Help It Won't Start !!!!

[zola1]

Hello Jim when i was round helping my friend with it he says the sensors are fine.

So looking towards the ECU then

hi,

Here is a simple test to see what is happening to the coil circuit,,,

Disconnect the wires from both sides of the HT coil, TERM 15 (usually a Black wire +12v ign feed to coil) & TERM 1(usually a Green wire this is pulled low then paused then low again, by the ECU/Amp to give mutual induction thus HT from the coil windings,,, ( leave the king lead in the coil tower)......Put a 21watt (indicator bulb) across the wires that you have removed from the coil.

Carefully insulate the connections you make, get some one to crank over the engine and observe the bulb........as you have said you have no HT, almost certainly the bulb will NOT light at all (please follow the instructions further down on continuity test of the wiring)
if it comes on and stays BRIGHT during cranking this shows a short circuit on the Green wire to GND this will result in a momentary production of HT (WHEN YOU TURN ON THE IGN).... then NO more as the coil is not being sw'd on and off which it requireS to give HT.

try this site for ALL motronic info ...

http://www.frwilk.com/944dme


here is pin out of A 911 ECU

before you condem ECU do a Point to Point continuity test on the wiring

motronic pin out.jpg

Here is a pic of a 911 ECU,

911 ECU PIC.jpg

is your ECU the same part no ?

any probs feel free to ask


Jim,

Are the ign drivers inside the Motronic on this model ? i know they are on my 87myr 944 2.5n/a, i'm not sure on a 911 !, they may have a external ign amp !!

Not sure, I think this era run very similar management to 944s. But I think the earlier cars run electronic ignition via a separate module & mechanical ignition. Then they ran DME 944 type system, in which case the ignition/coil drivers are internal.

This is the 944 motronic from the factory wiring diags, the coil is sw'd internal see GR WIRE pin 1 of the DME CONTROL UNIT..........

ScannedImage-7.jpg

ScannedImage-8.jpg

I would continuity test THAT wire then go through ALL the power and gnds and i/o's carefully to the ECU, ...then remove the ECU take cover off and carefully inspect the pcb ...you might see the large FET (FIELD EFFECT TRANSISTOR)...Look for any signs of heat damage.

derrick

[JG911]

I brought a new DME relay last year at the same time as the sensors but the only difference i can see on the outside of the relay case is the old 1 says 12v 15a and the new 1 says 12v 30a will this make any difference

My 911 carrera is a 1984 3.2

[zola1]

I brought a new DME relay last year at the same time as the sensors but the only difference i can see on the outside of the relay case is the old 1 says 12v 15a and the new 1 says 12v 30a will this make any difference

My 911 carrera is a 1984 3.2

Hi,

Not to the fault of No HT..they have just upped the contact load rating in the relay to make it more robust, let me know how you get on with the testing i suggested above.

cheers

[JG911]

It was low on petrol when i put it way last have they got a cut of switch !! i know some of the old Ford's use to have a kill switch in the boot

[zola1]

It was low on petrol when i put it way last have they got a cut of switch !! i know some of the old Ford's use to have a kill switch in the boot

No Inertia type fuel shut off sw fitted on that model.

[JG911]

Thanks Derrick it was just another idea .. thanks for the PM aswell

[zola1]

Thanks Derrick it was just another idea .. thanks for the PM aswell

Hi,

Hope the investigations are going ok,

Spoke to a very helpful guy on IB and he sent me this link :-

http://www.cannell.co.uk/Manuals.htm

Scroll down and download the 84-89 Workshop Manual form the 911 section.

He sent me these wiring diagrams/pinouts : -

DME Wiring Pinout 84_85myr.jpg

DME Wiring Pinout 84_85myr 2.jpg

911 84myr Motronic ECUPinout2.jpg

911 Functionality Motronic ECUPinout3.jpg

the ign coil driver is internal to the ECU, but do make sure ALL the I/O's are present, start at the top write down all results, take your time and inspect sliding contacts in the multiplugs and look for any signs of high resistance & poor connections (small 1-2mm terms don't like loose connections) and will not pass current in the case of the power and gnds. When it comes to signals in the crank and ref signals are obviously critical to providing the ECU with inputs.You will need a scope for these, but no probs if you don't continuity test the wiring will show any opencircuits and a resistance of the sensor coils will give you a base reading of the entire circuit fromthe ECU pins...hope that makes sense.... Have you got a safe gap in-line to the HT leads to cyl ?this will help a great deal in testing for HT, Much better than laying a spk plug across a gnd point

Anyway good luck, And let us know how you get on, BTW Where abouts are you ? and are you getting ready to come the autojumble at Husbourne Crawley next week.?

cheers

[JG911]

Hello Derrick thanks again for the info all getting very involed now with them diagrams

Im about 18 miles North of Peterborough

[zola1]

Hello Derrick thanks again for the info all getting very involed now with them diagrams

Im about 18 miles North of Peterborough

I live not that far in Bedford so if you need another pair of hands let me know ?

[JG911]

Thanks Derrick ill see how this week goes and let you know,my friend has got another friend coming round this Friday to do a few more checks on it,if no joy ill let you know,im going to pick up another new DME relay this week just incase

[zola1]

Thanks Derrick ill see how this week goes and let you know,my friend has got another friend coming round this Friday to do a few more checks on it,if no joy ill let you know,im going to pick up another new DME relay this week just incase

No probs don't spend any more cash on parts until you have proved its u/s these jobs can quickly drain wallets let me know how it goes ..there are a few optons so if the ECU HAS failed do'nt forget its the Husbourne Autojumble next Sat (22nd), Always a good meet with many helpful porsche experts in the carpark

[JG911]

Just brought a new DME relay just incase and a new rotor arm and cap fingers crossed for tonight

[JG911]

Hello Guys iv just had a auto sparky come round and he put a gadget on the coil and says the coil is on when it should be off and off when it should be on ...

So what would cause that ?

[zola1]

Can you get some clearer diagnosis from your sparky, e.g does he mean the supply voltage to terminal 15 is the problem ?, the correct function should be 0 volts ign switch off, then key on ign it should measure +12volts. the other side of the coil is sw'd on and off by the ECU whilst cranking/running , like the coil circuit test i mentioned, di he carry out that test ?...not sure what he means can you get some more info ?

cheers

[JG911]

He had a l-e-d test box and he says the light which is on should is off and when i crack the engine over the light goes out and another 1 comes on it's like the coil is working in reverse,the wrong light when not cracking and the wrong light is on when cracking...

The coil has 12v going to it but its switching the wrong way round.