Porsche Enthusiasts Club Forum

Hi guys,

As a lifelong Porsche fan, I recently decided to start my foray into classic Porsche ownership with a lovely black '87 924S.

The previous owner had the car for the past 15 years, however the last few years of its life had been spent mostly stationary (even though it had had yearly MOT's)

The car has just been through an MOT before I bought it, having had a fair bit of work completed (seized brakes/corroded fuel lines etc) and now drives very well indeed (although I suspect the engine mounts to be worn out)

One of the main problems that it does have however is that the engine turns over but does not start without bypassing the fuse box and connecting the battery straight to the coil (then disconnecting it to turn off the engine!) The mechanic that performed the MOT said that he could fix it by installing a separate relay and bypassing the relay box altogether. Given that someone has already tried wiring the cooling fan separately (leaving it disconnected with bare ends in the engine bay - another problem to fix!) this is a solution that I didn't like the sound of as I'd prefer to trace the actual cause of the fault and repair that instead!

I've searched though various forums and dug out this circuit diagram to help trace the fault. So far I've checked can cleaned the connections on the coil itself (also tested that there is no 12V on crank from term 15) and also cleaned out the 9 pole connector that houses the green wire that runs along the firewall, but have yet to take the fuse box off. (none of the fuses are blown on either board) Due to the fact that the car does start and run with 12V connected directly to the coil, does this rule out any issues with the speed and reference sensors? (even though there appears to be no tacho bounce) On the diagram, the wire that supplies power on ignition appears to the the black lead from A12 on the fuse box to terminal 15 on the coil, should this be the first place to start looking on the fuse box?



Whilst my mechanical knowledge is limited, I intend on using the car to gain experience and learn a bit more that way - passing it over to a trusted specialist for work that is way out of my depth!

Any pointers at this stage would be greatly appreciated!

Cheers,

Jonny

Have you tried a replacement DME relay? - this is often the cause of 944 starting issues.

There are 2 circuits in the relay IIRC, one which switches power to the DME (which in turn powers the coil), the other to the fuel pump. If the coil circuit has failed, you will also see no tacho bounce even if the sensors are ok. New parts are about £25 so worth a go.

Hope this helps...

Is the 924 the same as 944 with DME relay

If your car is a 924S with the 2.5 engine then yes it should be.

My port of call would also be the DME relay trick. Before going out to buy one you can try the wire jumper trick as described on Clark's Garage. If the car starts with this then it is almost certainly the DME relay which is at fault.

I actually just found a spare DME relay in the passenger door pocket which may suggest that it has been tried before.

I'll try the spare and also the jumper trick and let you know how I get on.

Cheers,

Jonny

... not necessarily! many of us have learnt to have a spare DME relay in the glove box as a get you home precaution, its a standard thing.... It does not suggest previous problems just a sensible previous owner.

Just don't want you to jump to conclusions

Cheers Rob

So I finally got round to trying out your suggestions, but the 924 had other ideas! (which should probably belong in another thread)

On starting it up (using the battery connected directly to the coil), I got out of the drivers seat to find oil spewing out of the engine onto the car in front!

At first glance, it seems as though leak is coming from the oil filter as it has become loose. For the very limited time I have enjoyed driving the car (3 full journeys so far!), I had not noticed anything of concern on the oil pressure gauge from what I had read. Pressure registers 4-5 bar on ignition, then drops to 1-2 bar when idle and 4-5 bar cruising at motorway speeds.

To compound the problem, I have also noticed a small build up of light brown milkshake-like sludge in the coolant expansion tank. (Although there is no noticeable coolant in the oil so far). After reading though various articles and posts online, it seems that it is most likely one of two common problems, a blown head gasket or a more likely a faulty seal in the oil cooler assembly.

As posted previously - after purchasing the car, I discovered the disconnected radiator fan which has meant that the engine temperature has crept into the red twice while stuck in traffic (although it is fine when in motion), so I'm hoping that hasn't caused the former of the problems!

Either way, since I'm going to have to change the oil and filter anyway, does it seem sensible that I should start with replacing the oil cooler seals and flush the coolant?

One thing that I do lack is the special tool for aligning the oil pressure sensor correctly so if anyone has a contact where I can get hold of one in the UK, that'd be really helpful! Also a recommended OPC for the parts (JMG? - I'm based in London though) It's an '87 model but I've not yet been able to get under the car and pull the existing OPRV out to double check the type, but I'll do it tonight.

Looking on the bright side, being able to work on the car is one of the reasons that I bought it - I just wasn't counting on being elbows deep in oil quite this soon!

Cheers!

baptism of fire lol, in at the deep end

Thought I'd resurrect this thread as I've still not been able to fix this issue due to time and other problems occurring on the way!

Just to recap, the engine will only turn over but won't fire unless the battery is connected directly to the coil. When it is directly connected, the engine starts and runs fine, although the electrics have a bit of a fit before you start the engine - certain instrument lights illuminate and the turn signal relay goes crazy - so something I'd prefer not to make a habit of doing! I've tried two different DME relays and the issue remains using both.

So...armed with a Dremel, contact cleaner and dielectric grease, I worked at all the ground points on the car, replaced the old battery,replaced the fuse board and cleaned all the connections on the loom that fed the fuse/relay board. Pretty laborious task but one that I thought would be worthwhile due to various other electrical niggles.

When I did take the original fuse board away from its mounts, the first thing noticed was the thin brown (ground?) DME relay wire hanging loose! I plugged it back into the DME relay mount, fired it up again, but still nothing.

So having cleaned everything up and checking continuity on the cable that runs down the loom from the fuse board (A12) to the coil -which appears to be fine, I'm now back to the drawing board.

I'm trying to make sense of the electrical schematics which lead me to suspect something to do with the DME itself or the alarm/immobiliser? I have checked the resistance of the speed and ref sensors (both around 950 Ohms) but as the engine does run with the coil connected, would this not rule out an issue there?

There is an immobiliser (factory I think) whereby you insert the long jack plug into the dash) and an alarm siren in the engine bay. There are also some knarly loose bare cable ends poking through the O/S firewall (pictured) so as soon as I get chance this weekend, I'll trace that back.

Any pointers again would be greatly appreciated!







Thanks

My 924 had an after market alarm fitted that was yanked out but left stray wires much like you have. That gnarly wire might be the one that goes to a switch that should be near the bonnet catch - that's where mine was placed - if you don't have that switch in your engine bay that might be contributing to the issue and not disabling the alarm. (By switch I mean one of those little on/off switches you get in the glove box that registers if the door is open or closed so the light switches on/off).

pm Rhett, he will be able to give you some wiring help I'm sure as he's an electrical genius!

I'll definitely take a look at that this weekend then (and contact Rhett) Thanks for the tip!

btw - your blogs are a great read. Definitely influenced the decision to go ahead and buy mine!

Hi Jonny, I saw my name mentioned so I thought I would drop in...

The alarm you have fitted certainly looks like an after-market device, so it is definitely in the frame as being the culprit here. That gnarly wire needs to be traced back, but probably only goes directly to the alarm unit, so it could be a switch wire as Steve mentioned. I also noticed from the photos that the wiring harness exiting the firewall and going down the drivers side engine bay looks like it has been taped up. This is probably where the alarm installer has taken the +12V feed that goes to the coil and sent it though a relay inside the alarm. You mentioned that you checked continuity from the fuseboard to the coil and it was good, I would expect that when the ignition is not on as the relay would normally be closed. However, when the ignition is switched on and the alarm is energised, this relay could open and prevent the coil supply from making it to the coil - thus stopping anyone starting the car. When I started on my 944S restoration the first thing I did was remove all traces of several after-market alarm and phone systems - getting it back to stock was a good idea. I found that the alarm in my car had been wired in this fashion, so a simple strip out of the wires and a joining them back together (bypassing the alarm relay) sorted the problem.

You mentioned that if you put +12V directly onto the coil, the car starts, so your crank sensors are fine and your DME relay is operating fine too. The weird lights coming on could simply be the alarm is wired into the sidelight or indicator circuit to provide an indication of arm/disarm or alarm conditions. I really think removing that alarm will help sort the problem..

Let me know how you get on.

Oh, and good work on the contact cleaning - nice and shiny

Well Rhett, deLux, I owe you fellas a beer!

Pulled out the old immobiliser (a rather messy install of an old AutoJack 101), reconnected the wires where they had been spliced and hey presto!...car starts without any hesitation or 'auxilary cabling' for the first time since I have owned her! Absolutely chuffed to bits!

Really appreciate your advice guys, you're certainly a very knowledgable bunch and its reassuring to know theres help available when you get stuck! Once I've cleaned it all up, I'll post a pic.

Next job will be to flush the cooling system as there is some oil residue in there from when the oil cooler seals went. I've bought a new radiator fan switch (and thermostat while I was at it) as the fan isn't switching on by itself...dealt with by the PO by installing additional wires connected directly to the battery via a separate switch! Also need to either have a go at cleaning up or buying another expansion tank as the PO thought it's be a good idea to paint it with thick black paint! (obviously)

Thanks again!

Good one! Well done.
I had the Quantum,s imobiliser removed when it left me stranded.
My 944 would sometimes fail to light up so I had that aftermarket imobiliser removed as well.

I hate aliens in the wiring.

Hi Jonny, glad to be of assistance and it is great news that you sorted the problem .

I am an electronics engineer by trade and like Pink Piggy I too hate aliens in the wiring! My motto has always been, it was designed to work, it did work, so find out why it is not working now...don't fudge it, bypass it, modify it, bodge it....just fix it! Poor third-party wiring in cars has caused so much grief it is great to get back to factory whenever possible.

Fitting a new expansion tank will brighten up your engine bay no end, but I have heard rumours that they are becoming rather expensive from the OPC. I paid about £90 for mine a year or so ago.


However, if you need an 'alright' used one I think I still have a couple (will have to look in the depths of garage!). They haven't been contaminated with oil, but they do have the usual discoloration and scale build up. If you want one, and I can find one - just pay the postage and I can send one out to you.

Here's how one of them looked...


All the best.