Went to get the car dynoed today and it was misfiring with an A/F upwards of 14.5 at WOT. Nothing has changed in my setup, and I even went racing about 2 weeks ago without any issues whatsoever. What could have caused this? Bad fuel? Clogged injector(s)? Something broken??

I just replaced my air and fuel filters today to see, and no dice.

The motor is completely stock. Mods are only exhaust (headers, ORY, catback) and lid, plus it was tuned by RWTD. Like I said, nothing has changed in the past 2 weeks, so it's something recent.

HELP!

 

Nothing, eh?

 

Possible bad fuel pump. I would check fuel psi. Second check for a nasty vac leak but i think it would run like ****.Are you down on power?

 

make sure the mad is clean, particles of dirt on it can cause it to misread the amount of air

 

make sure there are no exhaust leaks on your AIR fittings or around the header flanges; added air coming by would make it look like you are running lean. kind of unlikely, but give it a look

 

Definitely check for air leaks in the intake path. My old LT1 Firebird ran very lean when I had it dyno tuned, and we traced it to a tear in the rubber going into the throttle body. But the car ran great though, you'd never know it had a leak, since it wasn't that big (but big enough to lean things out slightly, to 14.0 to 1)

 

If the filter is dirty for the Wide band on the dyno it will read lean also... had this problem while tuning a car a while back.. make sure and have them put a new filter in when u go back

 

put new fuel in and clean the injectors and see how it acts

 

Put a decent scanner to it and look at the misfire history,
then some loaded runs looking at all 8 "misfire current"
cylinder values. That will tell you whether it's a single
cylinder problem or a global air/fuel one.

 

The car feels fine under normal daily driving conditions (partial throttle, under 3000rpm), except for an occasional miss now and again when starting from a full stop. When going WOT is when the motor starts cutting out and misfiring.

I have AIR blockoff plates and they're pretty secure. No leaks that I can find there.

Hmm...I'll check this one again. I looked yesterday when I changed air filters, but worth looking at. Thanks.

What filter?

This is what I'm trying now...running the rest of the tank with this crap with some STP fuel treatment, and will fill up again ASAP with some hopefully better stuff (if that's the problem). Besides using a fuel additive, what's good to clean injectors?

My laptop has a good scanner...but my laptop is FUBAR. I don't have a good scanner available.

 

Your misfires could be from running so lean I would still check fuel PSI.

 

Just an update...

Ran some STP fuel treatment through a half tank of gas. Used most of it, refilled with some more from a different gas station, reset my PCM, and the car seems to be doing a little better now. No more missing that I can hear at idle (it seemed to be burping a little earlier today).

Seems like I just had some really lousy gas or something. Gonna borrow my friend's laptop to hook up to the PCM and check how the O2s are reading, LTFTs after the PCM reset, etc...see if anything more happens in the next few days.

I hope I didn't do any permanent damage, though.

 

Do you have a K&N airfilter? Have you cleaned it recently? If so, you might have oiled it too much and that oil coats the MAF wires and will make it run lean.

I have seen this a few times, I cleaned the MAF and all was good again....


Bill

 

Nope...I've avoided getting a K&N just so I didn't have to deal with oiling. A fresh WIX air filter every 10k is better, IMHO.

 

Okay...a day later and it's still happening. Scanned the PCM and got two O2-sensor related codes.

Bank 1 Sensor 1 - No signal.
Bank 2 Sensor 1 - Heater something something.

Seems my O2s are fubar...although that doesn't explain my problems at WOT. I thought the PCM ignored the O2s at full throttle...right?

This is very aggravating.

 

Another update...

Bank 1 Sensor 1 is staying stuck at 445mv.
Bank 1 Sensor 2 is fluctuating...which is weird, since it's not actually there.
Bank 2 Sensor 1 is also fluctuating as it should.
Bank 2 Sensor 2 is staying stuck at 445mv.

I did my header work almost a year ago...has my driver side O2 been miswired this whole time??

The more I look into this, the more confused I am. ARGH. :rant:

 

check to make sure you havent grounded any wires on the headers or anything lke that. Bad o2's will cause the car to load up and run like ****

 

Okie doke...I'm completely lost here now.

Checked the O2 sensor wiring. Apparently, my front driver side sensor was plugged into the rear wire. Changed that and everything's fine there now. Both Sensor 1s are fluctuating as they should.

Also checked my MAF and everything in front of the throttle body for leaks, foreign objects, etc. Found some debris on my MAF screen, but the sensors looked fine. Cleaned, re-installed, tightened, etc.

Ran the car with some Techron added in the fuel, and also applied a bottle of GM Top End cleaner. The car seems smoother in daily driving and idling.

HOWEVER...all that checked and it's still making all sorts of problems at WOT. I can even spin the motor up at part throttle to 6k and without issues. This leads me to believe that mayhem is commencing once the computer goes into closed-loop mode. WHY, though? I haven't messed with the tune in almost a year. Can the fuel tables become corrupted or something?

 

Have you checked the fuel pressure yet? Everything you said points to low pressure.

 

No, I have not. I'm not even sure how to do that.

Upon other checking...I was watching my LTFTs and they're always in the positive side, while before this started happening, they were always in the negatives. The tune has not been changed, so you're right...this does point towards some form of fuel starvation. What else would cause low fuel pressure?