Engine won't take more than 10# of boost after rebuild. Need ideas please.

[jefffoxsr]

The engine won't take more than 10 - 12 pounds of boost without backfiring and having 15 degrees of retard.
Coil pack and module are good.
Fuel pump is good.
Fuel pressure rises appropriately with boost.
Spark plugs and wires are new.
Cam sensor is new and checked for proper setting multiple times.
Fuel injectors are not clogged.
Each injector is getting proper signal.
Tried multiple chips just to see if that made any difference.
Gas is good and has been replaced.
Turbo was just rebuilt two weeks ago and functions well.
The car has perfect running and driveability up to 10#
The maf has been swapped with a known good one.
Scan master numbers are good other than the knock retard.
Grounds were checked.
Boost hoses were checked again.
Roller cam is new and was degreed.
New stroker kit
Heads refreshed
New roller cam
I can't remember what else was checked but these are the ones I can remember.

As far as the question of what has changed since last time the car ran right at high boost here is the answer. The engine was rebuilt over the winter. It is ready to come home from the shop but the engine has the condition described above and we are out of ideas of what to check. This is a reputable shop that has years of experience working on these cars. I will not identify the shop because it is not necessary and I don't want to imply that this is their fault in any way. I just want my car to come home and I need help with ideas of what else we can check.

What else can I check? Thanks.

 

[john keskes]

Scan Master / Powerlogger #'s ?

 

[TurboDave]

The engine won't take more than 10 - 12 pounds of boost without backfiring and having 15 degrees of retard.
Coil pack and module are good.


What else can I check? Thanks.

Maybe good BUT, are they properly grounded????

 

[earlbrown]

Was the cam degrees when it was built? (and does the cam still have all 12 lobes?)

Gap set correctly on the crank sensor, cam sensor set correctly, plug wires on correctly, fuel pressure rising with boost, boost control hoses new?

 

[Slow91z]

The warped washer on the cam sensor might be killed allowing the shaft to come up and the "window" disappears from the sensor in the cap.

 

[jefffoxsr]

Scan master numbers are good other than the knock retard. Grounds were checked. Boost hoses were checked again. Roller cam is new and was degreed. I will add these items to the original post too for future readers of this topic. Thank you for the responses.

 

[TurboTdr3.8]

could be valve springs not set right for your roller cam

 

[Mike Licht]

compression check? an overly advanced cam could be a problem

 

[1fastcobra]

Scan master numbers are good other than the knock retard. Grounds were checked. Boost hoses were checked again. Roller cam is new and was degreed. I will add these items to the original post too for future readers of this topic. Thank you for the responses.

Does it do it if you ease into it? ?
Or when u just stabb it ?
Does it matter the rpm ??
What chip and injectors.??

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[Reggie West]

What kind of waste gate are you using?

 

[phil_jordan]

Where did you purchase the coil pack and module?

 

[jefffoxsr]

Stock waste gate. TE 63 old style turbo just completely rebuilt two weeks ago. If I punch it from a dead stop or ease into the boost it runs perfect. But when the boost gets over 10# that's when it stutters and backfires. I don't know where the shop purchased the coil pack and module. The injectors are 55# and the ECM matches for low impedence - I have run this ecm and injector set for about 1000 miles since 1999. Stock maf. I will ask them about some of the items posted here.

 

[phil_jordan]

Please do. As i state in every thread like this, one of the most important purchases is of the coil and module. Hopefully they got it right though. I don't trust the stock MAF either to be honest. Just my opinion though. Good luck and keep us posted.

 

[1fastcobra]

Ohm out the coil. 11-13 ohms I bought one from a.zone and it only has 8ohms

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[TexasT]

So, rebuilt. Was the block bored? New pistons installed? What was done to the heads? Were they or the block decked? Head gasket?

I'd try the module , maf and such but would be asking some questions such as cc of the heads. Compression checked? Maybe try some higher octane fuel to see if it goes away.

Just kinda throwin stuff out.

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[jefffoxsr]

The pistons are new. The crank and rods are new with the stroker kit. The block was not bored. I will ask what was done to the heads. I don't know who made the head gasket but he said they were steel reinforced. Thanks. You've given me a few more ideas to pursue with them. I will let you guys know.

 

[lrayzer]

Hey, just for sport change the fuel filter.

 

[larrym]

Check all your couplers on the up pipe make sure one isn't loose or just hanging on.


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[87buickracer]

Does this car have a alcohol kit on it?Mine had a similar problem with alky kit and maf interference...I would also check wire harness and plugs/connectors for bad connection or short..

 

[jefffoxsr]

It has an alky kit. The kit is turned off right now because the boost is only set at 15#. I will have the shop check some of these things you listed over the next few days and I will let you guys know. The up pipe is secure and has the good clamps. Thanks for all the great suggestions guys.