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Let me down.

T

the_dr38

New member
My car let me down for the first time in 2 years on the morning of my holiday. It started messing about and jolting when pressing the accelerator and being lumpy. It would die if left to idle unless revved quite high. Now it wont start although sounds like it wants to. The mechanic (A Porsche specialist) came round and said that without taking it in he would hazard a guess at the fuel pump which could be a few hundred quid give or take, prob more though. This sucks as the car has just had a load of money spent on it and has been running better than ever. Plus I want to sell it so want to avoid spending out when i want rid. Anyone had to replace one of these before? They are on the internet for like a hundred quid but I dont suppose he will really appreciate me buying it and him fitting it lol

Lloyd
 
Hi Lloyd,

Have you eliminated the obvious two culprits of DME relay (£20), or FPR? Both are very common, fuel pump isn't. [8|]
 
Could even be the DME temp sensor which causes exactly the same symptoms and costs £20 and 5 mins to fix - try disconnecting it and see if she runs.

Hope your holiday has not been ruined as a result [&o]
 
Could be the throttle position micro switch - if the problem is just at idle (sounds like when you press on the accelerator it runs OK?)

Might be worth checking the AFR at idle. Idle AFR is controlled separately from partial throttle AFR so if running lumpy at idle you could be running too rich. Once you press on the throttle the AFR is controlled by ECU maps rather than pure AFM position so you can get poor idling and fine partial throttle running. Another symptom is kangarooing in slow creeping traffic.
 
Thanks for the replies guys. I have replaced the DME relay which cured the problem of it randomly cutting out. As for the other possibilities I guess I can just hope that the garage choose not to fix it and still add another element tonthe problem (eg fuel pump :-()

I was hoping for somewhere in the region of £2,800 as the car really is immaculate and has had lots spent on it, as a result it 'usually' runs like a brand new car. Plus it has tons of history and receipts. I am
Open to offers. I'll throw in the Pioneer head unit too. What the hell u can even have my sub and amp too. Anyway I guess I will know by tomorrow. Shall keep you posted

Thanks again for taking the time to reply

Lloyd
 
This is the blue topped sensor towards the right hand side front of the engine, from memory just underneath the exhaust manifold - single electrical connector to the top of it is easily removed. Don't be confused by the temp gauage sensor which is further back and lower, and a lot harder to get to. If you can unplug with the engine running, any kind of surge in the idle could indicate a duff sensor - took weeks of head scratching to figure this out on mine. Testing with a multi-meter did not help as they seem to give trouble at different points in the temperature range, and intermittently. If yours is a later model, it should still run with it disconnected as I believe the later DME's incorporate a 'get me home' default setting which takes over if it gets no input from the sensor.
 
Might be tricky as it just won't start. Keeps on turning and then goes to start every once in a while but doesnt
 
Strangely the weather must be killing DME's this winter, had to swap to my spare 2 weeks ago!

Have you checked the Reference Sensor?
 
The first thing your mechanic should do is to attach a fuel pressure guage to the fuel rail and test the fuel pressure. That will confirm if your fuel pump or FPR is faulty

it is extremely unlikely to be the fuel pump. Its the first thing that mechanics assume is wrong because a). they do not understand how a complex Bosch fuel injection and engine mangement sytstem works and b). a fuel pump is easy to fit and nets them a tidy sum with no losses. If it doesn't cure the problem they will then say that it was probably a combination of things and offer to replace the fuel filter then the distributor cap and then the plugs etc until hopefully it starts but not before you've spent £500+ [;)].

As Paul says it is most likely the FPR (fuel pressure relief valve) . This is a valve on your fuel rail which releases excess fuel pressure by allowing some fuel back to the fuel tank. It is doing this continuously to maintain about 3 Bar pressure with engine running. If the fuel system is not maintained at sufficient pressure your fuel injectors will not work. ie no fuel delivery .

The other possibility is that the cold start injector isn't supplying fuel . Either sticky / blocked injector or as others have said the engine temperature sensor which controls the cold start injector.

Also if the FPR is allowing the fuel pressure to get too high the ECU will shut down the injectors. An easy way to check this is to remove one of the electrical connectors to one of the injectors and try start the car. if it starts then that is the problem right there, too much fuel pressure.

(Too much fuel can also be caused by a leaky cold start injector )

One last suggestion is insufficient head of fuel in the tank. If your car has two pumps then the immersed pump assists the external fuel pump to raise fuel pressure . If the fuel tank is allowed to run nearly empty it can either stop the immersed pump working which will then reduce the efficiency of the external fuel pump or running the tank empty can introduce air into the fuel system preventing the fuel pump working properly.

There are some very simple tests you can do yourself with our help before you give the car to a local indie.

Please confirm
1. how much fuel in tank ?
2. have you recently refueled ?
3 have you recently had any work done on the car at all ?
4 do you have an immobiliser.
 
Hi there,
We had an almost identical problem with our 944 a while back. We got all sorts of diagnoses from different mechanics (including fuel pump, timing belts, air mass meter) but in the end we took it to GT One in Chertsey, Surrey. They replaced the fuel pressure regulator and it ran like a dream afterwards.
Hope you have some good luck with yours! [:)]
 
Hi guys, sorry haven't replied but have been away. Got the car back and it's running well although not perfect, he replaced the cold start sensor and did an overhaul on the air mass meter as well as the fuel pump as he was aware I am selling it. Anyway it is slightly jolty still but is running never the less and has now been polished and is up for sale. I think maybe the fuel pump does need replacing as it's making a whurring sound. Would it point towards that?
 
Okay so this has cropped up a number of times and sounds like it could easily be the problem, any idea how much/easy it is to do?
 
Can I just double check: fpr? Fuel pressure regulator??? A google search returns DME fuel pressure relay? Is it basically a DME relay? They're like 21 quid and I can plug it in, replacing my existing one which is only a year old? I am confused, apologies?
 

ORIGINAL: the_dr38

I think maybe the fuel pump does need replacing as it's making a whurring sound.
Click to expand...

Yeah, ours made a whurring sound too but it hasn't since the fuel pressure regulator was replaced. It's a regulator, not a relay, it sits on top of the engine. (Although the DME relay is also a common fault with these cars - we replaced ours too but it didn't fix the jolting or the whurring). Definitely might be worth replacing the FPR first (you might even be able to do it yourself if you're fairly handy) before getting the fuel pump done as the pump is inside the tank and a bit of a mission to get at. Just my two cents anyway...
 
Can I just double check: fpr? Fuel pressure regulator??? A google search returns DME fuel pressure relay? Is it basically a DME relay? They're like 21 quid and I can plug it in, replacing my existing one which is only a year old? I am confused, apologies?
Click to expand...

Up until a couple of years ago almost every fuel-related issue was down to the DME relay. Hence we always keep banging on that every 944 owner should carry a spare in the car. More recently it's become less of an issue, mostly because people either have a new relay fitted, carry a spare or at least know it's always the first place to look, so they don't ask the question on forums.

The Fuel Pressure Regulators have started to become a more common fault now, at least from the questions posted here and the calls I get. To get it changed by a Bosch specialist near me is a little over £100, what the part costs or how much labour is involved I don't know.

It's incredible how often this turns out to be the problem, often after many other causes have been considered and parts changed. It certainly seems as if fuel pumps are being diagnosed as faulty by roadside mechanics and non-specialist garages, but I can't think of any occasions where it cured the problem.
 
ORIGINAL: the_dr38

Okay so this has cropped up a number of times and sounds like it could easily be the problem, any idea how much/easy it is to do?
Click to expand...


you should read all the posts properly and use the search facility before asking silly questions [:mad:]

The first thing your mechanic should do is to attach a fuel pressure guage to the fuel rail and test the fuel pressure. That will confirm if your fuel pump or FPR is faulty

it is extremely unlikely to be the fuel pump. Its the first thing that mechanics assume is wrong because a). they do not understand how a complex Bosch fuel injection and engine mangement sytstem works and b). a fuel pump is easy to fit and nets them a tidy sum with no losses. If it doesn't cure the problem they will then say that it was probably a combination of things and offer to replace the fuel filter then the distributor cap and then the plugs etc until hopefully it starts but not before you've spent £500+ .

As Paul says it is most likely the FPR (fuel pressure relief valve) . This is a valve on your fuel rail which releases excess fuel pressure by allowing some fuel back to the fuel tank. It is doing this continuously to maintain about 3 Bar pressure with engine running. If the fuel system is not maintained at sufficient pressure your fuel injectors will not work. ie no fuel delivery .

The other possibility is that the cold start injector isn't supplying fuel . Either sticky / blocked injector or as others have said the engine temperature sensor which controls the cold start injector.

Also if the FPR is allowing the fuel pressure to get too high the ECU will shut down the injectors. An easy way to check this is to remove one of the electrical connectors to one of the injectors and try start the car. if it starts then that is the problem right there, too much fuel pressure.

(Too much fuel can also be caused by a leaky cold start injector )

Here is a link to Clarkes Garage Workshop Manual which will tell you all you need to know about every aspect of your car. It will give you a detailed guide on how to test your fuel pressure and your fuel delivery and the various componants of your fuel delivery system.

If I were you I would put your car into a proper sports car specialist or a local Porsche workshop and get the job done properly.
http://www.clarks-garage.com/shop-manual/fuel-01.htm
 
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