Ignition system fault

[john lord]

Hi everybody.

I have a 944, registered June 1982.

Most of the circuit diagrams, seem to start from 1983 onwards, mainly 1985 on.
Knitting them together, can be a bit awkward. Non seem to exactly relate to what I have in the car.

I have asked around, amongst those that may be supposed to know but nothing productive apart from the usual advice that you should carry a spare relay or such like.

Now, I know that 'modern' electronics, even in 1982 were more sophisticated than in earlier times. But, in those days, there was always some one who could say, "Hang on, I'll draw you a circuit diagram of just that section, so you can trace the fault"

That way, you could follow it along until you found the problem. There is no basic reason why you could not do that today. Without replacing various parts in guesswork to see if that sorts it.

From my present experience, there does not seem to be anyone out there that has that ability and gift of knowledge to do so.

Or, can you prove me wrong ? Meanwhile, I shall labour on and shall eventually 'produce it myself'. Surely, that should not be necessary, I have other things to work on. I'll finish the cills on the 924S. And may be scrap another 944 !

 

[Masher]

This help at all...?

http://www.clarks-garage.com/

Regards
Mick

 

[Riverside]

I learned all I know about diagnostics & repair from owning unreliable cars and at various times not having enough money to pay for a reputable garage to fix it. I know my limit, and stuff I cannot do myself gets done by paying someone who does []

A relay is just a remote switch; you do something (or a sender (sensor or computer) sends a signal) via a low current wire, which switches on one or more high current circuits.

The DME relay switches on power to the DME (ECU) and the fuel pump. The ECU controls the injectors so if your car isn't starting because of a fuelling issue this is the first thing to check.

However if your car has no spark, you need to check the plugs, HT leads, coil etc just as you would in an older car. There are no points in the distributor, ignition timing is controlled by the ECU.

Relays can usually be opened & checked for corrosion, poor electrical contacts ('dry' solder joints), burnt components or physical damage just the same way a carb can be stripped & inspected. Other parts can be tested by substitution, which is the point where a specialist (who has spare 'known good' components available comes into their own.

What symptoms are you getting?

 

[barks944]

The DME relay is actually two relays in one. The first relay is turned on by the ignition switch and this supplies power to the DME and the injectors. The second relay is controlled by the DME which turns the fuel pump on when it detects engine rotation from the crank sensors.

 

[barks944]

Knew I had done a schematic: