Stumbling at 4000rpms

[CyberEye]

I'm trying to hunt down this problem, any help would be appreciated. At WOT when the engine reaches around 4000rpms it starts to jerk and stumble all over itself. It only does this at WOT, not partial throttle. When this happens O2 voltage drops to 0.

Plugs are brand new; BPR6ES gapped to .28.
Wires are maybe 6 months old; NGK
Fuel filter was changed today
O2 sensor is brand new

I changed the fuel filter today hoping it would solve the problem, but no luck there. I took it out for a drive after and the problem was still there. This time however when the car started to jerk, I heard a pop. Not a bang type pop, more so a pop like when a high pressure hose blows off. It may have happened before, but if it was I didn't notice it.

Could it just be that one of the clamps on my IC pipes is broken, and under wot and full boost (15psi) the hose is expanding letting all the air out? All the piping is still attatched so nothing blew off. I did a couple of 3rd gear pulls after I put the filter on and both times I heard the pop.

The only mods really done to the car are a 16g turbo, which was on when I bought it, and the fuel pump is re-wired.

Thanks
Mac

 

[Acezwild88]

booth i think that my car is royally fu**ed i have a huge problem with the boost that im still trying to figure out. but also the car dose stumble and thats why im posting cus it would be nice to set my car up to the potential my car has and that ive never seen. and have the car just run normally

 

[oldman]

Sounds like a boost leak test is in order.

Have you guys done this yet?

 

[1grrvalley]

i wo uld check the ecu

 

[Acezwild88]

thats what my machanic thinks. i had my balance shaft bypassed would that have anything to do with it?

 

[swarm]

al,

if i downshift and stomp on it, it immediately hits 0.00 on the o2

i have tried a new TPS

 

[Big Al 389]

Sorry it took so long to get back to ya'll but I been busy with yet another GS-T witjh a very problem very close to the ones in this post!
Here's the skinny on it,under any load above normal driving in other words anything that made it boost,it would start to stumble,the more boost it saw the worse it was!So I start checking-fuel psi,190 lph pump only a few months old with good psi.Next did a boost leak test, very good results no leak.Checked all conn.plugs no better.Then was plugs and wires,replaced em all,not a bit better!O2 readings would drop to nearly nothingat my wits end I thought it was going to whoop me,then the owner told me that it was alot worse when it was raining...........aha it has to be ignition I thought,replace both coils no more problem,didn't miss another beat.Maybe this will help.....Al

 

[swarm]

Can you please be more specific? I already replaced a coil pack (I think that's what it's called) - are there two? If so, can you please show me where?

 

[Big Al 389]

On the coil bracket the coils there are 2 coils,2 plug wires to each one.It is usually an assy.but if needed you can change one or the other....Al

 

[swarm]

gotcha. already changed that. any other ideas?
is there anything that can indirectly cause the coil to not function properly, even if the coil itself is good?

 

[Big Al 389]

I don't know of anything else to check besides your grounds,I hate to say this but every thing Ive' told you has fixxed similar problems for me.Maybe someone else can lead you in a new direction!I'm stumpped,sorry we didn't find the culpret.....Al

 

[swarm]

i'll go through grounds. the car has a full sound system and modified grounds at the battery.

 

[TurbochargedJt]

My car is doing the same thing except it seems to be more a boost related than rpm related. If I go past 11 psi the car will start to buck an stumble badly, but if I back off the throttle a little and then give it gas again I can get the rpms as high as I want. I turned down the boost level so I have to step on the throttle more before the boost will climb higher this helps me from having to keep my eye on the boost guage and worry about it peaking past 10psi. It's still very dissapointing that I can't drive my car at it's full potential. I'm seriously considering a tradeing the car in if noone can find a solution to this PITA problem. BTW...What are the mileage on some of your cars, I have 133,000 miles, maybe it only does it on cars with higher miles

 

[94EclipseGST]

Boost leak, poor tuning or... rocker arm came loose. These have all caused this problem for me in the past.

My car would run to 5000K beautifully, then it all of a sudden would studder and drag it's ass. Fixed leak, fixed car.

Then one of the rocker arms fell off (I probably didn't put it on all the way when i changed out the lifters). Same thing. Put it back on, car fixed.

Last problem. Installed MAF-T eight months ago and the car never ran well. I never could get it tuned right using the MAF-T. I couldn't boost past 4500K and it studdered and dragged ass all over. Took the MAF-T off and relied on the EPROM chip yesterday and the car pulled like a mofo.

Bottom line, check these things. I replaced the whole damn ignition system, ISC and many other things throughout the process and each time the easy fix was the cure.

 

[swarm]

Wow -- blast from the past.... I already fixed my car and sold it.... it was a rocker arm that came off...

 

[94EclipseGST]

I'm glad you fixed the problem. It's always nice to post when you have so the rest of us know and don't post on old threads!

 

[eclipsegsx68]

Ok Everyone. I Had The Same Problem As All Of You. I Installed A Evo 3 16g In My 96 Gsx And Took It Out For A Drive. At W.o.t. My Car Was Misfiring Or Stumbling Like You All Say. There Is A Problem With Your Air Fuel Ratio I Believe. I Took It To "performance Dyno Tuning" For Them To Do A Diagnostic. I Was Told To Purchase An Aem Uego Wideband O2 Sensor. The Problem Was My Car Was Runing Super Rich!!! The O2 Sensor In The O2 Sensor Housing Was Faulty. It Was Sending Wrong Messages To The Ecu Causing The Car To Pump Eccess Gas Into The Combustion Chambers. All That Eccess Gas Was Basically Flooding Everyting Causing The Car To Jerk At W.o.t. I Replaced It And Everything Worked Great After That. The Only Problem I Have Now Is With Boost Creep. It Sux!!

 

[swarm]

I Replaced It And Everything Worked Great After That. The Only Problem I Have Now Is With Boost Creep. It Sux!!

Well, that, and your excessive use of the shift key. Does it take a long time to type all those words with the first letter capitalized?