Hello everyone I'm having the worst misfire problem and I'm running out of ideas. I've already replaced the plus and tried gaps from 26 to 19 I've also replaced the Coils and wires with a COP set up. The injectors have been tested and a new fuel pump installed. I performed a compression test 151,150,146,150. And a boost leak test, It will hold about 20 psi before the compressor housing starts to leak. I intend to fix that soon but my misfires occur mostly while in vacuum so I don't believe the leak to be the cause. Another symptom is the A/F ratio seems to move all over. I get it dialed in and then an hour later it moves up or down .5 to 1.0, and even in closed loop it bounces form 13.9 to 15.6 The only thing I can think of at this point is maybe the fuel pressure regulator is failing. Is there a way to log fuel Pressure so I check that?

Anyway I could really use some ideas so Please share if ya have any!

FYI It runs on E85, Speed Density, and has 272 cams

 

I've decided to replace the regulator as I have no other ideas left. But would still appreciate some help?

 

Bump

 

Cam position sensor?

 

Check front o2 sensor voltage to see if its going bad, or has gone bad and refuses to run in operating closed loop (14.7afr).

 

I'd call O2 front O2 sensor all day given the symptoms. I'd say vacuum leak, but boost leak tests pretty much rule that out.

 

at this point sounds like the front 02 sensor is bad....i had similar issues with my afr bouncing around like you. replace the 02 sensor and fixed the bouncing afr issue. but the sensor wouldnt cause it to misfire...do you misfire underboost at all? or just under vaccum? post up your timing map if you can.

 

I know it's not the front O2 sensor cause I'm Running this:

https://www.evolutionm.net/forums/ec...o2-system.html

I also checked for vacuum leaks with a smoke test and found none.
And yeah it only misfires while in vacuum. I'll post my timing soon cause I have to get on my other computer to do that.

 

I can't post my map cause I Don't know how? But it's pretty much stock cause I'm waiting til it's fixed to tune.

 

If it was the cam angle senson wouldn't I get a CEL? Is there a way I can teast it?

 

Well I replaced the the cam position sensor and nothing changed. There's another $60 down the drain

 

Where is you O2 sensor mounted?

 

check your other thread. it MAY be your culprit.

 

Wideband O2 sensor is gone. what kind of wideband are you using.

 

it's an AFX wideband But I tested it and it's still good. Plus I've only been using it for closed loop for a couple weeks but I've had this problem for a couple months.