Some high end misfiring problem

[kwdiablo]

Hey, on my 92 Talon TSI AWD 5spd, I have a high end misfiring problem. Here's what happens. I'm accelerating (in any gear above 40% throttle) and when the rpms reach around 4-5 grand, the car violently misfires (like a rapid pop-pop-pop at a drum roll speed) and the car still accelerates at about half power.

Right away I thought it was either fuel cut, detonation, or preignition, but I get no check engine light, my EGTs stay in the safe range, my A/F gauge maybe jumps up one light, if that (Autometer). I'm not positive what fuel cut feels like, but I don't think the car would keep accelerating then. I've tryed messing with timing, swapping out coil packs, smelling ECU, and such. I did a boost leak check...found a couple tiny leaks and fixed them...no change.

Here's what I have: 20 over JE Pistons, Crower Rods, Aluminum Flywheel, ACT 2600 lb. clutch, HRC Super 20G (running 15 psi), HKS BOV, 3 inch manrdrel exhaust all the way back, FMIC with 2" off turbo to 2.5" to TB, 700cc injectors, Super AFC (which I've tuned for hours), NGK Plugz bpr7es (I think a .032 gap), Magnecor 10mm wires, & Cometic .057" head gasket (head and block slightly shaved).

This problem sort of went away when I switched from the NGK "bpr6es" to the "bpr7es" plugz....what gap do yall recommend? I've tried so many things, getting tired of it. Is my stock MAF holding me back, or any other part for that matter?? Sorry for the long post. Any advice would help.

[scottsee]

my first inclination was your plugs and wires. when they have carbon buildup they hesitate during wot, but that wouldnt explain your rapid misfire. in your parts list i didnt see any logging software. do you have any? it could be your 02's are bad abnormaly effecting your high and low fuel trims making your car run highly rich creating your problem. but your right, you might be running into problems with your maf too. i think the least expensive way to figure out your misfire would be to gain access to a pocket logger and log your 02's durring idle for 5 mins and see if their jumping around from .2v-.8v. if they dont your 02's are defently bad!

the probem with testing your maf with a pocket logger is the way the your afc2 will correct the maf readings to the ecu, when the afc2 interupts the signal and sends it to your ecu it will only send the corrected maf hz and not the actuall. the 1g maf reads upto 2000hz, but you will only see a max of 1600 because of the way your afc/logger interacts with the software. i would suggest if you have the $ or time trying either a 1g hack, swap it with a 2g, or just stepping up and geting the gmmaft set it to 0, and be done with the 1g maf. intresting problem. keep us posted!!

[kwdiablo]

Hey, nope, no logger yet. Actually I was just shopping for one 2 seconds ago. As far as checking the o2s at idle for 5 mins, can I do the "blue wire mod" to the afc and watch the o2 voltage on it? Ya know, the mod where you connect the afc's blue wire to the o2 sensor signal and switch to sensor check. I have been looking into the GM Maft for a while now any how, and I think thats what I'm getting as soon a I get some money flowing again.

Also, something that might point to the o2 sensor is, a while ago, this used to be more intermittent and now its all the time. It used to atleast pull through first gear. Maybe the o2 sensor was slowly going out, and now its pretty much dead...Time for a wide band anyway.

I almost like it when something goes bad ....it gives me an excuse to swithc it out with something better....thats how i got pretty much all my upgrades. Thanks for the help...I'll keep you info'd.

[kwdiablo]

K...just bought a datalogger cable on ebay...now we wait.

[scottsee]

yeah, i know what you mean, im the same way when somthing goes wrong! always looking for a reasion to buy a new tool! to be honist, i dont know about the blue wire mod. if your going to get a wideband dont worry about it. congrats on the logger! there are some great articals about data logging on pocketlogger.com.

[POWERGOD]

I have a 96 tsi awd and now all of a sudden it started cutting out on full throttle at about 4k -4.5k rpm's and the it is fine. It is not a misfire really it is just like the engine stops for a split second and then takes off where it was. When it does this it jerks really bad. Thanks for any help.

[kwdiablo]

Sounds like maybe a problem with the coil pack (maybe a dead spot?). This is just a thought if you've already checked/changed plugs, wire, timing, fuel filter, injectors, octane level...etc. Hard to tell. If you had a check engine light at all, maybe it would point a finger to what was wrong.
As far as my original misfiring problem on this thread...I changed the O2 sensor a day or 2 ago...but no luck...still misrifing at high rpms. I also check/cleaned the BPR7ES plugz. Still misfiring. Also I used to live in utah with the car and it was fast....but then I moved back down to Florida. Holy cow what a difference in performance (still misfiring tho). Now I really think the MAF sensor is being overworked, or it is not seeing all the air that is really being sucked in, so it is running rich at higher rpms...dunno. Any input is a help.

[spyderturbo007]

Originally Posted by kwdiablo

As far as checking the o2s at idle for 5 mins, can I do the "blue wire mod" to the afc and watch the o2 voltage on it? Ya know, the mod where you connect the afc's blue wire to the o2 sensor signal and switch to sensor check.

It is not recommended to do the "blue wire mod" because it is proven to degrade the reading the ECU sees. But, in your case (because it will be a short term thing) I don't see it being a problem. I just wouldn't leave it that way. How did you tune without a logger of some sort?

[kwdiablo]

Ok...Update...I finally got the palm pilot, datalogged, and found out I'm getting a high knock reading of 43 (maximum the ecu reads). And of course when the knock rises, the timing retards....thus my misfiring problem. So, I changed the knock sensor, thinking it was picking up false noises. A while ago I kept having problems running a bit hot. The stuff in the back of the sensor was half gone. Anyhow....the problem is still the same. Nothing changed. I've heard of knock sensors picking up noise from the lifters, so maybe my next step is to get the larger hole lifters. This problem is driving me insane...there was a porsche that came to chase me after I left this gas station, and I couldn't even put up a fight I didn't even try. Any help at all would be appriciated. Thanks.

[spyderturbo007]

I think the problem is going to be your tuning. The first thing to look at is the base SAFC settings. You should start the tuning process at about -36 across all of the Ne-Points. -36 is assuming your car had 450cc injectors to start with. I'm not sure about 1g's because the AT had smaller injectors than the MT (and you car info is not in your signature )

[kwdiablo]

Hey...I have a signature now :P I gots 700 cc injectors. I'm pretty confident I tuned the AFC correctly, but I was wrong once. I've tryed richening it up and leaning it out...no change...as far as knock is concerned. What do you think about the lifter noise causing the false reading? Also, my EGTs are staying around 1200 F on the highway. At full throttle it might reach 1300 F in 3rd (in hot FLA).
Also during my checks...I found that the knock sensor is getting around 6 volts, instead of 8 volts, like the book says it should. Now if the ECU sees that low voltage in return, then I may also get false knock readings. I think I'll try unpluging the sensor to see what happens...what do u think?

[96spyderman]

[quote=kwdiablo]This problem sort of went away when I switched from the NGK "bpr6es" to the "bpr7es" plugz....what gap do yall recommend? QUOTE]

I am clueless to all the other stuff but as for the gap... try .027 for the bpr7es's

[1stGenRocks]

i think your sig still needs some work. we still don't know what year you are, whether you are fwd or awd? manual or automatic?

[spyderturbo007]

Originally Posted by kwdiablo

Hey...I have a signature now :P

Excellent! But could you add the year, model and tranny type.

Originally Posted by kwdiablo

I'm pretty confident I tuned the AFC correctly, but I was wrong once.

Just to make sure, because this doesn't require any money , let's take a look at your base SAFC settings.

What settings are you currently using?

What do your STFT & LTFT look like?

How is your O2 voltage?

Phantom knock is possible, but not probable. You can get high EGT's because you are running too rich (most people think it's because you are too lean). If you are too rich, the fuel can still be burning as it exits the combustion chamber which will make your EGT's unusually high.