Strange Misfiring

[90spooledawd]

Hi guys,

My 90 TSi AWD misfires at 4.5k for some strange reason:

I put NGK BPR6ES in
I installed Magnecor 8.5 MM Wires
Boost is set only at 14 psi
I have whe Walbro 255lph

It misses ONLY at full throttle at 4.5k and on.

Why is this is it my coil pack?

But get this if I turn the boost down to 12- 13lbs it will not miss.

WHY?

Help

 

[nutshot]

What octane fuel is available in yer neck of the woods? Sounds like it could be predetonation...

 

[dsmtrick]

Any codes thrown? What gap are the plugs set at?

 

[zerofreez]

Im having kinda the same problem, anything past 4.5 just doesnt excellerate as fast as anything below, and it used to pull hard to 6

Except mine does it worse (or mabee more noticable) under low boost. I really noticed it when i ran no boost controller and only 12psi. It becomes alot less noticable when i run 16psi though.

I dunno, things like this just kinda piss me off. I spend 1000 on suspension, then my motor starts acting goofy.

 

[Mightyp]

he's talkin about a missfire, it feels like a stumble, and then pulls throug it, and then might do it agian. I think I'm having the same problem. your poor excelleration, is prob just a lil leak somewhere in your charged air system, hopefully somtin really minor.
I been looking into this and found this....

11) High boost motors require good ignition systems. Most top end
stumbles and misses are ignition problems.

I found the above statement over at clubDSM, under go faster recipes.

also my freind told my I might have to retard my timming..I need to look into this.

I'm rulling out predetonation, only becouse I still have the stock turbo, and 14lbs of boost still seems safe, I think... and I always use 94 octane. but wait.. when I put 104 octane boost in my car last week it stopped... thats why I thought it was my fuel injectors... hmmm very intresting. I going to put another high octane boost in my car to see if it stops agian.
90spooledawd do me a favor, do samething and see if it stops...
now if that is the problem, what steps would we have to take to elimanate this. upgrade the fuel system, Duh!

 

[Oreopride18]

Lol, did you buy your plugs used off of dsmtrader.com?

I did. And that bastard ripped me off. I put the 8.5mm magnecores I got for a "steal" at $40 with 5k (or 500k) miles on them. Low and behold the car would hesitate and misfire. I checked the engine code and I was basically firing on three cylinders. Switched the old plug wires back in and low and behold the car ran fine.

<---seriously anti-dsmtrader.com

Got my $25 boost gauge off of there too. The problem? The whore didn't tell me it came without a light.

 

[Mightyp]

Originally posted by nutshot
What octane fuel is available in yer neck of the woods? Sounds like it could be predetonation...

thanks, nutshot. Just woundering how bad is predetonation..?

 

[JJNovo]

How are you controlling your fuel pressure?
If your profile is up-to-date, where is your MAFT set at?
What are the fuel trims telling you?

 

[Mightyp]

I don't have anything to control my fp right now, I didn't think I nedded it yet.

 

[ivanr4g63]

But get this if I turn the boost down to 12- 13lbs it will not miss.

hey Dj, Have you tryed retarding a couple of degrees your timing when you turn up your boost level...?
are you at least using 89 octane fuel...?

 

[JJNovo]

Originally posted by Mightyp
I don't have anything to control my fp right now, I didn't think I nedded it yet.

I guess I should note/quote who I'm replying to. Mightyp, your mods in your profile don't mention a larger fuel pump, so you're right.

Those questions were directed at 90spooledawd. But anyway, I'd say that he's either too rich or too lean.

 

[Mightyp]

ok I put the 104 octane booster in. last night I pushed it really hard to 7,500 rpm's in evry gear. Not one stumble, or missfire, or pre-detonation

problem.... I don't want to run 104 octane evryday. My birthday is comming up on the 19 I talked my girlfreind into getting me the 3" o2 elimanater down pipe, but is there somtin I should get first to stop this evil pre-detontion.

 

[Sicstylz]

Before jumping around, are you making sure your plugs and wires are healthy? No leaks? I had that problem a while ago.

 

[Mightyp]

new plugs and wires 5,000 miles ago, pulled pugs checked them cleaned them with some sand papper, and checked the gaps. all good. as for leaks, well I do notice a slight, and very light smell of gas when I'm in the car. Do u think I have a gas leak somewhere?
I'll give u a lil history on my car. When I bought it, it had a bad idle, always wanted to stall on me, changed the plugs, still rough idle. Changed the spark plug wires, still rough Idle, changed my fuel filter, and I have had a nice stedy Idle ever scince. When the cars warm it Idles at 700/750 rpms. Now it did start that ticking sound. I have not locked down where the ticking is comming from yet. The car runs great untill it hits 14 psi in the high rpm range, where the stumble happens, just for a moment, then keeps on climbing up the rpms, and it will happen agian.
the problem dose not happen when I run a octane booster. I think I'm going to try and retard the timming...? or get a mbc set the boost to 12psi and only turn it up to 16 psi when I have a octane booster in.

 

[Slow99x]

I had a similar problem and it turned out that moisture had gotten into the plug wire and arched from the boot to the block. Pull your wires and closely examine them for what looks like a pinhole at about the middle of the boot. If you are getting a P0400 trouble code then it may be a random detonation but if there is a number of 1-4 like P0402 and no other misfires, then you're missing only on cylinder 2. Check that plug wire!

 

[90spooledawd]

Sorry I had been away for a while wid' school. Me and John (willracfor beer) tried the intake leak test and we heard sumthin' at the compressor elbow. . Meanwhile I went and got NGK BPR7ES (advised from Rob from Extreme) and it still did it, I also check the gap - .30. As for the compressor elbow, I tightned it yesterday till the bolt wouldn't turn n e mo' b4 I went to school and it didn't do it anymore but when I took this girl out (me and her are talkin') (also so I was trin to impress her) it hit fuel cut, BAD. I dont understand, WHY, I have the LS1 MAF, S-AFC, and Walbro 255, and I still hit fuel cut, WHY?

 

[t90tsi]

i had the same problem with stock injectors on a 14b, i put 550's in now i can run 20psi and no more fuel cut. =) try getting bigger injectors that was my problem

 

[screamin talon]

yeah im havin the same problem , i just got my 97 GST and it came with a hallman MBC but the guy forgot to tell me wich way to turn it to make boost increase or go down . the misfiring is mostly in 1st and 2nd. the injen intake i got doesnt fit too well with the bov dump tube and i may have a leak there . but im puttin in the NGK's tommorow. i live in GA and its gettin pretty hot down here and i heard if the intake temp would get hot it would also misfire . im running 12psi .