Ghost in the machine

[441120]

Bought the car new, started bolt ons right away. In 1987 Kenne Bell was the only vender with good parts, bought some always with good results. In 1997 Popular Hot Rodding did "Double Your Horsepower" with KB products, I followed that recipe up to turbo.
Ran that way with Translator, 50# inj etc. No problem
Time passed no problem, one day a run in with LS1 'vette with Patriot head, cam, electric dumps...in other words GOD to the local Corvette guys...Time to store the stock turbo, start shopping.
I chose a GT3255, the car lives on the street, stock torque converter.
Now under load/high RPM it pops
Check everything...OK
Spark blow out??
Install Boost-a-Spark,CR42TS 0.032",new Accel super coil,new wires.90% gone but will still pop
Go through all info I can find.
Finally I swap out 70mm throttle body, install stock T/B...pop gone
Still want to put some miles to make sure but appears to be gone.

Question:
Would stock 2 1/2" up pipe from innercooler going into approx 3" throttle body cause turbulance or pressure drop resulting in the popping/missfire?
I noticed other cars with 70mm T/Bs but they appear to have 3" up pipes from the innercooler.
Car run great with 70mm up to approx 80% throttle then it would pop a few times but could get through it most times.
Scan tool =835 O2 0.5 KR
Drove me insane

 

[VadersV6]

How are all the grounds?
Crank sensor loose or aligned wrong?

 

[Roc87]

popping sounds like a coil pack/ingition module problem. I've run the 70mm throttle body/plenum since before I read this forum (And found I didn't need it) anyways, I still have it and it's run in the 11's (also have the RJC plate on it)

 

[mybuick]

see if your rev limiter is turned on, that was the problem with me.

 

[441120]

Grounds are good.
Crank sensor good.
Installed new GM coil, then Accel Coil didn't notice difference.
Friend has '87 GN with same mods except PT51 and still running factory exhaust manifolds. He also has the pop and the 70mm with the 2 1/2" pipe leading to the T/B. He swapped ignition module... No change.Coil, plugs etc.
I hear the stock T/B good to easy 10s so I am probably only losing a little throttle response, maybe a few ponys...but still courious
If it doesn't rain tonight I'll try again, got to retune, cranked the translator up to 8% rich WOT, F/P 45# idle line off, 65# WOT with 20# boost trying to stop the pop.
Turned translator back down, start all over.

 

[TurboTnZ06]

I had all kinds of popping at higher rpm too. Tried different plugs, gaps, wires, no help. Then switched coil pack w/ a new one. Popped less, but still popped. Then I toyed with the plugs gaps.I tried 0.032 and still popped. Then I started at 0.020 and moved bigger. I ended up on 0.028 using custom accel 8mm wires and voila~ no more popping through 6400 rpm. It's what my tune wanted, yours could be different...Maybe you should index the spark plugs too?

 

[441120]

pop free

Took the car out tonight, no pop!
Doesn't feel as responsive with stock T/B obviously, but runs good.
A rev limiter was mentioned by "mybuick", does the shift light setting in the Extender chip also function as a rev limiter?
I tryed setting that higher before, 5600 ,stock cam, didn't help.
I also went from CR43TS @ 0.035" to CR42TS @ 0.032", thought about indexing, even marked my socket but never ordered shims.
The KB Boost a Spark, a hot wire set up for the coils, all but eliminated it.
Now I'm wondering about stock throttle body on KB upper intake vs. stock throttle body and stock upper with RJC power plate
On the RJC site it appeared the plate doesn't help the KB plenum.
Do the power plates help that much?
All I know is when I installed the KB 70mm/plenum with the stock turbo you could feel a difference, just wondering how much is being left on the table going back to stock T/B.


Being rich and having your own dyno would be great

 

[Nojug]

I would probably say its the valve springs because youre flowing alot more air with the new turbo and the springs may be weak and by changing back to the stock TB you might be cutting back on airflow just enough.

 

[441120]

valve springs

I thought about valve springs (85,000 mi) but seemed to pop out exhaust if that means anything.
Car has never been to track, mostly easy miles....seriously.
I know the springs from the factory were not the best, but I thought if they were weak you would get more like a valve float.
You know like the engine would lay down, not pop/missfire.
Like I said, my friend has the same symptoms,maybe I can talk him into doing the springs on his car.
I know I should probably do my springs anyway, then timing chain and while I'm in there a new cam wouldn't hurt and while it's apart.......

 

[83ttypecooled]

Hi,
Did you verify that fuel pressure is up to snuff? I know, you have a Walbro 340 installed, but they are not immortal.How's your O2 voltage at speed?

 

[441120]

fuel pressure

Walbro 3 weeks old. < 200 miles
Fuel pressure 65# @ 20# boost from 45# line off idle.
O2=835+/- KR=0.0-0.7
All stated in above posts
That's why I was chasing spark, then thought pressure drop from 2 1/2" innercooler pipe to 70mm T/B @ T/B was causing some problem.

 

[441120]

dead horse takes a beating

After all was said and done I installed RJC's ADPP for the Kenne Bell 70mm throttle body and upper plenum to eliminate the popping under load that drove me I also install his Boost Controller
AWESOME!!!
To any one listening, get these products!
Currently looking for '87 T for daily driver, 100% stock. The first mods will be the power plate and boost controller, every car should have the plate