Misfire with no dtc's
 

So, here's the story; I have used 42 lb ford injectors on my ls1. After a header install I accidentally left the 6 th cylinder injector unplugged, the ran awful and I got out and fixed it. When I run diagnostics with my predator I see that the 5 and 6 cylinder misfire counts go up and them back to zero. It sort of feels like there's a slight miss, but it could be my imagination. There's no ses light on or any trouble codes - is this how the misfire counter is suposed to work?

my car has 3 misses every 60 seconds on cylinder 3. Doesn't throw codes, but you can damn sure feel it.

I just swapped 3 and 5 plus and wires, then I sat there and logged, and saw missed on 3,5,6 and 7.
I suspect it's the damn used ford injectors I bought (paid 175 for them too :( )
weather's nice, so I'll be taking the motorcycle to work the next few days, but I'm going to swap wires again, and then if that shows nothing, just buy new plugs (if they don't work I only wasted like $10), if that fails, I'll get new injectors (or maybe switch back to gasoline and run the stockers)

The misfire counts have to get up to a certain number before they set a code. Im not sure on the number but I think its pretty high.

http://img411.imageshack.us/img411/1183/misfire.th.jpg

here's a condensed graph of misfires
cyl 2 had only 1 peak.
5 and 6 are the worst.


since they ALL had misfires; is this rather normal, should I be concerned?

Just put in new plugs (NGK tr-55's) air filter and fuel filter - same results.
Will run the tank down, switch back to gas, and swap the injectors for the stock ones and see if the misses go away.

The only thing I can think of after that could be the 02 sensors, but like ti shows above, cyl 2 almost never misfires, while 5 and 6 do a lot.

put the stock injectors back on, same issue cyl. 6 has the most misses, still no check engine light.
It does this at idle, haven't checked to see if it does while cruising, but it feels like it does. It also does it before the car is even warmed up... so I dont think it's the 02 sensors.

actually, there are still some misfires, but a lot less than before (seemingly)
I think the stockers might nor be in the best of shape themselves, or something else is causing it.
now cyl 1, 6 and 8 seems to have the misses.
car does run better (though it feels more sluggish running on gasoline as compared to ethanol w some advanced timing)

Have you tried swapping parts from a cylinder with a miss to one that doesn't show a miss to see if the miss moves? Only do one part at a time so you can eliminate or know which part is the problem.

If you move all parts and the miss doesn't move, then you have an internal problem. Such as a bent pushrod, broken rocker arm, low compression in that cylinder, etc....

swap the coil pack, wire, injector to another piston see it it follow as 99345hp said. If it does start doing the elimination game. Do 1 thing at a time see if you get the same results.

damn.. I hope you find out what it is. I have heard of these issues but no one that has found the cause.

Couple suggestions if you haven't tried them already...clean your MAF, and check your O2 sensors.

I think the o2 sensors are dying, ses came on yesterday for running lean, ltft is 23%, ordered some from rockauto, will try them out. How do you clean a maf?

Go to your local autoparts store and look in the section with fuel injector cleaners, carb cleaners, etc...there's a specific can of MAF cleaner. About $9 for the can. Spray it all over the MAF wires and such, and be extremely careful not to touch the little wires, as they break extremely easy.

You can also get new O2s from any NAPA, etc. If you have headers, you can get the long O2 sensor wires and you won't need extensions anymore...Bosch 13111 if you need them.

well, I put denso 02's in and after a few miles logged with my predator, and dslogredux says to adjust the ltft's to -26%
I believe that is the max on 02 can swing by, so it looks like they aren't reading accurately (plus, the exhaust smells rich to me).
NAPA closes at 5:30, so I'm going to pick up some bosch's after work tomorrow.

well, i put the boschs in, and it says to adjust the slope by -24%, not much of a chnage, it smells very rich.

Cant find any vaccuumm leaks, cleaned the maf, this is the 3rd set of o2 sensors. I really cant tell what it is wrong!!! its expensive and frustrating.


disregard all of the above
the predator has a lame way of storing custom tunes. reuploaded my original-noo2-noegr tune, and my ltft's are ~3
at idle they are -10 though and the exhaust brings a tear to my eye (literally)

so I'm back to my tiny misfire issue (seems like it went down after i went back to the original injectors)
cleaned the MAF today, noticed no difference.

swapped wire from plug 1 with plug 5, misfire moved to cyl 5.
Time to order some wires.
I'll try MSD's since I cant find a part number for the GMPP's