MAF...?

My '99 152K daily driver's CEL came on when the car started to misfire.
I took it to a local shop and they read the codes for me.

P0304 Cylinder 4 misfire
P1126 Oxygen sensing cylinders 4-6 rich threshold
P1124 Oxygen sensing cylinders 1-3 rich threshold
P1314 Cylinder 2 misfire

The mechanic cleared the codes and the car ran great through one drive cycle and then the CEL came back on. Misfiring again.
The car runs best on cold start.
I've cleaned the MAF and replaced the cylinder 4 ignition coil.

Took it to AutoZone to have the codes read again. This time got:

P0304 Cylinder 4 misfire
P1317 Cylinder 5 misfire
P1313 Cylinder 1 misfire
P1314 Cylinder 2 misfire

I'd like this to be an easy fix like a bad MAF. I can do some stuff on the car but I'm a novice when it comes to diagnostics. At the same time, the thought of having to take the car to the dealership and pay shop rate to diagnose just galls me.
Thoughts...?

There have been items posted here that say even an oil soaked MAF will still function without metering errors.



Edited 1 time(s). Last edit at 08/27/2013 02:06PM by Laz. (view changes)

Edited 1 time(s). Last edit at 08/27/2013 02:07PM by Laz. (view changes)

for P1124/P1126 codes.

Intake system leak.
Fuel pressure too low.
Fuel injectors contaminated
Volume supply of the fuel pump too low.

My WAG is there's an air leak and the most common air leak is a failed AOS.

... this sounds more like a bad air leak.
I would guess a cracked oil fill tube or similar, unless you've had some work done just before the misfires in which case I'd say check all hoses and vacuum lines.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Thanks guys. If it was a failed AOS would I be getting smoke...?

My experience with 2 AOS's under my belt is the smoking comes later. In both cases it was a last stage -- well as last I was willing to let things go -- symptom.

In the first failure there was hesitation, rising and falling idle speed, I can't recall now if there was a CEL and if so what the DTCs were, a lot of vacuum at the oil filler tube.

In the second failure there was just a CEL with one or more DTCs the numbers I forget now but they had my thinking MAF but I can't recall why now, either.

This went on for a few days as I was making my way east from CA to MO. I made it to MO alright but the next day when I started the engine the smoke came billowing out of the exhaust and didn't stop. It was then I realized the errors were related to the AOS not the MAF.

There is kind of a test to eliminate the MAF. Disconnect it at the wiring harness. Clear the DTCs to reset the fuel trims among other things. Then just drive the car normally. You have to drive it more than around the block. The engine should be up to temperature. I would advise you to avoid straying too far from home and remaining in good cell phone coverage.

Also, pay attention to the engine. Should it start to act up show any signs of untoward behavior shut it off ASAP and have the car flat bedded to a dealer for attention by a pro.

If the MAF is not the cause of the misfires and other errors some of these should come back.

You'll need of course a scan tool one that you can use to clear DTCs and read codes. The CEL may come on with the MAF disconnected but this can be from the MAF being disconnected, not the original symptoms you are trying to diagnose.

If the CEL and DTCs come back with the MAF disconnected it is probably not the MAF at fault.

If the CEL and DTCs do not come back then connect the MAF and clear the DTCs again then drive the car again. If the CEL and DTCs come back, the MAF is pretty much confirmed.

Handle the MAF and its wiring with care. Those pins in the connector lead directly to the MAF. A static discharge into one of them ruins the MAF. And the sockets in the connector lead directly to the ECU. Static discharge into that and oh oh...

Also, the pins can bend over or break. Working with electrical connections on a used car requires a combination of gentleness and strength.

Thank you. I will see if I can give that a whirl. Also, is it easy to inspect the oil filler tube or AOS for cracks? Is the oil filler tube a difficult DIY job?

I note this is done from outside the car and from under the car.

From under the car is in the air on a lift and the tech is underneath the car and looking real close.

From outside the car the engine compartment is opened up and the engine exposed.

Be sure to use a blanket or car cover to protect the paint as one really has to lean over to look close.

The idea is to not only inspect the oil filler tube but to look at other areas that can be an air leak or an oil leak.