VMacKenzie
New member
- Joined
- Dec 9, 2007
- Messages
- 625
My '98.5 has a weird problem where the power is very flat between 3-9 psi of boost, started right when I pulled the original injectors to check them out then reinstalled them. This is on a stock truck.
From a stop it initially takes off fine, but about the time it reaches 3psi boost the power begins to go flat, pretty doggy. If you keep on the go pedal it rolls some black smoke and the pyro soars to 700-900F without much Go to show for it. Once boost hits 10psi it suddenly becomes a different animal, comes alive and goes like a rocket, shoots right to 22psi, no smoke, and EGTs actually fall. Something isn't right, it's bad driving down the freeway because it loses speed and I have to downshift out of OD on every grade that's steeper than about 3%. And we're talking about an empty short box 2wd!! It runs and idles very smooth, I doubt the injectors or tubes are the issue.
Here's the sequence of what I've attempted to remedy:
Checked injector lines for leaks, OK
Checked intake system for leaks, none found
Replaced cracked exhaust manifold, installed a Polydyn tubular header I had on hand, did not help at all
Swapped out the stock HX35 for another stock one, no effect
Cleaned IAT and MAP sensors, no change
Replaced IAT and MAP sensors, slight improvement
Replaced stock turbo with Garret GT3788 (stage 3) and installed 4/5" exhaust
Interestingly putting the Garrett on improved the bottom end response even with stock fueling, but still has the flat midrange power. I threw on the old school van Aaken box I had lying around (good for about 45hp) and while it improved the midrange it essentially masks the problem, EGTs rise a bit more and it smokes pretty good until I hit about 10 psi.
The next step is swapping out injectors, maybe reusing the non-reusable cross tubes is part of the issue, I have a newer set of tubes to put in. I doubt it's the issue though. My other theory is the VP44 is the problem, maybe the timing advance piston is hanging up and keeping the timing too retarded then it suddenly frees up and goes around 10 psi.
Other than that I'm out of ideas. . .anyone else ever heard of this sort of problem??
From a stop it initially takes off fine, but about the time it reaches 3psi boost the power begins to go flat, pretty doggy. If you keep on the go pedal it rolls some black smoke and the pyro soars to 700-900F without much Go to show for it. Once boost hits 10psi it suddenly becomes a different animal, comes alive and goes like a rocket, shoots right to 22psi, no smoke, and EGTs actually fall. Something isn't right, it's bad driving down the freeway because it loses speed and I have to downshift out of OD on every grade that's steeper than about 3%. And we're talking about an empty short box 2wd!! It runs and idles very smooth, I doubt the injectors or tubes are the issue.
Here's the sequence of what I've attempted to remedy:
Checked injector lines for leaks, OK
Checked intake system for leaks, none found
Replaced cracked exhaust manifold, installed a Polydyn tubular header I had on hand, did not help at all
Swapped out the stock HX35 for another stock one, no effect
Cleaned IAT and MAP sensors, no change
Replaced IAT and MAP sensors, slight improvement
Replaced stock turbo with Garret GT3788 (stage 3) and installed 4/5" exhaust
Interestingly putting the Garrett on improved the bottom end response even with stock fueling, but still has the flat midrange power. I threw on the old school van Aaken box I had lying around (good for about 45hp) and while it improved the midrange it essentially masks the problem, EGTs rise a bit more and it smokes pretty good until I hit about 10 psi.
The next step is swapping out injectors, maybe reusing the non-reusable cross tubes is part of the issue, I have a newer set of tubes to put in. I doubt it's the issue though. My other theory is the VP44 is the problem, maybe the timing advance piston is hanging up and keeping the timing too retarded then it suddenly frees up and goes around 10 psi.
Other than that I'm out of ideas. . .anyone else ever heard of this sort of problem??
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