GMC Troubleshooting Questions? Ask a Mechanic for Answers
Hello my name is***** for the wait.
What engine do you have? Could post your VIN#
Have you checked fuel pressure?
Do you have any codes set?
Please get back with me
I know you said fuel pressure is good. Can you tell me what it is?
Also does it hold after shutting it off?
When you are in neutral can you increase the engine rpm?
Does it run down the road ok?
If yes on both questions.
I recommend cleaning the throttle body and disconnecting both battery cable and touching the together.
This will reset the idle.
Let me know if this helps.
Do you have a flashing engine light when its shaking?
Ok that tells me that the engine computer is seeing a misfire.
Do you have a scan tool that can show live misfire graph?
There are several things. Injector or connector at injector,Low compression,I have seen intake gaskets causing a vacuum leak.
Why did you replace the fuel pump? How did all the problem start?
Need to know if all the injectors are clicking. May have a plugged one.
Does the engine sound like it's holding back?
Can you tap on each injector lightly with the engine running. May get them working.
If you can find a auto part store that can read code and live data of the misfire.
That would help
Can you tell which 3 cylinders are missing?
They are all on the same side?
When you pull the wire off you do have spark?
Can you take a long rod or screwdriver and listen to each injector. Should here a clicking noise compare it with a good cylinder. With engine running
It could be stuck injectors
You could have a intake gasket leaking vacuum. If you sprayed carb cleaner around the intake see if it starts to run smooth.
I also have seen the exhaust convert plug causing some misfire. If you pull the front O2 sensor on the side of the misfire. see how it runs
That means the are getting power and ground.
Just because there clicking does not mean they can't be plugged
You could see if auto part store has a cleaning kit.
You have to clean them by running them and flushing a cleaner through them