Replaced MAF, still errors.....

[sparker]

Hi guys,

my car has been running rough lately and all things were pointing towards the MAF going off. Well, last night I replaced the MAF and took the car for a drive. It was not any better, if anything it was worse and even threw a CEL...

I took the car back to the shed and scanned for errors. I got the following:

P0303 - Misfire Cylinder 3 (I did have this one a little while ago, starting to think it could be a coil?)
C2D04 - No further information
B0407 - No further information

Also, while looking at real time values via the OBD2, I noticed that only 3 of the 4 02 channels were giving a voltage (despite this being an Australian model with only 2 oxygen sensors....)

Can anyone suggest I start looking somewhere? I noticed via my wideband sensor that the car was idling and running a bit lean (which also explains the small 'pops' at idle.) I have a few suspects, thinking any of the following: 02 sensor, coil, still a bad MAF or even perhaps a bad cat?

Any suggestions?
Sam

[jhandy]

well start with the misfire code.

the easiest way to tell if it is the coil pack is to take number three off and swap it to another cylinder.

clear the codes, and then run the car. cel should pick it up again, and this time the code will pick it up at the new location.
If it still says number three, then it is not the coil pack causing the misfire.

it will get really expensive if you start replaceing parts without diagnosing first.

the maf could have been worked out if you would have unpluged the maf and drove the car. Still driving bad, then not the maf.

the other codes are....B codes are body codes, and C codes are chassis codes. I will look around for my book to see if we cant find out what they mean.

[sparker]

Appreciate the response - thanks.

I will try swapping the coil around to see if I can single out the problem tonight.

The MAF was tested (car did seem to idle and drive acceptably without MAF plugged in, so perhaps it was bad as well?)

Also appreciate you looking up those other codes, I'm curious to hear what they are. Seems strange!

Sam

[jhandy]

B0407, Air Flow Control # 2 - heater - low signal input


it would help if I had your model year, CC displacement to find C code.

[sparker]

Ok thanks, what exactly does that mean? Something wrong with the heater?

Car is a 1997 2.5l base model.

Cheers,
Sam

[jhandy]

The C code is going to be a little harder to crack. Someone here that has a Porsche OBD service manual that can look it up.
But basically it is a error with something that gets input from the chassis. In my limited experience it is commonly the ABS system.
with the boxster, it does not have traction control, no roll sensor, manual trans. there really not many other choices aside from temp sensors, and speed sensors.

Also it could be a non USA code, in which case, the Piwis manual will tell us the code.
Porsche tech guys usually gaurd this book like it is the bible and it is not easily had.

[Topless]

Interesting. I have never seen these codes. Damaged DME or DME harness? I don't see a code indicating a lean mixture. Lean could mean intake air leak, clogged injectors, cracked exhaust manifold.

[jhandy]

If you think that the cylinder three is lean and this is causing a misfire, then I would move to injector plugged up, valves not working right... I say this because I do not think that the DME controls mix rates per cylinder, rather by bank 1 or two. Picking up values from the 02 sensors.

Look at the most common and reasonable things first. Look at the wire or connection. Move coil pack to another bank, rather than another cylinder on the same bank.

[Dale_K]

I'd say a compression test would be a good idea but I don't know how you do it on a Boxster.

[jhandy]

its either Air, Fuel, Or electrical.

does it only trigger the cel on cold start up? IE: warm the car, clear the code, start the car. If no cel, then allow car to get cold. start the car, cel light immediately go on? there are different diagnostic tracks to pick of it is a cold start lean misfire vs a hot lean misfire.

If you prove to your self its not the coil pack or plug, and the wires and connection is fine, then move to fuel.

Clogged injector will trip a lean misfire on cold or hot start up. Carbon build on the intake valve from EtOH added fuel, low octane fuel use can lean misfire.

If it only does it on cold- then what could be happening is that the secondary air induction system is triggered like normal, and if it is not functioning ok, then lean mix misfire happens.

So...back to algorithm. not electrical, then pull the fuel injector and swap it with another from the other bank. If CEL comes back, then its not fuel.

look then to Air....back to the carbon on valves, clogged secondary air intake. Run several tanks of high octane gas with high quality fuel additive system to clean off the carbon. Run the car hard and hot to burn and blow off any buildup. (the next statement will come with debate)--correctly run a motor flush in the oil system. The purpose of this is to easily fix the next statement. Next look to the Cam. Remove the Cam and CAm seats. look for a clogged oil hole that supplies pressure to the lifters.

these issues can result in low fuel in relation to air- IE the reason for your lean misfireing cylinder.



And finally- if none of these steps work, then get a 1/2 inch piece of black electrical tape and .............cover the CEL light on the dash.

[sparker]

Haha thanks guys, hopefully it doesn't get to that!

I do have some good news to report, it appears my new MAF is bad. I happened to start the car with the intake off and it ran fine. So I put the intake back on and the car stumbled and stalled again. With the intake still on, I unplugged the MAF and she ran better. Put the old MAF back in and it runs much better.

So it appears that my new MAF threw me a curve ball. I still suspect my old MAF is on the way out, so will exchange my new one and try again.

Will drive her later to see if I avoid CELs. Frustrated with how obvious it was, I never had CELs before swapping MAFs... I did have a low rpm stutter that was getting worse though, although at this stage I'd gladly have that back!!!

Will keep you updated, thank you all so much for your help thus far!
Sam