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Pete, GMC Technician
Category: GM
Satisfied Customers: 28268
Experience:  14 years GM dealership technician and training.
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1996 GMC Suburban: the 5.7 L V8 EFI engine..misfires..hesitates

Resolved Question:

I have a 1996 GMC Suburban K1500 w/ 142000 on the 5.7 L V8 EFI engine. The engine misfires? or hesitates occassionally, but is most noticable at speed (>50 mph+). The fuel pump was changed and profeesional valve job completed by the last owner. The last owner kept a very detailed log of repairs.
Submitted: 5 years ago.
Category: GM
Expert:  Pete replied 5 years ago.
Hello,I will be glad to try and assist you with this,Welcome to Just Answer.


I just need a little more info to assist better.

Was the fuel filter replaced as well when the pump was replaced or has it been replaced recently?

Is or has the check engine light come on with this problem?

Let me know so we can continue,Thanks Pete!
Customer: replied 5 years ago.
Fuel filter was replaced and the check engine light has not come on. I read somewhere that there is a module outside the fuel tank that should be replaced when replacing the fuel pump.
Expert:  Pete replied 5 years ago.
On this vehicle the fuel pump is a module assembly and when replacing the fuel pump all that needs replaced is the module assembly as it will come with the pump and the fuel filter.In some of these vehicles the module is a separate component and the pump sits in the module and has to be replaced separate,it is possible the electrical contacts on this module can heat up and cause this issue as the contacts usually burn and wear over time and mileage and can cause this type of fault here.

The mass air flow sensor which is in line from the air filter box to the engine can also become dirty and cause this issue as I have seen before.You can remove it and purchase some mass air flow sensor cleaner and spray off this sensor to clean it up and see if it corrects the fault.This wont cause a check engine light to set when this sensor acts up.

Make sure your engine air filter is clean,your fuel filter needs replaced once a year or every 15,000 miles whichever comes first.

Dirty fuel injectors can cause this issue under load/at higher speeds,you can add some injector cleaner to the fuel tank and run the vehicle to see if it clears up these injectors.

Let me know if you need anything else,click accept if you feel satisfied with your answer as this is how I get credited for my time,Thanks Pete!
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