I have a 1998 GMC 3500 Dually Diesel. It has I guess what you would call the OLD waste gate vac setup with NO electrical plug. The turbo fan is spinning but it does not seem to be building boost. The aftermarket gage that came with my truck is at an almost constant Negitive 20. No matter what.. Towing or not. I have very little power all the time even when not towing. Can someone help me out here.. I am not sure why its not building boost and was wondering if this is why I have NO power. Also if anyone knows what the TRUE towing capacity of this truck is could you please let me know too.. The owners manual says 7000 LBS max trailer weight.. Not sure how that can be on this truck when my 3/4 ton can tow 14500 LBS and has a gas engine. Thank you all for the help in advance.

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I had this code in the system when I checked. But it had been cleared previously.

P0236 Turbocharger Boost System

Very Vague.

 

Your vacuum system may be bad, the waste gate is controlled by the vacuum system. If its not functioning correctly the waste gate will be stuck open and you'll get no boost. You could either go along with repairing the vacuum system or do a DIY turbo waste gate mod (which will probably be cheaper and more adjustable) Just make sure you get a boost gauge if you do the diy controller

 

Google turbomaster.

Check the vacuum produced by the vac pump,then move to the wastgate solenoid and checwhat comes out of the solenoid for vacuum and finnally check at the wastegate itself.

A simple test of the vac system is to try and force the wastegate open when the engine is idling-the wasget actuator should be pulling up on the linkage and it should take a strong finger to move it downward-compare the lvers location before you start and once running.

If the vac system is not working at all you wont be able to move an already open wastegate and may draw the wrong conclusion.

 

Hate to throw a question that might be construed as an insult, but, have you checked for a boost leak between the compressor and the intake? It's a possibility that the turbo is doing its job, the wastegate is closed, and you're losing boost pressure on the way to the intercooler, at the I/C, coming out of the I/C, or heading into the intake manifold.

 

Another cause of lack of boost is a plugged soot trap and/or collapsed exhaust crossover.

The code you have is related to the boost sensor directly though.