Engine Misfiring: CEL

[kameraguy]

Not sure if you guys remember the issues I had in December, but they are back after one month.

Back then, I had some intermittent misfiring, and the TCs indicated a possible bad MAS. The MB techs said the MAS was definitely off, so we replaced it. They did not find anything else wrong.

I also promptly replaced the K&N for the stock MB air filter. Damn K&N.....

This week i've started to have the same symptoms. Engine misfiring, CEL.

I checked the TC and the only thing stored that I can read is the confirmation Cylinder 2 misfired. Aside from that there is more data than last time, but my scanner can't read it. I hope this data is useful in troubleshooting the problem once and for all.

Question for you guys, for those who have had misfiiring issues, does the engine go into a "limp home mode" immediately after? Because when my engine misfires, the car immediately loses power, but is still able to be driven until I can pull over. Then a restart clears the power issue and the car runs normally, but with the CEL of course.

Well, i'll hopefully have more info by this afternoon. IWhatever it is, i hope it won't be one of those things that can't be found because it's intermittent. I hate those.....

[1SIKBNZ]

hey lemme know what happens with your car. ive experiened the same a few times but only on occasion and then my cel would go back off for a hile but then sometimes pop back up. and my two on the left "bas asr" and "abs" go on (seems only when makin like a right turn *shrug* but sfter a restart they are gone until i turn again...=( doesnt always go "limp" but ive had it happen like 3 times....

[Eurosport]

Kam
when you have misfire, engine goes auto in limp mode so it won't damage itself, it's a preprogrammed thing and stays in limp mode until you turn off the car and turn it back on

when i had this issue happen to me last spring, no one could get an exact diagnosis, trust me i was at the best mechanics even a guy that i know that worked on Gary Payton's blue Gwagon. But what they all failed to diagnose, i found out the problem with lots of trial and error, but it came down to my Oxygen sensor the one after the cat. At first i would get misfire like you have w/out any codes for Oxygen sensor. I guess when Ox sensor is about to go bad but not 100% bad it does mess up fuel/air mixtures readings and throws random misfires. But like I said it was very hard to actually figure out it was that O2 sensor it only threw the code after a long time.
So if i were you i would really check that out first and save a lot of time and hassle, it's about $130 or so on importec, that's where i got it, just need to have your car on the lift because it's hard to reach it between the muffler and the car. (plug and play easy change)
hope this helps

[pnsji]

Actually for a mechanic to be able to diagnose if a Mass AirFlow Sensor is failing or not is somewhat difficult. The way it works is that there is wire in there that is given an electricity current. The wire has to maintain a certain temperature. Depending on the air flow coming into the intake tube, the amount of current is *recorded* to adjust the air/fuel mix ratio. To be able to say that your MAS is off, is somewhat hard.... unless the code from OBDII tells you that you MAS is off.

If you keep having missfire, I would check to a good mechanic who could diagnose properly. This could be an easy wiring issue, or could be a complicated problem. Did you do any maintanance recently?

[manny]

So, maybe you cursed that K&N filter prematurely?
;)

[kameraguy]

Regarding the K&N...well I figured that definitely caused problems with my MAS as there was an oily residue on the MAS grill. I'm sure that's not normal...or is it? Either way, I never saw any real performance benefit anyways. Just want to go back to stock to eliminate any doubt for future issues.

As for the MAS troubleshooting, i'm no mechanic, but I trust the people I bring it are. It will be my word against theirs, and to even question how they troubleshoot would be pointless as once again i'm no mechanic. As with anyone, I just hope where I bring my car is reputable. At the very least, i'm trying to eliminate any doubt by going direct to a dealership vs. an independent. On paper it will at least show I did try and fix my car where MB would suggest.

As for finding a "good" mechanic....i'm all ears for anyone in the bay area. As much as I like Topline, it's just too expensive. It's almost like the dealership, so I may as well go there.

Euro, thanx for the O2 sensor info. This may explain why I get a P040 open fuel system code every now and then. It occured in December, but was not present this time. if anything i'll ask the mechanics if they have looked at it.

[714guy]

Sorry to hear about you car problems man, it sucks.

anyways back when i had my MAS problem and misfiring i when back to stock air filter and a new MAS and problem solved. I dont know if you've replaced you boot cover for you spark plugs b/c they can cause misfiring also. you should have 3 boots every othere clyinder.