97 6.5 losing boost under throttle
 

I just put a boost gauge in my truck under Howard throttle it builds about 10 pounds boost then drops to about 5 and holds till I take foot off of throttle is that normal or is my turbo going bad?

Normal with GM factory programming

If I put a mechanical waste gate on would that help out

To a point it would help, if you run a mech boost control on your 6.5 and it being OBD-II all you will do is get more boost for a while, but when the boost does not reduce tike the PCM wants it will code on overboost or WG performance issue then go into tier 2 defense and defuel,

That can be controlled somewhat by adding a "fooler" that limits the feedback signal from the boost pressure sensor (MAP) to the PCM so it thinks it is making less boost than it thinks you are, actually if your vac boost management system is still operable, then you could try that alone first. a 10 turn 10K pot set to about 8.5K resistance is sufficient to fool the PCM into letting you sustain 10 psi boost physically and PCM only seeing 3 psi boost.

Trade off will be more boost but potentially higher EGT/ECT due to higher sustained turbo back-pressure, and less mpg.

tune and a turbo master and itll be all better :choochoo:

Or put a real turbo and tune on your rig.

I have just bought a 2002 C3500HD with the 6.5 with 60900 miles on the odometer. The truck has a crane on it and I am not sure how much time it has spent at idle running the hydraulic crane.


The engine has a noise around 1500 rpm when driving between 0 to 35. the noise goes away with more throttle.


I removed the Vacuum pump, installed a boost gauge and a mechanical waste gate. My target was 12psi under load. This was the number I was shooting for based on all the miss-information the internet suggested.


This worked good for a quick trip at around 5 psi cruising and 12psi under load ..... until I got a P0236 code and the boost went to around 3psi.


Is it possible to make the ECM happy with a mechanical waste gate? I feel like I am chasing my tail trying to find a noise and now caused another puzzle. Does the vacuum pump really fail so often and rob power so much that I really need to keep going down this road? The truck did seem to run better with out the ECM in control of the boost...