Yeah... wouldn't the SES light come on also? It seems like if it was one of the sensors the ECM would be having a field day with throwing SES/codes when the misfire starts.

*Sigh* Yep, I have considered that the fuel pump/sending unit could be to blame. I have been avoiding the urge to rent a fuel pressure tester and tape it to the windshield for two days. Ignition and (arguably) CPS are much easier so I would rather try those first.

Luckily, the entire fuel pump/sender assembly is only about $90 shipped from RockAuto. I've been wanting to do it anyways, the fuel gauge has been unreliable and I suspect the float level sensor is shot. I just really dread dropping the freaking tank. I have heard horror stories about 20+ year old steel fuel lines snapping when trying to disconnect them. I also don't even know if my floor jack will raise the car enough to get the tank out from under it once it'* dropped.

Well, I really appreciate you guys trying to help anyways. Really.

Honestly at this point I am wondering if I should just take it to a Buick dealer one day after the problem starts and have their service department put it on the Tech I scanner.

Liberty Buick is reputable and they quoted me $100 for a diag, which is way less than I'll spend on new ICM + coils, CPS, fuel pump/sender assembly (this is the order I'd go with based on part cost/difficulty.)

Especially if none of those turn out to be the cause.

Side thought ... I am guessing there is little or no chance these problems could be caused by either a bad fuel injector controller, a bad injector, or a fuel pressure regulator with a bad diaphragm? I would assume no, since the problem is intermittent and only seems to happen when engine is hot.

They are all easy to check actually. You can bend wires out on a 194 bulb, and plug it in in place of an injector. If there is an issue, you will notice inconsistent blinking of the bulb. The injectors are controlled directly by the PCM, in which it simply grounds the injector to fire it. This would be resolved by replacing the PCM.

The other issues will be apparent when you start checking fuel pressure. Namely, that pressure won't hold when the car is shut off. Also if the diaphragm is bad, it will typically push gas through the vacuum line of the regulator, but that tends to cause the car to run rich, with a different set of symptoms.

And on the subject of CPS codes, I have never seen OBD 1 in this application throw a CPS code. The computer simply thinks the engine has stopped turning and stops fueling and spark. There may be some instances where the computer sees one reference signal and not the other (one of the two sensor sides), but again, I don't ever remember seeing a code for that.

I have seen it pop up once on my '94 regal however, but that was a one time fluke however, and it is also the feared OBD 1.5 system (the enhanced version), so a different animal.

If you are handy, you may be able to pick up a scanner that can serve your needs for the same $100 you would spend at the dealer. It may be worth looking in to.

One other thing I totally forgot to mention (we could use a post edit button.)

Right after I did the Delco ignition swap today, the speedo was magically working again. But it only worked for a mile or two. After that it returned to the 'sit at zero or jump around' behavior.

Here'* some more history on the speedo, just in case that may help diagnose the main problems. It supposedly was working intermittently when my dad originally bought the car. When it wasn't working, which was most of the time, it would either jump around or sit at the points I described in the original post. This was regardless of actual vehicle speed. It exhibited this behavior this right up until I parked it in the driveway last year.

When I started driving the car again it worked most of the time for a day or two, then less and less intermittently for the rest of the first week. This past week it hasn't given any accurate readings at all. Until today.

I'm not sure if it'* related, could just be a coincidence.

The speedo may be a faulty cluster, which, again, would be confirmed with a scanner. The scanner can read vehicle speed.

I guess fuel pressure and injectors would be the next thing to check, then.

Ah. With that being true, I guess the CPS is unfortunately back in the running as a suspect.

I can't seem to find any aftermarket GM OBD-I scanners that provide live data display. From what information I can gather online, I would need a GM Tech I scanner kit with the GM 88-92 Brake and GM 88-91 ECM/PCM cartridges, plus a mass storage cartridge, to get any live data from the PCM. Is this correct? That stuff together costs like $300-$500 on eBay, that'* just not a feasible option.

I already have the Actron CP9001 OBD-I code reader, but that unfortunately does not give any live data. Will the PCM in this car even provide any live data?

I did find this one that seems to be able to display live data, but it'* $242 + whatever the OBD-I connector cable costs.

https://www.summitracing.com/parts/a.../model/lesabre

I run an Actron cp9145 that I picked up on eBay for$40, with a gm aldl cable (another $20). Admittedly that price iz unheard of for that unit, it accomplishes all of my needs including gm obd 1.5. It doesn't catch a lot of the advanced functionality of obd2 unfortunately, but it is one example of many of things out there. That'* not even counting the pc based solutions

I have a diagnostic appointment next Monday at 9:30am. I'm gonna try to get the car to induce the misfire before I head over. With any luck, I'll know what to replace next.

Yeah, about the PC route, do you guys have any recommendations for a USB -> GM OBD-I ALDL connector?

I did also find a few Bluetooth scanners that range between $50-$80, those would also work as my laptops all have Bluetooth. The issue I see is that hours of Googling suggests TunerPro/ALDL PCM profiles don't yet exist for the LN3 3800 engine in this year LeSabre. Which is very, very unfortunate.

If anyone knows where I can find the PCM profile for a '91 3800, please let me know! I'd sure like to have one of these scanners.

With what you wrote below the poor gas mileage , is it possible that you have a fuel injector leaking ? TheReaper!



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.