Marty McFly

Hi

Further to an earlier post about cranking but no starting, I've narrowed down the symptoms.
Definitely fuel (new relay)
No spark at plug
No power at injectors

The roadside recovery guy did some diagnostics, and said he thought it was the crankshaft position sensor which had failed. He wasn't a Porsche specialist, but does this sound likely ?
Also just before the problens started, I was getting constant 'Toothed Belt Change' messages, although the belt was checked out by the Porsche garage and found to be fine (and fairly new).

Basically, does a crankshaft sensor failure sound like a likely cause of the problem ?

Thanks

Martyn

928GT 1989 Slate Grey Metallic

John Speake

Hi MArtin,

Your car has built in diagnostics. Try and get a Bosch Hammer on it, it will find the fault quickly.

Just as a first check, make sure that T belt is OK. Take of one of the long hoses going to the air filter, and look through the small hole in the timing cover that it covered. You should be able to see the belt turning.

The problem could easily be the flywheel sensor, the Bosch Hammer would check that one out, or you can put an oscilloscope on it.

Marty McFly

Thanks for the quick reply

Fortunately it seems I have somewhere nearby who can read the brain, so I'll take it to them and see what happens.

M

Drewster67

MArty -

The reference sensor or speed sensor is located on the top of the bell housing. You need to lift the air box off for access. On my s2, it is a metal sleeve which slides down into the bell housing and is held in place with an allen bolt. On the the other end it has a three pin connection that has it's on bracket.

If it has failed, you can crank it all you want, but it won't start - Trust me I know.

0261210003 (after market part number but it's good for cross referencing) is the part number - Devek has them stock for 75.00 - Call and speak to Susan Thomas. Very nice, very pleasant sounding LAdy - Price may vary according to year.

Simple to remove and install - before you remove youir brain, make sure the three pin connection is in place.

Good Luck

dr bob

I often wonder how many "no start" mysteries are related to the basic Porsche alarm system, combined with my lack of serious knowledge of how it works and what it does to disable the car.

If I accidentally trip the alarm, the car won't start. If I close the doors, cycle the key switch in the drivers door through a couple open/close cycles Using The Longer Alarm Key the car will start and drive just fine.


If you have an aftermarket alarm installed at some point, you are at the mercy of the creative mind and hands of the installer. The alarm on my Explorer, for instance, is designed to interrupt the starter signal. I decided to 'improve' on that by interrupting the fuel pump instead. Next owner will hear about it from me, but will he remember? Probably not.


Anyway, the dr's advice is to make sure the battery is well charged, and try the key in the door a few times on the off chance that you tripped the alarm and didn't know it. Takes a few seconds.


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WallyP

When I trip the alarm on either of my 928s, not only do I know it, but so does everyone else within 200 yards!

Marty McFly

Funny you should mention about the alarm, as I initially thought the problem was a new immobiliser I had had fitted.
After getting the supplier to remove it, the problem was still there though. Also they had removed the original immobiliser, so I don't think it can be that which is causing the problem.

M

dr bob

[quote]Originally posted by Marty McFly:
<strong>Funny you should mention about the alarm, as I initially thought the problem was a new immobiliser I had had fitted.
After getting the supplier to remove it, the problem was still there though. Also they had removed the original immobiliser, so I don't think it can be that which is causing the problem.

M</strong><hr></blockquote>

Funny you should mentin the immobiliser!

One of the basic diagnostic methods I like to teach is the one where you look at the list of things that you have changed since everything was last fine. Your immobiliser installation is definitely a candidate. It's obviously not the unit itself if it's been removed, but can easily be something mucked up during the original installation.

My first step at this point would be to contact the installer and get a very detailed lesson in what they did when they installed the unit, and what they did when they removed it. See what wires were cut, which were spliced, which were tapped into. Go look at the actial wires they worked on to confirm what they state. Too often alarm/stereo/cellphone installers just dive in and hook up to any wire that has 12 volts, and any wire that has 12 volts only with the key on. There are circuits that are supplied for that service, but the 'stab and spark' method remains popular for some reason.


Let us know what you discover.

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Marty McFly

When I was buried in the footwell deciding whether to remove the brain for testing, my other half turned the car over, and it *almost* caught - which means there was a definite spark at least momentarily. Now I've tried pushing in all the connectors and wiggling / replacing the relays, but I'm wondering whether it could possibly be a loose joint or connection on the back of the fuseboard ?!?
Although the problem became worse after immobiliser installation, it did happen a couple of times before, but was fixed by the lock/unlock doors trick. It could be that on installation of the new unit, the fitters nudged a connection which was already on it's way out.
I'll have a poke around the underside of the board tomorrow and see what I come up with

Thanks for all your help so far !

Marty

Marty McFly

Thanks for all your suggestions above, but things have now got a bit odd! I haven't had chance to do anything over the holiday period, but yesterday I just had the urge to turn the key again - lo and behold the car started first time. I left it for 20 minutes and tried again - it started once more. I tried again this morning, and again no problem.
Any idea why it should not work for 6 weeks no matter what, and now seems fine ? In a way it's worse, as I don't dare drive it anywhere in case I get stranded !!!

Thanks in advance

Martyn

Old & New

Part it out

Thom1

Hi Marty,

Check the spare tire area, and all engine grounds.

My most recent no start sound scare was due to a loose connector in the spare compartment forward of the black plastic cover in the upper forward nook. I went in there to polish up the ground (brown wires go to ground there). A mechanic did not fully push together the connector.

An earlier no start problem was due to a loose connection at a battery terminal back there. The mechanic had not tightened down the nut that secures wire connectors to the battery cable terminal connector. I have also heard that battery terminal corrosion will cause start problems.

There are more grounds to clean in the engine compartment area. See earlier posts, or I can send you info.

There is also a hot start relay fix. I replaced my starter before I knew about this one. The problem rears its ugly head on hot summer road trips. However, I got some more hot start problems just driving around town. So. I installed the bosch relay, and got rid of the problem.

If you need more info. on any of the above, search the archives or let me know.
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Thom1

An afterthought,… when you check electrical connections, clean them, coat with dielectric grease to prevent corrosion, then make sure that connections are tightly secure.
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