Intermittent Stumbling and Dying

For a year or more, my 1994 Roadmaster wagon very occasionally would act kind of like it was running out of gas for 30-60 seconds, then recover. Sometimes it was days between these events, sometimes weeks. Then, a few weeks ago, it got really bad and finally wouldn't run at all, leaving me stuck on the side of the freeway to call AAA. Of course, once back home, it started right up and ran fine.

Based on some things I read here, I replaced the evap purge valve. The car seemed just a tiny bit peppier and I thought maybe I'd fixed it. Then, today, sitting at a stop light, it started stumbling again, died and wouldn't restart until hours later.

I've just replaced the ignition control module (just grasping at this point), but don't know yet if that fixes it and have little confidence that it does.

When it acts up, there's no codes, although the "Service Engine Soon" light does come on occasionally, but only for a minute or two, then goes off. But the light does not coincide with the times when it runs bad. This is a 1994, so no OBD-II.

Any ideas? Are there other parts of the evap system that could cause this? If so, how easy is it to drop the tank to get access to that mess (this is a wagon).

Could be the fuel pump or the hose that connects it to the metal line. There has been a rash of issues like yours lately.  Did you try swapping out the fuel pump relay? You can hear the fuel pump run for about 3-5 sec. when you turn the key on, because it is priming the injection system.

The light coming on occasionally could be the EGR valve not working. It could also be an O2 sensor, but a single one will not cause your engine to not start.

Whatever your issue is, it is a heatsoak issue, because when it cools down, it seems to act normally.

The evap system is likely not the issue, although changing the PCV valve would be a cheap item and probably needs to be replaced anyway.

Your temp sensor for the computer may shut the engine off, or not let it start. The engine temp sensor for the computer does not work the gauge, or idiot light.

Dropping the tank is not all that difficult, but is a lot easier with a helper. If you disconnect the filter at the front, and put a line on it to a gas can, you should be able to use the FP bypass connector to run the pump, and pump the gas to the can (if this works, it is probably not the fuel pump). Make sure you have enough gas cans for all of the gas. You must disconnect the three lines to the tank (you may need a tool, or they may be quick release), then there two long bolts with 13mm heads at the rear, and two vertical bolts with 15mm heads at the front. You can remove the three screws at the filler neck 7mm or Philips head, and unbolt the ground strap for the filler tube 10mm. Remove the heat shielding on both front sides of the tank, and the one along the driver's side 7 mm and maybe 10mm. The connector for the pump/level sender is on the driver's side of the frame, at the rear. You do not have to remove the filler tube if you jack it far enough off of the ground. The nuts on the top of the sender are 10mm head. Other than being awkward, it is not really difficult.

If the check engine light came on, even momentarily, wouldn't there be a DTC stored in history? If you have access to a code reader (parts store?) perhaps that could give you some direction?

I just dropped my fuel tank (no fuel pressure post) for the 2nd time and it was so much easier with a transmission jack. I was also able to get most of the fuel out, by disconnecting the fuel filter and pumping into a gas can, even though the hose from the pump to sending unit was split. It would pump but could not build pressure. Since I had most of the fuel out I was able to remove just the front strap bolts and tip the front down then slide it out the side.

Haze5736 wrote:

If the check engine light came on, even momentarily, wouldn't there be a DTC stored in history? If you have access to a code reader (parts store?) perhaps that could give you some direction?

I just dropped my fuel tank (no fuel pressure post) for the 2nd time and it was so much easier with a transmission jack. I was also able to get most of the fuel out, by disconnecting the fuel filter and pumping into a gas can, even though the hose from the pump to sending unit was split. It would pump but could not build pressure. Since I had most of the fuel out I was able to remove just the front strap bolts and tip the front down then slide it out the side.

with OBD1 you need a special code reader that most part places do not ever stock as it is outdated and they wouldn't be able to make money selling them.

I've looked into it myself to try and find a way to actively watch sensor inputes to the ecm to try to figure out a performance issue with my 94 rmw, but my issues are usually only when the car is cold, or started up after sitting for a couple hours.

sadly with OBD1 unless you can find someone who has an old code reader from that era the only way to get codes is to try to catch it with the check engine light on and jump terminals A and B with a wire or paperclip, or there is a "code reader" available that all it does is jump those two terminals and then you have to count the flashes of the check engine light to get the codes.

if you have an air mattress pump that can pull air out aswell as pump air in set it up to pull air through the distributor vent the way air would normally flow through it and have a section of clear hose, run the pump for 15 to 20 minutes once the car heats up and see if you can notice any condensation on the inside of the clear hose, did this on mine to make sure I wasn't getting excessive moisture in the optispark to cause my problems.

Otherwise I would try to find a way of testing your ignition coil and ICM, before you replace them, as if they are original once you get the bracket off the cylinder head, you will have to drill out rivets to get both off the mounting bracket, you might also want to check the MAP sensor or Manifold Absolute Pressure sensor, little black rectangular sensor off on the passenger side of the top of the intake behind the throttle body.

The 94 and 95 need a specific code reader, because you can not jump the terminals to get a flashing SES light like the 91-93 cars. The codes are stored for about 50 starts, and then they will be automatically erased.

Fred Kiehl wrote:

Could be the fuel pump or the hose that connects it to the metal line. There has been a rash of issues like yours lately.  Did you try swapping out the fuel pump relay? You can hear the fuel pump run for about 3-5 sec. when you turn the key on, because it is priming the injection system.

The light coming on occasionally could be the EGR valve not working. It could also be an O2 sensor, but a single one will not cause your engine to not start.

Whatever your issue is, it is a heatsoak issue, because when it cools down, it seems to act normally.

The evap system is likely not the issue, although changing the PCV valve would be a cheap item and probably needs to be replaced anyway.

Your temp sensor for the computer may shut the engine off, or not let it start. The engine temp sensor for the computer does not work the gauge, or idiot light.

Dropping the tank is not all that difficult, but is a lot easier with a helper. If you disconnect the filter at the front, and put a line on it to a gas can, you should be able to use the FP bypass connector to run the pump, and pump the gas to the can (if this works, it is probably not the fuel pump). Make sure you have enough gas cans for all of the gas. You must disconnect the three lines to the tank (you may need a tool, or they may be quick release), then there two long bolts with 13mm heads at the rear, and two vertical bolts with 15mm heads at the front. You can remove the three screws at the filler neck 7mm or Philips head, and unbolt the ground strap for the filler tube 10mm. Remove the heat shielding on both front sides of the tank, and the one along the driver's side 7 mm and maybe 10mm. The connector for the pump/level sender is on the driver's side of the frame, at the rear. You do not have to remove the filler tube if you jack it far enough off of the ground. The nuts on the top of the sender are 10mm head. Other than being awkward, it is not really difficult.

Thanks, Fred! Yes, I learned all about the fuel pump relay last year and gained deep understanding of it when I found, once started, I could drive to Autozone with it in my shirt pocket.

I discovered last night that the evap canister is nowhere near the fuel tank, as I assumed, so for now I won't be dropping the tank. I've ordered a new canister and valve so I'll swap those in along with new hoses later this week. Even if that doesn't fix the problem, it should prevent future ones. Just like the new ignition control module I put in last night. Yes, heat does seem to be somewhat involved, as it usually runs just fine for the first number of miles, which also makes me wonder if it has something to do with the evap system, as from what I've read the PCM doesn't open the valve until certain factors, including temperature, are within its specs.

Long as I'm under the hood, I'll do the PCV, too.

Thanks!

And thanks to everyone else who replied. This will be my evening activity for the next few days. I absolutely must have this car running reliably. Thanks!

Change one thing at a time, so you know what fixed it.

quick way to check your EGR, get a cheap hand vacuum pump from someplace like autozone, hook it up to the EGR and see if the EGR hold vacuum if it does good, then watch the EGR as you apply vacuum, if the diaphragm opens smoothly then the EGR is fine, then you just need to check the vacuum control solenoid, hook the hand pump up to the line going to the solenoid and start up the car, you should immediately have vacuum, if you do then the final thing really is to see if the control solenoid activates.


The only other thing I will add, when I was checking my distributor vent system, I had my vacuum gauge hooked up on the intake side so the inside of the distributor was pulling a vacuum, at idle the car was fine, but if the throttle opened at all the engine would stumble and nearly died on me before I would release the throttle, so it might be an out there thing but maybe there is something causing an issue with the distributor vent harness when the engine heats up as the lines do run almost right next to the block.

OK. So weird. I replaced the evap canister, along with all the hoses, and so far it's running great. Before I started working on it I tried to start it to move it into the driveway and it wouldn't start. So I had to do it in the gutter on the side of the street. But once I replaced the canister, it started right up.

One thing, critical, I'm assuming: when I took the air hose off the old canister, the nipple was completely clogged with plants parts -- little twigs, bits of leaves, etc. I can only assume that's what the problem was. No air could get in from the outside.

However, I do NOT understand why any off this should keep my engine from running. Fuel, air, compression, spark, it should run. If anyone has any insight into that, I'd love to hear why engineers would make something that can be so easily crippled by such a dumb thing.

But then, we all know through painful experience that automotive engineers are cretins.

Fred Kiehl wrote:

The 94 and 95 need a specific code reader, because you can not jump the terminals to get a flashing SES light like the 91-93 cars. The codes are stored for about 50 starts, and then they will be automatically erased.

Sorry to disagree, but my 94 RMW  doesn't need a code reader, I can access the diagnostics from the climate control.

From Buick forum and there's a code list specific to the 94 lt1 somewhere.

[You must be registered and logged in to see this link.]

Instructions for putting ACC in diagnostic mode -
- turn ignition to ON position (or start vehicle)
- press and hold the "temp up" and "OFF" buttons at the same time until the unit does a full segment check.
- Release the buttons.
- Display should read -00... you are now in diagnostic mode
- Using the fan up/down buttons, select desired function from above
- press the "middle" Button. It should be in the top right corner on the CC.
- To Exit the trouble code area, and go back to the -00 display, hit the "Middle" button again.

Is the climate control diagnostics documented in the FSM anywhere? I looked once but couldn't find it. I had a 94 Cadillac DeVille with the climate control diagnostics and it was well documented in the FSM. On the Caddy you could override parameters and basically had bi-directional control so you could activate solenoids, valves and motors.

m00ntan wrote:

Fred Kiehl wrote:

The 94 and 95 need a specific code reader, because you can not jump the terminals to get a flashing SES light like the 91-93 cars. The codes are stored for about 50 starts, and then they will be automatically erased.

Sorry to disagree, but my 94 RMW  doesn't need a code reader, I can access the diagnostics from the climate control.

From Buick forum and there's a code list specific to the 94 lt1 somewhere.

[You must be registered and logged in to see this link.]

Instructions for putting ACC in diagnostic mode -
- turn ignition to ON position (or start vehicle)
- press and hold the "temp up" and "OFF" buttons at the same time until the unit does a full segment check.
- Release the buttons.
- Display should read -00... you are now in diagnostic mode
- Using the fan up/down buttons, select desired function from above
- press the "middle" Button. It should be in the top right corner on the CC.
- To Exit the trouble code area, and go back to the -00 display, hit the "Middle" button again.

Personally I don't the EVAP system is the cause. It simply doesn't contribute enough fuel vapor to the engine to cause stalling. If a hose was busted, there may be a vacuum leak when the EVAP solenoid was activated but it only activates under load anyway, so you'd just see higher long term fuel trims as the PCM compensates for it.

If it was my car, read the codes FIRST via the climate control. The PCM is trying to tell you what's wrong.