Replaced MAF, still errors.....

[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

[sparker]

Ok just drove the car for the first time in a week... Barely drove and threw a misfire on cylinder 5 CEL. I have not swapped coils across banks!

Does this suggest any area I need to look? Mis fires across both banks???

Sam

[sparker]

Good news, I am at least back to the low rpm stutter I had before with no CELs! While I wait for a new MAF to arrive, I thought I'd clean the throttle body. When taking it off, I noticed that one of the rubbers holding the plenum in place had moved and was allowing air to bypass the entire intake.

With that fixed, the car is drivable again and hopefully with a new MAF, better than new

Sam