Misfire

[½cwt]

OK, not my day today ( see ABS Light thread...). On collecting car from OPC after they coded a new key, they reported a minor misfire but no error code to detect. It had run clean on.the journey down, about 25 miles. I took it away and the issue got a bit worse nearly stalling on me with the occasional pop from the cat or silencer on the passenger side bit ran OK with revs. Next start up after a few miles and got CEL and a fully missing cylinder, again I suspect passenger side / Bank 2. Next restart planning to limp home and it ran clean on all 6 but obviously CEL remains on even afteranother stop and start for fuel.

Got to get it fault read but first thought is a coil pack that wasn't keen on cold and wet today. Anyone agree or got other ideas?

[½cwt]

Got a fault codes read:

   Multiple misfires all cylinders (and it also then lists misfire cylinder 1,2,3,4,5,6 each as separate codes)

   Ambient pressure sensor

Is the ambient pressure sensor the same as MAF?  Also unlikely to be coil pack(s) I imagine with these faults.

 

 

[usman10316]

It could be cracked coil packs, old spark plugs - try the easy stuff first. 

 

[edc]

2 X faulty solenoids? Seems unlikely. 

[½cwt]

5 minutes ago, usman10316 said:

It could be cracked coil packs, old spark plugs - try the easy stuff first. 

 

I thought a cracked coli pack first, but to get a misfire on all cylinders would mean all 6 have failed in about a week as this was a sudden problem last weekend having run sweetly on the same day for about 30 miles before that.  Also the ambient pressure sensor (MAF) would influence all cylinders?

Cost of 6 BERU coil packs is about the same as a BOSCH MAF so I don't really want to double the cost when likely to be only one fault, although fresh coil packs might pep it up a bit.

Plugs were changed in March last year.

[usman10316]

Have you unplugged the MAF and see how it runs without it in? If it runs fine - that would indicate a problem with the MAF.

[usman10316]

5 minutes ago, edc said:

2 X faulty solenoids? Seems unlikely. 

variocam solenoids? would be an engine out job and worst case scenario here I think, mine had 1 solenoid faulty, but the car would feel like an American muscle car idling, but would run fine - have had it all sorted now, the cost is too much for me to look back on!

[½cwt]

4 hours ago, usman10316 said:

Have you unplugged the MAF and see how it runs without it in? If it runs fine - that would indicate a problem with the MAF.

I'll dig into the engine bay tomorrow if I get the chance and see if this confirms.  It is my main suspicion.

If I need a MAF, do I go BOSCH or are there other good (as opposed to just cheap) OEM aftermarket options?

[½cwt]

4 hours ago, usman10316 said:

variocam solenoids? would be an engine out job and worst case scenario here I think, mine had 1 solenoid faulty, but the car would feel like an American muscle car idling, but would run fine - have had it all sorted now, the cost is too much for me to look back on!

Boy, I really hope not but that won't prevent it being the case if it is the cause.  Might be off the road for a bit if it is....

[naim22]

Check the readings from the MAF with a handheld tool, this allows you to confirm the failure mode without changing it first.

unplugging and driving is a good check but you must clear adaptations after otherwise the car may use fuel trims that have been thrown out of whack by the bad MAF

The MAF measures both mass airflow and Intake Air temperature, I believe ambient air temp is measured at the front of the car near the bumper and is used primarily for HVAC and instrument pack display 

As your code is on all cylinders, I suspect the MAF (likely IAT reading) as the intake is common to all, whereas exhaust/lambda sensors and camshafts are split per bank, and coils/plugs per cylinder. When both my MAFs failed, there were no codes as the IAT values were inaccurate but plausible 

Bosch is fine, both I've had had the Porsche part number on and worked well

If a 2000MY car remove the old one and check the part number before ordering, it's not easy to tell which new one is required without so as it is dependent on DME Software level.

Watch for the screws! They were a real pain on both cars but the actual swap of the MAF was easy.

[usman10316]

25 minutes ago, ½cwt said:

I'll dig into the engine bay tomorrow if I get the chance and see if this confirms.  It is my main suspicion.

If I need a MAF, do I go BOSCH or are there other good (as opposed to just cheap) OEM aftermarket options?

For the MAF I believe buying genuine is always the advice and not aftermarket! You may get lucky at some breakers ofc. 

[½cwt]

4 minutes ago, naim22 said:

Check the readings from the MAF with a handheld tool, this allows you to confirm the failure mode without changing it first.

unplugging and driving is a good check but you must clear adaptations after otherwise the car may use fuel trims that have been thrown out of whack by the bad MAF

The MAF measures both mass airflow and Intake Air temperature, I believe ambient air temp is measured at the front of the car near the bumper and is used primarily for HVAC and instrument pack display 

As your code is on all cylinders, I suspect the MAF (likely IAT reading) as the intake is common to all, whereas exhaust/lambda sensors and camshafts are split per bank, and coils/plugs per cylinder 

Bosch is fine, both I've had had the Porsche part number on and worked well

If a 2000MY car remove the old one and check the part number before ordering, it's not easy to tell which new one is required without so as it is dependent on DME Software level.

Watch for the screws! They were a real pain on both cars but the actual swap of the MAF was easy.

Thanks, brilliant info.  Mass flow and temp allows you to derive a pressure reading but also allows for density if I recall my Fluid Dynamics of 30 years ago correctly.

The car is e-gas and is after the chassis number split on the parts drawing on the Design 911 page so should be 986 606 125 01, but at around 3 times the price for the Porsche supplier part, the BOSCH OEM spec one will do for me.  Best price I've found currently is onlinecarparts.co.uk at around £180.

I guess priming the screws a couple of times in advance with penetrating oil spray should help a bit.

[½cwt]

3 minutes ago, usman10316 said:

For the MAF I believe buying genuine is always the advice and not aftermarket! You may get lucky at some breakers ofc. 

 

17 minutes ago, naim22 said:

Bosch is fine, both I've had had the Porsche part number on and worked well

Given info from @naim22 above, and that BOSCH I believe is the OE supplier to Porsche, I'll roll the dice with the BOSCH from a third party supplier at 66% off rather than apparently the same part full price from Porsche....   Around £500 for a MAF with no housing when most I've seen for other brands are sub £100 making even £180 dear.  Same with some suspension parts that are very costly direct from Porsche.  However I am with you @usman10316 on sourcing from Porsche or at least second hand genuine Porsche for a lot of parts.

[usman10316]

8 minutes ago, ½cwt said:

 

Given info from @naim22 above, and that BOSCH I believe is the OE supplier to Porsche, I'll roll the dice with the BOSCH from a third party supplier at 66% off rather than apparently the same part full price from Porsche....   Around £500 for a MAF with no housing when most I've seen for other brands are sub £100 making even £180 dear.  Same with some suspension parts that are very costly direct from Porsche.  However I am with you @usman10316 on sourcing from Porsche or at least second hand genuine Porsche for a lot of parts.

Good luck with it. Hope it's something simple!

[Boxob]

The "screws" holding the MAF into its housing are (at least on mine) security torx so you'll need a security torx bit to remove. I bought a set of ebay for about £7. 

[John2000]

I got a Bosch MAF from euro car part website site put my reg in and it tell you the type you need or should do.

I could not remove the screws no matter how I tried so booked it in with Le at CPS but they he told me they had supplied me with the wrong one.

He kindly cut a slot in both screw heads that made it easy for me to swop when I got ECP to supply me with the correct one.

No more error codes.

[naim22]

3 hours ago, ½cwt said:

Thanks, brilliant info.  Mass flow and temp allows you to derive a pressure reading but also allows for density if I recall my Fluid Dynamics of 30 years ago correctly.

The car is e-gas and is after the chassis number split on the parts drawing on the Design 911 page so should be 986 606 125 01, but at around 3 times the price for the Porsche supplier part, the BOSCH OEM spec one will do for me.  Best price I've found currently is onlinecarparts.co.uk at around £180.

I guess priming the screws a couple of times in advance with penetrating oil spray should help a bit.

This is the correct MAF number if removing a 125.00 or a 125.01

Apparently some early 2000MY egas cars that have not had a DME flash take a MAF that ends in 124.00, to use the later 125.xx the DME needs to be flashed as these MAFs are not cross compatible. 

I've never come across one of these however, both my cars are 2000MY and both had a 125.00 MAF which I replaced with a 125.01 part. I have no idea what change caused the uprevision of the part number.

If the screws are corroded, it wouldn't surprise me if the MAF is damaged, I have a theory that the water is what kills the MAF, as cleaning it with MAF cleaner didn't help at all in both cases.

On one car I did as above and slotted the screw, but in the other this wasn't enough as the screw snapped anyway, and I had to remove the airbox section in the end.

[½cwt]

3 hours ago, naim22 said:

This is the correct MAF number if removing a 125.00 or a 125.01

Apparently some early 2000MY egas cars that have not had a DME flash take a MAF that ends in 124.00, to use the later 125.xx the DME needs to be flashed as these MAFs are not cross compatible. 

I've never come across one of these however, both my cars are 2000MY and both had a 125.00 MAF which I replaced with a 125.01 part. I have no idea what change caused the uprevision of the part number.

If the screws are corroded, it wouldn't surprise me if the MAF is damaged, I have a theory that the water is what kills the MAF, as cleaning it with MAF cleaner didn't help at all in both cases.

On one car I did as above and slotted the screw, but in the other this wasn't enough as the screw snapped anyway, and I had to remove the airbox section in the end.

My chassis number is well beyond the break in which the cable to e-gas swap was done.  Searching 124.01 does not throw up any results on the web and doesn't show on the Porsche parts diagrams.  Must have been a small run a the beginning of e-gas production I guess. I imagine 125.00 to 125.01 is a totally backwards compatible minor change by Bosch that makes no material difference to the component as is often the case with up issues.

If I do have to take it out, I hope the screws come out or can be slotted at least 

[½cwt]

6 hours ago, John2000 said:

I got a Bosch MAF from euro car part website site put my reg in and it tell you the type you need or should do.

I could not remove the screws no matter how I tried so booked it in with Le at CPS but they he told me they had supplied me with the wrong one.

He kindly cut a slot in both screw heads that made it easy for me to swop when I got ECP to supply me with the correct one.

No more error codes.

On the Porsche parts list my chassis number is clearly an e-gas car but the ECP and Car Parts 4 less (same database) only offer the non-e-gas MAF when I use my reg no and even if I put the model in by hand and make it an '01 car rather than '00 it still offers the older type.

[John2000]

That's exactly what I did and it was a good job I'd booked a service or I would have had a 2 hour round trip for nothing.

The best thing I can suggest you do is take out the old one check the number then ring your local branch Lee at CPS rang his and they said they would not have supplied that one for my car so it seem that the website gets it wrong often.

[sa utah]

The fixing screws aren’t just normal security torx.   I can’t remember what they are called but they have a different t number of points on them.  Normal ones wouldn’t shift mine at all.  

[½cwt]

9 minutes ago, sa utah said:

The fixing screws aren’t just normal security torx.   I can’t remember what they are called but they have a different t number of points on them.  Normal ones wouldn’t shift mine at all.  

The two online videos I have checked show the screw heads require a 6 point tool with a hollow tip.  I've seen a few German manufacturers use these in tamper proof applications including Bosch on some of their power tools.  From a personal pint of view I have a set of these and various other tamper proof bits, was about £4 on eBay a couple of years ago I think... Quite handy from time to time.

[naim22]

6 point security torx (T20 I think) on both of mine and all new screws I've ordered from Porsche 

I had heard of different 5 point ones but not sure if these are only used on models like the 9x7/986 SE where the housing became serviceable with the MAF, in which case you wouldn't have to remove the actual sensor as the orderable part includes both

[½cwt]

I've got to the MAF, can get enough purchase to unplug it and release the retaining clip on the plug so need to unscrew it.  I've got the inbord screw out eventually with one of the security bits I have, however I can't get on the out board one and apply lots of downward pressure as it feels like it had already started to burr off. Think I'm going have to slot it, but how the hell to you get in there to do that, big disc on a Dremel that will reach its shaft over the MAF loom??

[John2000]

This is why I had CPS do my screws I have the tools but could not move either screw until they slotted them for me.

I suspect they have a special long extension to be able to apply the pressure needed.

I feel your pain!