1999 Saturn SL Bad Misfire

[datafan]

Hi All,
I'll jump right into it here. My sons SL, which has been a fairly dependable car, suddenly went from running well to misfiring bad. The car died on him due to the misfire, then ran perfect again for a couple short trips, then started the misfire again and hasn't stopped.

I made a youtube video of the car running but can't post the link here since I'm new. My youtube channel is my name, Jim Marquardt and the video is called 1999 Saturn SL2 Bad Misfire.

So far I have:
1. Checked fuel pressure and found 50lbs at the rail.
2. Replaced the ignition module making sure to clean the contact patch with the engine well with a wire brush on the drill.
3. Checked both coil packs across the posts getting 8.5K Ohms resistance, which is within spec.
4. New copper spark plugs gaped correctly. (of course, who doesn't throw a new set of plugs at everthing first).

Pulled all the engine codes, none of which seem like they would cause this bad misfire:
P0137
P0404
P1404
P0741
P0452
P0446

Next step is to replace the ECTS (Engine Coolant Temperature Sensor). I wouldn't expect this sensor to be the cause, but from what I have been reading, these are known to fail and linked to several systems. Apparently they can cause havoc when they go bad, but can they cause an engine to run this bad?

I forgot to say that when I took the video, I had the ECTS wire unhooked. Just thought I would see if it made any difference, but it runs exactly the same when it's hooked up.

Any ideas are welcome. Thank You!

[Waiex191]

No ideas yet. Link:
https://youtu.be/vFqjf--FzrU

I did have a misfire that I fixed by new coil packs at about 150K. Was not that bad, as I think it still idled. Could not achieve highway speeds though. There could be a breakdown inside the coil pack that is not picked up by the meter but could cause insufficient dielectric resistance for the higher voltages. This was on my '99. I still have the original ICM.

[OldNuc]

Wrong type of spark plugs, failing ICM, failing coil(s), bad plug wires. If it is not ignition then it is mechanical.

[Waiex191]

...and if it comes and goes it is not likely to be mechanical. I'd do coils and wires if you haven't already. It sure seems like ignition to me.

[OldNuc]

Platinum plugs cause things like this.

[datafan]

I think it's also ignition related due to the way it comes and goes.

I got the recommend AC copper spark plugs and gapped them at .040.

I might try throwing a set of coils at it if replacing the ECTS doesn't help.

I haven't priced coils yet, still stinging from the $115 ignition module.

Could the crank sensor cause this?

[mattwithcats]

Plugged catalytic converter?

Pull the O2 sensor out, see if she runs....

[454cid]

I fixed my mis-fire/rough-running by changing plugs, wires and cleaning up the ICM/coils/bolts.

It came and went, especially when hot. It was not as bad as yours, Though. It easily stayed running by itself.

[termite]

Stuck open EGR valve? Here is a video from Pine Hollow Auto Diagnostics. https://www.youtube.com/watch?v=oyoW7GKGmPk

[billr]

Alas, the video shows mainly your foot and the steering wheel. I would have liked to watch the tach more and see how the engine is shaking.

Live-data can save a lot of guessing. A ECT sensor problem will be easy to see, and you can probably see rpm fluctuations if it is CKP sensor problem. Look at fuel injector pulse-widths.

One trick is to try running it on just one or two cylinders at a time. If the problem is isolated to one cylinder or coil, it will show up boldly.

As already said, it is not likely to be a mechanical problem, but take compression anyway.

I gotta ask... did you check fuel pressure while the engine was running poorly?

[OldNuc]

Originally Posted by datafan

I think it's also ignition related due to the way it comes and goes.

I got the recommend AC copper spark plugs and gapped them at .040.

I might try throwing a set of coils at it if replacing the ECTS doesn't help.

I haven't priced coils yet, still stinging from the $115 ignition module.

Could the crank sensor cause this?

The ECTS is not likely and neither is the CKP. Aftermarket ICM may be bad out of the box or you have bad plug wires. If you really want to fix this go to the local pick and pull and pull a complete module out of a 96-99 Saturn.

FLAPS coils are in the 30-40 ea range.

[OldNuc]

Try blocking the EGR valve.

[termite]

I saw this was listed. P1404 Meaning The Powertrain Control Module (PCM) determines that the EGR valve is stuck open if the actual Exhaust Gas Recirculation (EGR) position and the learned closed EGR position vary by more than a predetermined value. Maybe it can be removed and cleaned. It seems to be intermittent right now.

[datafan]

Originally Posted by termite

Stuck open EGR valve? Here is a video from Pine Hollow Auto Diagnostics.

The car in the video seems to present the same symptoms, not to mention the EGR code we are getting.

I tried tapping on the EGR valve a bit tonight, but it didn't make any difference. Either it's really stuck, or it's not the issue, but I'll find out for sure soon. I intended to take it off and clean it, but got rained out tonight. Definitely worth a try this before throwing any more new parts at it.

[billr]

Try blocking off the EGR first, as suggested. It is far more definitive a test, and easier, too.

[datafan]

Solved! I removed the EGR and could clearly see it was stuck partially open. When I pushed the plunger in the rest of the way it stuck all the way open.

Copious amounts of carb cleaner and wd 40, while spinning the plunger with a star bit in the drill, had it operating freely again in no time.

I reinstalled it, and the car fired right up and purrs like a kitten again.

Thanks everyone for your help!

[termite]

Good Job👍