Lean Misfires at 2700-2800 rpm

[deyer]

I think this might be the same problem i'm having right now...

Any help would be greatly appreciated

It misfires between 2,000 - 2,500 RPM. Not horrible misfireing, but it's not very driveable. You can also hear it slightly at idle.

So far the mechanic has tried:

NEW
Spark Plugs
Spark Plug Wires
Coil Pack
Air Flow Meter
Fuel Filter
Drained the gas tank and tried new fuel
Cleaned Fuel Injectors
O2 Sensors
TPS

Also the Cam and Ignition timming are all correct.
The Compression is correct as well.

Everything is stock on the car, not one after market part.

I read about the ECU... if that won't fix it then.....??????

[DoctorDex]

What kind of plugs are you using and what are they gapped to? What year,make,model of car do you have?

I used to have a little misfire at idle when I was using copper plugs gapped down to 0.026. The misfire went away when I opened up the gap to 0.040, but I started having trouble with spark blowout. To fix both the misfires at idle and the spark blow out I ended up shelling out for iridium plugs (0.040). However, this did nothing to fix my part throttle misfires.

Declan

[deyer]

1992 Dodge Stealth TT

OEM Platnium plugs

They are the same plugs that were put on about 3,000 miles ago before it was garaged and it worked fine.

It worked in Dec 05 just fine, but now it has this problem.
When you thottle it, it'll still misfire as well.

They said when they put the air flow sensor on and it got better, but it was still there.

[F27Corsair]

I've had this problem too, mostly occurring at 2300rpms when i am accelerating from a stoplight. Usually happens in 2nd or 3rd gear. When it bucks and backfires, my tachometer needle will bounce up and down. Does yours do this?

Notable mods include:
Arc2, SAFC, Fuel pump hotwired, krankvents, HKS SS Bov, 660cc injectors.

[F27Corsair]

More notable stuff about my car:
-Old (8-12mo.) copper NGK plugs
-EGR blockoff complete
-ECU caps have been replaced (back in '02 i believe)

[DoctorDex]

Originally Posted by F27Corsair

I've had this problem too, mostly occurring at 2300rpms when i am accelerating from a stoplight. Usually happens in 2nd or 3rd gear. When it bucks and backfires, my tachometer needle will bounce up and down. Does yours do this?

I can't say if my tach needle bounces up and down, but I have noticed that the rpm measured by my logger seems to bounces around. With that being said, the rpm bounces around throughout the majority of the rpm range on the logger, especially if I export the log to MS Excel and examine it there. Does anybody elses logger show oscillating rpms @ WOT?

[badass3000]

that sounds interesting, ill have to check.
but the other two people having this problem, try another ECU, I bet your problem will be gone

[John Monnin]

Add me to the list of people with this problem.

I have been fighting erratic behavior in my car that I just couldn't describe consistently. Luckily it has gotten worse and the problem is fairly consistent.

While accelerating my wideband shows that the car spikes a high a 19.1 lean at about 3000RPM,as long as I am running in a vacuum condition If I accelerate hard enough to a little boost I usually don't get this lean spike.

Its very annoying and the lean spike is bad enough that I often get 2-3 counts of knock in this zone. If I accelerate hard some times the knock goes away but sometimes it jumps to 9 to 10 counts. This a real knock, race gas will significantly reduce the knock but it won't completely eliminate it.

I have converted the car as far back to stock as I can go.
- Stock ECU (turbobob replaced the capacitors and installed a overclock chip but I have the stock crystal installed right now.
- Stock 360CC injectors
- Supra fuel pump with relay to hotwire it to maximum voltage at all times
- AEM fuel pressure regulator set to 43psi at 0psi.
- Vacuum reduction, No EGR, No fuel regulator solenoid, no canister purge

I have already checked/ replaced the following:
- Fuel pressure is where is supposed to be -33psi (at 10psi vaccum) 43psi at 0 psi, and 48 psi at 5 psi of boost.
- Intake pressure tested, not perfect but it holds 10 psi of pressure for a minute or two
- New fuel pressure regulator
- The 02 sensors are cycling, they look pretty good, maybe a little bit lazy but not as bad as have seen on decent running cars.
- TPS Switch The idle switch turns on and off correctly when I tough the gas pedal.
- TPS Sensor, reads 14 at idle which is a little high but I set it to the service manual.
- Disconnect the electronic suspension control module, The caps were leaking in it but it didn't seem to help.
- I had this problem running a MAFT-PRO in speed density mode so it shouldn't be the MAF sensor. I added 30% more fuel at this RPM and it still didn't help.

[F27Corsair]

Just wanted to update you guys- i fixed mine. My Apex'i ITC (Ignition Timing Converter) had a wire that must have been coming off. On each buck, the timing was dropping to 1 and then going back up to regular timing (around 25). I re-checked my wires and its been doing pretty good since.

[badass3000]

I have an ITC tooo!
it was working fine when i installed it.
what wire, and where was the problem?????
John, im sure you can find a known good ECU to test?