dom1102

I have posted about this before and got some helpfull responses, if anyone can help again would really apprieciate it!

I have got an ongoing starting problem with my 1988 928 S4 (auto). So far 2 garages have failed to fix this ongoing problem…any ideas?

It starts perfectly every time when cold but when warm quite often wont restart after being turned off, it is fitted with a brand new battery that is fully charged (both garages diognosed a faulty battery cell and replaced it so this is the second new battery it has had fitted)

Changed the starter solenoid made no difference also I tried changing the starter relay with one of the other identical ones in the fuse box, to no avail. Does the 928 have a “control” for the starter system? Whether it starts or not seems to be determined by a few other factors…

If it fails to start (turn the key, all dashboard lights come on but nothing else happens) there are 3 things that seem to get it going (I am not imagining this) but none of them seem to work every time and any one of them, in any order can sometimes get her going!!

1.Just gently pushing the brake pedal sometimes brings it instantly to life (whilst holding the ignition key in the start position)
2.Locking and unlocking the doors using the round control **** on the drivers door (then retry ignition key)
3.Putting the gear selector into Neutral (then retry ignition key)

Strange thing is even if none of the above actually works if you just sit there with the key turned to the cranking position it will eventually after a few minutes suddenly crank and fire up. The car is fitted with a Clifford alarm and what looks like an original Porsche immobiliser (dongle thingy on key ring goes in little slot under steering column). Both seem to work fine.

NickT

I would check the starter lockout that is part of the gear selector, meaning that you cannot start the car if it is in drive. The fact that you move the gear lever, then retry might point to this. Should be easy to bypass the switch and test.

dom1102

Ok thanks for that, I am not convinced that this is the issue but I will have a look. Do you know if you can get at it from inside by taking the selector apart?

Leon Speed

So when it runs and you wiggle the key without actually turning it, does it shut off?

Alan

Well its obvious it isn't the battery (don't take your car to those places again).

Its either the starter relay, starter solenoid, ignition switch, trans selector switch, battery or starter terminals or ground strap (battery or engine). This is pretty much the list of culprits for what you describe. If the dash lights never dim I think we can rule out some others that could be on this list and it also makes the battery terminals & engine ground strap seem fairly unlikely.

The most likely are the starter relay (if you haven't swapped this already its #1) and the switch part of the ignition switch and the trans selector switch...

Alan

dom1102

Hi, If I wiggle the key it still keeps running, infact I changed the circular connector block on the back of the ignition switch a while back and it obviously didnt cure it. thanks for the advise though!

dom1102

Hi Alan
I have swapped out the starter relay with an identical one from elsewhere in the fusebox and fitted a brand new starter solonoid (even though it bench tested ok). The dash lights do not dim. Engine ground strap sounds possible, actually it was mentioned by someone else recently and I couldnt find it. Do you know the location of it?? I will check the transelector tonight, I assume you get at it from inside the car (?)

dom1102

Anyone know if the 928 S4's have a “control box” for the starter system?

Rich9928p

Check the Temp II sensor. Some fail with a non-linear resistance. Best to remove it. Put it in an ice water bath and slowly heat up to near boiling. Watch the resistance and note the resistance change with the increase in temperature. If it radically changes from the published specs it should be replaced.

0 C / 32 F: 4.4 - 6.0 k-ohm
15 – 30 C / 59 - 86 F: 1.4 to 3.6 k-ohm
40 C / 104 F: 0.9 – 1.3 k-ohm
60 C / 140 F: 480 – 720 ohm
80 C / 176 F: 250 – 390 ohm

dom1102

Hi Rich
So what would be the effect to the starting of the car if the tempII sensor was out of calibration??

Rich9928p

Improper air/fuel mixture, not sufficient for the engine to start.

There are two separate temperature sensors (one for the LH, the other for the EZF spark module), each should be tested. The test is the resistance between the pins and the body of the sensor (which is grounded to the engine in real life).

dom1102

Ah ok, well when I say "turn the key and nothing happens", I mean she doesnt even crank over, literally nothing happens, not even a click from the starter solenoid. I feel the key to all this is here someware...

If it fails to start (turn the key, all dashboard lights come on but nothing else happens) there are 3 things that seem to get it going (I am not imagining this) but none of them seem to work every time and any one of them, in any order can sometimes get her going!!

1.Just gently pushing the brake pedal sometimes brings it instantly to life (whilst holding the ignition key in the start position)
2.Locking and unlocking the doors using the round control **** on the drivers door (then retry ignition key)
3.Putting the gear selector into Neutral (then retry ignition key)

Strange thing is even if none of the above actually works if you just sit there with the key turned to the cranking position it will eventually after a few minutes suddenly crank and fire up. The car is fitted with a Clifford alarm and what looks like an original Porsche immobiliser (dongle thingy on key ring goes in little slot under steering column). Both seem to work fine.

StratfordShark

It also sounds to me that there is a fault with the switch which prevents starting unless auto selector is in P (can't recall if it also allows starting in N).

Do you have a workshop manual? May be section in there to troubleshoot this, otherwise search through posts relating to that system for where to access it, tests etc.

The JDS 'Spanner' includes test for signal from park/neutral switch to the ECU. I suspect that if it is included in the actuator check routines, then there should be a matching section in the manual allowing similar check 'by hand' (in other words using multimeter and poking at pins on the LH connector).

The strange behaviour with unrelated systems is typical of what happens when one component fails, and there are then odd current paths set up in the electric system.

dom1102

Hi Stratford Shark, unfortunatley I do not have a workshop maunal. Do you know if the shifter postion switch is on the shifter inside the car or on the gearbox end?

Alan

It is on the drivers side of the gearbox and connects in the spare tire well.

There is no fancy control box - the complete list you need to worry about is in my last post.

Sounds like it is either the trans selector switch or the ignition switch (starter terminals).

You can check the trans selector switch - it puts ground on the 85 pin of the starter relay only when you are in Park - wiggle it about with a meter in ohms mode connected between 85 & ground.

OR

The starter switch (the starter terminals only go to the relay pin 86). Note that wiggling the ignition key once its running proves nothing about the starter terminals...?.

So - for this check for 12v on the stater relay 86 pin (voltmeter) when the switch is held in crank mode.

BTW there is no Porsche immobilizer - they are all aftermarket - often rather badly installed. This may have been installed by the dealer - as delivered new - but it is still not a Porsche part and probably not cleanly installed since the car was not designed to accept it.

Alan