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Pete
Pete, Auto Service Technician
Category: Chevy
Satisfied Customers: 24682
Experience:  14 years GM dealer Technician.
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C8500 diesel 2004 - vehicle came in with a power problem,

Customer Question

C8500 diesel 2004 - vehicle came in with a power problem, Had trouble accelerating change the mess airflow system confirmed no leaks no air leaks intercoolers good air to air is good check turbo turbo is good change the throttle position sensor how the problem got a lot better but when you start to slow down the vehicle the problem happens again and I'll just lose acceleration.
Submitted: 1 year ago.
Category: Chevy
Expert:  Pete replied 1 year ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.My info is somewhat limited on your model here but I had seen no one else has responded and would like to see if I can help here.If at any time you feel that I cannot help with this please let me know.

One common issue I have run across several times before is a restriction with one of the exhaust components.I have seen restricted catalytic converters as well as resonators or if this model uses a DPF this can restrict and cause this issue.If you have not had the exhaust checked/tested at all this should be done to see if a restriction is found.If a fault is found with a restriction with one of the exhaust components the restricted component needs replaced.

The other issue can be the fuel injection pump acting up intermittently.I have seen some fail or act up when deceling it wont produce the correct pressure intermittently when trying to accelerate again.If the exhaust tests o.k. I would have the fuel injection pump tested to see if it is faulty needing replaced or repaired at all.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 1 year ago.
I sm being told that this problem only happens when you slow down or stop.
Expert:  Pete replied 1 year ago.

If this model uses the electronic accelerator position sensor on the gas pedal (electronic gas pedal with no cable attached) the sensor on the pedal may be acting up needing replaced.I have seen this fail before several times needing replaced to correct this type of fault.It is a potentiometer and a certain section in this sensor may have a dead or weak spot causing loss of signal which will cause loss of acceleration like this here intermittently.If this has not been checked this should be done.This will cause this type of fault here.

Thanks Pete

Customer: replied 1 year ago.
That was changed this morning, problem still there.
Expert:  Pete replied 1 year ago.

It is possible still that the injection pump isnt pressurizing the fuel properly when trying to accelerate again after a slow down or stop.I have seen some of the pumps fail like this before needing replaced or repaired.If the fuel system was not tested this needs done to see if this is the cause here.

Thanks Pete

Customer: replied 1 year ago.
What is the best way to test the pump?
Expert:  Pete replied 1 year ago.

My info doesn't list the procedure on how this is tested but most of the time the actual and desired fuel rail pressure signal can be checked with a compatible scan tool plugged into your vehicle to check pressures but in most cases the pump needs removed and tested by a diesel repair facility that has the tools and test equipment to test the pump itself.

Thanks Pete

Customer: replied 1 year ago.
Fuel system is fine exhaust is fine I found out some information from the tech he saying that the symptoms I'm explaining to you is that what the problem is that's just the vehicle going into limp mode something is causing day to go into limp mode because when you turn it off and this is some recycles it goes away and then while you're driving limp mode comes on and then it takes off the throttle and you lose power but that's because it's in limp mode so the question is what would cause it to go into limp mode keep in mind Messier sensor was changed and the throttle position sensor was changed and the turbo was checked
Expert:  Pete replied 1 year ago.

The tech is correct,if you are able to turn off the key then turn it back on and the problem resets itself or goes away this usually indicates one of the components with the engine or transmission is causing the limp mode here.it is difficult to say for sure from here which component for sure is causing this fault.

One big issue on the diesel engines I have seen is when the engine computer sees a lack of fuel or fuel rail pressure difference between actual pressure and commanded pressure this can cause this and can be a fault with the fuel filter being restricted,an injector leaking or a fault with the injection pump.I have also seen issues with transmission shift or pressure regulating solenoids acting up causing the limp mode as well as sensors like speed sensors in the transmission.

There are several components that will cause the limp mode here and what will have to be done since no codes are setting (if you havent had the fault codes checked yet this should be done to see if any codes are setting as this will help diagnose and locate the fault here) is to operate the vehicle with a scan tool/computer connected to it to monitor data from sensors and solenoids to see if you can catch what is reading out of specification or acting up when the fault occurs.Then it can be further diagnosed or checked into to pinpoint and repair this fault.

Thanks Pete

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