Cutting out

[the_dr38]

My car has began to suddenly cut out when I am driving along. It is as if all fuel is suddenly cut off. Then it wont start for a few minutes. I notice this is happening more often now, maybe due to the cold weather. Has anybody experienced this? I think its going to be hard for a mechanic to diagnose because it's bound not to happen when he has it.

Any advice would be much appreciated.

Thanks

Lloyd

 

[robwright]

The first thing I would try would be the DME relay. It seems to be the common favourite in this situation. A failing DME relay can stop the fuel pump from working. They are around £16 new and well worth carrying as a spare actually for the money.

 

[zcacogp]

Does it splutter and then cut out? Does it lose power and have very little go and then finally die? When it re-starts does it struggle to get going, or does it happily spring into life once the requisite few minutes is up? Fuel starvation often causes a 'soft' cut-out (it will splutter and die.) Electrical problems usually cause much of a pronounced cut. (Fuel pump giving up will probably be a pronounced cut-off as well. When was the fuel filter last changed? Oli.

 

[pauljmcnulty]

Happened for ages with a neighbour's Lux. He eventually got a Bosche specialist to fix it, can't remember what but it was about £100 all in. Fuel pressure regulator rings a bell somewhere in my tired old brain. Certainly try DME first though.

 

[the_dr38]

It is certainly a sudden cut off, unpredictable. Once it starts, it's absolutely normal again, it's just getting it to start again which is the problem. It happened just now on a dual carriage-way and started again on the 2nd attempt, where as it's usually it's more like the 10th or 11th. Probably part of the reason I'm only getting around 70/80 miles to £20 of fuel, combined with the freezing weather. Also I dont know if it's related but the heater now only blows hot when the car is revving high, this is once the engine has warmed up. As soon as I let it idle, its luke-warm/cold again. Thanks for the replies, anything up £100 sounds not too scary. Lloyd

 

[Eldavo]

I'd say dme relay too, due to the cold weather it is cooling down quicker than normal hence restarting much sooner.

 

[Mike_Pollock]

I had a Lancia HPE injection many years ago with a similar Bosch set up, the regulator went on that and the symptoms were rather different. It would run fine then cough and splutter whilst driving, occasionally stalling, but would always restart ok. When in the garage it would run ok then pick up revs up to 3500 and then drop right down maybe stalling. Fuel line should be 3bar but it was slowly increasing to 6-7bar then dropping suddenly to less than 1 - if it stayed running it would build agan! If thats any help! Mike

 

[peanut]

I would say that temperature might be a clue. If the increase in coolant temperature has just recently happened and coincided with the cutting out. There are several temperature sensors that effect the ECU's fuel delivery control . I would start by checking those . If the FPR is not regulating the fuel pressure correctly I would expect the car to have difficult starting and have unstable running.(Injectors are very sensitive to fuel pressure.) FPR is easy to check. Do a fuel pressure check on the fuel rail.I just connected a £5.00 fluid pressure guage (ebay) with a bit of garden hose to the fuel rail.

 

[the_dr38]

Ok finally got a chance to get to the local German cars parts shop and picked up an alleged 'DME' relay, stupidly not checking it. Once I got back it would appear that they've given me the wrong relay and I now have to go back. Anyway this leads me to wonder whether or not my rad temp sensor which controls the fan is actually the right one and seeing as it was from the same place I could exchange that too seeing as I havent yet fitted it. Could anyone tell from looking at it if it looks right? [link=http://s192.photobucket.com/albums/z140/the_dr38/Fan%20Switch/]Fan Switch[/link] Cheers Lloyd

 

[peanut]

well it would be helpful to know the year and model of your car. 944S2, turbo's and other 944 with aircon have twin fans and have a sensor with three electrical pins the others have two pins.for a single fan. The more important thing is the temperature spec. You need to make sure that your switch is activating at the right temperature depending on climate and whether you commute or race the car suggest you ring your local Porsche dealership parts dept give them your chassis number and ask them for the part number

 

[the_dr38]

Thanks Peanut. I can see now I should have a 2 pin one and I have been given the 3 pin one. Cant they get anything right?

 

[pauljmcnulty]

well it would be helpful to know the year and model of your car.

Yep, it's a great help if people can put the model etc. in their signature, and location in their profile. Often makes answering the question easier and quicker!

 

[ChasR]

Whilst the DME relay could be the cause I would be looking at the fuel pressure regulator. Apparently one way to see if it is the regulator is to unplug one of the fuel injector connections and see what happens when your car stalls. If it restarts again, it may well run rougher, but if the car continues to run, it will almost certainly point to your Fuel Pressure regulator being at fault if your DME is fine.

 

[the_dr38]

Ok I am gonna add my car details to my display blog now. I fitted the 3 pin sensor even though a 2 pin came out and the fan is working perfectly now. coming on and going off at the right time. I blew the heater through at max heat while the engine fan was running and it is now blowing hot again, maybe there was an air block. The DME relay was purchased from Porsche, Byfleet, and has now been fitted and the car hasnt cut out once. Although it still sounds like it doesn't want to start in the cold morning and chugs quite a bit for the first 5 mins but at the end of the day the car is 20 years old. Just out of interest does everybody elses do this? So everything seems fine once again, thanks everyone who posted. Lloyd Oh and I also managed to blag a brand new service stamp booklet from Porsche while I was there for peanuts.

 

[robwright]

You still might want to look at changing the leads and dizzy cap at some point. They can be very sensitive to damp and moisture especially if they are old and have started to break down. Never under estimate the benefits of good spark. This may cure your cold morning chugging. My car usually starts within 3 or 4 revolutions no matter what the weather and runs pretty OK. It's never perfect for a minute or so but hey like you said and mine is nearly 22 years old []

 

[Mike_Pollock]

Mine starts in approx 2-3 seconds and doesn't chug at all, but is running 3 month old dizzy / rotor and plugs, and they did make a difference , even in the warm (ish) weather! Mike

 

[peanut]

ORIGINAL: the_dr38 Oh and I also managed to blag a brand new service stamp booklet from Porsche while I was there for peanuts.

thanks dr38 thats very thoughtful but quite unecessary [][] Two things control cold starting and running and thats the cold start injector and the AFM and their associated temperature sensors Thats where I would start looking

 

[the_dr38]

LMAO, I thought I'd treat you to it as you've taken such good care of me so far. I will look into these things, the distrib cap especially, must be cheap.