944 S2 - Crank but No start diagnosis help please

[Brummiebluenose]

Having had the car off the road for a bit she started briefly (reluctantly and after I changed the DME Relay) and then wouldn't start again - annoyingly on my drive but downhill from my garage.

Engine Cranks but no sign of ignition. I've been through some other threads across various forums, doesn't seem like the coil is getting a 12V supply.

Immobiliser bypassed years ago before I purchased the car.
DME Relay replaced - no change
DME Relay bypassed with jumper lead - no change
No sign of spark
Ignition coil resistance (primary and secondary) correct.
Ignition coil supply no voltage
Fuses test good
Doesn't look like there is tacho bounce.
Speed sensor (only one sensor on an S2) - replaced - no change.

I looked to do a check on pins 47,48 of the DME but the connections seem to be different to the diagrams I have seen (some look unused where on the diagram they have a use) - picture of mine attached.

Is there a different Pin Out diagram that matches what I have?

It feels like the DME is either not reading the speed sensor output or is not sending the signal to energise the coil - is there a wire that might be disconnected under the fuse box that could explain why it started once and then died whilst being moved (I thought I'd just stalled it).

Any help would be much appreciated. If the rain ever eases off (wouldn't be an issue if it was stuck in my garage!) my next step would be to jumper 2 Speed sensor pins feeding DME from the connector although without knowing exactly what pins at the DME end the best I can hope for is to confirm circuit continuity.

 

[VanhireBoys]

If there is no 12v supply to the coil Id look at the ignition switch - I had a similar issue where my coil was breaking down and causing the ignition key to heat up - Now mine is an 87 Turbo but its likely the same idea ... Worth a check anyway

 

[Brummiebluenose]

Thanks - will try and have a look - had initially ruled out the ignition switch as the engine is cranking and the volt needle moves etc when it goes to the position. Foolishly what I haven't checked is that there is 12v going through the ignition fuse. The rain has now stopped but it is dark - so one for Friday.

 

[VanhireBoys]

I disconnected the + side of the coil as this is directly connected to the ignition switch itself - Well it is on mine - If you are getting 12v down from the ignition switch then look at the coil itself - Hard to get motivated to go out in the rain but hopefully you you will get to the bottom of it

 

[scam75]

Clark's Garage is always helpful, guy knew his onions with 944's. No spark trouble shooting here:

Ignition System Troubleshooting

 

[Brummiebluenose]

So I've been trying some more things and rechecking measurement.

Still crank, no start - no spark. We are getting fuel.
At the input to the coil black wire 12v when key is in position 2. Green zero (measured disconnected from the coil)
Ignition coil resistence measured and within tolerance.

Dizzy cap and rotor replaced about 6 months ago as part of a bit of an ignition overhaul as she was hesitating and running rich (injectors also cleaned and AFM refurbished)
Crank sensor replaced.
Ignition control unit replaced.
Alram by passed Pelican Parts Forum. Word of warning if your alarm starts with a 928 don't use Clarks Garage instructions as bridging pins 1 and 4 on the newer version will result in smoke and possibly fire.
DME relay bridged
Alarm Bridge bridged (pins 4 and 5 - part of the bypass procedure).
Ignition relay swapped out with another one that is the same.


All to no effect.

I'm now confident that the ignition switch works although thank you Vanhire Boys as it did make me recheck the black wire which somehow Id measured badly previously.

Whilst looking for info on a different car that I have which is also unwell I stumbled across the "Operation Charm" which has the wiring diagrams (and more) which indicate that the green wire goes to the ICU (left hand behind the headlight) - which I've changed for a new Bosch part. Is it normal for this to be 0 on new cars.

Next step will be a continuity test on the green wire - annoyingly its a bit of a big to get to the clip on the ICU without removing its heatsink.

If anyone knows how the Ignition Control Unit/Module functions that would help

 

[Brummiebluenose]

So I've been trying some more things and rechecking measurement.

Still crank, no start - no spark. We are getting fuel.
At the input to the coil black wire 12v when key is in position 2. Green zero (measured disconnected from the coil)
Ignition coil resistence measured and within tolerance.

Dizzy cap and rotor replaced about 6 months ago as part of a bit of an ignition overhaul as she was hesitating and running rich (injectors also cleaned and AFM refurbished)
Crank sensor replaced.
Ignition control unit replaced.
Alram by passed Pelican Parts Forum. Word of warning if your alarm starts with a 928 don't use Clarks Garage instructions as bridging pins 1 and 4 on the newer version will result in smoke and possibly fire.
DME relay bridged
Alarm Bridge bridged (pins 4 and 5 - part of the bypass procedure).
Ignition relay swapped out with another one that is the same.


All to no effect.

I'm now confident that the ignition switch works although thank you Vanhire Boys as it did make me recheck the black wire which somehow Id measured badly previously.

Whilst looking for info on a different car that I have which is also unwell I stumbled across the "Operation Charm" which has the wiring diagrams (and more) which indicate that the green wire goes to the ICU (left hand behind the headlight) - which I've changed for a new Bosch part. Is it normal for this to be 0 on new cars.

Next step will be a continuity test on the green wire - annoyingly its a bit of a big to get to the clip on the ICU without removing its heatsink.

If anyone knows how the Ignition Control Unit/Module functions that would help

Green wire from coil checked - 13v at Ignition module (battery has been on charge in between start tests) - ground checked by putting voltmeter across pins 1 and 2 - still good voltage. Ignition module ground cleaned for good measure whilst I was in the area.

Pin 1 DME to Ignition module - continuity check OK
Power to DME from pins 18 and 37 both 12v (37 when ignition at pos 2)
Pin 47/48 crank sensor at DME - approx. 150Hz approx. 4.8-5.0v AC (both measured on multimeter). The value at pin 18 dropped to about 10V when headlights were on.
Alarm re-instated Pin 1-3 12v measured (which is what you'd expect if it was bridged)
DME from another 1989 S2 tried - no change

I've missed something but I don't know what. Is it back to rechecking spark or maybe making a 12v light to see if coil is being pulsed?

Any further ideas appreciated

 

[VanhireBoys]

I am at a loss as well - You have gone through it all

I am scraping the bottom of the barrel but here goes

Get a H7 bulb and ground it - Take the black wire off the coil on the + side, connect to the bulb and switch on the ignition - This loads the circuit back to the ignition switch - Your coil is directly wired to the ignition switch just like mine. You might measure 12v on the black wire but this is an unloaded measurement. The halogen bulb will root out any bad connection.

If the above test is good then try another coil if you have access to one

Crank Sensor set correctly?

You might have fuel in the lines but is the fuel pump running while you crank? If it is then this rules the crank sensor out

I hate to say this and it goes against my principles but if you have access to another known working ECU you can definitively rule it either in or out - The ECUs are all 35 years old now and with this age joints on the circuit board can be dry and cause all sorts of nastiness - A 10 year old car I would discount this theory but its a possibility - A remote one but something to check.

A problem like this drains your enthusiasm but keep the chin up and you will get to the bottom of it

 

[TTM]

Try another battery.

 

[dlknight]

Are you sure this isn't an immobiliser issue? I know you said you've bypassed it but are you positive it doesn't have an aftermarket one. These cars are several decades old and in all likelihood most of them have had aftermarket immobilisers and/or alarms fitted by now for insurance reasons, e.g. my car has a Laserline aftermarket unit.

 

[Brummiebluenose]

Try another battery.

I was thinking that sadly after a few days waiting - brand new battery on - no change.

Next step rig up test lights for injetors - after I've finished sorting out the other half's daily driver.

 

[Brummiebluenose]

Are you sure this isn't an immobiliser issue? I know you said you've bypassed it but are you positive it doesn't have an aftermarket one. These cars are several decades old and in all likelihood most of them have had aftermarket immobilisers and/or alarms fitted by now for insurance reasons, e.g. my car has a Laserline aftermarket unit.

I'm pretty sure it isn't an immobiliser - I've had the car for 18 months and its not done this before. The original was bypassed when I got it and I think had been for some time. - I suppose what I was doing was bypassing a bypass (never a sound basis) I've been down in the footwell to check if something has come loose - . Did find a random blade fuse but can't see anything that may have come out of.

If it's dry tomorrow I'll be back there again. The fact that it happened when the car was out of its garage just adds insult to injury.

 

[Brummiebluenose]

I am at a loss as well - You have gone through it all

I am scraping the bottom of the barrel but here goes

Get a H7 bulb and ground it - Take the black wire off the coil on the + side, connect to the bulb and switch on the ignition - This loads the circuit back to the ignition switch - Your coil is directly wired to the ignition switch just like mine. You might measure 12v on the black wire but this is an unloaded measurement. The halogen bulb will root out any bad connection.

If the above test is good then try another coil if you have access to one

Crank Sensor set correctly?

You might have fuel in the lines but is the fuel pump running while you crank? If it is then this rules the crank sensor out

I hate to say this and it goes against my principles but if you have access to another known working ECU you can definitively rule it either in or out - The ECUs are all 35 years old now and with this age joints on the circuit board can be dry and cause all sorts of nastiness - A 10 year old car I would discount this theory but its a possibility - A remote one but something to check.

A problem like this drains your enthusiasm but keep the chin up and you will get to the bottom of it

As it happens I'm about to have a spare H7 since my daily blew a bulb

 

[dlknight]

I'm pretty sure it isn't an immobiliser - I've had the car for 18 months and its not done this before. The original was bypassed when I got it and I think had been for some time. - I suppose what I was doing was bypassing a bypass (never a sound basis) I've been down in the footwell to check if something has come loose - . Did find a random blade fuse but can't see anything that may have come out of.

If it's dry tomorrow I'll be back there again. The fact that it happened when the car was out of its garage just adds insult to injury.

I had a similar issue with my turbo when I was trying to start it for the first time after the rebuild, no spark at the distributor or rotor cap.

I felt quite stupid when I noticed the reference sensor plug was loose, worth double checking.

As you said above the ECU won't activate the coil unless it sees input from the reference sensor, so that is likely your problem.

Could be that the reference sensor connector is damaged.

I thought there was a way of testing the reference sensor (might be on clarks garage) but it probably involves a scope.

Have you checked for spark at the coil by plugging a spark plug into the short cable?

I think you are back to one of these as the culprit:

DME - you say you've tried a unit from another S2, was this a running / driving S2?
Bad Coil
Bad signal from reference sensor

https://www.clarks-garage.com/shop-manual/ign-04.htm

Help diagnosing no spark - Rennlist - Porsche Discussion Forums

924/931/944/951/968 Forum - Help diagnosing no spark - Hi, I'm having a no spark issue on my '83 944. There seems to be no power getting through the ignition coil. I have looked through Clark's garage quite a bit and followed the troubleshooting guides on there, but i've met some roadblocks and...

rennlist.com

 

[Brummiebluenose]

Thanks for taking the time to provide the detail.

I've been through Clarke's and also the SAAB DME pin test guide. The crank sensor is providing voltage and I've measured the speed of rotation using the frequency function on my multimeter (saves getting a small oscilloscope (although it is almost Christmas) at the DME socket so chased it back all the way into the footwell. Both check out with the new sensor. I may put the old sensor back in having cleaned it just to minimise number of things that I've changed since I last knew it to be working.

I'm told the DME that I tried is good and also came from an 89 S2 - haven't got access to another S2 to stick mine in which would be the ultimate test (unless there is someone out there in Kent that doesn't mind).

I couldn't get a spark from the coil direct which is what took me back down chasing the ignition route - may re-check if the weather is OK as I am questioning myself and it was the end of a day when I checked. I'm happy that it is getting 12v when the ignition is on. The dizzy and rotor were replaced a few months ago so I don't think it is them. Have chased contiuity of the ignition circuit for the coil back through the Ignition Module and to the DME - again it looks fine. If push comes to shove I'll fire off another round from the parts cannon and change the coil. I see a lot of it as good practice on an old car anyway.

Annoyingly this is all getting in the way of the preventative radiator hose set replacement that I had planned to do and have the parts sitting in the back of my car.

If I solve it then I'll put a consilidated S2 no start fault finding guide in the Tech section to bring together the various information sources as there is a lot that Clarke's doesn't cover for the S2.

 

[Brummiebluenose]

She starts!!!

But is this the end of the saga? Maybe - may also be the start of another problem set.

So here we go - standby for an anti-climax.

New Bosch coil recieved and fitted (terminals and coil are smaller - Brazil manufactured). - No start - no spark

Fuse panel removed, stared at angrily - replaced - No start.

Then (And what some say I should have done earlier) - I went back into the footwell and wiggled cables/remade connectors like a man possessed.

Start. Tappetty and also a bit of a louder noise - but started.

Put old cam sensor back in - Start - same noise.

Secured coil, put headlight motor back. Start - same knocking noise near top that wasn't there before this saga.

Now I think she needs to go for a local run tomorrrow (can't afford the time for a breakdown today) as its been a few months - voltage from alternator also looks a bit high. Hopefully the noise will abate or whatever tool I've left behind will fall out (too big to fit in bell housing I hope). There is a small torch I can't find which may be there (I'm normally a stickler for tool control).

Just got to carefully put all the wires away in the footwell.

Thanks to everyone who has helped - I'll work on a No Start guide over the next few days (checking connections will be in there).

Hopefully it will all be over by Christmas

Trev

 

[scam75]

Well, that's mostly good news! The cam buckets will be noisy for maybe 5 to 10 mins till they fill up, hopefully that is your only noise.

I once dropped an elbow socket into the bell housing whilst replacing the small water hose directly above it. Amazingly it landed, and sat very precariously, on top of the flywheel. Got 2 extended magnet stick things and had to play a real life game of operation whilst sweating buckets but it was a game I won mercifully. Many swear words of all descriptions were used.

I got a new Bosch coil as well, and it has 2 x 8mm terminals instead of 1 x 8mm and 1 x 10mm like the old one. What a stupid idea. I just used the existing (but now oversize) ring terminal and a fresh 8mm bolt to tighten it down. It's been fine. The new coil has also been on a diet and needs a gastric band so it fits the clamp, came with one in the box.

My alternator puts out about 14.2v on start up. Put a mulitmeter across the battery and see what the voltage actually is. You can then (if needed) calibrate your dash gauge to match your actual voltage. There is small resistor pot on the back of the gauge that you can turn with a small flat head screwdriver. You may be getting different voltage to the cluster now if any weak or dodgy connections are now fixed.

Lastly, enjoy your breakdown, at least this time it will be the car and not you having a breakdown!

Cheers

Stuart

 

[Brummiebluenose]

Lastly, enjoy your breakdown, at least this time it will be the car and not you having a breakdown!

Cheers

Stuart

Didn't know about that pot. Very handy as I ended up going back to the car, she sounded better and measuring at the battery was about 13.8 which will do nicely even though the dash said higher. Had the cluster out only a few months ago refoiling the reflectors for the dash lights.

Agree about the coil, since the red wire is already black!

Now back to the planned maintenance.

Thanks for helping keep me sane Stuart