Help with afr [Archive] - Forum


View Full Version : Help with afr

11-12-2009, 08:35 PM
i finally got around to installing my wideband gauge. I have a random muliple cylinder misfire that i cant seem to get rid of. im trying to figure out if its fuel or spartk thats causing this. so i need help with finding out what is normal afr at diff. rpm's. heres my findings. obviously these numbers fluctuate in between the two listed, as they are supposed to.
idle is usually between 14.5 and 15:1
cruising with tc lock up at 1200 is a little lean i believe, ~14.8 and 15.6, and occasionally a blip of 15.8:1.
cruising at 1800 is ~the same as idle
Cruising at 1600 is usually ~14.6 and 15.4, with and occasional blip of 15.8
Light accel, meaning ~40% throttle is ~13.8 and 14.8, with and occasional blip of 13.6.

i know without a scan, all of this is speculation, but id atleast like a general idea of what im dealing with here.

My FPR is also supposedly bad due to a fuel smell in the vac. line that goes to the map sensor.

Any insight is much appreciated.

11-13-2009, 06:49 AM
RPM doesn't matter. AFR is determined by throttle position. Anything below 70% throttle with stock programming, the pcm tries to maintain 14.7:1 AFR at all times. Above 70% it targets 13.6:1. It is pretty normal for it to bounce back and forth a little, especially at idle, but it should stay around 14.5-15.

Misfires aren't usually caused by fuel issues unless they are severe. First place I always look is ignition, spark plugs, wires, etc.

11-13-2009, 12:14 PM
well, that was the first place i looked as well is ignition. plugs are iridium w/ ~45k on them, and they were regapped to .060 when i put the new motor in. and the wires are brand new as well. only thing left is the icm, but i would think that it would cause a severe misfire if that went out. ive talked to mark, and we went over what he thinks the issues are. but i cant for the life of me think that its the icm thats bad. the ses would be flashing wouldnt it? what do you think about the fpr issue? you think thats bad too, and could that cause a misfire? thanks btw aaron

11-13-2009, 05:20 PM
I don't think the FPR would cause it unless it was really bad and causing a major fueling issue like I said, and in that case you'd have way more problems than a misfire. I suppose it's always possible though. In either case, if you suspect there is a problem with it... it might be a good idea to replace it anyway to rule it out.

It's possible to have a problem with the ICM that will not show up as a DTC code. There are other possible things that can cause a misfire like problems with other sensors. Has the car had or does it need a CASE learn? That has a big affect on timing control below 3500rpm. The 7x crank sensor controls ignition above that. Also the cam sensor controls injector firing and a problem with that could cause an issue. Or dirty injectors maybe? How old are they? Without scan data and seeing the car in person all we can do is shoot ideas. :)

11-13-2009, 10:02 PM
well, when i put the new motor in, i melted the wire that goes from the ckp sensor to the icm. when i replaced that, mark said something about doing a case learn, but that hasnt been done. also, when i had to pull the motor the second time, while removing the cam sensor, the part of the harness where the wire conects to the connector kind of got pulled out, but only a little bit. its still in there pretty well. so maybe thats causing the issue. i have no idea at this point.