Help with stumbling at WOT

[cool_g_83]

I would like to know what the possible causes of this stumbling are. Here's a little background.

First mod i did to my car was the defi boost gauge, shortly thereafter the Type-S BOV. I noticed after those two installations all was normal with the exception of the boost now going to about 14.5 or so (neat!). Next a few weeks later i install my intake. A week or so after that i noticed that in any gear besides first (WOT just breaks the tires loose) when i go WOT from any rpm, the car kind of hesitates/stumbles for a split second (needle on boost gauge bounces around 15 psi or so) then it throws me in my seat and runs smoothly. Now if i continue to keep WOT and shift to the next gear, a great deal of the time it continues running smooth.

The most violent (which really doesn't seem too bad) that it hesitates/stumbles is if I'm going around 40-50 in 5th gear and punch it. The needle on my boost gauge kind of dances around 15 psi, +/- 1 psi.

Now what i want to know is there anything in particular i should look at. I do not have a boost leak tester, but yesterday i tightend all my IC pipes and BOV down really well. The BOV i have not tampered with (i left it at the setting right out of the box), but I'm a little curious how some of you have yours set. Straight out of the box mine had 10+ threads showing (it seemed out a lot, but sounds good and seems to work well at all boost levels), but i doubt that is the cause of my stuttering.

What I've been considering after much searching on the subject is i have one of the following: plugs gapped wrong, need new spark plug wires, boost leak, lack of fuel pressure (which i highly doubt tho because once it stops stuttering it runs smoothly at the same boost level) or ?wastegate problems? ( I'm not very knowledgable on that subject).

Any ideas or suggestions on what i should do/check would be MUCHLY appreciated. I hate sitting around at work knowing there is something i need to fix on my car and i cant fix it because I'm at work. Bleh, oh well Thanks in Advance!

 

[Mirage1]

That sounds very similar to what my 1998 is doing. Do a boost leak test just to make sure everything is cool there. Then pick up a datalogger/pocketlogger.

My Car:
As my car starts building boost, you hear the turbo spooling up and sometimes it just takes off (usually when the motor is still a little cool). Other times, you hear the turbo spooling up but the car just isn't going any faster (usually at full operating temp). I picked up a Pocketlogger and see that my ignition timing is being pulled extremely low under boost. [currently running a new T25, stock exhaust, 1G BOV, UICP, cone filter, MBC set to max @15psi, and one step colder NGK plugs] Most of the time I'm getting pulled down to 2-4 degrees of ignition advance in the 4,000RPM range. Then back up to 9-11 degrees at 6,000RPM. O2's are good (.92-.96), TPS is working fine, and the car is in great shape.

Basically I'm troubleshooting to see if I have a real knock issue or just a rattle somewhere setting off the knock sensor. If this sounds similar, then is sounds like you are in the same boat. The best recommendation I have read lately is to verify your timing belt alignment. I guess it is common for people to accidentally retard the exhaust cam by a tooth. Just something else to check.

 

[evolvingGS-t]

You should try adjusting the BOV to hold the boost better.

 

[Patterson]

do a boost leak test. (check out vfaq.com) and if that doesn't work, my car did the same this and it turned out to be that the timing was off and therefore it was misfiring. keep us posted..

 

[Mirage1]

My timing marks were perfect. I did a combustion chamber cleaning today and it made a huge difference. I would highly recommend trying this to clean out the carbon buildup on your pistons and valves.

I also suspect that 15psi on the stock exhaust causes too much back pressure on the exhaust valves. The T25 alone creates too much back pressure.

 

[cool_g_83]

Maybe this is a dumb question, but could the problem possibly be that I didn't reset my ECU after each upgrade? Could that be a problem?

 

[Something Rudy]

Check and make sure that the battery is secure.

 

[Kollide]

That post above was from me, I accidentally posted under his name, at work we have only one computer, so if you have an questions direct the to me.

 

[oldman]

Boost leak test.

 

[cool_g_83]

I have a www.boostpro.net gauged tester on the way! As soon as i check that i'll check back here, thanks guys

 

[cool_g_83]

So today i was driving around trying to diagnose a what the problem could be and got some more info. It only hesitates if i punch it to WOT at <4500rmp or so, if i punch it at anything after that it seems to pull fine. Does this still sound like it could be a boost leak?

btw boost leak tester hasnt arrived yet...

 

[oldman]

So today i was driving around trying to diagnose a what the problem could be and got some more info. It only hesitates if i punch it to WOT at <4500rmp or so, if i punch it at anything after that it seems to pull fine. Does this still sound like it could be a boost leak?

btw boost leak tester hasnt arrived yet...

Yes, leaks get overcome by higher flow. Doesn't mean it's not there, just that you can't feel it. Refrain from WOT until the leak test, you can easily over-spin your turbo depending on how large the leak is.

 

[cool_g_83]

UPDATE: So today I tightened ALL intercooler piping and vacuum lines and changed the spark plugs. Problem FIXED! I'm thinking it was the plugs, thanks guys!

 

[oldman]

UPDATE: So today I tightened ALL intercooler piping and vacuum lines and changed the spark plugs. Problem FIXED! I'm thinking it was the plugs, thanks guys!

Good deal, follow through with the leak test anyway, you might be surprised to find how tight those clamps have to be.

 

[cool_g_83]

vvvv

 

[cool_g_83]

Good deal, follow through with the leak test anyway, you might be surprised to find how tight those clamps have to be.

Will do good sir still waiting on a coupler to arrive...

 

[GSTBlack95]

I had that problem with my car turned out to be spark plugs.

 

[cool_g_83]

I had that problem with my car turned out to be spark plugs.

Could have been the plugs, but also could have just been a Colorado thing...