Hot Start Fault and Stalling

[Guest]

Re: Porsche 911 (993) 1994 Tiptronic S
(LHD, no mods - standard factory porsche)

I've had the car for 6 months, it was inspected by Mr Morgan, has a solid service history and drives superbly
but my ownership has been blighted by an "˜intermittent' fault.

The symptoms include:
1 From cold engine fires up fine and settles into smooth idle
2 From hot the engine cranks but won't fire (usually after time taken to refuel, approx 5-10 mins)
3 Note: engine starts perfectly when hot within approx 5 mins of stopping
4 If left for 15 mins engine fires up fine and idles smoothly
5 After this event, the engine occasionally stalls on the go "" resulting in painful 15min wait on hard shoulder before firing again!

Fault finding so far:
1 Replaced fuel pump relay
2 Full OBD1 diagnosis with AFN Chiswick: work inc Replaced Air Mass Sensor
Faulty wire in Immobiliser unit (Factory Porsche)
3 AFN had apparently checked obvious things like distributor caps/rotor arm, fuel accumulator, fuel press regulator, ignition module etc

Having spent half my life's savings with AFN, and no nearer finding the source of the problem, I'm hoping that there might
be someone within the club who may have experienced similar problems (or recognise the symptoms)?

It may be worth noting that at my last visit AFN mentioned that a second diagnosis had picked up a faulty
Oxygen Sensor (why this hadn't been apparent at my first visit they were unable to explain). Also can the
Hammer Test identify a fault with the Cylinder Head Temp Sensor? AFN said this appeared OK "" Could these
be causing the problem?

I'm wary of carrying out any more "˜shot gun' repairs and plan to take the car to JZMachtech for a second opinion.
However I would be exceedingly grateful if you could throw any light on the problem before I embark on another series of
costly repairs"¦


Are there any likeminded 993 owners out there who can help?

Huge thanks

Tom
Region 19
Tom Delhanty
28 Langham House Close
Ham Common
Richmond
TW10 7JE
02089402573
PCGB Membership no. 50557

 

[Shane Hodges]

Tom, I have an occassional problem with hot starting after, for example, refuelling. When the car does fire, all is fine, but it is a worry wondering whether she will fire.

I have yet to get the latest suggestion checked out, but Mark Geraghty suggested there might be a fuel evaporation issue (thanks for this by the way Mark.) I have to admit that for some time I haven't head the fan kicking in when the ignition is off - this might be part of your problem ... I am hoping it is part of mine!

 

[Mark Elder]

ORIGINAL: Shane Hodges

...I have to admit that for some time I haven't head the fan kicking in when the ignition is off ...

Shane,
Is this the fan like noise I hear when I switch off most times (but seems to come from front of car)??

 

[Porker993]

The fans at the front are different altogether. The O/S one is for the oil cooler, and the N/S one is for the aircon condensor.

There is a big fan in the engine bay, which kicks in after a hot run. It's all detailed in the workshop manual - from memory, the fan kicks in at high and low speeds at different engine temperatures. E.g. if the engine oil is still at 95 plus degrees centigrade within 15 minutes after ignition switch off, then the fan is supposed to come back on. After 15 minutes it comes on if the temp is more than 75 centigrade etc. There are lots of rules governing it which I can't remember without looking it up. Sometimes in the summer after a hard run I hear it start up in the garage, or in the car park where it frightens old ladies.

I believe the function of the fan is to prevent fuel evaporation. It seems a simple enough thing to check and eliminate in this case.

 

[Gordon Attar]

Tom
Stick to the independants for this type of problem as they will have seen far more 993's and will have come across it before, where as an OPC will probably not, also their labour costs are twice as much whilst they are 'training themeselves' looking for the issue with the diagnosis tools which normally dont show this type of error.

Ring JZ up and they may tell you the likely answer over the phone! but it looks like AFN have done the sensor and checked the obvious, I would just check that all the hoses/pipes are connected in case theres some extra air sneaking in.

 

[Guest]

Thanks Shane/Mark/Maurice/Gordon

I shall discuss all your suggestions with JZM.
Phil Hindley contacted me earlier today with the theory that it could be the wiring loom. He has seen several
cars experiencing similar symptoms, and it is known that some early 993s did have a fault with the harness
that in the worst case could result in an engine fire!

My car had a faulty loom and cracked distributor cap (causing slight misfire) prior to pre-purchase inspection, and the seller
was unable (or unwilling) to provide a receipt for the work. Ever since I've been suspicious the loom was ever replaced (JZM can
hopefully confirm).

Will keep you all posted...

 

[day1zero]

Exactly same fault mine had.......Oxygen sensor.

The OBD would not report it directly as a fault as the OBD just tests that the O2 sensor is outputting a voltage. (-0.45v). This voltage should vary as the load is increased etc but mine just kept outputting -4.5V. Mine kept stalling under deceleration and then struggled to re-start. Ocassionally idled unevenly especially when hot and could eventually stall.

Need to plug OBD in and then investigate the sensor from the diagnostic menu and not through the fault menu. The sensor can be highlighted and then press accelerator to see if the figure changes...if it does O2 sensor should be ok. If not needs changing...only took mechanic 30 mins to change ... not sure of cost was done under warranty.

Defo worth a look

Hope this helps

 

[zrcg1]

Can confirm my car suffered similar but not identical problems - misfire & stalling.

Similar to your finding, the OPC had the car in several times to find out what it was, they eventually cleaned the Idle Stabilizer Valve which didnt help one bit. Took it back to them mentioning I thought it might be the DME unit or the O2 sensor, they ran diagnostics again and found the O2 sensor faulty.

Changed it, and its been fine since. (12 months)..

 

[Guest]

Thanks all

Its starting to look like either the loom or o2 sensor.
I will be checking my service record re: manufacturers recall for the loom fault
or I'll contact OPC with chassis no.

If this checks out ok, the o2 is the likely candidate (AFN did mention last visit
that a fault had been picked up with this)

Can you recommend any other Indeps more local to me (Richmond, W London)
I know JZM rates might be higher, and their not exactly nearby but I've only heard good things about them?

Thanks again

Tom

 

[zrcg1]

If your car has been through an OPC at any time since the loom recall was announced, it would have been highlighted on their service system via your chassis number.

I would suspect this would be very unlikely, and even less likely since you've personally been to an OPC recently.

I would be tempted to replace the O2 sensor first.

 

[Gordon Attar]

Can you recommend any other Indeps more local to me (Richmond, W London)
I know JZM rates might be higher, and their not exactly nearby but I've only heard good things about them?

Thanks again

Tom

Try Tognola's nr Slough quite a few people recommned or further out Northways nr Reading(£45/hr) whom I use