P304 cylinder 4 misfire

[Jpross]

Just to discount the tune, I reverted back to factory tune and performed the same misfire code test. I had the same results... Right at 1200 rpm the misfire count climbs on cylinder 4 like crazy. Thought maybe the tune could have advanced the spark enough to create a ping where cyclinder 4 saw the first effects of predetonation. Next step is fog test of some sort. Maybe number 4 inject isn't seating properly and pulling additional air.

[Jpross]

I just sprayed carb clean on injector 4 while engine was running and no difference in idle.

[Jpross]

Fixed! It was the map sensor! Really weird, most misfires were on 4 with a few on the others but relatively nothing compared to 4. Now I have zero misfires on all cylinders! Yeaaah! I talked to a lot of mopar mechanics, engine builders and jeep stroker tuners and no one recommended the map sensor. I have been throwing parts at it but recently I have been suspecting that the vacuum system was the culprit since idle was erratic and fuel ratios were all over the place. Hope this helps others!

[Retlaw01XJ]

Congrats on finding the problem!
Where there any indications there was an issue with it? ..... were readings normal otherwise?

[jeepxj3]

Erratic idle and AFRs is all, ? leaking MAP internally or rubber elbow connection. ?bad connection at MAP? No MAP CEL either.

[Jpross]

back to square one. When I replaced the map sensor everything was good for the day and night. idk I guess the senor to pick up the misfires stop checking or something for a little while then once it started again it found the misfires. I took it to get a vacuum smoke test a found a pretty big leak in the throttle body shaft so I replaced with an after market one... and still same symptoms. The weird thing is when I drive around for a while and come to a stop light, the fuel air mixture will go very lean and really struggle to correct itself. Last night I was driving home from the bar and felt a couple misses on acceleration one time. I thought it was just a fluke, but tonight I had the same miss happen again on acceleration.

[Jpross]

looking at the misfires on a 3 mile trip from somewhat cold start, most of the misses were on cylinder 3 instead of 4. I am getting a number of misses all across the board though. The fact that it sometimes goes lean at stop lights is the only thing other than the cel that makes me think something is even wrong.

[jsawduste]

Define lean at stop lights.

The ECM will look at the VSS/MAP and the TPS signal and adjust the AFR for closed throttle coast down. Once at idle it should return to 14.7.

[Jpross]

If it takes a while to return to 14.7 what does that mean? could the fuel pump be an issue? I dont have any issues at high rpm, so it is getting enough fuel up there. Like I said though I am starting to feel a miss every once in a while when accelerating around 2500 and 3100 I feel a miss sometimes after I have been stopped for a minute or two.

[SilverXJ]

What is your fuel pressure? What injectors are you running an what is their history?

Edit: Are you 100% sure the cam sensor is indexed correctly? Also, what are your long and short fuel trims looking like?

[Jpross]

The injectors are from rock auto
'01-'02 Chevy LS1/LS6 28.6lb/hr injectors for '05-'06 engines. I had to use plug adapters.

The cam sensor was indexed at the dealership so I can only assume it is correct unless it moved since then. That was back early this year in Feburary.

lean at stop lights, going off the wideband range and you can feel and hear it stumbling. I can give it gas and it will go normal 14.7 ish but will go back to very lean.

at idle
stft bank1: -3.9%, bank2: -2.3%
ltft bank1: -11.7%, bank2: 0.0%

Not sure on fuel pressure, I will try to test that and see what it is.

I can now feel a very noticeable miss on accelerating from stop light about 1 out of 5 times just shy of 3k.

[jsawduste]

You have a fuel delivery issue.

[Jpross]

I think I agree with that considering the ltft should probably be about equal.

The bigger question, what could be causing the ltft to look like that?

As far as the fuel pressure test, I have yet to find a kit that has that special tool for the 2005-2006 year to tap into the connection right before the fuel rail.

[SilverXJ]

Those injectors might be too large. Do you know what PSI 28.6# is at?

[Jpross]

28.6 at 58 psi. The 2005-2006 jeep is supposed to be around 50psi. So if the calculator I used is correct, that gives them an effective flow rate of 26.6. I estimate the engine is probably around 320hp at the flywheel. I had it dynoed back before I got the tune... and it was running right and I got 199 rwhp.. with 37" mud terrains. The tune made a very noticeable difference.