Need help with stumble under boost problem

[SlickTR]

I guess stumble is the best way to describe it. The car idles and drives fine, drives fine under a load and boost under 5 psi. But when ever i get on it and boost starts to build to 5-10 psi is stumbles and will not accelerate anymore, boost and rpms acutually drop. It does it both jumping on the gas and gradually getting into it. Its consistent and at the same boost level every time. Doesnt pop or anything. What else I know so far...

-No codes or flashing check engine light
-its not the coil or module or the plugs
-nothing obvious on my DS when it happens, MAF values seem normal, BLMS/02 voltage looks normal, voltage is 13+, TPS signal is normal.
-have a fairly new caspers cam sensor cap and the LED stays steady lit which makes me think that is should be functioning normal.
-fuel pressure at idle is fine and it holds pressure once the engine is off.

-I did notice that my wideband goes pretty rich when it happens no black smoke or anything but its like 9:1. I'm not sure if this is related to the cause or if that happens because im close to or at WOT but it wont build boost/rpms.

I'm at a loss and need the help of the experts once again.

 

[Boostdeznuts]

Check the Turbo for in and out play . I have the same problem and found out that the turbo was bad

 

[SlickTR]

Check the Turbo for in and out play . I have the same problem and found out that the turbo was bad

i'll check it out to be sure, i would hope its not that, its a precision 6776 that is not that old and has low miles on it.

 

[SlickTR]

definately not the turbo, very minimal play, spins freely, and blades look good.

 

[BlackBandit]

Have you tried unplugging the DS and seeing if it still does it?

 

[datquick6]

how about a loose coupler before the tb.

 

[SlickTR]

Have you tried unplugging the DS and seeing if it still does it?

Should have mentioned that, but yes, i did that too. Like every DS owner i think lol, I've been there in the past with the interference to the DS ribbon cable problem.

i checked the couplers but ill double check and see if some how one the t-clamps came loose

 

[whitehot1]

I guess stumble is the best way to describe it. The car idles and drives fine, drives fine under a load and boost under 5 psi. But when ever i get on it and boost starts to build to 5-10 psi is stumbles and will not accelerate anymore, boost and rpms acutually drop. It does it both jumping on the gas and gradually getting into it. Its consistent and at the same boost level every time. Doesnt pop or anything. What else I know so far...

-No codes or flashing check engine light
-its not the coil or module or the plugs
-nothing obvious on my DS when it happens, MAF values seem normal, BLMS/02 voltage looks normal, voltage is 13+, TPS signal is normal.
-have a fairly new caspers cam sensor cap and the LED stays steady lit which makes me think that is should be functioning normal.
-fuel pressure at idle is fine and it holds pressure once the engine is off.

What's the history leading up to this happening? were you racing it or running it hard? How did you determine the ignition parts to be good?Any additional info you can provide will be helpfull.

 

[SlickTR]

At the track, first run went good no issues all the way until right before the traps it did it, after that it has done it everytime i get into the gas. I had a spare good coil pack and ignition module, i swapped them to see if it would fix the problem. put new plugs in it to see it that helped, they didnt, i didnt change the plug wires though.

 

[1quick6]

Are you sure your intercooler and up-pipe hoses are tight and sealed? I chased mine for a day before I discovered the up-pipe had popped off underneath. I couldn't see it or feel it was off until I disassembled.

 

[SlickTR]

all pipes couplers and clamps are good, just double checked them.

 

[whitehot1]

Have you done a compression or leakdown test?

How many miles are on your engine?

 

[SlickTR]

Have you done a compression or leakdown test?

How many miles are on your engine?

no not yet, the motor doesnt act or sound hurt, feels good as long and im not in boost too much, drives just like it did before any thing happened. Not sure on exact miles, somewhere around 25K i think.

 

[BlackBandit]

Definitely check for headgasket damage. (look for milkshake and do compression/leakdown) If that looks good consider cleaning all of your grounds.

EDIT; just re-read your original post. You're wideband is most likely reading rich do to the missfiring sending raw fuel down the exhaust. I'm assuming you dont' have any wideband correction going on but if you do I'd turn it off until you get this sorted out.

 

[TurboTnZ06]

Original plastic timing chain?

 

[SlickTR]

Original plastic timing chain?

no that was changed when the motor was rebuilt.

compression and leak down are fine. I also think the problem is better described as bogging as opposed to a stumble, like i said boost and rpms actually decrease and it just wont go. I also noticed a little stumble a couple times at WOT before this problem started, and lately a couple times it has died while at idle. I think its gotta be a spark or fuel issue, it seems just like when the ignition cuts out when "valet mode" is on my anti-theft or like severe spark blow out. I know its getting plenty of fuel. Plugs are new and coil/module are new but the plug wires are still the same, they are MSDs but i have no idea how old they are. I will try to see if i can get a set to swap out at try it.

 

[whitehot1]

no that was changed when the motor was rebuilt.

compression and leak down are fine. I also think the problem is better described as bogging as opposed to a stumble, like i said boost and rpms actually decrease and it just wont go. I also noticed a little stumble a couple times at WOT before this problem started, and lately a couple times it has died while at idle. I think its gotta be a spark or fuel issue, it seems just like when the ignition cuts out when "valet mode" is on my anti-theft or like severe spark blow out. I know its getting plenty of fuel. Plugs are new and coil/module are new but the plug wires are still the same, they are MSDs but i have no idea how old they are. I will try to see if i can get a set to swap out at try it.

Have you done an ohm test on the coil pack with the engine cold and warmed up? What brand of coil pack and ignition module do you have?

 

[SlickTR]

Have you done an ohm test on the coil pack with the engine cold and warmed up? What brand of coil pack and ignition module do you have?

Yep, I have two sets both ohmed out fine warm/cold, the set thats on there now is a High Output Coilpack from NOS4GN and the module is a GM NOS from Kirban. Put new plugs in too, like said previously the only thing that isnt new or that I havent changed/checked with the ign system are the plug wires. I'll work on finding another set to see if thats it.

 

[GullsGN]

Does the TPS rise smoothly as you step on the gas with the car off? Dead spot?

 

[VIN7]

I had a similar issue a while back, so bad that it would stumble and sputter and shut the car off once it got above 5lbs of boost. Turned out to be some build up or corrosion on the chip pins. Pop it out and use a pencil eraser on the pins and try it.

Mike