i just bought a 95 C3500HD for $1500, it had a bad vac pump so was making no boost as the wastegate was wide open... their loss my gain, i wired the wastegate closed to test, it makes 10lbs boost at wide open throttle and 1-2 lbs at cruise, should it make more boost than that with it wired closed? i figured it would over boost but just wired it to test...

limp mode question, when i hit 70-75mph it pops a SES light and boost drops back down to 3-4psi at full throttle, since waste gate is wired closed im figuring it is pulling fuel and causing this low boost situation? i pulled the DTC and it came up as 39, TCC Stuck Off.

i dont see how the TCC has any play in the boost and fuel, but what do you guys think? what should i do?

 

anytime the pcm senses a problem (transmission or engine related) it can go into limp mode, it limits fuel, which limits boost. i have a manual wastegate controller and it will still draw the max boost down to about 5 psi when it goes into limp mode.
check fuses
check tcc brake switch on brake pedal
google more

 

just looked at the pedal switch, looked good to me, plus my cruise works so thats another sign that its okay,

my overdrive is working and from doing a bit of reading it sounds like it wouldnt be if the TCC was bad? or is it just that it wouldnt lock up? im going to test the solenoid and see what happens