utkinpol

Hi,

I suddenly got misfires on all cylinders - quite a bummer. I suspect faulty MAF sensor as i was stupid enough to clean my k&n filter and spray a bit of WD40 on it - but looking at real time data it seems to report something reasonable - value of 5-7 at idle, stepping on gas to 2K-3K rpms it goes to 70-80. Is it in right ballpark or too low?
I naturally removed k&n filter now and washed MAF sensor completely, engine ran a bit better after that but still showed CELs. It also sounds quite diferent and still misfres I think.
I know on 996 cars typical test was to disconnect MAF sensor completely and it should result in proper operation below 4K rpm. Is it same for 997 cars? I had quite bad misfires and loss of torque below 4K but when I drove home 4K-5K rpm range was sort of OK. not sure what got broken there, just want to confirm how to check if it is MAF sensor to eliminate this cause.

Regards, Paul

Mike in CA

Paul, wish I could answer your specific question but it does sound as though the MAF has become contaminated. Although the link below pertains to BMW it does have some info you might find of interest and points out how cleaning the MAF can be a delicate and problematic excercise. Good luck and hope you can resolve your problem.

http://www.louv.tv/cars/m5/MAF/

wwest

Your engine ECU is still confused, it was trying to sort out the mixture with a contaminated MAF so now you need to wipe the slate, memory, clean via disconnecting the battery for 10-15 minutes.

Macster

I do not have much in the way of MAF readings at various rpms and engine loads for my cars let alone other models, so I can't really offer you any guidelines as to what's ok and what's not.

You have several things to consider. Last thing touched is always the first thing suspected and that air filter is suspect #1. And because of what it is and what it does and where it is located relative to the MAF then the MAF is suspect.

So, I'd advise you to properly clean and re-oil the air filter.

Then while I think the engine would be ok with the MAF disconnected I can't be sure having never tried with with a 997 car, so my advice would be to carefully remove the MAF and clean it very carefully.

The actual working hot film surface is located inside that hole that begins at the leading or upstream edge of the MAF and ends at the bottom of the MAF.

Do not jam anything in that hole. Just aim the MAF cleaner spray at the hole and let the spray/fluid do the cleaning.

Be sure you let the MAF dry naturally. Do not wipe it down or attempt to pass anything through that hole.

The MAF is a very sensitive and expensive piece of electronics so handle it with care. Do not drop it or subject it to static electric discharges.

Reinstall the MAF, carefully connect it to the wiring harness and ideally use an OBD2 code reader to erase error codes. Even though none are present this resets the DME's learned fuel maps back to their defaults. These might be horribly wrong (relatively speaking) from the input from oily MAF.

If the symptoms do not improve with the above, then disconnecting the MAF and seeing if the symptoms improve could be the next step towards id'ing the source of the symptoms but see how the engine behaves after the filter clean/re-oil and MAF clean first.

Sincerely,

Macster.

911SLOW

Model year: as of 2005

Vehicle Type: 911 Carrera (997)/911 Carrera S (997)/911 Turbo (997)/911 Turbo S (997)

Concerns: Diagnostics on hot-film mass air flow sensor (referred to below as MAF sensor).

• If the complaint “Rough-running engine at idle speed” or “Vehicle jerking while driving” is received, and/or• If a fault code is entered in the fault memory of the DME control unit the following steps must be completed before replacing components:⇒ Check the MAF sensor voltage, and ⇒ Run “Guided Fault Finding” using the PIWIS Tester (with software version 21.000 or higher) to find and correct the fault.

Information

We would like to point out that the replacement of the MAF sensor or other components because “you suspect a fault” and without first performing the required troubleshooting steps (using the PIWIS Tester) is not permitted.
Only parts with a confirmed defect will be covered under warranty. If this is not the case, the cost of parts will be redebited to the Porsche Centre or importer.

Tools: Battery charger
PIWIS Tester 9718 with test software version 21.000/04/2008 (or higher)

Preliminary work:
Check the MAF sensor voltage: Information

Other sources of current must not be connected to the electric connections for the MAF sensor because this will immediately destroy the MAF sensor.
Information

To ensure that the mass air flow sensor is diagnosed correctly, please observe the following points:

• Engine is off,
• Mass air flow sensors are installed and
• Air-cleaner box with air-cleaner element is installed.

Before getting started, connect a suitable battery charger with a current rating of at least 40 A to the battery/jump-start terminals.1 Connect the PIWIS Tester (with test software version 21.000 or higher) to the vehicle and switch it on.
2 Switch on ignition.
3 Go to the PIWIS Tester Start menu and select ⇒ “Diagnosis”.
4 Select vehicle type.
5 Press >> to start the control unit search.
6 Select ⇒ “DME” in the “Control units” menu and confirm by pressing >> .
7 Select ⇒ “Actual values” in the “DME function selection” menu and confirm by pressing >> .
8 Press F5 (filter) in the “Actual values” menu.
9 Select ⇒ “Mass air flow” in the “Actual values filter” menu and confirm by pressing >> .
10 “(H030) Mass air flow sensor 1 (sensor)” and “(H031) Mass air flow sensor 2 (sensor)” must then be selected and confirmed by pressing >> .
11 If the displayed voltage (mass air flow sensor 1 or 2) is less than 1.1 volts (1.1000), the mass air flow sensor is functioning correctly and must not be replaced.
Further fault finding must be performed by running “Guided Fault Finding” using the PIWIS Tester.
End of remedial action.

12 If the displayed voltage (mass air flow sensor 1 or 2) is greater than 1.1 volts (1.1000), this mass air flow sensor must be replaced.
End of remedial action.

Procedure: Start “Guided Fault Finding” using the PIWIS Tester:1 Switch on ignition.
2 Go to the PIWIS Tester Start menu and select ⇒ “Diagnosis”.
3 Select vehicle type.
4 Press >> to start the control unit search.
5 Select ⇒ “DME” in the “Control units” menu and confirm by pressing >> .
6 Select ⇒ “Fault memory” in the “DME function selection” menu and confirm by pressing >> .
7 Press Guided Fault Finding/F5 in the “Fault memory” menu and read and confirm the information that appears.
8 Select “Guided Fault Finding” in the selection menu and confirm by pressing -1- .
9 Select a fault code in the overview and confirm by pressing >> .
10 Work through the test plan instructions.
End of remedial action.

utkinpol

thanks guys, great info here. i drove car with MAF disconnected, it did not generate any CELs and ran OK so it got to be it and not valves/etc damage. I will try to visit dealer today, as I think i still have CPO so will see if they will give me new sensor or not. If not, will get new one from Suncoast. I tried to clean my sensor twice now, used 2 full cans of MAF cleaner, but it does not seem to do much.

I was mostly surprised as it definitely does generate some info, but apparently it is incorrect as car still misfires. Strange stuff.

utkinpol

i just got back from a dealership, they got car running in 1.5hr. It was dead coil on 2nd cylinder. Not sure if MAF was ever affected or if after i cleaned it MAF sensor recovered - who knows. Bottom line is cr runs fine now, everything was covered by CPO, I am quite happy.

They say it not an uncommon thing for coils to fail after 30K miles. My car got 52K miles now, so, will see how it will go next.

Gibbo

Id be changing all six coils if I was you to be honest.

utkinpol

my budget is exhausted right now, cannot just buy it for 'in case' cause... but it does make sense to have them replaced. franly i was so happy it was not a case of bended valves or stuck lifter that I even forgot to ask dealer to replace rest of them.

well, all in good time, there is winter for all this fun to get done.

bigozuk

this is a fairly old thread, but I would like to resurrect it having suffered similar issues recently. i'm getting engine misfire codes for cylinders 1,2 & 3 within seconds of starting up. If I unplug the MAF there are no error codes when starting up or running. So i'm thinking faulty MAF, but above post suggests the MAF is fine if less than 1.1v measured with ignition on - which mine is. so how do I know for sure if the MAF is the issue? the problem in the post above turned out to be coil pack related - but why would that disappear when MAF disconnected?

anyone got any ideas what my problem could be?

jhbrennan

Have you tried cleaning the MAF - sometimes simple solutions work.

Macster

I note you are in Scotland. If you tell me you drive the car year 'round, coils could very well be due. Years before I read of coil issues here in the USA I was reading about then in the UK. Seems the weather there is particularly hard on coils. Also, 997 coils are a bit of an issue. Seems they have some extra circuitry and this can flake out and the coil can act up.

The misfires disappear when the MAF is disconnected because the engine is fueled in such a way the mixture ignites better would be my WAG.

However, I know of one case where a bad MAF did cause misfires on just one bank.

bigozuk

Rain, wind, sleet and snow I drive the car, so agree the coil packs could see a lot of water/dirt/abuse

I tried soaking the MAF yesterday, but it made no difference. still getting misfire on the three cylinders. might try swapping the coil packs over to the other side to see if problem moves - just not sure how easy they are to get at with my limited tools.

just find it a bit strange that its all three cylinders on the one side, why would they all fail at the same time?

user 72902

I would agree with the coils being the cause of the misfires rather than the MAF.

Petza914

Could also be a bad O2 sensor on that bank (there are 2 per side). When I was chasing what turned out to be a bad ground to my MAF, the car would fall on its face if trying to give it any real throttle below about 2,500 RPM, but would pull fine at higher rpms at full throttle. There was no difference in this case with the MAF connected or disconnected but that makes sense because with no ground it was essentially disconnected all the time. I'm not sure if a failing MAF would behave differently, but think it probably would.