2007 GMC W4500 I:E: Isuzu Turbo help

TominClarence

New member
Hello .... I am hoping I'm at the right forum. I have a 2007 GMC W4500 the is giving me a code, P0299. (Turbo underboost condition) My turbo boost sensor reads 14.4 lbs key on engine off. I thought it should have read "0" so I replaced it. Same thing, 14.4 lbs. with the new sensor. Did a little research and apparently it is supposed to read that? next check was the waste gate. It was closed, not stuck open. I put a manual gauge on it and just sitting in park and revving it it will go to 4 lbs of boost. Test driving it, under a load it still only reaches 4 lbs of boost. I removed the EGR valve and checked to make sure it wasn't open and therefore bypassing pressure back to the exhaust. It was closed. I am thinking no that either A) I have a weak turbo or B) a possible leak in the inter cooler. Does anyone else have any insight? These turbo's are expensive, I hate to throw one at it ... Uggggggggh ... Thanks for the help !
Truck has 130,000
 

javajoe79

Fabricator
The wastegate can be faulty. Wire it shut and see if it makes more boost. Be careful not to let it overboost for too long though.

If it had a boost leak you would probably hear it as a loud hissing noise.

If the turbo is making any boost and not making noise, it's probably not bad. You can check the turbo by removing the inlet pipe to the turbo, engine off and manually spinning the turbo and wiggling the shaft to see if it's sloppy. A ball bearing turbo will have a little play normally and a journal bearing turbo will have even less play or no play at all.
 

TominClarence

New member
Thanks for the advise .... I will wire the waste gate and check boost pressure again this morning. I did remove the hoses on the turbo and check shaft play. All seems good there and no oil residue anywhere. I will update this as soon as i know more, Thanks !
 

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