[long story - skip this if you dont wanna read it]

A while back, I had a CEL come up shortly after I had put new K&N air filters in. After some debate w/ the local techs and some attempts to get rid of the CEL, we came to the conclusion that the MAF got contaminated by the oil off the K&N air filters.

While the tech had checked over the car w/ the fancy computers they use, he had discovered that my car was throwing codes w/ missfires. This scared me because I saw him just delete them thinking they were caused by the goofy MAF and because the car is running just fine (no loss of power/acceleration/mpgs and no sputtering or wierd engine noises). We replace the MAF + get stock filters and they car is good to go!

Fantastic. A few months later while driving my car through the city, the CEL comes back on after coming to a stop at a light on a bumpy road (this is exactly how it first came on a while back..) At this point, Im pretty short on time and am unable to actually talk to techs and what nots, so i just let the CEL stay on. A few days later it goes off. a few days later it comes back on... and off... and on... and off... nothing goofy is goin on w/ my car...

W/o the time to actually talk to techs I turn to mbworld's search! Where I discover some past mbworlder have had similiar problems.

[long story end]
[begin reading here ]

My car's Check Engine Light is turning on (with misfire codes) when i drive in the city on bumpy roads, but runs fine and the CEL will turn off in a few days w/o city driving. Im thinking that my CEL is being caused by a bad spark plug/coil, but would like the mbworld opinion. Should I replace the plugs in the cylinders w/ the missfire code or should i replace all of the plugs?

General question: What exactly do these coils do? and how much do they usually run for? I have found ignition coils for my car, but am unsure if those are the coils mentioned in previous threads. In addition, do spark plugs generally come in a standard size? Ive seen a poll on the spark plugs used by mbworlders, but would also like to find a good place to buy plugs - any suggestions would be nice

TIA!

-j0hn

 

Get an OBDII code reader/clearer and read the codes. Reset it each time and see if there is a pattern. Throwing parts at intermittent problems can get expensive and frustrating.

 

So explain to me the misfire codes, are they cylinder specific like P0302 or are they general like P0300 and if they cylinder specific, do you get them on one, two or all cylinders? Are the pending codes or permanent codes?

The reason it turns off is because there are pending and permanent codes. A CEL starts out life as a pending code, if the condition persists it turns into a permanent code and triggers the CEL light. If the condition goes away, the permanent code reverts back to a pending code.

There's a common issue that K&N refutes on their website that K&N filters contaminate the MAF and they say it's not true. Seems to happen mostly on the 3.2L motor from what I've heard on the forums. True or not, if the MAF is contaminated (a fancy word for dirty), why replace it, just clean it (a simple word for de-contaminate) with CRC MAF sensor cleaner and it's as good as new, $600+ saved, I've done it and there's no downsides. Also, when the MAF is dirty it gives false readings and makes the car run too rich or too lean and usually you get a fuel trim code error like P0170 or P0171 as the ECU can no longer correct for what MAF is saying... Rarely would you get misfire codes for a MAF. Typically what gives you misfire codes can come from one of 2 sources, fuel and spark. If the fuel is bad, contaminated, fuel injectors clogged or weak or not working, low fuel pressure (weak pump or fpr), clogged fuel filter. If spark is bad it can be the plugs, the coil packs, the wiring harness for the coilpacks, etc. It could also be a major engine problem with a blown head gasket, cracked head, cracked block but heck, we don't want to go there, do we?

 

Its funny, right after I posted this the CEL would not come back on until yesterday! Id like to say. Ill probably never be so excited to see my CEL come on again.

Anywhoos, I went and plugged in an obdII scanner and discovered that I am receiving the codes P0170 and P0173. Fuel trim! AHHH. Thanks for the long reply Buellwinkle... sadly (am i really saying this?) the codes for misfires did not return this time.

I thought I had previously dealt with this by putting in a new MAF and stock air filters that I thought I foulded up w/ K&N air filters.... That was the advice of my techs at least..

These codes suck.... Fuel trim is such a wide area to cover

Any advice out there?

TIA,

-j0hn