: Misfire



Skiller.
03-12-10, 04:17 PM
Apparently my car misfires at idle. I'm at a muffler shop having an exhaust leak fixed and he mentioned that he noticed a misfire. I don't notice it at all, I think it idles and runs great. They don't do engine work here, so that's why I'm wondering why he would say something unless something was wrong. I just replaced the plugs and wires..plugs are delco, wires are not. I don't want to pay anybody to do such easy engine work. What could be the problem? He said I shouldn't leave it alone because it could lead to the converter melting.

Thanks dudes

Ranger
03-12-10, 06:20 PM
Converter melting? :hmm:

If you don't even notice it, ignore it.

Skiller.
03-12-10, 06:56 PM
The computer would throw a code if there was a misfire..wouldn't it?

I mean, the car might not idle PERFECT 100% of the time, but that could be from dirty injectors or something else. The RPM's do not budge at idle, no matter how heavy of a load. I looked at him puzzled when he told me that lol.

Beaudreau
03-12-10, 07:45 PM
Skiller is right, you are the guy that drives it and if you can't sense a difference, there probably isn't one!

As far as codes go, I'm not sure that you can expect anything. I just went though an ordeal were one coil pack was dead and I had no codes! Long story but there were ICM problems!

Skiller.
03-12-10, 08:22 PM
Alright, I see no reason to address it as the car is running fine.

Ranger
03-12-10, 08:40 PM
It will not throw a code for a mild misfire. When my '97 was missing after the fuel rail recall it threw no codes until I finally induced a severe misfire by brake torquing it to 2000 RPM.

Skiller.
03-12-10, 09:51 PM
So I can test it in D by applying the brake and revving to 2000 RPM's?

Ranger
03-12-10, 11:08 PM
That worked for me, but your results may vary.

By the way, I think I held it at 2k for a few seconds.

Skiller.
03-13-10, 12:15 AM
So the fuel rail was causing your misfire? :eek:

Ranger
03-13-10, 12:08 PM
No, there was a fuel rail recall for the '95 - '97's. In order to R&R the fuel rail, the wires had to be removed as they are routed over the rail. Moving those old wires around must have caused them to break down somewhat and caused a misfire. We heard a lot of that right around the time of the recall.
http://www.cadillacforums.com/forums/northstar-performance-technical-discussion/25119-stutter-engine-trans.html

Skiller.
03-13-10, 01:30 PM
I read through pretty much that whole topic and I came up with a few things to try. I know I need a new EGR valve anyway, so I'll replace that, and also dirty injectors could be the problem he mentioned.

I already checked all the wires; they are fine.

I need gas anyways, should I try filling up with 91 or 93 octane and run WOT a few times and try to clear up the injectors?

Submariner409
03-13-10, 02:20 PM
Find a 20 oz. jug of Chevron TECHRON (one of the components of Top Tier certified gasolines), pour it in the tank, fill up with 93 and go for a long road run.

Pull the EGR and clean it and the gas passages with choke cleaner. Scrub away with a toothbrush but DON'T turn the valve upside down to soak it - cleaner will tend to weep along the pintle shaft, through the silicone shaft seal, and eat the valve operating coil and/or diaphragm. That pintle (tapered valve pin) should move up and down freely with moderate finger pressure. Not sure if your EGR is operated by vacuum and/or electrical solenoid, but the cleaning is the same - if it's a vacuum EGR, check the lines for leaks.

Skiller.
03-13-10, 04:28 PM
I recently cleaned the EGR, and the pintle moves freely as it should. I'm still getting the P0404 EGR code, so I'm guessing the electrical part of it is bad?

Thanks for the suggestion about the TECHRON. Will give it a try.

Ranger
03-13-10, 06:37 PM
I already checked all the wires; they are fine.
FWIW, you can't tell by looking at them. Mine "looked" fine too.

Skiller.
03-13-10, 07:41 PM
The wires have 1,000 miles on them.

Ranger
03-13-10, 09:07 PM
Oh, that's another story.

Skiller.
03-13-10, 11:58 PM
I guess if I pay really close attention to the idle, there is a miss, but it's ever so slight, and it's intermittent. With brand new plugs and wires, I don't think there is really anything I should do, especially since there is no studder during acceleration or anything like that. I ran into misfires twice with this car already. The first time, I replaced the plugs, second time it was the wires. It was obvious to me when there was a misfire before.

I will take sub's advice and use the TECHRON fuel cleaner and fill up with premium fuel.

Also, could a dirty TB, or a dirty air filter cause imperfect idling?

Ranger
03-14-10, 02:35 PM
I don't understand why, but I have heard of the TB causing some idle problems. Can't hurt to clean it, especially if it has not been done in the last 30K or so. I do mine every spring.

Skiller.
03-14-10, 04:41 PM
I think I'll be cleaning the tb and changing the air filter very shortly.

Skiller.
03-15-10, 05:44 PM
I think I can rename this as a "rough idle" rather than a mild misfire, since there are no signs during acceleration, or cruising speed.

It's not that rough either, it's just not perfectly smooth. Would I be looking at the same things to try and solve the issue (Fuel Injector cleaner, TB, Air filter, EGR Valve)?

Thanks

Ranger
03-15-10, 05:50 PM
You can probably rule out the air filter and plugs and wires in it's place.

Skiller.
03-15-10, 05:53 PM
Alright, so I'll give the TECHRON a try, clean the TB, and get a new EGR valve from eBay asap.

I might as well change the air filter when I clean the TB, though. I've put 7k on the car, and I have no record of the air filter being changed.

Ranger
03-15-10, 10:25 PM
Don't waste money on a new EGR. Clean the one you have per the instructions in the Tech Tips section.

Skiller.
03-15-10, 10:31 PM
I already cleaned it. The pintle moves freely with moderate finger pressure. It isn't stuck closed or stuck open, yet I'm still getting an SES light with a P0404 EGR code :confused:

Ranger
03-15-10, 11:01 PM
Moderate finger pressure? It should take nothing at all to move it. Does it sort of break free when you push on it?

Skiller.
03-15-10, 11:29 PM
It was a few months ago, but it seemed pretty easy to move it. After I cleaned it, the SES light didn't return for several days. Now, the SES light is on 90% of the time.

Are there EGR codes that signify that the electrical part of the EGR is bad? Is my code definitely the pintle part? If so, I'll try thoroughly cleaning it again, because buying a new one won't be any different than mine after a good cleaning.

Ranger
03-15-10, 11:55 PM
OK, I checked the P0404 DTC in the FSM. It talks about the EGR valve position sensor. The position sensor reports the pintle valve position to the PCM which compares it to the commanded position. There is a page and a half of tests and as usual a Tech II is needed. Assuming that the pintle valve is clean, not sticking and closing COMPLETELY, it's probably a bad EGR or (if that tested good, the PCM). PCM was last on the list. If you are 100% sure that the pintle is free and seating so there is no leakage in the closed position, then I'd lean towards replacing the EGR.

Skiller.
03-15-10, 11:59 PM
I'll tackle this on Thursday. I'll clean the EGR valve, clean the TB, and replace the air filter while im in there.

The more and more I read online, dirty EGR valves and TBs can cause mild rough idling. I see no reason to suspect the plugs, or wires.

Skiller.
03-16-10, 12:07 AM
OK, I checked the P0404 DTC in the FSM. It talks about the EGR valve position sensor. The position sensor reports the pintle valve position to the PCM which compares it to the commanded position. There is a page and a half of tests and as usual a Tech II is needed. Assuming that the pintle valve is clean, not sticking and closing COMPLETELY, it's probably a bad EGR or (if that tested good, the PCM). PCM was last on the list. If you are 100% sure that the pintle is free and seating so there is no leakage in the closed position, then I'd lean towards replacing the EGR.

Thanks for that information. I think I might just replace the EGR valve. I already cleaned it pretty well and made sure the pintle has proper motion.

Skiller.
03-16-10, 07:24 PM
An update..Today when I started my car, there was no SES light, and the rough idle was still present. Should I still suspect the EGR for the rough idle, or does that eliminate the possibilities of the EGR causing the rough idle? If I do start the car and the SES light is off, it usually goes on (caused by P0404) within a few miles of driving and it's pretty consistent.

jsiddall
03-16-10, 08:29 PM
If the computer is happy then the EGR is probably working correctly. Still, if it is throwing codes just replace it. If you have a scrap yard around you can find tons of them. IIRC a bunch of the 4.3 V6's in the light trucks use the same EGR. Check the Delco site's cross reference to be sure.

Skiller.
03-16-10, 08:32 PM
Thanks..I just bought one from eBay for $40. I think I might be looking at more serious problems than just a faulty EGR, or a dirty TB. I will make another thread about it.

Skiller.
03-19-10, 06:20 PM
Hey Ranger, I replaced the EGR valve today...I compared the one I got from eBay to mine and mine is definitely sticking lol.