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Discussion Starter · #1 ·
Hello my name is Willie Roberts. I own a 1998 Pontiac Grand Prix gtp 2 door. I am trying to get it back on the road as it has been sitting for a few years. It has the following mods :
Lq4 maf
Northstar tb
Ported gen 3 m90
Stage 2 zzp intercooler
Ported lower intake
Zzp xpz cam
Tog headers
Slp loudmouth exhaust
Prj fuel rails
42.5 lb injectors
Double roller timing chain
Stage 2 zzp heads
Pullies from 3.2 down to 2.55
I am having trouble with it not running 100% I have a laptop but cannot get my dhp tuner to connect. I am planning on getting hp tuners and hopefully get it scanned. I think I might have a leak in the upper heat exchanger, is there any way I can pressurize it and check. Any help would be appreciated. Thank you and have a blessed day.

Super Moderator
885 Posts
Hello, again.

Are you hearing any whistling at idle? You can take a small hose and use it as a stethoscope around all of the sealing surfaces, to see if anything is abnormal.

Another decent way to check the top-end sealing will be a compression test, which can also rule out a head gasket issue, and you may be able to retain ~10-20psi in the top end (if your PCV paths are plugged). Most likely it'll find somewhere to get out, but you can chase it to anywhere you wouldn't like it.

You can also unbolt the M90 and I/C to carefully re-seal with fresh RTV. Despite clean machining on the core and engine parts, I/C's don't always like to seal without RTV accounting for some warping as they get tightened.

All of the above is $20-40 in items to try out over an afternoon or weekend (RTV, compression tester, s/c gaskets).

Good luck, and hope to see you have success.
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