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1999 Gmc 2500 Crew 4x4 454 Fuel Issue

Chilledspode

By Chilledspode
in Ask A GM Technician

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Chilledspode Enthusiast

Chilledspode

Posted
Posted

VIN 1GTGK23J2XF049426 with 185,000km

 

The best way I can describe the issue is it keeps giving codes related to rich conditions at the O2 sensors. I have replaced every sensor I can think of over the last 4 years including crank position sensor, temp sensors, new injectors, EGR, etc. The truck on very light throttle (think of moving in traffic at 20 mph and smoothly feathering in throttle to maintain speed) the jetting comes apart and the truck stumbles and breaks up - more throttle/accelerate and things cleanup.

 

As part of this issue if you get the truck hot and then let it sit for 2hrs and come back to start it - it floods, it runs on the starter for 10-15secs blowing black smoke and starts on a few cylinders at a time followed by a full start - you can smell the raw fuel from 100ft away. Everything we can think of is in spec, fuel system has been leakdown tested all the regulators have been changed out, all sensors are in spec and the only thing that makes any sense to me is the truck keeps thinking it's cold and calls for more fuel than it needs but no one can figure out why.

 

We are currently chasing a possible bad wire between the ECT and the ECM as a possibility but after that the shop has nothing left to try other than replace the ECM.

 

The truck is in a small town so it doesn't do any highway running and I have spared no expense in maintenance trying to fix this long standing issue - I am wishing it had a carb so I could just rejet the stupid thing...

 

Any suggestions would sure be welcome.

 

Thanks for your time

 

Mark

redvett Senior Enthusiast

redvett

Posted
Posted

Have you replaced the CTS on the intake manifold with the yellow & black wires? It controls fuel enrichment. I suggest that you go to some shop with a Tech 2 or similar scanner and have them watch live data.

Chilledspode Enthusiast

Chilledspode

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Posted

Sorry, I wasn't very clear on that aspect - the local GM shop has been doing all this work and they are stumped.

 

The Tech 2 isn't providing any indication of what is causing the rich trim codes at the O2 sensors only that it is occuring..

 

Cheers

 

Mark

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