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.

 

[sgosa]

I checked the exhaust temps at the entrance and exit of the Cats. They were within 15-20 degrees or so. Is that a reliable way to check them?
I checked that the coils are firing.
I checked the injector harnesses with a noid light. All were good.
Last night unplugging some of the injectors seemed to effect the idling. Today none of them being unplugged affected it at all. It idles very rough. Just barely staying running. I felt sure last night that I was going to find a bad injector today. And I guess that’s still a possibility. But at this point I’m not sure.

 

[sgosa]

If the cats were clogged to the point of causing this much of an issue, would it sound like it has an exhaust leak under the hood? It’s got that steady poofing sound when idling. That’s a silly way of describing it but I’m sure y’all know what I’m referring to.

 

[Scottydoggs]

manifold to cats would be much hotter then the post cats pipes. if you drive it at night, when its good and dark, you can drive it somewhat hard, then pull over to see if they are glowing red.

best way i can describe a clogged cats sound is a vacuum with a full bag, it wants to suck in, but it cant any more.

you can also remove both front o2 sensors and run it. yes your making exhaust leaks, but that lets the back pressure off if the cats are clogged, and it should run better, sound like crap, but run better.

when was your last tune up? if recent what plugs you use?

 

[sgosa]

manifold to cats would be much hotter then the post cats pipes. if you drive it at night, when its good and dark, you can drive it somewhat hard, then pull over to see if they are glowing red.

best way i can describe a clogged cats sound is a vacuum with a full bag, it wants to suck in, but it cant any more.

you can also remove both front o2 sensors and run it. yes your making exhaust leaks, but that lets the back pressure off if the cats are clogged, and it should run better, sound like crap, but run better.

when was your last tune up? if recent what plugs you use?

I replaced the plugs and wires this weekend. I used Taylor wires and AC Delco plugs.

 

[89Suburban]

I checked the exhaust temps at the entrance and exit of the Cats. .

No check the exhaust manifold exits at each cylinder head. If there is a dead cylinder it should be cooler than the others.

 

[sgosa]

Probably a dumb question. But does it need to be at full operating temp to check them all? I would think so but I’d rather ask and know.

 

[sgosa]

I checked the exhaust temps at the point of exit at the head. Seems like a wide range to be honest. Almost makes me doubt my thermometer is working properly.

Driver side
front cylinder 287
second cylinder 347
third cylinder 333
rear cylinder 311

Passenger side
front cyl. 288
second cyl. 214
third cyl. 210
rear cyl. 186.

 

[Kraig]

If you had a dead cylinder on a cold (not warmed up) engine, you’d have an exhaust passage just above room temperature.

 

[Kraig]

When you say the cat con temps are within 15-20 degrees—they’re hotter at the aft end than the front, right? That would indicate they’re working.

 

[sgosa]

Yes sir.