Stuttering at WOT

[OzzmosisDSM]

I recently bought a 92 TSI and need some help with tuning. What happens is when the car is at WOT it tends to stutter in the upper RPM range, from about 3000-3500 on up. It doesn't feel like fuel cut, if it is then it's very mild. When at half throttle the car will pull hard at full boost and no stuttering, it only happens at WOT.

Here's a little history of the car. It has a big 16G with 2.5" piping, 2.5" turbo back exhaust, walbro 255, mbc set to 15lbs, greddy BOV and k&n. There are a few other mods but nothing major. I was getting some bad fuel cut at WOT so upon reading the vfaqs and some other info I decided to hack the mas. I removed the lower honeycomb and backed out the adjustment screw. For about a week the car ran fine and pulled hard with no stuttering and no fuel cut.

I think screwing the adjustment screw back in all the way would help with the stuttering but then I'm afraid the fuel cut would come back. I know the car is running safely though. At WOT the a/f guage reads rich and my EGTs are around 1450-1500. I may be getting a datalogger next week so that may help, but until then does anyone have any ideas where the stuttering is coming from and how to smooth it out. Thanks.

 

[evotuner]

Any other mods? Injectors, fuel management?

 

[R3dR]

also check the ignition setup as a weak system can allow the spark to be too weak under full boost etc.

 

[realitytb]

it may not feel like fuel cut, but im willing to bet that it is fuel cut. check your plugs to see if maybe your running a little bit lean. (the tips of them are white) if so, then its definately a fuel problem.

 

[OzzmosisDSM]

No other mods other than rebuilt engine 35K ago and balance shafts removed. I think tomorrow I will check the spark plugs to see if they are gapped properly and if they are too white/black, etc... When I bought the car it had some cheap plug wires on it and I imagine the plugs are the same. I have NGK wires and plugs on my NT that have about 30K miles on them, I may switch over the wires and get new plugs soon, hopefully that helps.

 

[OzzmosisDSM]

I screwed the adjusting screw back in "almost" all the way. I replaced the spark plug wires with NGKs off of my NT and checked the gap on all spark plugs. One plug was gapped at about .020" so I re-gapped that one. Now the car seems to be running a lot better, there is still a very slight stutter but I'll just have to wait til I get my datalogger before I try to figure that out. Not sure what fixed it, the wires or the screw but thanks for the advice, I didn't think about looking at the ingnition system.

 

[OzzmosisDSM]

Sorry to keep babbling in this thread but I don't want to start a new one. When I looked at the spark plugs they had a light greying tint on the tips and the electrode and the base of the plug was dark black. Is this OK? I wouldn't say the tips were white but definitly light enough to look into. If it is an indication that I'm running lean then I'm confused because my a/f guage says I'm rich at WOT and the EGTs are no higher than 1450.

My next mod is to do a fuel pump rewire so maybe that will help a little. When I bought the car the guy I bought it from claimed that he installed a Walbro 255, however I can't hear that "whine" that the 255 is known for. I really don't feel like ripping the pump out of there just to check to see if it's a 255 or not so maybe after the rewire do you think I'll be able to "hear" the pump better?

 

[PaleDSM]

Depending on a narrow band a/f gauge for determining if you are rich or not at WOT is asking for disaster.

Sings of detonation will show as small flecks of aluminum on the plug. Grey or black is usually common.

90% of the stuttering problems that DSMers complain of come down to the ignition system. Properly gapped plugs and good wires usually do the trick.

Have you pressurized the intake system lately to eliminate any boost leaks?

 

[OzzmosisDSM]

I think the stutter was due to the #1 cylander being gapped wrong.

I'm going to make a intake leak tester soon so I can check for boost leaks. One question though, when the intake is pressurized should it hold a steady psi or slowly leak? If so, what would be a normal period of time for the pressure to drop?

 

[PaleDSM]

After you stop supplying pressure it will bleed off. I'm trying to think of a way to describe the rate at which it bleeds off......

 

[OzzmosisDSM]

OK, I replaced all the plugs with BPR7ES NGKs. The stuttering has gone away, with the exception of when the car is cold. When I first start the car in the morning, it basically runs like crap until it warms up to normal temp. Is this due to the plugs being one range colder than stock? I know that with the BPR7ES plugs it takes longer to reach thier self cleaning temp, is this why it runs crappy when cold? By crappy, I mean the car has trouble getting boost and stutters under acceleration until warm.

Thanks for all the help guys. My datalogger is in the mail and I should be getting a SAFC next week so I can't wait to start doing some real tuning.

 

[FiReBReTHa]

OK, I replaced all the plugs with BPR7ES NGKs. The stuttering has gone away, with the exception of when the car is cold. When I first start the car in the morning, it basically runs like crap until it warms up to normal temp. Is this due to the plugs being one range colder than stock? I know that with the BPR7ES plugs it takes longer to reach thier self cleaning temp, is this why it runs crappy when cold? By crappy, I mean the car has trouble getting boost and stutters under acceleration until warm.

just seeing what other input people have on this,

did it also stutter while at idle?

im trying to figure out my issues as well and I think this is what it comes down to.

 

[Sic95gst]

I had the same kind of problem under full boost the car would studder. I had and still have no major upgrades to the car. I decided to change my plugs to NGK Bpr7es and got some magnacore wires, Problem was fixed and hasn't been a issue in over a year. The car can hit max boost without studdering. Give it a shot it may do the trick.

 

[FiReBReTHa]

WOW!~

no more stutter, or random chug.

the plugs were white with a little bit of carbon pieces, I retained the old plugs so when I get my hands onto some seafoam I will use the old plugs.

but the power difference is amazing! its like.... adding bass to your music, I love it!