car sputters at 4k?

[ATLDSM96]

car runs perfect until i hit 4k then car sputters terribly, it does it in every gear. the only thing i can think of is my spark plugs, i first thought fuel cut, but theres no way i should be getting ful cut on 9psi on a t25 with basically no mods. anything would help.

 

[Dave532]

This sounds exactly like what happened to me at a rally in 2002. The ECU went bad
causing the injectors to run full rich. At 4K the motor just couldn't run with that much
fuel. The ECU went bad because I was using a MIG welder and plasma cutter on the
car without pulling the ECU. Disconnecting the battery was not enough.

Pull the plugs and see if you are running rich or lean and post again.

 

[strykout88]

I had the same problem and it was a mix of things, my plugs were gapped incorrectly, i needed a re-tune (judging from your mods list that isn't the problem), and I also had a boost leak, so i would do a leak test and check your plugs. My guess is the plugs because with my boost leak the car would run fine then practically fall on its face at about 3500.

 

[ATLDSM96]

so the plugs are good, how do i see if my ecu is shot? i really hope its not

 

[Dave532]

The only way I troubleshoot a bad ECU is to swap it out with a known good one.
I know that probably isn't much help but hopefully someone with a better answer will post.

 

[tsi8820]

mine sort of had the same problem i swapped plug wires and my MAS and the prolem went away.

 

[slcorman91]

Have you done a boost leak test yet? Could be possible that you have a leak somewhere that is not showing itself until it gets under alot of pressure.

 

[Ryn1727]

i had the same problem until i changed my wires

 

[jerry_69]

I've had the same problem on my car too for a while now. I changed the spark plugs & wires. Performed the boost leak, found none. I'm afraid it is going to be the ecu.... I'm going to swap it with my buddies and see if it is.

 

[hedrick]

It sounds like the car may need a tune up. Does the car drive normal when your not boosting?

 

[meliketoball]

Maybe, the sputtering is your car hitting its face against the concrete. For sure, you probably need a tune up.

 

[ATLDSM96]

yea it runs fine when not under boost until i hit 4k and if i am at WOT it doesnt happen in first and second.? i could probably use a tune up.

 

[jkimes]

Probably a Boost leak, a bad tune, or a clogged fuel filter. Worst case scenario.... could be a bent valve or two... I always assumed bent valves would make a car undriveable but my car did the exact same thing after my timing tensioner failed an let the belt slip a few teeth and bent several intake valves. WTF

 

[jasonwinnell]

i knew some one that had a n/t and he had bad oil in his car and when he would drive on the high ### at about 3500rpm it would spit and sputter real bad, but it wouldnt do it any other time

 

[turboglenn]

Check all your power and ground wires from the battery to motor to chassis first. Bad grounds are usually the culprit to first be checked. I'm going through something similar except mine's happeneing at 7220 rpm and above. I've replaced everything but the wires. I've put in a new transistor, coil packs and all new cleaned up grounds and power wires in the engine bay.

I'm still getting it, but the grounds helped the most. New wires are next. YOu can tell a bad ECU from the CAPS leaking (if they are) you can read about that on vfaq.com