misfiring

I did a bad bad thing... Sadly, I knew I was doing a bad thing when I did it, but did it anyway. I was dropping the fuel tank on another car that had been sitting for maybe 2-3 years. I drained the tank (about 5 gallons). Not knowing what to do with the gas, I figured, I'd burn it off in the P5. I realized the gas was probably flaky, so I cut it with fresh gas (the bad gas appeared clear, there wasn't any rust, or any other contaminants). I put in 2 gallons of the bad gas, with 5 gallons of fresh gas, and there was probably an additional 3 gallons already in there. I drove the car without any incident whatsoever, until it was down to about 3 gallons. I then figured what the heck, the gas seems okay, so I dumped in the remaining 3 gallons. The car drove fine initially, but then got worse, and intermittently seemed to go into a "low power" mode. The car ran rougher, idled lower, and just generally had no power. I call it a "mode", because it seemed to just transition between being fine to running rough and then back. There was very little in between. Some times it would go into the mode, if you shut off the car, waited a minute and restarted it'd be fine, other times it wouldn't. Sometimes it'd just switch back and forth.

I put in another 5 gallons of fresh gas today, so for those keeping score at home, 15 gallons of fresh gas to 5 gallons of questionable stuff. It initially drove in rough mode, but within a few minutes switched back to normal mode, and seems fine. After it switched to normal mode, I've been running it in low gear/high rpm to try to give it an Italian tuneup. When it first went into rough mode, it threw a P0300 (misfire on all cylinders) -- and continues to do so whenever it goes into rough mode. I've also seen it throw a P0421 (inefficient catalyst warmup) after the P0300 came on. I hope I haven't damaged the cat, I haven't heard any backfires or loud/abnormal noises.

I'm wondering what the deal with this modal behavior is. I didn't expect anything like that. Only thing I thought was maybe the plugs are fouled or something. I'm also wondering why its continuing to do that. I doubt that the concentration is more than 20% of the questionable gas, and it was probably at 25% on the first round where it drove fine. I assume if I run it down to 2 gallons again, add 5 gallons it'll be down to about 7%, and if I do that one more time it'll be down to 2%, and at that point its hard to imagine that it's doing anything. I've heard most gas cars can run fine with up to 10% diesel in them.

Thoughts? Other than I'm an idiot?

I fit were me, I'd put 2/3 can of Seafoam in the gas and 1/3 up the brake booster.

You might be lucky and just fouled things up and hopefully didn't fry your pre-cat.

But does the "modal" behavior make sense to you? I'm trying to figure out if:

1) I damaged the cat, and I'm getting chunks of cat rattling around and blocking the exhaust (this actually seems least likely because of the behavior. The "rough running" almost always starts out early in the drive and then goes away). After driving for 10 minutes or so, I haven't had it start -- which to me suggests possibly fouled plugs, because hotter combustion chambers will make it easier to ignite).
2) I fouled the combustion chamber (perhaps Seamfoam could help with this, but it makes me nervous because when you get chunks of carbon coming off, guess where they go)
3) I am running into pockets of bad gas, still, despite it being fairly dilute (perhaps Drygas would help with this)

None of these really make sense to me for the modal behavior though.

From what I recall the car goes into stupid mode as soon as it detects a misfire then the cell stops flashing after the ECU compensates and stops the misfiring then the cell stays on solid.

Either way, I don't see a problem with using seafoam. I don't think any carbon would come off in big chunks... Pretty sure it just burns off slowly... Besides, your only other option is to probably disassemble your engine ???

Your injectors may be fouled as well as plugs and the seafoam should really help.

Even if you do cook your pre-cat just do the non-fouler trick and you're good to go.. Both the Seafoam and non-fouler are $10 fixes.

Seafoam treats bad gas and water and makes it combustible.

Yes, the problems are correlated to the MIL flashing and then it goes solid. I don't remember if the car drives normally all the time when the light is solid. It normally does, but it may still be in stupid mode after the light stops flashing. I'd be curious to know what its actually doing. I'm not really against using the Seafoam. If it does clean up the bad gas, it might be worth a shot. I was hoping the problem would go away on its own after its diluted enough and an Italian tuneup to clean up the chamber. I was assuming the big problem would be the plugs getting fouled.

hpmaxim said:

I'm wondering what the deal with this modal behavior is.

Click to expand...

Probably not the plugs - they would either stay gunked up or it would burn off and they would be fine.

I'm thinking there may be crud on the inlet filters of one or more injectors. This stuff could move around and temporarily block fuel flow, and then shift back out of the way and the car would run (more) normally. A blocked injector would throw a CEL and when the car's computer tries to compensate for too much O2 coming out of that one cylinder it might result in too much fuel going into the other three, which might account for the code you saw.

Maybe pull the injectors and clean them out? And as long as those are off, flush out the fuel system a bit too.

If the "crud" consists of nothing more than some water then you might be able to fix this with just a can of seafoam (or some other similar agent) in the gas tank.

hpmaxim said:

Yes, the problems are correlated to the MIL flashing and then it goes solid. I don't remember if the car drives normally all the time when the light is solid. It normally does, but it may still be in stupid mode after the light stops flashing. I'd be curious to know what its actually doing....

Click to expand...

From what I remember, an engine miss fire is the only code that flashes the cell, then the ECU freaks out and tries to stop the misfire by retardng the ignition, flooding your engine with gas and maybe some other things I forget.
As soon as the misfire is under control the MIL goes solid and your in stupid mode with no power and you waste all kinds of gas.

I would assume that the ECU would slowly try to go back to normal mode while keeping a close eye on misfiring.
I would also assume that it's possible for the code to clear on it's own and you are back to normal mode.

I don't think you can be in "limp" mode (I call it stupid) without the MIL being on but I'm not sure.

Okay, so here's an update. Pulled the two plugs I could access without pulling the coils. The center electrodes looked dome shaped, like they were a little worn, but otherwise b there were no significant carbon deposits, looked pretty clean.

I drove to work yesterday. After a minute of diving problem started and continued for about 5 minutes. Pulled over, stopped, waited a couple minutes, restarted, and then it ran fine. I stopped at Walmart and got a can of drygas and of Walmart brand Seafoam. Put in half a can of drygas (probably enough to treat 12 gallons, and there were maybe 5-6 in the tank). I've put 80-100 miles on the car since including 3 cold starts and its run and driven flawlessly. No P0300, no flashing MIL, no limp home mode. Maybe an occasional stumble, maybe... But I think the problem is essentially gone.

Unfortunately, it took forever to set the Catalyst monitor and when it did the P0421 came back. I reset it and the Catalyst monitor is back to incomplete but I'm not optimistic, so it sounds like either I, or an unnecessary stupid limp home mode may have destroyed the cat. It's hard for me to see how a little water in the gas would cause the cat destruction, but running rich could.

hpmaxim said:

... It's hard for me to see how a little water in the gas would cause the cat destruction, but running rich could.

Click to expand...

That's why flooding the engine with gas seems so counterintuitive with too much gas wrecking the pre-cat.

You may now needs couple of these... And a drill bit.



Your car may stay in limp mode until you fix it... Keep an eye on your codes.

Could you please elaborate? As I said, the car seems fine now except possibly the precat. Limp home mode hasn't recurred since the drygas. I'll dump in another 10 gallons of fresh gas once I'm down to 1-2 gallons, and maybe the rest of the can of drygas. At that point, I think the gas in the tank will be fine. I could try to use the Seafoam, but like I said no real noticeable carbon deposits on the plugs.

If your MIL is off and stays off then you are fine.

If your MIl throws a P0421 code that won't go away then you can do the non-fouler mod. to clear the MIL and pass emissions.



Or you can replace your pre-cat... ($400-$1200 plus labor)

1) Can you confirm that you know the mod (I did google it) actually fixes the problem?
2) I'm watching the O2 sensor output using Torque. I presume that the Bank 1 Sensor 1 O2 sensor is the front sensor. Is there two rear sensors (one after the pre-cat, one after the cat) or what? Which is the name of the second sensor (Bank 1 Sensor 2)?

Everyone that puts on a header does the mod. The headers don't have a pre-cat. It always seems to work for them. But there is one brand of O2 sensor that is too fat to fit in the non-fouler.

We have two O2 sensors P0421 refers to the second one,... Bank 1 Sensor 2,... It's the lower one after the pre-cat.

If you can clear the code and it doesn't come back then your fine. It only takes a few seconds of unburnt gas on the pre-cat to wreck it..... Apparently even bump starting our car can put enough unburnt gas onto the pre-cat to wreck it.