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Brand new 5.3L is being very sluggish..

kleinjesse

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kleinjesse New Member

kleinjesse

Posted
Posted

I have a 2000 Silverado 1500 Z71 4WD. About 6 months ago the original motor gave up and I installed a Class 1 Jasper 5.3L. I have put about 9000 miles on this new motor and have been experiencing the same problems since installation.

 

Sometimes the motor runs amazing, but most of the times it is so sluggish, lots of hesitation. There is almost no throttle response under 3000 rpms. If I push the pedal down to the floor, it down shifts, makes a lot of noise, but does not accelerate as it should. The old motor had this same problem, but with 250,000 miles, I thought it was just worn out and had given up. Apparently not the case.

 

Here is what has been done to attempt to fix the problem:

 

  • New intake gasket
  • New knock sensor
  • New crank sensor
  • New throttle position sensor
  • New mass air flow sensor
  • New b1s1 02 sensor
  • New fuel pump
  • New fuel filter
  • Rebuilt rear end due to destroyed spider gears
  • Injectors cleaned and flow tested within spec
  • Cat. Converter back pressure tested and passed
  • Tested a used ECU from the exact same truck
  • OBDII throws abosolutely no codes
  • Chevrolet dealership diagnostics report nothing strange or out of spec
  • Transmission has been checked, non intrusively, no problems suspected
  • Have driven an identitcal truck, drives as expected, not sluggish

 

The only other problems I have with this truck is when I go to pump fuel. I have to pump VERY VERY SLOWLY of the filler neck will over flow and it will cut the pump off. We are talking 15+ minutes to go from Empty to Full. This is very annoying, I doubt the problems are related, but figured I would disclose this issue as well.

 

Any help on either issue would be greatly appreciated. If you need any more information just let me know.

Jvs Enthusiast

Jvs

Posted
Posted

Am tuned in on this. Sometimes my 99 does this same thing.

 

Some days runs great, some days feels REAL sluggish. No codes or running issues otherwise.

kleinjesse New Member

kleinjesse

Posted
  • Author
Posted

Have you done a smoke test? Is the fuel pressure within spec?

What is a "smoke test"? fuel pressure was at 60 psi when it was last check 4-5 months ago.

CapitalTruck Senior Enthusiast

CapitalTruck

Posted
Posted

Try driving it without a fuel cap for a moment. I can't help but wonder if the two are related. If the venting in the tank is messed up would it be possible that the pump would have problems moving fuel to the motor? Again, it's just an absolute moon shot.

 

The other theory would be that there is still some sensor somewhere that is intermentantly acting up. That of course isn't helped by the lack of codes.

 

I'm not a mechanic, but just for grins try operating it without the fuel cap the next time it's acting up.

 

I know one thing, I guarantee you there was a moment of total sickness when that new engine did the same thing as the old.

 

The making noise but no acceleration sure makes me thing tranny though. What makes you think the tranny is okay? When it is acting sluggish under 3000 rpm, does it sound normal or is it acting like it doesn't want to run?

oldmann Senior Enthusiast

oldmann

Posted
Posted

What is a "smoke test"? fuel pressure was at 60 psi when it was last check 4-5 months ago.

Smoke test checks for vacuum leaks.

 

kleinjesse New Member

kleinjesse

Posted
  • Author
Posted

Try driving it without a fuel cap for a moment. I can't help but wonder if the two are related. If the venting in the tank is messed up would it be possible that the pump would have problems moving fuel to the motor? Again, it's just an absolute moon shot.

 

The other theory would be that there is still some sensor somewhere that is intermentantly acting up. That of course isn't helped by the lack of codes.

 

I'm not a mechanic, but just for grins try operating it without the fuel cap the next time it's acting up.

 

I know one thing, I guarantee you there was a moment of total sickness when that new engine did the same thing as the old.

 

The making noise but no acceleration sure makes me thing tranny though. What makes you think the tranny is okay? When it is acting sluggish under 3000 rpm, does it sound normal or is it acting like it doesn't want to run?

 

I tried the fuel cap thing yesterday, still experienced the same problem.

 

I think the tranny is ok because our local transmission expert said it. He drove it and said it was an engine management issue. He is the most respected transmission guy in our area, has been doing transmission work since before I was born.

 

Also I would have assumed if it was a transmission issue the problem would be consistent not intermittent.

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