Desperate Need In Help For High AFR Idle Misfire

[fs125]

Car is a 2009 BMW 335xi with about 80k miles.

A little back story, at the tail end of 2019 my car went down with a bad HPFP. As the car was already down and I'd have take it apart, I decided I'd install my mods and maintenance parts I'd been gathering. The misfire started pretty much after installing all the parts. Here's a list of those parts:

Maintenance:

• Primary and secondary O2s
• Map sensor on intake manifold
• High Pressure rail sensor
• Low pressure sensor with new line
• HPFP OEM unit from FCP
• Intake valves cleaned manually w/pick and GDI cleaner(not walnut blasted)
• Intake manifold gaskets
• Throttle body gasket
• Injector 4 replaced, recoded. Car already had index 12 injectors

Mods:

• VRSF 7 inch stepped intercooler
• VRSF charge pipe with Tial BOV
• 3.5 Bar TMAP n20 sensor
• Dual BMS catch can
• BMS DCI
• NGK 97968 plugs gapped to .022
• Bimmer life r8 coils conversion
• PFS single shot bucketed pump
• VRSF catless downpipes
• CPE downpipe back exhaust

Car is running MHD Stage 2+ on ACN 91, and was already on Stage 2 MHD when I bought it.

Problem and symptoms

The car has a misfire, according to the DME, its on cylinder 4. The car basically misfires really violently at idle on cold starts, with the AFRs being really high like >20 on bank 2, and > 15 on bank 1. The fuel trims will also be pegged, sometimes hitting max at 34. I've noticed its linked with the weather, if its hot, its less severe with slight hiccups, but when its cooler (<70 deg) its really bad. The car will run like crap until its warmed up, and I can erase the misfire code without it coming back. When driving all warmed up, the car drives perfectly, and pulls hard. I don't like driving the car with this issue, so I rarely drive it, until I can figure it out.

I tried looking for a vacuum leak, and did a smoke machine test and couldn't find anything. I've replaced the cylinder 4 injector because I pulled the plug and it did have a fuel smell, but now I'm thinking it might of been related to the fuel trims being so high. As the weather is getting cooler, the problem is getting worse.

Grateful for any help, thanks!

Here's some data logs of the problem:

datazap.me | sb335 | Log 1631031975

datazap.me

 

[SLOWESTN54]

Have you checked compression cold?

 

[tony@codewerx]

Walnut blasted ?

do a leak down test too …

 

[fs125]

Walnut blasted ?

do a leak down test too …

Not walnut blasted, but cleaned with pick and GDI cleaner, to the best of my ability. Of course not the same results as a walnut blast.

 

[fs125]

Have you checked compression cold?

I have not, I'll try to get one done. What are your thoughts leaning towards?

 

[SLOWESTN54]

I have not, I'll try to get one done. What are your thoughts leaning towards?

engine tolerances cold and hot are very different, if your low on compression cold that's probably your misfire, and as metal heats it may properly seal and the misfire goes away.

 

[Dumaurier7]

If you AFRs ar high and fuel trims pegged high as well then the motor is not beig properly fueled, a lean motor will misfire too, go back and recheck all your fuel system mods and if necessary try re-installing some of the parts you changed out in your fuel system, you should also have the car scanned/codes read to see if there is any additional causal factors (sensor issues) being reported.

PS: why did you change your FP sensors? were they going bad?

 

[fs125]

If you AFRs ar high and fuel trims pegged high as well then the motor is not beig properly fueled, a lean motor will misfire too, go back and recheck all your fuel system mods and if necessary try re-installing some of the parts you changed out in your fuel system, you should also have the car scanned/codes read to see if there is any additional causal factors (sensor issues) being reported.

PS: why did you change your FP sensors? were they going bad?

Prior to my HPFP going out, the rail pressure readings were sporadic, so I changed the rail sensor to confirm that it was the pump. When I changed the pump, as I was already in the area, I changed the LP sensor as part of maintenance.

I'll take a look at the LPFP again, but all pressures seem to be in the right range. As per MHD, the only codes I get are 29D0 which is misfire for cylinder 4.

Thanks for your thoughts.

 

[135boost]

tune is for 3.5 bar tmap, yes ? because if that is stock tmap tune, it will throw that off by that amount.
that struggle is sure from extreme lean, ignition limits is somewhere close to 17 afr anf you got there values
close to 26 on one bank what indicate 1 cylinder shut off and on other bank 17 what is on limit of ignite.

from start this engine run from "map" until it warm lambdas enough to switch over to closed loop.
if that tmap is ok selected in tune, then you have some basic value in tune very wrong.

check that tmap, what ever you use MHD, JB4 or something else..