Massive overfuelling on 87 944 turbo at full throttle

[ukmastiff]

Sorry but this wont be short.

Today my car went on a rolling road. The man did his pre checks and his companion , listened to my engine through a stethoscope to rule out any pinking. As they ramped things up still listening etc ( pre power run) the car showed massive overfuelling. I was told to expect up to 3000 ( of what ever it is parts per blah blah in the exhaust) but it was rocketing to over 12 or 14,000 basically off the scale. At one point when pushed the car started to completely cut out.

Now the reason I know this is genuine is that on the 944 run a couple of months ago , my car did this if I really flawed the accelerator , and I did mention it to Paul Mc n or Jon , I cant remember which. However the car has never done it since and I put it down to bad fuel or something.

Now I know of course that the car was overfuelling and cutting out.

So even though I only went for a rolling road session with a view to having the car
'Pro Maxed' and then going on the same rolling road again , I now have a problem .
I now know I have a sick car. The garage tested the fuel pressure regulator and tell me that is working fine. They then tried to tweek the setting inside the top of the AFM gradually backing it oiff the spring. Now I hve taken the car back but it is doing it worse than when the car went in. I am not taking it back there as clearly I only went to them for rolling road in the first place and I want a specialist to tell me whats wrong not someone else to fiddle for hours ( at my cost) and not even fix it ( or make it worse as has happened here) The man with the rolling road has suggested it may be the wrong AFM ? , I think if anything more likely the /AFM is up the duff.

Obvious question is does anyone have any idea what would cause this overfuelling problem as I clearly need help. To be clear if you wack your foot down the car will completely shut itself off until you lift your foot especially over 70 MPH and the best way to drive the car is gently tickle the accelerator. This is now worse since he tampered with the AFM though he marked its position and put it back ( alledgedly).

Regards Mas

 

[barks944]

I don't think you should mess with the spring in the AFM . Its laser tuned by Bosch.

http://www.the944.com/afm.htm

This link should help. I would also check the output of the throttle position sensor. I wonder what he is measuring in the exhaust, was it air fuel ratio or some kind of emmissions test? I.E if the ignition was failing would the presence of unburnt fuel in the exhaust screw up the reading? I would install a wideband sensor, its a great bit of kit for diagnostics.

 

[DivineE]

I counter your massive richness on boost with massive air leak somewhere. You can be near certain that'll be what's causing it. Probably many tiny leaks that have built up. Do a pressure test and you'll soon hear where its leaking from.

 

[Hilux]

Or the engine thinks its cold all the time thereby over enriching?

 

[ukmastiff]

The most important question is who is going to be properly capable of fixing it not just looking around under the bonnet and charging me for not fixing it ( as has just happened)
Baring in mind im in Herts not the N/east or S/West.

Regards Mas

 

[barks944]

You?

 

[944 man]

What did you/they see on the boost gauge when it was overfueling?

 

[barks944]

944 man do you think a boost leak capable of screwing up fuelling that badly should be apparent by the inability of the turbo to maintain the boost pressure in the manifold? Would a turbo and boost control system be capable of compensating for small ish boost leeks by making the turbo work harder?

 

[ukmastiff]

Im sure if you have read my previous posts you will know that I have always been candid in that I dont have any car mechanic experience at all. I have never made any mechanical knowledge claims whatsoever so im not sure the 'you' posting is very helpfull but possibly I have misunderstood the post , I do hope so.

In answer to the question , I have always noted on driving the car that it seems to hold boost ( according to the guage) well up to close to the red. My last 944 Turbo certainly didnt do that and dropped off much quicker. I obviously am aware how boost drops off and it has never seemed to drop off much at all in my car if that helps.

I am certainly going to have to take the car to an expert , the question is who is up to the job ( not me tis clear). I wouldnt even know where to look for these leaks. I found a tiny crack in one of the thin blue silicone hoses whilst he was under the bonnet and cut it off the end and put the hose back on. Not that it made any difference I just didnt want to leave the crack.

Regards Mas

 

[barks944]

I have no idea what your mechanical knowledge is, although you seem to think it is minimal and I certainly don't think badly of you because of that. I was merely suggesting you might give it a go yourself, most of the basic tests that we have described here aren't difficult with a few basic tools. Just attempting to offer encouragement to give it a go yourself. Most of this stuff isn't really hard although it may seem a little daunting, it just takes a bit of knowledge and some problem solving.

 

[ukmastiff]

Reading that data sheet it says " dont mess with the AFM spring as it is lazer calibrated by Bosch"
Barig in mind I am in a garage that alledgedly tunes cars , and he says he needs to try and alter the springs position I was very hesitent ( thinking no , porsche specialist ) He though tells me he needs to check the fuel pressure regualtor and check how the AFM flap is opening something about is it being quickly forced back by the airflow under boost. I politely asked if this was within his specialist knowledge and he said totally, the puel injection system in question is a very common and ordinary one and so I agreed.

He did take the top off the AFM and show me that it appeared to have been re sealed before. He also showed me that the screw that is in a little oval track was right at one end of the ovel not in the middle , suggesting someone had possibly already maybe trid to back it off as far as it would prior. This may make sense if you knew what im barking on about and have seen th said screw and its little eliptical 'hole'. One thing is without dispute the car ran far better before he touched that AFM, because I thought it was a bloomin good car !

I am wondering if this is an AFM problem and it has been messed with in the past, it has certainly been messed with now but of course how could I know in all honesty.

Regards Me

 

[Diver944]

If you're in Herts then I would take it to either RPM http://www.rpmtechnik.co.uk/ or Promax http://www.promaxmotorsport.com/

Both of these are known and trusted by many local members to know their way around a 944T and will soon put you on the right track.

 

[Frenchy]

Keep us posted on this my Turbo S has developed the same problem, not realy looked at it properly as it is still off the road and not being used. I had a quick look around the main hoses for the turbo system but nothing obvious, i will be fitting a silicn vac hose kit shortly and will give it a good once over, if it is not a hose problem i eill then suspect AFM.
Does anyone know if the AFM is the same animal on the 220 turbo as the 250 ?

 

[Suffolk944]

Yes either RPM or Promax will see you right Mas, I am off to Promax tomorrow (hmm just noticed the time make that "today") to get my MAF fitted and a couple of other things fettled. I would give Andy there a ring if I were you and chat to him about it imho.

 

[DivineE]

I really would be surprised if it was the AFM not least because the signal from the AFM is not used under full throttle at the higher RPM's. The airflow passes the maximum it can read so wouldn't have any affect on a dyno where your doing full throttle runs.

There are a million places where boost leaks can occur on the 944t Rick's website www.cannell.co.uk describes a good few he found whilst tuning his car such as the throttle body & wastegate but on a car still using standard vacuum lines and DV valve I would suspect those first.

Overfueling is not 'always' a boost leak but 9 out of 10 times on a turbo car it is. For the 5 mins it takes to test it thats where I'd start. I'm sure I read Promax have the proper equipment. You can test with a foot pump but using a pressure line allows you to listen where the air is leaking from a lot more accurately.

 

[pauljmcnulty]

If you're in Herts then I would take it to either RPM http://www.rpmtechnik.co.uk/ or Promax http://www.promaxmotorsport.com/

Thirded. []

I use RPM as they're a bit nearer me (still an hour round trip), but I'd go the bit further from me to Promax if I needed to. I've never used them, but Auto 2000 in Bedford have been spoken highly of by 44/68 owners lots of times as well.

I'm firmly of the mind that any half-competant mechanic can find his way around a 944 perfectly well, they aren't time machines, nuclear-powered, or Italian cars, so quite straightforward. I do think, though, that you'll get a better diagnosis and faster repair from someone who isn't using your car as a learning experience, so specialist is the way to go. Every hour you're paying for hurts, but at least you know there will be less hours involved and so the cost can often be less overall.

 

[ukmastiff]

As you can probably tell from my previous posts , I have always been of a mind that Promax or RPM would most likely be the people with the knowledge to fix or upgrade my car.
I have checked out both places in the past and for a couple of reasons was more drawn to Promax and Andrew so Promax it is. I wish they were even closer but its not so far

I have spoken to Andrew and my totally untrained educated guess is still the AFM to be honest but he mentioned the temperature sensor and I have heard that one suggested before. I dont know why im not convinced re the leak ( so it likely wil lbe lol).
I'll drop my car with them off Monday and leave it there.

I'll report back when he has fixed it which I'm sure he will , I just hope it doesnt take much finding

Thanks for the emotional support []

Mas

 

[paulf968]

I did have a fuel injector stuck open last year - that gave massive overfuelling!

After it was sorted I had wondered whether it was some fuel with too much bioethanol in that had caused it to seize. (humble apologies for adding to a turbo thread..............)

 

[Porka944s]

Oh good luck Mas just think how good it'll be when its back!

 

[Hilux]

Auto 2000 in Bedford have been spoken highly of by 44/68 owners lots of times as well.

Yup

Really nice chaps, good value and expertise - recommended.