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Discussion Starter · #1 ·
I have been fighting this problem and still cant get it.

My truck will generally not build for than 10-15 psi. and it is very choppy, the boost gauge does move smooth. goes smooth to 10 and jerks to 15 and then wont move.

I can sometimes get in the truck and it randomly runs great. builds 27psi and runs like a raped ape. but 99% of the time I can not get it to run smooth.


I have replaced the wastegate, old one wouldn't move when air was put to it. New wastegate didn't solve the prob.

Did full boost leak check. all good no leaks.

replaced the boost gauge because I thought it was bad and I was crazy, even though the truck is slow.


What am I missing???? I really don't want to dig into the turbo, but if I have to............
 

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Discussion Starter · #2 ·

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Moved to LB7 for more help--

How old is the fuel filter-?? You need to monitor the rail pressure-- sounds like it is starving for fuel.
 

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Discussion Starter · #4 ·
Moved to LB7 for more help--

How old is the fuel filter-?? You need to monitor the rail pressure-- sounds like it is starving for fuel.
Brand new Cat Filter and rebuilt filter head
 

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Discussion Starter · #5 ·

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Have you checked for codes with your efi?
If no codes have been thrown i'd log your maf and map/boost pressure sensor and see if it corresponds to your mechanical gauge.
It seems the ecm is limiting fuel and those are the only ones I've heard of that will give false readings and not always throw a code.
 

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Discussion Starter · #7 ·
would not enough fuel cause me to not build boost??


Also, I mailed my ecm into ATP a long time ago for my tunes, I don't have an autocal or anything. no way to data log
 

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Looks to me like it's your gauge that's the issue. Have you tried reading boost through the OBD2 port?
 

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Short answer is yes, boost is primarily generated by fuel in the duramax.
However if it were a mechanical fuel issue like injector pump or filter restriction I doubt it would randomly fix itself and run right.
Also the service engine light would likely be illuminated from low rail pressure and such.
That is assuming your service engine light isn't on when it wont build boost?
 

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When you say it breaks loose and takes off, do you mean just the boost gauge or the gauge and the truck?
 

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Discussion Starter · #11 ·
Looks to me like it's your gauge that's the issue. Have you tried reading boost through the OBD2 port?


Brand new gauge. Truck doesn't run good when I cant build boost.

Also had a Tech 2 hooked up at the dealer and gauge was reading accurate.
 

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Discussion Starter · #12 ·
Short answer is yes, boost is primarily generated by fuel in the duramax.
However if it were a mechanical fuel issue like injector pump or filter restriction I doubt it would randomly fix itself and run right.
Also the service engine light would likely be illuminated from low rail pressure and such.
That is assuming your service engine light isn't on when it wont build boost?
Right, no lights or codes. That's why I am at a loss. It varies how well it runs by what side of the bed I wake up on. There is no regularity.
 

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my guess is turbo bearings are going bad, check the impeller for excessive movement, and oil in the compressor outlet.
 

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If the turbo checks out you really need to get some kind of scanner on it to read what mm3 of fuel is being commanded by the ecm.... IIRC it should command at least 89mm3 injection rate at wot anywhere above 2200 rpm. If its not then you know the ecm is limiting fuel and your problem is electrical.
 

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MAP and MAF sensors will regulate fueling based upon the air coming in. If they read low then no matter what the truck will not fuel properly. When the truck isn't fueling the turbo wont spool up because it spools off exhaust pressure.

Based on that info, I agree with Tom. You need to start reading the information being sent to the ECM. Fuel pressure (command vs actual) and air readings. Without getting a scan tool that reads this data your going to just be throwing parts at it till it is fixed and that could cost thousands.
 

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Discussion Starter · #16 ·
MAP and MAF sensors will regulate fueling based upon the air coming in. If they read low then no matter what the truck will not fuel properly. When the truck isn't fueling the turbo wont spool up because it spools off exhaust pressure.

Based on that info, I agree with Tom. You need to start reading the information being sent to the ECM. Fuel pressure (command vs actual) and air readings. Without getting a scan tool that reads this data your going to just be throwing parts at it till it is fixed and that could cost thousands.
Ok, Because I don't have an autocal to datalog with. What other options are there to take these readings? Just go to the dealer?
 

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It might be worth investing in an Autocal. A forum member just bought one off craigslist for 50 bucks. Deals are out there. Or you could buy a OBD2 bluetooth adapter and get the torque pro app for android, or dash command for iphone.
 

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Discussion Starter · #18 ·
It might be worth investing in an Autocal. A forum member just bought one off craigslist for 50 bucks. Deals are out there. Or you could buy a OBD2 bluetooth adapter and get the torque pro app for android, or dash command for iphone.
Edge insight will not get me what I need will it?
 

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Edge insight will not get me what I need will it?
Yes the Edge Insight CTS will do all the things you need to monitor.
 
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