Engine/Transmission (1998.5 - 2002) Where is my missing boost?

[Big P]

For the past couple of months my truck has been down 2-3 psi on every level of the Comp, along with higher egt. I really have to load the engine for 5-10 seconds before the boost gauge will jump to its previous levels. Things I've checked so far, all clamps from the turbo to the engine, rubber boots, K&N is still pretty clean, didn't see any cracks in the exhaust manifold, anti-freeze looks oil free and at a safe level, no leaks on the outside of the head that I can see. I will be changing the oil soon but I don't expect to find anything there. Fuel pressure is fine. The shaft on the turbo rotates freely, no exessive play. When I shut the truck off though, I don't think the turbo spools down as long as it used to, but it could be me. Does anybody know where it went?

 

[cumminspwr01]

Is there a chance your wastegate may be stuck open a little bit. I also see you have an intake on there. Did your numbers drop after you changed the intake.

 

[Snow man]

make up an adapter to fit over the turbo inlet,pressurize the turbo to 15psi or so, with regulated shop air,,and listen for leaks, could be a ripped boot,or intercooler problem. Sounds like you have a leak somewhere.

 

[mediccummin]

What snowman said, I did this and sprayed some soapy water all around, looked like a bubble machine going off. All my boots were leaking even though I tightened them up. Good luck

 

[Turbo Tim 1]

I was having an issue with boost on mine, turned out the bleed port on the boost elbow had a little blockage in it making the wastegate open too soon. That hole is tiny and it doesn't take much. I was only able to get 28 psi with the comp on 5x5. I put on a new elbow and now I get 38 psi and EGT's are in check.

 

[Big P]

Thanks for the help. I'll try to pressure test the intake system this weekend.

 

[GIT-R-DONE]

How does one pressurize the turbo via air compressor? What do you use to plug off the air inlet to seal the turbo/pressurize the system?

 

[Big P]

I went to Home Depot and got a 4" rubber cap made for PVC pipe and installed a valve stem in it. Remove the air filter and clamp the cap to the turbo. This is the part that did't dawn on me at first, you have to block the intake into the engine or else the will go right out the exhaust.



Now here are the results of my test. To block the intake I removed it from the grid heater and put foil tape on the bottom of the intake and bolted it back on. I put 10-15 psi in it and found no leaks at any of the clamped sections. I did hear air leaking at the air horn. I sprayed it with soapy water but I didn't see anything, the air was breeding down fairly quick. It could have been air getting by the tape or leaking from the gasket. I did notice when taking off the air horn that one bolt was a little loose and same with the boost fitting. So I put everything back and went to take it for a test ride. Once I got out of my neighborhood I was going to hammer down but I noticed the check engine light on the dash and went back home, the truck was running fine though. I got a 238( MAP voltage is too high) and a 1475( Aux 5 volt supply voltage too high Sensor supply voltage for ECM sensors is too high). After thinking a bit I remembered that I did turn the key on with the ground for the Comp disconnected, didn't start the motor though.



So now I don't know if it's just a coincidence, my doing, or a bad Comp. The truck was acting a little weird the other day, had flat spots in the powerband under light throttle. I'll check the ground and pump wire tomorrow because I was working around that area. Maybe I shorted a connection on the ECM with the soapy water, but I doubt it.



If it is a bad Comp, I guess it's time to step up to the Drag version anyway. :

 

[RobbyRam]

Map sensor probably the culprit.