OEM package and you guys say they're not great, I think I'd rather just grab an updated Delco package anyways. Seems like that would be easier to diagnose and cheaper to replace when they fail?

This is a fairly comprehensive writeup on the whole swap:
http://padgett.performanceresearch.us//coils.htm