hard start when warm and run-on

htseat2000

Original poster
Member
Jan 25, 2013
62
hey guys,
i have a 2003 GMC envoy with 242K miles on it. i have never had a engine problem with this thing till now. The oil pressure gauge started reading erratically and going to 0 and check gauges would come on. i replaced oil pressure switch which solved that one. the problem i have now is that when starting the envoy when warm, it either instantly starts which is uncharacteristic or it will crank longer and normal and when it catches, it sounds as if it is not going to run, but does end up running, then sometimes when we shut it off, it will diesel for a second at the most before shutting off. any ideas?
 

mrrsm

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Supporting Donor
Member
Oct 22, 2015
7,641
Tampa Bay Area
Hard Starts can sometimes be symptomatic of having Low Fuel Pressure from a Failing Fuel Pressure Regulator. This component is easily located and R&R'd on the front, upper left side of the S/S Fuel Rail-Fuel Injection Assembly fitted into the Driver's Side of the Motor:

This is just one of many YT Videos explaining this FPR Repair:


The other problem component can be also be a Failing Fuel Pump. Fortunately, unlike many of the Later Model GMT-360s which house the Fuel Filter inside of the Fuel Tank, checking for Fuel Pressure and Fuel Rail Bleed-Down can more easily be made on the 2002-2004 Trailblazer and Envoy vehicles:

Follow this instructive Video and use a Fuel Pressure Tester like this inexpensive $15.00 version from Harbor Freight. Connect the Analog Fuel Pressure Gauge and Black Hose with Brass Fittings with internal "O"Rings to the External Schrader Valve Access Port near the Fuel Filter mounted on the Lower SUV Frame Rail underneath and adjacent the Driver's Side Door of the SUV. Nominal Fuel Pressure for the GM LL8 4.2L Inline Six Cylinder Motor when running is around 45 to 50 PSI.


...and another "On Topic" Video...




FUELPRESSURETESTERKIT.jpg
 
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NJTB

Member
Aug 27, 2012
612
Flemington, NJ
Seems like you have a leaking injector(s) and carbon buildup. Try a can of Seafoam in the gas tank to clean the carbon and maybe the injector. Have the injectors bench tested at a shop.
Is your cat converter OK?
 

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