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Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 1672
Experience:  GM Grand Master Technician 2007. 14 year experience.
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2003 GMC Yukon 5.3L sudden misfire, engine stutter, will not

Customer Question

2003 GMC Yukon 5.3L sudden misfire, engine stutter, will not idle without pressing gas pedal. Codes for random misfire and MAF. used spark tester on all coil pack. good. replaced MAF, fuel filter, camshaft sensor no change. Fuel pressure about 48 psi. IDEAS!!!
Submitted: 1 year ago.
Category: GMC
Expert:  Dan replied 1 year ago.
Hello, my name is ***** ***** I'm here to help get your problem solved. Does the check engine light ever flash?
Customer: replied 1 year ago.
yes
Expert:  Dan replied 1 year ago.
Both at idle and while driving?
Customer: replied 1 year ago.
the problem started very suddenly while driving and had a flashing CEL. The vehicle is now non drivable in my driveway. It does Idle but very rough and flashing CEL sometimes
Customer: replied 1 year ago.
seems to run smoother reved up in drive way. as it starts getting warm you can hear it pinging under the truck
Expert:  Dan replied 1 year ago.
When you checked fuel pressure was that key on engine off or engine running?
Customer: replied 1 year ago.
both
Expert:  Dan replied 1 year ago.
What is the 8th digit of your vin? It was 48 psi key on engine off and running?
Customer: replied 1 year ago.
I have a flex fuel Z 8th digit vin. 48 both
Expert:  Dan replied 1 year ago.
What maf code are you getting?
Customer: replied 1 year ago.
I don't remember exactly. I believe it was a p0102
Expert:  Dan replied 1 year ago.
Unplug front oxygen sensors and let me know if vehicle runs better.
Customer: replied 1 year ago.
I don't want to bias a response but I had been running the vehicle very low on fuel for a long time. 5 dollars here and there. when it first hiccupped I thought I was out of fuel. limped to gas station and put fuel. no help
Customer: replied 1 year ago.
What would that be causing (the front o2)
Customer: replied 1 year ago.
almost forgot I had been driving in very heavy rain. Vehicle ran fine when parked. Parked about 4 hours. Then drove 2 minutes and problem started.
Expert:  Dan replied 1 year ago.
If one of the front oxygen sensors are failing it can cause this problem. Your fuel pressure is very borderline also. Does engine almost run perfect if keeping rpm up or only a little better?
Customer: replied 1 year ago.
It runs mildly better while keeping the RPM's up
Customer: replied 1 year ago.
I'm headed out to unplug the sensors
Expert:  Dan replied 1 year ago.
Ok, thanks.
Customer: replied 1 year ago.
I'm back. No JOY same problem
Expert:  Dan replied 1 year ago.
Disconnect battery for 10 minutes to reset fuel trim and see if that changes anything leaving sensors disconnected. If that doesn't change anything remove fuel pump relay and see how vehicle runs when spraying fuel alone into throttle body.
Customer: replied 1 year ago.
I did notice that at Idle the CEL flashes when reved it stays solid
Customer: replied 1 year ago.
sorry it took so long somebody put a drive shaft right in the way of one of the sensor plugs
Expert:  Dan replied 1 year ago.
These vehicles are common for intake gasket leaks which can cause it to run rough, but not usually this rough. Let me know, thanks.
Customer: replied 1 year ago.
One more piece of info. when the problem first started I did notice the master brake cylinder making noises when I pressed the brake pedal hard. I unplugged the vacuum line to it which allowed more air into the intake manifold and it idled much better.
Expert:  Dan replied 1 year ago.
That makes me think maybe you should make sure the air filter is not clogged. If good, still continue with above.
Customer: replied 1 year ago.
Filter not clogged removed completely to make sure. Oh yea I even took off the electronic throttle body and cleaned it. I did not move the butter fly valve
Customer: replied 1 year ago.
I will not be able to do the next step until tomorrow evening ish. will that be ok for you.
Expert:  Dan replied 1 year ago.
Ok, then continue with disconnecting battery for 10 minutes to reset fuel trim then leave sensors disconnected. If it still runs rough remove fuel pump relay and see how it runs on fuel sprayed into throttle body. I'll talk to you tomorrow, that is fine. Thanks.
Customer: replied 1 year ago.
thanks
Expert:  Dan replied 1 year ago.
No problem.