Chevy truck with strange loss of power

Jeff Diagnostician California Posted   Latest  

2008 Chevy Silverado 3500 6.0l 

I got this truck that acts like it hits a rev limiter @ 4500 rpm , has tons of power right until 4500 rpm then it just flattens out like a rev limiter or speed governor. Has no codes . If I back off the pedal a bit it will shift and then flatten out at 4500 rpm again​.​In park it wont rev past 3000 rpm. I did a crank relearn and it revved right past 4500 rpm no problem. . It came to me from another yard and they already put an OE crank sensor. Doesnt have an exhaust back psi problem . I noticed on a test drive that at WOT the APP shows 100% but the actual throttle angle doesnt get past 27%. To me if feels like its a commanded condition like the pcm has shifted its rev limiter down a few thousand rpms. Im wondering if the programming got corrupted somehow, Anyone run into this ?

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Frank Manager
Tennessee
Frank Default
 

Hello-I have seen trucks in rental fleets that have a governor cooked into the pcm programming. could this have come from an auction or from hertz or the like?

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Jeff Diagnostician
California
Jeff Default
 

This is a fleet truck , some of my units have governors that keep you at 70 mph. This truck doesn't have one tho.

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Bill Technician
Saskatchewan
Bill Default
 

Did you happen to run the calibrations through acdelco tds or read the program with hptuners etc.?

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Zeke Mechanic
Kentucky
Zeke Default
 

I’d check fuel pressure under a load condition if it’s not a tuning issue

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Paul Mechanic
Illinois
Paul Default
 

How about a VE test to see what maf reports and where the O2s voltages are at during episode. May be a fuel supply issue? Does this one have variable valve timing?

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Louis Mobile Technician
Texas
Louis Default
 

"Doesnt have an exhaust back psi problem ." I had one about a year ago with a similar issue. The above quoted statement was true based on the scanner info. Just to clear the slate, we loosed the exhaust at the manifolds to the point where the bolts were just barely holding it on. Test drove the unit and the problem was gone. Further analysis of the exhaust system found a broken baffle in the…

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Jim Owner/Technician
North Carolina
Jim Default
 

Any modules reporting a fault for a brake light switch? Check your MAP reading when this occurs, incorrect MAP reading can cause the throttle body to failsafe sometimes without a fault code.

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Jeff Diagnostician
California
Jeff Resolution
 

I appreciate all the responses, Turns out this is a programmed governor. I test drove 4 other trucks same year they all do the same thing. Some of the older trucks don't have the Governor. Some of the other same year trucks don't have the governor either. The driver is new to this truck and his previous truck didn't have a governor so he assume there was a problem.

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Cody Diagnostician
Arizona
Cody Default
 

I would perform a VE test and also a WOT test watching upstream 02's to make sure they are over 700mv. I also don't like the 29 percent throttle and seems like its a command. I would run bi directional tests on the tb unit to make sure there isn't an issue there.

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