Hey guys,
I know this is a old thread, but hopefully someone with this or similar issues will check here before taking their Yukon/Tahoe to the "stealership", only to have them take your money and leave you scratching your head when it happens a day after they "repair" the issue.
*quick breakdown on my issue. 02' Yukon 5.3 flex 360,000+ miles when this sort of engine trouble originally occurred. It was a hot day and I was about an hour from home. Normal driving and had only been on the road for 20-30 min (total for the day), when it cut out, started chugging and left me stranded on the side of a back road. After letting it sit to cool down a bit, and checking all my hoses, fuel rails/lines, plug boots and battery, I decided to try cranking it over and had to damn near flood it to get her going. Long story short, I made it to a store, had it towed and the mechanic couldn't replicate the problem. That coupled with the miles, no codes and a good crank after towing, pointed the error towards the fuel pump. I changed it, the fuel filter, and fuel sensor, (along with cleaning out the fuel tank, and the lines). *Note that this was the first time I have replaced the fuel pump (still factory from 02'), although I've done several fuel filter replacements.
Those repairs seemed to take care of the problem until two weeks later, while on my way to a jobsite (towing my work trailer), it did the same thing. Again, no codes and by the time I made it to a mechanic friend of mine, he couldn't duplicate the problem...yet I sure did on Monday morning on my way home after picking it up from his shop.
After reading several posts, calling around, and talking to other owners who had 5.3l flex fuel engines, I came up with a list of potential cures, causes and things to repair.
The following repaired items all have caused loss of power, the engine to chug hard, die, and/or not crank or start up:
battery, (dirty/loose terminals, a bad ground)
fuel pump, (bad fuel, dirty lines, sending unit, fuel filter)
fuel pressure regulator, (This should definitely be checked when doing a fuel pump replacement, as it can go bad over time. Also be sure to check and replace the FPR vacuum line elbow connectors, and the line itself.)
random sensors, (crankshaft position sensor, map/mass air flow sensor, throttle positioning sensor)
throttle body intake, (dirty carbon buildup preventing the butterfly from opening or closing)
*the last thing I found while doing all of this research was the potential for vapor lock, although found primarily in carbureted engines over injected. To correct this issue its suggested to use insulation wrap on the fuel lines (silver adhesive backing works best) rear of the engine along the firewall and close to the tranny/exhaust (anywhere your fuel lines could overheat the fuel).
I hope this forum helps anyone with this issue (past or present). If anyone has tips or pointers on this topic, please feel free to ask or speak up.
~a
