Boost issue, any ideas?

[Rob Hogan]

I've been having an issue with my boost during acceleration. The boost will top out at 5-6 lbs, the acceleration will crap out / or become pretty unstable, accompanied with a loud "buildup" noise.
The acceleration up to that point is good.

Also, thinking back, the issue started with the turbo topping out at 10 lbs of boost, and then worked its way to 5-6 where its seemed to settle. So this was somewhat gradual degredation.

I've taken it to one high performance shop, and another general mechanic, and so far everything they came up with doesnt seem to be the case.

One thought It might have been rusty fuel valve springs, but the other did a test (sorry dont know what its called, still learning about these things) that showed a steady intake as far as the valves were concerned, and then dismissed any kind of issue with the valve springs.

The wastegate sounds like it is working, and after I let up on the acceleration, the waste gate can be heard. One of the mechanics also dismissed the issue being a waste gate issue.

I just put new coolant in, and the engine runs between 165-170 degrees, and I dont have any issues with overheating. One of my friends that works with trucks may have suggested that my intercooler might be clogged as a result of dirty collant at some point.

The spark plugs are stock, and good, the coil pack has power, and all the wiring is new. The exhaust is stainless steel flowmaster, and haven't had any issues with the exhaust so far.

Has anyone encountered an issue like this, or have any ideas? Any help would be much appreciated.

Thanks

 

[Geoff87]

Need waaayyyy more info on your car!

Starting with, your cars current modifications if any?

 

[Slow91z]

Originally posted by Rob Hogan

I just put new coolant in, and the engine runs between 165-170 degrees, and I dont have any issues with overheating. One of my friends that works with trucks may have suggested that my intercooler might be clogged as a result of dirty collant at some point.

Woah...for one thing Coolant doesn't o anywhere NEAR the intercooler.

 

[XLR8]

Plugged Cat?

 

[Slow91z]

Originally posted by XLR8
Plugged Cat?

Good call...That would do it.

I guess it could be a bad turbo also.

 

[BJM]

Measure your fuel pressure under boost, it should rise with the boost and not fall off at all.

If that is fine, you still have not done anything that rules out a bad coil(s) or module. I bought a Type II ignition from a junk yard really cheaply and it fixed my car. It could simply be poor grounding for the module, its basic ground is through the bracket it sits on to the intake manifold. Any loss of connection and the ignition can do what you describe.

What does your scantool show the MAF is doing when this happens? What does the O2 show? If you don't have a scan tool this could take along time to fix.