Misfire, rough idle, and lacks power. spark okay.

Hey what's up guys? How is everyone? I haven't posted on here in years. I think I joined about 8 years ago or something. I've had my Riviera for about 12 years now! And besides Lots of cosmetic issues especially the paint and door handles and hinges, the car has run great all these years. Seeing as it's an 18 year old car that's pretty damn good. I started having a problem with the engine misfiring and idling rough after getting gas but it could be a coincidence. Below is something that I typed to a mechanic friend of mine so excuse if there's any typos or unprofessional text I just don't want to have to type it all over again Thanks.
1997 Buick Riviera 3800 Series II, Supercharged, VIN code 1, 3.8L SFI: car started to have overheating problem and overheated twice. Took into mechanic to repair, replaced coolant intake "elbows" which were cracked, flushed radiator and replace thermostat. Car ran fine for 1 month. No cooling issues. Got gas at Murphy (Walmart gas), 93 Octane and 2 minutes into running, car started to hesitate and had rough idle up to 2000 rpms. Not sure if the gas has anything to do with it but brought to autozone and Car had check engine light on and then started flashing so I did diagnostics and it pulled 3 codes: p1200 p0302 p0341, which point to cylinder number 2 misfire cam sensor problem and, fuel injector. I performed a vacuum line seafoam treatment as well as seafoam in the crankcase and gas. With the vacuum line seafoam treatment, white smoke started to pour out and then disappeared so the car is definitely cleaned out! but the hesitation at idle and upon take off still exists. Also the car is lacking power so I brought it to the mechanic and they noticed a misfire in cylinder 2 so he took out the spark plug of cylinder 2 and noticed that the electrode was rusted so he replaced the spark plug and did some cleaning and also used that electrical connection grease stuff. Put the spark plug back in and the engine was running fine but then within a minute the misfire happened again. He reset the codes and the only code that came back was cylinder #2 misfire so he said it probably isn't the sensor and it probably isn't the fuel injector but who knows...could be? they discovered intake gasket leaks and also my supercharger coupler bearings are starting to wear out and they said that that could be contributing to the problem but I know that's not the problem because it's been that way for about a year... and also I ran without a supercharger for a year and it never pulled any codes. so it's not the spark plug, it's not the wire because we wouldn't see a spark, not sure if its a coil pack but why would you see a spark is a coil pack was bad? Also there was no coolant on the spark plug but I could be leaking coolant into the engine but I'm not sure. also it could be because of the gasket leaks but then again I had gasket leaks for 2 years and this problem Just happened out of nowhere so I'm completely puzzled and my mechanic said that if we go any further and attempt any repairs and that don't result into the problem being fixed, then we're looking at doing multiple repairs until we can pinpoint it and I don't have the money for that.

So has anyone else experienced test? What do you think? and thank you so much for taking the time to read this long post.

-Chris K, Florida

Did anybody bother to pull the spark plug wire off of the coil and look for rust/corrosion? Did anybody check the plug wire itself? How about swapping coils around to see if the misfire changes cylinders?
Injector Balance test?

These are super simple tests to do.....

yeah, i would swap coils and wires. process of elimination, get that stuff out of the way right off the bat.

90% of the time isn't it the wires anyways..?

I would go after the gas first - suck it all out into cans and put some fresh gas in there. Look for the last thing you did before the problems started. In your case, the gas station stop exactly coincides with the beginning of your trouble. Takes a minute for the new gas to make it up through the lines.

deekster_caddy wrote:

I would go after the gas first - suck it all out into cans and put some fresh gas in there. Look for the last thing you did before the problems started. In your case, the gas station stop exactly coincides with the beginning of your trouble. Takes a minute for the new gas to make it up through the lines.

you would flush the fuel out before checking wires and coils?

No way. He's getting a misfire in cyl 2. It's spark related, I think.

charlieRobinson wrote:

No way. He's getting a misfire in cyl 2. It's spark related, I think.

Spark or Injector. Bad fuel would misfire on all cylinders or not run at all. Cmon deek....you must've skimmed over the cyl #2 part.

Abaddon wrote:

charlieRobinson wrote:

No way. He's getting a misfire in cyl 2. It's spark related, I think.

Spark or Injector. Bad fuel would misfire on all cylinders or not run at all. Cmon deek....you must've skimmed over the cyl #2 part.

yeah, guess it could be an injector. But wouldnt you be seeing KR if it was clogged? or something?

I would for sure start with swapping wires and coils to cyl 2. Do that and report back, bro.

charlieRobinson wrote:

yeah, guess it could be an injector. But wouldnt you be seeing KR if it was clogged? or something?

Not everybody monitors KR, Chuck. This is a daily driver. Besides, it's misfiring.....

I wouldn't suspect the coil either. That coil also fires cylinder #5. Also, he mentions an intake leak but never says whether the gaskets were replaced or not. Could be a leak into the cylinder that just got worse enough to cause the misfire. It wouldn't hurt to replace all the wires.

Thanks for the replies everyone! There was rust on the electrode of the cylinder #2 spark plug. Replaced new spark plug and it fires up fine but about a minute after running, misfire and misfire code comes back. As for thr gas, I think that it was either a strong coincidence or it helped contribute to the problem but, since then, I have put in ethanol treatment, seafoamed the vacuum line, put in crankcase and gas tank plus about a half of tank of fresh 93 octane. Its been about 10 days since the "bad gas" if it even was. The gaskets have not been replaced since the mechanic discovered the leak but the gaskets were in the same shape or at least I thought for about 6 months now. Unless the overheating caused it to become worse. Anyhow, I don't know which step to takr next without guessing and wasting money. Btw, after the new spark plug was replaced, the injector code went away and hasn't come back after clearing codes.

Put the cylinder 2 wire on a different coil/plug and vice versa. That will tell you if it's wires.

I was just leaning towards gas being the cause because this started immediately after a fill-up. Maybe crap in the gas clogged the #2 injector? It has to land somewhere and ended up there.

After the easy stuff (swapping wires) try swapping the #2 and #4 injectors and see if the problem follows the injector.

Thanks guys, i will try and swap the wires and report back. The problem is, I don't have an OBD scan tool to see if the cylinder misfire code swaped to another cylinder after the wire swap. As for the gas, I was strongly leaning towards that since yes, I did happen a couple minutes after getting that gas. I spoke with the manager of the station and he pulled the levels for that fuel for that evening and he said there was no water in the tank, all levels were normal and he sold anout 1000 gallons of 93 Oct. (which is what I got) this month. Wouldn't all the seafoam treatment I did plus ethanol treatment and fresh gas unclog the injector by now?
As for swapping the injectors, I wouldn't even know how to do that.

Update: I just started it about 15 minutes ago and upon putting it in drive, it sounds like a 2 cylinder engine. When putting in reverse, it almost stalls and when conning to a near stop, say, 10 mph-1mph, I have to put it in Neutral to prevent it from stalling.

LARRY70GS wrote:

I wouldn't suspect the coil either.  That coil also fires cylinder #5.  Also, he mentions an intake leak but never says whether the gaskets were replaced or not.  Could be a leak into the cylinder that just got worse enough to cause the misfire.  It wouldn't hurt to replace all the wires.

Hi Larry - about that coil I'd give that a maybe. I had a coil (the 1-4) that became a dog - apparently something went wrong with one of the posts. I think the failure was induced by the spark plug terminals loosening over time. With this high energy ignition that will mess up the coil over time. I still have to send those plug wires back to Magnecor -- they are interested in seeing what the issues are in the wires after 200,000+ miles of use. In the meantime I got a set of OE ACDelco wires.

I read thru this thread - it's just going to take a while to fix this one. I am thinking theres a problem with one or more coils, brought on by running bum wires. No way to know the wires are bad until you see this kind of failure, however it's known that the OE wires work well and only last but so long. If you're running non-OE wires, or non-high-spec wires (Taylor, Magnecor, couple others come to mind as high-spec) the high energy ignition in the Riv will kill them off. There's no way around it - you have to use good wires. Buying the ACDelco wires at the best discount you can find (rockauto?) is one way to save $$.

Another problem might be the coils. The standard coils can be installed on the supercharged engine coil pack but they don't run all that great. Especially if you mix the SC and non-SC coils on the module. I did that inadvertently, had a light lope that annoyed me but I could not figure out -- until just for fun I picked up some SC coils off a junkyard Park Avenue. Why? They still had the numbers stenciled on and readable... yeah I know... anyway, I put that on for the replacement coil and bang -- no more lope. Looked up the replacement coil and found that it was for the non-SC ignition...

So the question I have is, what happened to this car before you got/bought it? maybe this is simpler than it looks?