Interminent Misfire

[MKCoconuts]

So let me start by giving the basic info, '05 LLY 142k miles. Lately I've been having an issue with my truck where it will idle and run like crap....but only sometimes. To give an example, I drove it work the other night, ran like crap and I had to limp it there. Left work that morning, ran like a raped ape. Go to the store that afternoon, ran like crap. Ran it back home, no issues.

It won't throw the SES light and this all began shortly after I changed the fuel filter. I thought maybe it was pulling air in so I pulled the filter back off and found the o-ring was little too big so I put the old o-ring back in, which fit much better. Now, since I've owned the truck, I've only used AC Delco fuel filters but the place I buy from could no longer get them so I went with a Carquest HD. I can't imagine the fuel filter being the issue but I've seen dumber things.

Any ways, fixing the o-ring didn't help. So I scanned it for codes. Pulled a P1232, Injector 4 Output Circuit. Cleared it and looked online. Found a wire exposed by the alternator. Got that all fixed, still has an issue, again though, only sometimes. Sometimes it'll run like crap then clear up for a few miles and then run like crap again. Went kayaking, ran great going there. Coming back, ran like crap so I stopped by the parts store and pulled the codes. This time I got:

P0300, Multiple Misfire
P0301, Cylinder 1 Misfire
P0304, Cylinder 4 Misfire
P1223, 1226, 1229, 1232, 1235, 1238, 1241, 1244 (Output circuit for all injectors)

Cleared those codes and haven't seen what's come back yet. I've let the truck idle while I wiggled wires to see if anything changes and haven't found anything (and of course at that time it was idling like normal). I looked at the C107 connector and didn't find any exposed wires there either. I'm ordering a OBD connector so I can download TorquePro and look at things with my laptop. I am at the point where I'm ready to start removing stuff and pulling the whole wiring harness to go over every little thing. But before I go through the trouble, I wanted to get others opinions on what it could be. I'm starting to lean towards the FICM, but I've never had an issue with the truck till now. I even thought about putting the old fuel filter back on and see if things clear up.

Thanks you for any and all ideas

 

[Ron Nielson]

Start by looking here: https://www.dtcdecode.com/Chevrolet/P1232. Most likely, it's electrical, not fuel filter related.

 

[MKCoconuts]

I figured as much. I will go look through the wire harness again. I may still end up just removing the entire harness and inspecting it one by one if I don't find any thing today. Funny thing is last night I started it up and it was idling fine, even stuck it in gear with the brakes to the floor to see if it would bog down and instead started spinning the tires. Will see what happens today.

 

[zakkb787]

Have you done the ice pick truck for the injectors? Google this. LLYs are bad to lose connections at the injector harness. There’s a great write up on it with a video that shows what it sounds like as the first search result if you Google “LLY ice pick trick”

Also, rock auto sells the AC Delco filters last time I checked.

 

[MKCoconuts]

I read about the ice pick trick but haven't done it. I ran the truck yesterday to the gym and it ran back and forth fine with zero issues. The OBD reader should be here Friday so that should help with things. I should mention that I unplugged both connectors on the drivers side of the engine, blew them out and reconnected them before going to the gym. I am wondering if one may have gotten loose. I am going to drive it to work tonight (15 miles one way) so we'll see how she runs

 

[2004LB7]

as Zak stated. it's a common issue with the LLY engine. it doesn't hurt anything to do the ice pick trick. may as well do it now before you are doing it on the side of the highway

 

[MKCoconuts]

Maybe I'll do that this weekend. Truck ran great both too and from work last night. We'll run it again tonight and see what happens. Almost hate to piss with anything else since it seems to be running normal again.

As far as the fuel filter goes, I only buy my parts from the local store (unless it's a performance part). I like to keep business local and I am not a fan of Rock Auto.

 

[zakkb787]

I get wanting to buy local, but when it’s a part that could be the difference in 4K of trashed injectors from a lesser quality filter, I’d rather buy right than buy local. There’s a reason almost everyone here uses AC Delco filters

 

[MKCoconuts]

So the issue came back. Ran great for about 2.5 weeks. I let it sit for two days while I drove my Jeep and then it came back the first day I drove it again. Thought maybe the connectors came loose again, so I reseated them. Issue was still there. Ice picked cylinders 2 & 7 since those are supposedly the common issue ones and also did cylinder 4 since that was initial cylinder fault. Still misfires and stutters. Not nearly as bad as originally, but still bad enough it sounds like a tractor. I'll probably ice pick the rest today, but wanted any other things to look at.

I stopped at the parts store today and pulled codes since my Torque app doesn't seem to bring any faults up and all 8 cylinders had a injector output circuit fault. I cleared them and will see what comes back but I am starting to lean towards the FICM going bad or a major wiring issue that I can't seem to trace. Should also mention that this time it seems to kinda sort itself out when you give it some more throttle, takes a moment, but then it'll get up and go. I also have screen shots of the balance rates that I can post.

 

[MKCoconuts]

Pulled passengers wiring harness and went through all the injector connectors and didn't find any thing wrong other than the cam sensor wires were a little pinched, but they've been like that for over two years now. I didn't get to the drivers side but something tells me that my luck the problem is gonna be down under the upper radiator hose or in spot that will require tearing more apart than I prefer.