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 Post subject: 928 S2 won't start
PostPosted: Sat Aug 12, 2017 10:17 pm 
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Hopefully someone can offer some advice.. I have a 1986 928 S2. I was driving it yesterday, it was running perfectly then it just suddenly cut out while doing 50mph. It wouldn't start (cranked but non start). It refused to start for a while, I called for help (a tow!). While waiting for help, it started and ran for 3 seconds then cut out again.
We towed it home. This morning I went to it again, it started and ran for a minute then cut out, it wont start now, it just cranks.

Does this sound like a common failure? I know if this was a 944 I would be looking at the fuel pump relay for example...

I have only had this car for a few days and the previous keeper can shed no light on it.

Thanks!


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 Post subject: Re: 928 S2 won't start
PostPosted: Sat Aug 12, 2017 10:41 pm 
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Hi :)

I have an S2 ...

One check you can do is as follows...take off top of air filter casing and remove air filter..... then go to motor shop and buy some EASY START...its basically ETHER which will start any engine if the engine is getting no fuel...

So you spray the easy start into the round hole you will see with air filter removed.... you need one person to spray and one person to try and start engine...

IF it starts and runs for as long as you keep spraying, and stops running when you stop spraying you HAVE A FUEL PROBLEM....


If the easy start makes no difference and it wont start then you HAVE AN ELECTRICAL PROBLEM....

If you come back and post here once you know which it is we can help you more....

Hope this helps ...

All the best Brett :)

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 Post subject: Re: 928 S2 won't start
PostPosted: Sat Aug 12, 2017 11:33 pm 
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Great tip and thanks, I will do that and come back. More info: while cranking, the rev counter will go right round to the red line and bounce about, is this normal?


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 Post subject: Re: 928 S2 won't start
PostPosted: Sat Aug 12, 2017 11:37 pm 
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Username wrote:
Great tip and thanks, I will do that and come back. More info: while cranking, the rev counter will go right round to the red line and bounce about, is this normal?


Hi :)

No it isnt normal and it implies its an electrical fault...but do the easy start test first....

All the best Brett :)

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928S2 AUTO V8 4.7 1986-XPIPES ANDERSON RACE EXHAUST,K&N, WIZARDS OF NOS MAXX RACE CONTROLLER & WON RACE REVO NITROUS KIT 2000 HP CAPABLE.
-UK 928 1/4 Mile and Top Speed Record Holder-208.10 mph- Email managingdirector@pchealthcare.co.uk


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 Post subject: Re: 928 S2 won't start
PostPosted: Sun Aug 13, 2017 8:24 am 
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ETHER best way to FCUK an engine your problem will be crank postion sensor .


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 Post subject: Re: 928 S2 won't start
PostPosted: Sun Aug 13, 2017 10:51 am 
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Thank you for the diagnosis sand help everyone, this is something that I thought it could be. I will order up a new sensor and go from there.


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 Post subject: Re: 928 S2 won't start
PostPosted: Sun Aug 13, 2017 11:26 am 
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Instead of throwing parts at the problem, your best bet of finding solution it to work logically through possibilities.

I agree the crank position sensor is a likely cause, but it can be awkward to replace so you should first check whether you have spark or fuel problem. These are things you can test with very little/if any disassembly.

A little inductive spark tester will show you immediately if HT is on the plug leads, or you can pull out a plug lead and insert gas discharge type spark check.

You really need a fuel pressure gauge to check fuelling (there is handy test point for it at end of fuel rail), but again you can check the electrical side of things by disconnecting one of injectors and plugging in a 'noid' tester light, to verify whether the injectors are being pulsed correctly and their wiring loom is OK.

With everything turned off, you can still bridge fuel pump relay with short jumper lead to listen for whether fuel pump is running (if the crank sensor is faulty, the fuel pump relay will not be energised).

Fuel pump relay is possible failure as it carries most current, but it is unlikely to fail in intermittent way you describe.

PS it seems quite a coincidence that this should suddenly happen with new owner!

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 Post subject: Re: 928 S2 won't start
PostPosted: Sun Aug 13, 2017 12:56 pm 
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I have had it looked at today by a (qualified) friend.. after a few tests (much same things tested as described above) it's an electrical problem. We are in agreement the next thing to look at is the crank sensor.
Thanks folks, I will keep this thread updated.


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 Post subject: Re: 928 S2 won't start
PostPosted: Sun Aug 13, 2017 4:38 pm 
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stratfordshark wrote:

PS it seems quite a coincidence that this should suddenly happen with new owner!


Yes..me too! However, I'm thinking if he knew about it (random cut out, non-starter) how would he have had the confidence to put the car out the door? I mean, it may not have started when it was collected or broke down on the test drive etc. Maybe it's been an intermittnet problem and it has just got worse, but as you say, strange to have happened the day after I buy the car. I guess i'll never know.

Looking through the history file, 4 years ago it broke down, was recovered and the crank sensor replaced due to non start issue. I guess this is the same problem again..it says.. "Investigate non starting. Found crank sensor corroded. Supply and fit new sensor. Carry out repair to wiring of crank sensor" Parts £124. labour £150. Bourne Performance Ltd, Kent.

With some luck a new crank sensor will do the job. If a new one was fitted 4 years ago hopefully it should come out easier than a very old one.


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 Post subject: Re: 928 S2 won't start
PostPosted: Sun Aug 13, 2017 8:46 pm 
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Just a thought, before you go heaving the sender out, check its output. Do you have a DVM with a hertz function? Or just use the ac volts function, you should get some sort of signal. If not, try ohms, a bit more dubious as the impedance of the coil is huge, mine was open circuit but the vandal known as the PO had glued it in to the casing. It took me four days of fiddling about to extract the broken bits, as otherwise it was a case of separating engine from transmission. For what it's worth, the best way ended up using a tiny hole saw which came with a reversing sensor kit and burrowing into the plastic and copper then extracting the core magnet in sections as I managed to break it up, finally I hoovered up the shards and cast a length of studding in the casing with Araldite then setting the stud up with a tubular spacer(box spanner) and a large washer and nut and dragging the case out. It fought to the last few mm. I hope yours, if it needs to come out, isn't such a struggle. Beggars belief.


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 Post subject: Re: 928 S2 won't start
PostPosted: Sun Aug 13, 2017 10:07 pm 
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Interesting comment in the service records on wiring repair - with the crank sensor it's more common for the connector to fail (it crumbles, just like the very similar knock sensor connectors) than the part which is just a coil.

If you are going to install a new CPS, good use of time waiting for the new part is to keep applying good penetrant to the CPS where it sits at top of bell housing, and let it soak for a few days.

May be too pessimistic as some owners report extracting the CPS has never been a particular problem. Mine is fine but I have a spare waiting, and am thinking of installing it just out of curiosity to see how easily the original comes out!

If I did suspect CPS failure, I am regretting recently selling a very nice oscilloscope I had (I also mess about with radio/electronics). The WSM has a section explaining where to connect 'scope to the EZK plug while cranking, and what the pulse should look like in shape and amplitude.

But I would still recommend you check the simple/more common failure modes things first. For a 928 that means...

Have you checked/changed the 3 critical relays (fuel pump, LH, EZK)? Apart from the EZK they are standard 53 relays, so you can just replace each relay with a good one and see if she starts. The EZK relay can be replaced by a 53 relay too, but the original relay incorporates a handy fuse tester.

Have you checked condition of the 14 pin plug next to the jump post? Very common to find insulation/disintegration problems here where critical circuits are plugged in.

Have you cleaned and checked that the connections are tight for the small wires at the battery positive terminal? They power the pump and LH.

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 Post subject: Re: 928 S2 won't start
PostPosted: Wed Aug 16, 2017 10:52 pm 
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stratfordshark wrote:

Have you cleaned and checked that the connections are tight for the small wires at the battery positive terminal? They power the pump and LH.


Correct, we have a winner.. 1st prize to stratfordshark!

This was the problem, wiring at the battery terminal. The car is now repaired. This should have been checked sooner but I was unable to get into the boot which has also been sorted now. Thank you everyone for your contribution.


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 Post subject: Re: 928 S2 won't start
PostPosted: Wed Aug 16, 2017 11:28 pm 
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Pleased that the car is running properly, well done Adrain. :)

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 Post subject: Re: 928 S2 won't start
PostPosted: Thu Aug 17, 2017 9:32 am 
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Thanks Sean.

Shows value of good service records - username had info new CPS was fitted a few years ago. Originals are suspects for non-start/cutting out, but a new one is good for another twenty years.

Adrian

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