intermittent starting

[nicholas.stockley]

Hi all hopefully someone may be able to help, I have been to 3 garages (not Porsche) to try and solve this problem
Last year I took it out of storage and it started ok, following week it just kept turning over and not firing up, charged battery even jumped it, no joy over the week, I called out AA there Mech turned up and stood with me while I explained the problem, then I turned ignition and it fired up , I did say he was magic, following couple weeks all good no problem, covered about 1500 miles then the same thing happened again
went into garage, they put a larger battery on to turn it over faster, worked for couple weeks
then into another garage new fuel pump, relay control, pump out kit, electrical fit kit, works ok for couple days then same problem , kept turning over and not firing up then out of the blue it would start and run ok,
wouldn't fire up again, immobiliser disconnected and taken out new Coil pack fitted
in storage for last 6 months and started every week ok
today I picked it up started ok, run it to garage filled it with fuel and washed, drove 2 miles de accelerated at roundabout and it stopped running, turning over but wouldn't fire up, towed back to base, tried again to start, fired up no problem and left it running for 5 mins, turned it off and tried to start, just turning over
any suggestions would be very helpful and please don't say sell it like the wife
thanks
Nick

 

[GeoffB]

Nick
I had similar experience on a 3.2 Speedster I owned years ago. Turned out to be the earth lead that goes from gearbox area to chassis. Where it goes over the rear frame it was green with corrosion, I had previously checked and cleaned ends but not spotted this. On way back from Le Mans refused to hot start battery seemed dead . Needed to bump start a couple of times on way to Chunnel. After arriving in UK started ok. Changed lead and never had another problem with it. Might be worth a check
If yours is a 911 check above pedal box the harness has (if I remember correctly) three round connectors that join harness through bulkhead, you can catch these with your foot and dislodge them so check they are fully home

 

[Alpha10]

Glad to know I am not alone!

My ‘84 coupe has started doing very similar!

Only three times so far, but the engine turns over strongly and just won’t fire. I tried swapping out DME relay last time and nothing BUT literally leave it 5-10 minutes and starts first touch of the key as normal. I have no idea what is going on. I am now always worried it could happen at a difficult situation or not start at all.

Mark

 

[pse_SC]

any suggestions would be very helpful and please don't say sell it like the wife

sell the wife

 

[chas3.2]

Do fuel pressure test first.

 

[Alpha10]

Do fuel pressure test first.

Interesting, it has only happened since I had a new fuel pump fitted. The bit I really don’t understand is the waiting only 5 mins and nothing being touched or changed starts straight away. Almost like it was flooded?

 

[chas3.2]

When were the fly wheel sensors fitted.

 

[911hillclimber]

Changing the above, the box/chassis earth strap and another added too, fixed everything.
sensor change is an awkward job, but just take your time, or take to a Porsche independent garage.

 

[sesame]

Glad to know I am not alone!

My ‘84 coupe has started doing very similar!

Only three times so far, but the engine turns over strongly and just won’t fire. I tried swapping out DME relay last time and nothing BUT literally leave it 5-10 minutes and starts first touch of the key as normal. I have no idea what is going on. I am now always worried it could happen at a difficult situation or not start at all.

Mark

Anything to report back yet please?
Re the above "worried it could happen at a difficult situation..."
If you are in danger engage first gear release the clutch and crank yourself out of danger (on the starter)
Steve

 

[Alpha10]

Anything to report back yet please?
Re the above "worried it could happen at a difficult situation..."
If you are in danger engage first gear release the clutch and crank yourself out of danger (on the starter)
Steve

Cheers Steve, mine hasn’t done it for awhile now, that is what is so strange. It was even fine at Porsches by the Lake last weekend, which is the location it did it last.

I am currently heading for the Lake District in my ’87 targa so the coupe is tucked up at home for a couple of weeks anyway .

Mark.

 

[Alpha10]

Anything to report back yet please?
Re the above "worried it could happen at a difficult situation..."
If you are in danger engage first gear release the clutch and crank yourself out of danger (on the starter)
Steve

Mine has decided not to start again, just now, so will wait 15-20 mins and see if it just randomly works again!

This is starting to annoy me now

mark

 

[LesGTS]

Bearing in mind the age of your cars could the issue lie with rust in the fuel tank?
Many moons ago, not in a Porsche, l experienced frequent intermintent cut outs and non starting which was eventually diagnosed as loose flakes of rust in the fuel tank occasionally blocking the fuel pipe to the carbs.
Long shot but you sound desperate!

Les

 

[911hillclimber]

Sorry to repeat myself, but have you changed the flywheel sensors, cleaned the earths etc?

The 3.2 has a good filter system due to fuel injection. Does the car continue to run well once started? If so fuel is there, just the ECU does not know where to fire the spark to get combustion.
Sensor change is ok if you are good at DIY on these cars, but would suggest a good indie who are used to the 'approach' of replacement.

 

[Alpha10]

Cheers all, happened again this morning, but as I was trying to get to work, I just left it and took the Targa.

I change the fuel filter regularly and always inspect the old one, no debris, so don't think it is fuel either.

Sensors are the next logical place, but it is very odd if it is them as leaving the car 10-15 mins and it starts and once started runs really well. I am going to clean the earths I can get to over the weekend, but I don't think it is that. I think it must be electrical, I am starting to wonder if it is a fault in the actual DME (not the relay as that is a solid state one and I have tried swapping to a known working one when it is misbehaving) but why would that suddenly work after a short time?

Thanks for all the input, the search continues.
Mark.

 

[911hillclimber]

My 3.2 did all this a few years ago. The sensors were all 1985, original parts, so about 40 years old.
The one had corrosion at the wire/sensor junction and a good tug separated them. This was the intermittency.

There was no rhyme or reason to the issue, just did it now and then, hot or cold engine.
It did however get more regular which I feel is happening to you now.

Got new parts from Type911.
There is a critical gap between sensor and timing ring on the clutch cover which can/could be closed by dirt, I think it is only 0.5mm or of that order, and must be set accurately.
Awkward job with the engine in the car hence suggestion to save a lot of frustration and get an Indie to do it. Threadding the cables through to the conection bracket on the engine (next to the fuel filter) can take as long if you follow the factory routing, I cheated.
Good luck!

 

[Alpha10]

Thanks, I am becoming more convinced that it is the sensors, that is my next step. Paul Stephens in Essex looks after my cars, I think the best way (for my knuckles and sanity) is to ask them to replace them.

For my own education, I think there are three sensors: Speed Sensor (RPM), Reference Sensor (TDC) and Cylinder Head Temperature (CHT) Sensor.

The likely culprit here is the speed sensor, but probably worth getting them all done while it is in there?

Cheers
Mark.

 

[Alpha10]

Just got home from work, jumped in the coupe and of course started first touch of the key and ran perfectly!

Can this be sensors, doing this, nothing has been touched/moved/changed Since this mornin?

So strange, maybe he couldn’t be bothered with the M11 this morning

Mark.

 

[911hillclimber]

Yep, mine was like that.
suggest take it to the specialist, I changed the 2 on the engine/box.

 

[Alpha10]

Yep, mine was like that.
suggest take it to the specialist, I changed the 2 on the engine/box.

Thanks, that is very reassuring! I will get it booked in - supposed to be taking this one to Classics at the Castle and Goodwood revival in a few weeks....

Thanks
Mark.

 

[911hillclimber]

Maximum a morning's job and that's me on the drive of the house.
A good specialist an easy morning max I would suggest.