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Broken down on the way home...

Thanks Geoff.

I've carried on looking at it today and it's a little inconclusive. Having cleared all the old fault codes, with everything plugged back in it still does the same, starts, ticks over, but won't rev. Scanning it afterwards reveals no new codes at all so nothing pointing to the problem.

I have ordered a new pair of genuine Bosch MAFs that I hope will arrive tomorrow as they're not a bad thing to renew even if they're not at fault and I found a place selling them at a very reasonable price.

Fingers crossed that will solve the issue, but I have a nasty feeling that I'm going to end up chasing electrical gremlins due to the strange behaviour of the PSM and gear shift displays and lack of 'check engine' light or fault codes.....
 
The systems are interlinked , with no mafs then it will throw up faults in the gearbox as its doesnt know the engine load ( dme tells the tip control unit that data ) .. mafs disconnected and it kinda goes into limp mode .. it uses the data from other sensors and trys to work out what the failed sensor should read from any other sensor reading but the gearbox is just left in the dark so to speak .

It may well just be a faulty maf .. you can depending on the tester read the voltage of each maf , that will show different readings i would have thought .. im actually working on a similar fault atm but i have different readings on the maf voltages and am leaning towards an air leak .. which is going to be a total bitch to find !

This car drives but with a stutter though .

If a sensor fails but fails inside of its normal limits then there will be no eml and the car will still work on the assumption that the sensor data is correct even though its faulty .
 
Perfect, thanks Demort that's reassuring. I think electrical problems of the kind I've read about caused by water ingress would be the absolute worst to diagnose and repair so good to know that the behaviour is normal.

I did have a look at the o/s MAF with a meter, of the four wires one is negative earth, one is full 12v +ve and the other two read around 1v +ve and 5v +ve. I would expect one of these last two to give a higher voltage when more air is moving (higher revs), but revving the engine had no effect on the voltage displayed so I'm pretty convinced it's faulty.

The car you're working on, are you suspecting an air leak between the MAF and the turbo? Or is it normally aspirated?
 
The one i have is an air leak .. found several leaks on the system today .. not easy to pressurise each intake but a combination of smoke and a rigged up tyre pressure gauge confirmed it.

On a tester i was seeing 1.23 volts for 1 and 1.33 volts for another .. on a rev up the sensors where too far appart and it logged a fault on full boost .. but thats not your issue :)

This is a turbo im working on .

The car looks at the volume of air passing over the MAF sensors and then compairs it to the amount of pressure seen on the MAP sensor .. this should be inside of a certain range and mine wasnt due to an air leak .. if yours has a failed MAF but its reading inside of limits then im guessing the car is reacting to the live reading and running according to the wrong value.

Yours could be a MAP sensor fault as unplugging a MAF will drop the car to default values and it will only look at throttle pedal / throttle valve and substitute a set value that it thinks is correct for the MAF .. getting complicated here aint it lol .

On a turbo then the max boost pressure is at 2500 rpm .. higher rpm and it actually lowers the boost .

Strange that we are saying a MAF failed just as you where giveing it some beans though .. thats the bit that bugs me and makes me think of a blown pipe / air leak .. but then you should have a fault code for that .. i have lol .

MAF first and see what we get after that before continuing i think .


EDIT ..

Btw .. remind me after this and ill tell you about water leaks .. and the main places that cause problems .. your ok atm though .. your car still starts !!
 
All absolute gold, thanks Demort.

Yes, the car was making boost (and showing on the car's gauge), so I eliminated a popped off hose, although if I'm understanding you correctly, it could still have a leak or split which could mess with the sensors and confuse them. I can't hear anything, but it is hard to get away from the fact that it happened when I floored it, seems too coincidental!

The MAFs should arrive today, so I'll fit them and see where we're at.

Thanks again for taking the time to help, this kind of knowledge is invaluable.
 
An air leak wouldn,t give the symptoms you have got .. mine runs pretty much ok but logs a fault for air leak between maf and throttle , im of the opinion the car then adapts to this so no real driveing symptoms .

My hope is a maf has failed but in range so no code and its reacting to the maf reading .. soon find out when you replace them .. unplugging just makes the dme drop to defaults so it masks any fault , still strange though how it happened .

Anyways .. if it doesnt fix it then i have a challenge on my hands .. i do love a good challenge :D
 
Haha, well I'm very happy you love a challenge!

A small amount of progress was made today, but unfortunately the company I ordered the two MAFs from only sent one and it was a pattern part rather than genuine.

I fitted the one that did arrive to the offside as that was the one I tested and didn't seem to work. It's not a great fit though, the diameter at the air filter side is too small so doesn't seal. I did however fit it, reconnect everything and clear the codes and started the car....... it works!

I decided a test run was in order, so I drove to the nearest petrol station 9 miles away and everything was fine. Filled up with some of the 97 ron good stuff and headed back and (of course) put my foot down. Straight away back came the PSM warning :sad: Still drives, but in that 90% OK mode.

Pulled over and scanned it and got P2281 and 1314. Cleared those and set off again gently but the PSM warning immediately came back (same codes when scanned). When I got home I took the new MAF off and refitted it with RTV so it will now seal and left it to dry. Back on it again tomorrow!
 
Thought everything was fine today, went out for a 20 mile test drive this morning and all was well. Took the car out to actually use it this afternoon and the PSM warning came back (under quite gentle acceleration this time!) with those same fault codes.
Each time they're cleared they come back and Googling their meaning it looks like I too may be chasing an air leak. Or maybe in need of a MAP sensor?
 
Interestingly, the Torque app brings up two different codes. P2187 and P2189.....
 
The fault codes are ..

Air leak between MAF and throttle body
Misfire cyl 2
Bank 1 Too lean at idle
Bank 2 too lean at idle.

You didnt have these faults before you fitted the new MAF sensor i belive and they all relate to an air leak or an incorrect reading from a MAF sensor.

Cayenne MAFS are air flow tested with the tube it comes in , if you are just replaceing the MAF without the tube then its not correct .

The Porsche ones are something like £350 each .

It doesnt take much of a difference in MAF signal to cause running faults.

Your car has gone from not running unless MAF disconnected to running ok .. ish but with different faults with this new MAF .. so logically its the MAF thats not very good .

MAP sensor is always a possibility .. all i can say as a basic check is there should be approx 1.8 volts at idle but i use a tester to confirm that reading .
 
Thanks Demort, I must admit I did feel a little dirty inside fitting an obvious pattern part (that didn't fit well) :lol:

I thought I'd ordered a pair of Bosch MAFs along with the housing/tube (0280218071) What I actually got was one pattern equivalent sensor/tube and the following day I received a genuine Bosch sensor but without tube (F 00C 2G2 047).......

Although I ordered the 0280218071 as I thought it would be nice to have complete, clean units I wasn't aware that just changing the sensor on it's own wouldn't be right, so looks like both items I have here are fairly useless!

I'll put that down to experience and have this morning ordered two complete genuine Bosch units from a different supplier. Although these were not £350 each from Porsche, I assume that the OEM supplied part is a re-boxed Bosch part as was fitted to the vehicle?

I feel like it's very nearly there anyway and in the brief time when the car has functioned correctly I absolutely love driving it. It'll be nice to get this resolved so I can move on to the other issues :lol:
 
Pattern parts can be either cheap and nasty or genuine reboxed items , i leave that to the parts guy to sort out but as a garage we tend to use OEM or porsche parts mainly .

I had a look at an 05 turbo that is fine today just to have a look at some of the figures .. when hot after a good run the mafs read 1.19 volts and 1.17 .. i had to rev it to 1k rpm to get the same readings i do on my faulty one .

There was also an imbalence on this one but through the rev range they were pretty close to each other

So take the above as a guide to the correct values for mafs .

If the mafs are over reading then the car compairs these to the pressure sensor and flags up an air leak code so i know the mafs are faulty on mine .. that and one is covered in oil lol .


Ive already said it wants x2 mafs on mine but as there is a fault with a turbo as well then the customer when quoted for the work is not continuing with the repair .. cant say i blame him .. repair is more than the cars value sigh .

I have checked it and the maf and tube are one unit .. Porsche say not to replace just the maf as its air flow tested as one unit .

Btw .. when its all good and you give it some stick and enjoy the power .. keep an eye on your fuel usuage .. might use a little more than you expect ;)

Mine ran out today but came in with over a quarter of a tank .. opps .
 
Haha, easily done I'm sure! I'd think single digit figures would be achievable given a little effort... :lol:

Continuing bad luck with parts for mine, I ordered two Bosch MAFs yesterday morning and paid extra to have them sent Royal Mail 1st class to get here today. Postman has been and gone, turns out they sent them FedEX next WORKING day instead so won't get them until Monday at the earliest, although the tracking number they've supplied isn't even recognised on the FedEx system so who knows....

Still, gives me time to look at some other bits, but I'll start new threads on those.

Turbo writes the car off? Is it true the engine needs to come out to fit then?
 
So, thanks for taking the time to check the voltages Demort, I've just checked mine again with the new MAF that I fitted the other day.
Of the four wires connected to it, I have a green that is 12v negative, a thick black that it 12v positive, a thin black with yellow trace that is 5v positive and a thin black that is the variable positive. On the old non-functional MAF, this voltage would remain a little over 1v regardless of engine revs. With the new one at 3000rpm the voltage increases to a little over 2v.

More specifically:

With the engine off, both read 1v. At idle the o/s (new) reads 1.17v while the n/s (old) reads 1.23v.

At 2500 rpm both read 1.75v give or take 0.02v

At 3500 rpm o/s reads 2.23v while the n/s is 2.12v.

So, there is an imbalance there currently (and the new o/s MAF has a greater range, starting lower at idle but ending up higher at 3500 rpm than the n/s), it will be interesting to see how the readings are when both sides have been replaced for the new ones arriving Monday (hopefully!).
 
I'm pleased to say I think I can now bring this to a positive conclusion :D

I fitted the two new Bosch MAFs and also for good measure a new Bosch MAP and all is well. I've now taken it for a couple of thorough drives and everything appears to function as it should. Very happy!

Once again, thanks for all the contributions while I'm getting to know this vehicle, and especially Demort - I certainly owe you a drink! :lol:
 

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