Misfire and no power....

[sgosa]

2003 Yukon, 5.3 flex fuel, 200K miles. CEL came on, but it still ran fine. A week or so later it started fluttering or missing when accelerating to merge with traffic. Within the next 10 miles it lost almost all power. Had to be towed home. Now it will barely idle. Runs very rough, seems to have a definite miss. Checked for codes and got P0101 and P0300. Replaced battery, MAF sensor, plugs, and wires. I cleared the codes. No improvement at all. Checked fuel pressure, it holds at 45 or so psi. I have found varying specs for the fuel pressure. Some say 45 is sufficient, some say it needs to be 60-65. When idling, it sounds as if there is an exhaust leak under the hood. I sprayed carb cleaner around the intake and hoses to check for possible vacuum leaks. Nothing appears to be leaking there. I checked all the coil packs, all are working. I thought maybe the catalytic converter is stopped up. The only test I have done on that was with an infrared thermometer. The temps before the converter and after the converter are within 20-30 degrees of each other. Any ideas on what else I can check? Im about to give up and take it to a mechanic, but I would much rather repair it myself.

 

[cmc76]

I had very similar behavior when injector quit. I was told its rare. My scanner couldn't tell me which one.
Needed a tech II

 

[sgosa]

Is a Tech II one of the more expensive scanners?

 

[Doubeleive]

Is a Tech II one of the more expensive scanners?

the clones run about $300 online, they usually pay for themselves over time.

 

[Kraig]

Unplug injectors one at a time and see if any have no change to the idle when unplugged

 

[sgosa]

Unplug injectors one at a time and see if any have no change to the idle when unplugged

Driver side rear definitely did not change the way it was running when unplugged. The second from rear didnt change it much if any. The other 2 made a noticeable difference when unplugged. That would suggest at least one bad injector?

 

[Doubeleive]

Driver side rear definitely did not change the way it was running when unplugged. The second from rear didnt change it much if any. The other 2 made a noticeable difference when unplugged. That would suggest at least one bad injector?

yes, or bad coil pack, try swapping coil packs around see if you get the same or different results, I know you said you checked them but wouldn't hurt to confirm, you can get the "herko" injectors off of ebay very very reasonable, they are essentially oem I believe they are made in the same plant I have bought a couple complete sets and had excellent results, just get the ones with 4 nozzles as those are the flex fuel ones.

**you may want to check the voltage on the harness connector to the suspect injectors as well to verify they are getting power

 

[Fless]

@sgosa, per Haynes:



Note key ON, engine OFF.

 

[Scottydoggs]

really sounds like a clogged cat or two. or you need a tune up something fierce. those are the only two things that make the cel flash and misfire.

 

[89Suburban]

If you have a timing light check those two wires for a spark signal. An infra red thermometer would be helpful here to read exhaust port temps.