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Pete, GMC Technician
Category: GM
Satisfied Customers: 24142
Experience:  14 years GM dealership technician and training.
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1995 gmc yukon: 5.7 l running very rich..tail pipe

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1995 gmc yukon 5.7 l running very rich. smells like raw fuel out the tail pipe. any ideas? running rough.
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 anything done that may have caused this recently?

Do you have a scan tool to observe the engine data and to also check for fault codes?

Does it feel like an engine misfire when running?

Let me know so we can continue,Thanks Pete!
Customer: replied 5 years ago.
Nothing was done before I started trying to get it to run better. I do not have a scan tool. It does feel like it is missing. idles really low like it is going to stall. All wires are going to correct plugs. this is a replacement engine but ran better. just started running bad.

An engine misfire or multiple misfires can cause this problem here on your vehicle.

First I would make sure there is spark at each cylinder by checking spark at each plug wire where it connects to each plug.

If spark is o.k.,and the distributor is installed correctly to where it is timed right then the next step is to have a compression test done,this is done with a compression tester.

The compression should be fairly close to the same on each cylinder,if one is found lower then the rest then this is most likely the problem.This can be a common fault of one of the valves for that cylinder.If found a valve is at fault then the head will have to be removed and repaired or replaced.

If spark and compression are o.k. then I would visually examine each injector in the throttle body when the engine is running,look for one of the two that looks like it is spraying allot more fuel then the other,this can cause misfires and raw fuel smells.This can be caused by a faulty injector or the oxygen sensor reading incorrectly and causing the rough running condition as well as other components at fault.

Check and see if your egr valve is stuck open,you can remove the vacuum line from it and see if it runs better,if it does then most likely the egr valve solenoid has failed and needs replaced(this is the component that directs vacuum to the egr valve).I have had to replace both and always recommend if one is at fault either the egr valve or the solenoid to replace both.

All of these here can cause this problem and need checked/tested to find the fault then repaired.I would also to be safe have the fault codes checked with a code reader or scan tool to see if any codes are set.This will aid and in some cases can pinpoint the failure.Most shops or dealers can do this and I have heard of parts stores checking codes for free in some places.

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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