Stuttering under boost

[racerdude7730]

Ok guys i have been fighting with this for over a year now and im about out of ideas. The car runs fine when its idling and everything but the problem is that once im moving and goto the gas and it dont even have to be that hard once the power is laid down and the boost if rising it starts to stutter and almost bang and sound like its getting a back fire. Also i can control it if i just baby the gas as im getting upto driving speeds. A few months ago i had changed my plugs and plug wires and i found out my one plug wire was bad. I had no problems for about 2 months and now its back again. I have replaced the O2's in the car made sure there were no boost leaks that i could find. My hoses all seem to be fine to me. I was thinking it could be the fuel sysstem but i doubt thats what it is. If anyone has any ideas please let me know or if you would like more information ### ask. By the way its a 1999 GSX and it only has 70,000 miles on it

 

[Ace_gst]

When you say you checked for boost leaks did you actually pump up your ic pipe to see if it holds pressure?

 

[Firegst]

This is a boost leak 100% I just went through the same thing,

http://www.vfaq.com/mods/ICtester.html

^Follow the above link, make sure you use soapy water and are patient, I would take off your front bumper so that you can see/hear/and test every connection.

I also was leaking at the BISS screw which is right on top of the throttle body, and my BOV. I would check in and round the TB and the Injector area as well.

http://www.dsmtuners.com/forums/new...itate-fail-while-boost-1-2-full-throttle.html

^ my old thread, what is said in there is what you will get told here...DONT BE LAZY take a good 30mins to and hour and do a boost leak test, I did mine at 20 psi.

 

[racerdude7730]

thanks for the help guys I will run another boost test after work tomorrow and see if i can find anything I will let you know how it turns out. If nothing changes i willl hook up the Gopro and get some audio and video of it thanks again guys

 

[Firegst]

Thats what we are here for, I got your PM BTW no worries man.

 

[ChiTownHussla]

I am having same issue. test your fuel pressure bro. I will subscribe for updates

 

[Brinker]

Im having the same issue it sounds like. Ive narrowed mine to to a knock problem(major issue because im running E85 which shouldnt knock) but i just put new plugs in, the wires are good, and i have no boost leak so its somewhere in the tune for my car. if you have your boost turned up and a way to tune, turn down the boost to stock and slowly work up to your goal

 

[jconcepcion4g63]

I am putting my money on crank or cam sensor, I am not sure which the 99 has.

If your boost leak test checks out, I suggest getting the proper testing procedures from the Tech articles or service manual and check your crank/cam sensor with a Multi Meter. But if you are feeling froggy or do not have a good multi meter you could find a cheap senspor to swap or buy new and swap to see if that works which I strongly do not recommend doing without properly diagnosing the problem first.

 

[cnordelo]

Guys i notice a common pattern. People replacing plugs. I did the same thing bit still had a stutter or just wouldnt pass 4 grand. I had to step down in heat and to a marine ngk. Cleared up. Hope this helps

 

[Spoolin92GSX]

Couldn't hurt to physically check the knock sensors themselves.. If the black "goo" is oozing out of the back, replace the sensor. Without a logger phantom knock can be a gigantic PITA.

 

[A_USER_NAME]

I am also in the same boat, but for myself it only occurs if I am at WOT. Im thinking minor fuel blockage (dirty fuel filter), causeing a minor fuel cut like symptom.

 

[Brinker]

Im still getting the issue, and the knock sensors are good. put new plugs in it and still no change. bad coil possibly?

 

[Spoolin92GSX]

Im still getting the issue, and the knock sensors are good. put new plugs in it and still no change. bad coil possibly?

What plugs are you running, and at what gap?
You mentioned you were on E85 so I'm assuming you have a somewhat recently inspected/refreshed ECU?
When does the knock begin- RPM, manifold pressure/vacuum, part/full throttle..?
What are you using to tune with?

 

[ChiTownHussla]

Any updates?

 

[Diamond Star Werks]

Bad maf or fuel filter. Granted there are no boost leaks.

 

[Cody Nelson]

wondering what kind of coil and plug wires you have. heat range of the plug wires can be an issue. when accelerating the spark v increases as the primary coil fires. my guess would be to get different plug wires because with the voltage and heat factors the wires loose internal resistance

 

[smbgsx]

Having the same issue. Started recently when boost hits 23psi and wot I get a stutter starting at about 5k rpm. Everything before that pulls hard. I replaced plugs a while back and the issue went away but then came back worse. But I don't think the plugs are the cause, I think they're a symptom.
I know I have an small exhaust leak where my EGT sensor goes into my header and my exhaust manifold gasket.
I also suspect that I may need to change my fuel filter. I also pulled my walbro 450Lph not long ago and noticed the connector was a little deformed like it was melting a little. Going to redo my wiring to my full blown billet pump hanger with GM weather pack connectors, change the filter and fix my exhaust leaks and perform the following
Boost leak test to 30 psi
Compression test.
Leak down test.
Check alternator belt tension and output.
Pressure test cooling system.
Check fuses/relays/breakers for faults.
Perform injector balance test.
Maybe some of these things will point you in the right direction as well.
At times recently I'll get a check engine light momentarily and it feels like a misfire but then if I let off it goes away. No codes are stored. Don't know if anyone knows what that is . I have ecmlink and damn near every box is unchecked that could make a CEL come on.

 

[enriquez2000]

So many things can cause this... usually boost leaks ill share my oddity one

Car was boosting and driving great then all of a sudden it started acting like bad ignition when getting on it around 4k. I did what most do

Blt
Plug swap
Wire swap
Even tried swapping good coils
Swapped known good cas

Nothing worked. Well i decided to open my valve cover(cant remember why). Well I found a rocker arm laying in the valley. Turns out this was the issue all the time.

Start with the easy stuff and definitely a BLT 1st.

 

[smbgsx]

I recently made a post in this thread having the same issue, a recent stutter at 5000 rpm and up every pull. The other day i removed my fp header and noticed one of the header studs bores was stripped out and I had a small leak around the port that leads to header runner number 4. I helicoiled it, installed the header with a new gasket and icleaned my K&N air filter which was pretty dirty. Runs perfect again.
I recently had purchased a billet oil fill cap that vibrated loose and fell out on a drive and oil sprayed all over my engine bay. Assuming the oil also sprayed all over my filter and restricted it enough to have a rich misfire under boost. I wouldn't think the exhaust manifold gasket leak would cause the stutter because I ran with virtually no gasket left at one point and all I ever noticed was excessive engine noise and poor spool. But either way, the helicoil, gasket, and cleaned air filter are the only changes I made and it runs like the day it came off the Dyno again. Was great until my 11 year old TRE trans finally gave up and called it quits yesterday 11 years at 400 tq and hard launches I can't complain tho, I drove that car like I stole it every weekend. Finally have an excuse to pull everything and install the new setup. Hope you find the cause of your issue.