924Board.org

Sy924 · Joined: 07 Jun 2008 Posts: 11 Location: Warwickshire

Hi Guys,

1988 924S not starting; there is:
- no 12v getting to the ignition coil
- 12v getting to the relay board where it meets pin #30 of the DME relay (so I'm guessing everything from the ignition key is good)

So any help appreciated as to what might be the most likely culprits next...ECU??

Thanks,

Simon

Sy924 · Joined: 07 Jun 2008 Posts: 11 Location: Warwickshire

Ok, so I screwed up the testing of current reaching the coil. There is actually:

9.5v between the ground and both coil terminals with the ignition in 'on' position
5v-6v between the ground and both coil terminals when the engine is cranked over.

I'm presuming 9.5v is not enough to generate a spark so problem could lie 'further back'. Battery seems good, engine turns over strong. Could bad earths cause this kind of drop? Any ideas out there?

bcblase · Joined: 23 Oct 2007 Posts: 574 Location: Winchester, VA

Check to see if you have 12v at the key cylinder.

The switch/contacts on the key cylinder have been known to go bad. New cylinder is a pretty easy fix.

Brad
_________________
1987 Porsche 924S - track toy
1986 Mercedes 190E 2.3-16v - autocross
2007 F-150 5.4L Lariat Supercrew - tow beast
1994 Volvo 850 Race Wagon - 24 Hours of Lemons Car
2001 BMW 325xi - daily driver

Sy924 · Joined: 07 Jun 2008 Posts: 11 Location: Warwickshire

Thanks for the reply; If it were the key/barrel, would I not get 0v at the socket of the DME relay? (I'm not, there's 12v there)

Further (better) diagnosis has revealed that with the ignition coil disconnected there is only 12v getting to the secondary coil, (0v getting to the primary).

This (green) cable leads back to the DME I think, so I'm hoping it's not that....

bcblase · Joined: 23 Oct 2007 Posts: 574 Location: Winchester, VA

DME relay = weak link.

DME relays are pretty likely culprits also - most of us keep a spare in the glove box.

Brad
_________________
1987 Porsche 924S - track toy
1986 Mercedes 190E 2.3-16v - autocross
2007 F-150 5.4L Lariat Supercrew - tow beast
1994 Volvo 850 Race Wagon - 24 Hours of Lemons Car
2001 BMW 325xi - daily driver

Matt924S · Posted: Thu Dec 16, 2010 5:01 am Post subject:

Yeah the DME is often the culprit. Also, check all leads and distributor - with all the wet and cold weather lately you might find there's some moisture in there.

Sorry to jump in here - but coincidentally I've also got a 1988 924S which isnt starting. I've tried 2 other DME relays (one from a working 924S) and that didnt change anything. I'm getting a spark (albeit a bit weak), definitely getting fuel, and the engine is turning turning but not starting.

I'm very interested to know what other things I might look out for. I just spent the afternoon totally stripping out the annoying immobiliser thatcham alarm and have sacrificed the central locking - as i thought this was the problem but still turning not starting.

I have a spare ECU - is it worth trying that out? if so - where would i find the ECU to swap it out?
_________________
1987 924S - Daily Driver (still needs engine mounts)
1988 924S - Driveway Decoration (needs new seats - can you help? Pref Linen colour)
1990 944S2 - Needs a new drivers seat - Linen leather - anyone got one?

bcblase · Joined: 23 Oct 2007 Posts: 574 Location: Winchester, VA

The DME or ECU (Motronic Brain) or whatever you want to call it is located under the driver's side dash right next to the steering column. It's a big metal box with thick cable connected to it. It is held in place with 4 screws.

If you are careful, and pry it apart, you will find two circuit boards connected by a ribbon cable.

I took mine apart a few years ago to install a performance chip (FR Wilk) and it still works fine, but I keep a spare on the shelf just in case.

Brad
_________________
1987 Porsche 924S - track toy
1986 Mercedes 190E 2.3-16v - autocross
2007 F-150 5.4L Lariat Supercrew - tow beast
1994 Volvo 850 Race Wagon - 24 Hours of Lemons Car
2001 BMW 325xi - daily driver

ole billy · Joined: 03 Feb 2006 Posts: 49 Location: Lafayette, CA

Have you looked at "Bennington Motor Sports.com" They have a good write up. Also check Speed and reference sensors with meter for resistance.

Happy New Year

Matt924S · Posted: Sun Jan 09, 2011 3:41 am Post subject:

Sy924 - Have you had any luck yet?

I feel like I have just wasted the whole day! I have spent the past couple of weeks seeking advice and reading 924board and others with most people pointing me to the speed and reference sensors. Today I swapped both sensors out with the working pair in my running 924s and still no joy. So I then swapped the ignition coil. Nothing. All the parts out of the non-starting car are now in the working car and they seem to be fine. Also tried the DME relay one last time for good measure. I even filled a jerry can with fuel just to rule out the obvious.

Anybody got any more ideas? I'm fortunate to have a working car to pull parts out of but I'm running out of ideas.

I did pull a really annoying alarm out of the car because someone else thought that might be the problem but it hasnt changed the fact the engine turns and turns but will not fire up.

I appear to be getting a very weak spark if at all now - and swapping the coil did nothing to improve this. (all the swaps were permanent by the way just to see the parts I'm swapping definitely work). I checked the terminals supplying the coil and I'm getting a good 15V there.

I'm on the verge of having a scrap metal dealer pick her up and take her away!!

Anyone please help!
_________________
1987 924S - Daily Driver (still needs engine mounts)
1988 924S - Driveway Decoration (needs new seats - can you help? Pref Linen colour)
1990 944S2 - Needs a new drivers seat - Linen leather - anyone got one?

joecitizennn · Joined: 12 Sep 2005 Posts: 2096 Location: no mans land

matt924s, what does your car do when you try to start it? What is its exact behavior and what have you ruled out?

joecitizennn · Joined: 12 Sep 2005 Posts: 2096 Location: no mans land

I went back and read all your posts on the car. I suppose you have tested the rail for fuel delivery? You can get scientific and test it for pressure and fuel volume output if you want, but as long as you know there is fuel pressure getting to it for sure, try swapping fuel pressure regulators and let us know what happens.

joecitizennn · Joined: 12 Sep 2005 Posts: 2096 Location: no mans land

Fyi, the fpr is a small round canister located at the rear of the fuel rail on the intake side.

bcblase · Joined: 23 Oct 2007 Posts: 574 Location: Winchester, VA

Swap the entire ECU/DME (computer box) from under the dash, if you haven't already tried it.

Brad
_________________
1987 Porsche 924S - track toy
1986 Mercedes 190E 2.3-16v - autocross
2007 F-150 5.4L Lariat Supercrew - tow beast
1994 Volvo 850 Race Wagon - 24 Hours of Lemons Car
2001 BMW 325xi - daily driver

Sy924 · Joined: 07 Jun 2008 Posts: 11 Location: Warwickshire

Hi Guys,

The reason for my delayed reply is that I've been going round in circles with this, but think I've finally found the problem. If it helps anyone else...

After some red herrings of faulty ignition coils and theories the immobiliser was unduly cutting in, the problem seems to be down to dodgy connections on the rear of the fuse box, probably due to corroded terminals.

There is some current getting to the coil (hence why my readings were confusing) but not enough. As soon as I traced a cable from the battery +ve direct to the +ve ignition coil terminal she fired up.

Wish I'd thought of doing this to start with as a temporary solution to get her moving; would've saved a load of grief!

This seems to explain the intermittent cause of the problem as well (you can twist the fusebox moulding and watch the voltage at the coil drop from 12v to 9v...).

Matt, if you're getting a spark then you've got a different problem to me; I had absolutely none whatsoever, but cracking open the injector fuel rail union showed good fuel pressure (well, filled up a baked bean can in 2 seconds, not very scientific, I know). Yours couldn't be a poor earth/ground problem could it? Try tracing a thick cable straight from the battery -ve to the engine block and starting it then?

Thanks for all the replies, and good luck if you have a similar problem!

Simon

Matt924S · Posted: Sat Jan 15, 2011 12:10 am Post subject:

Hi All,

I finally managed to get the car started this week. And before I tell you how, let me tell you what I tried - in order;

- Swap ECU with a spare I had been given with purchase of another car.
- Swap out DME relay with one spare, and another from my working car.
- Totally strip out and remove Alarm/Immobiliser (surprisingly VERY easy to do)
- Replace plugs
- Loostened nut before fuel rail and turned over engine - massive spray of fuel.
- Removed distributor cap and cleaned / scraped all points
- Removed rotor arm and cleaned point
- swap speed and reference sensors with pair out of working car (putting the sensors from faulty car into the working car which continued to run fine)
- Swapped the coil with one from working car (again, a permanent swap which did not affect the ability of the other car to continue running fine)
- Topped up fuel (rule out totally obvious and avoid embarressment)
- Removed all grounding point bolts, cleaned all contacts to as new, smooth sand down and treated with electric contact spray (included one in the boot, one on either side front next to headlights, one above fuse board) FYI the two on the front were particularly bad and its probably a job anyone should do as a preventative.
- Between all this spend countless hours reading posts, various forums, chatting to several mechanics, lost untold hours of sleep running through it in my head.
- Soldered together a 3 point jumper to test fuel pump via removing DME and reconfirmed fuel pump fine.
- Did various tests -including screwdriver test to check for spark. Issue by this point is definitely lack of spark.
- Checked for 12 volt power to ECU
- Screamed and threatened the car with talk of breakers yard
- Felt bad and washed the car (I'm a believer that cars respond to care and attention - i don't have any pets)
- Gave up and spent more time on forums
- Stumbled on a yahoo-answers post from someone with same car and problem and an answer talked about things I had already done - DME, Fuel, ECU.... EUREKA!! ECU! I swapped the ECU with one I had not tested as working!
- Left work early, installed original ECU. Insert Key and turn, ITS ALIVE!!!

Sure I could have told you that in one line but I could have used a post like this so if anything I've written this for my past and future self. I was absolutely blind to the simple solution that was always going to be the case because I hadn't kept track of my progress. It's also worth mentioning that the car runs far better thanks to the many red herrings (thank you Sy924) that I tried out along the way.
_________________
1987 924S - Daily Driver (still needs engine mounts)
1988 924S - Driveway Decoration (needs new seats - can you help? Pref Linen colour)
1990 944S2 - Needs a new drivers seat - Linen leather - anyone got one?