911 Not Starting !!!

[JG911]

Hello Everyone

Right my 911 will not start iv had my friend pop round today and we have checked for a spark and there's not one for some reason iv replaced the DME relay and we have checked the voltage on the battery and it's fine and so are all the fuse's but we checked the voltage on the coil and it's 4.5 volts which my friend says it should be 12 ish

Has anyone got any ideas

[RWebb]

does the motor crank over?

make clicking noise near the starter?

turn headlights on then try to start car - what happens?

[red964]

Is it turning over?
Have you checked your earth strap off the gearbox/starter to the body.. sometimes these rust through or come loose or somethign

[rick-l]

Originally Posted by JG911

but we checked the voltage on the coil and it's 4.5 volts which my friend says it should be 12 ish

Does this mean

• you put your voltmeter on the wire that goes to the DME without cranking the engine and it measured 4.5 volts.
• OR
• You put your voltmeter on the wire that goes to the ignition switch and it measured 4.5 volts.

[JG911]

Originally Posted by RWebb

does the motor crank over?

make clicking noise near the starter?

turn headlights on then try to start car - what happens?

Yes the engine turns over fine

[JG911]

Originally Posted by rick-l

Does this mean

• you put your voltmeter on the wire that goes to the DME without cranking the engine and it measured 4.5 volts.
• OR
• You put your voltmeter on the wire that goes to the ignition switch and it measured 4.5 volts.

We put the volt-metre on the coil terminals and it was 4.5 volts.

Also does the fuel pump keep pumping or does it meant to turn off when it's built pressure up ?

[RWebb]

OK - the motor cranks fine

we still do not know what motor you have

and... turn headlights on then try to start car - what happens?

[JG911]

Originally Posted by RWebb

OK - the motor cranks fine

we still do not know what motor you have

and... turn headlights on then try to start car - what happens?

Hi iv got a 1984 3.2 carrera.

Iv just been out to try the lights and when turn the engine over the lights dim.

[rick-l]

Originally Posted by JG911

We put the volt-metre on the coil terminals and it was 4.5 volts.

Also does the fuel pump keep pumping or does it meant to turn off when it's built pressure up ?

That doesn't really say anything specific either.

The fuel pump runs when the key is in the start position or when the DME commands it on when it determines the engine is running.

[JG911]

Originally Posted by rick-l

That doesn't really say anything specific either.

The fuel pump runs when the key is in the start position or when the DME commands it on when it determines the engine is running.

So the pump is work fine then,you can hear it running so petrol must be getting there

[Christien]

Perhaps a stupid suggestion, but did you check all the electrical connections in the engine bay?

[JG911]

Originally Posted by Christien

Perhaps a stupid suggestion, but did you check all the electrical connections in the engine bay?

yeh we checked the fuse's with a volt-metre and they seem fine

It was running fine when is was going

[charlesbahn]

Check for good ground contacts (ground wires to the engine bracket and tranny ground strap) ?

[JG911]

Just seems funny it was working 1 day then not another ... bleedy thing ol

[ischmitz]

With the ignition ON and the engine not running or cranking you should measure 12 volts from each terminal of the coil towards a metalic engine surface. If you meaure the voltage across the coil by putting each lead to one terminal there should be no voltage.

If you measure a voltage across the coil terminals your DME module is damaged and needs repair. Essentially, the output stage is shorted and that is a problem.

Ingo

[TibetanT]

You posted:

Hi iv got a 1984 3.2 carrera.

Iv just been out to try the lights and when turn the engine over the lights dim.


1st) I am not an expert.
2nd) Have you looked at the battery voltage? Is it at least 12.5volts because if your lights go dim, it sounds like a bad battery or one of the cells is bad.

3rd) If battery is at least 12.5volts, then try checking your reference sensors. Maybe they are loose at the connection or are going bad. Bad reference sensors would make your car not start.

Hope this helps and good luck!

[ischmitz]

It sounds to me JG911 has already isolated an issue when he measured the 4.5 volts across the coil. This is wrong and has nothing to do with the reference sensor or speed sensor.

He needs to confirm that the battery voltage is around 12 - 13 volts. If that is the case and there is really 4.5 volts across the the coil with the igntion ON the DME has an internal short in the ignition output stage.

[JG911]

Hi all ill get my friend around later to check again and to do some of the ideas people have said.

As for the test on the coil we put both volt-metre leads on the ends of the terminals - / + and when we tryed to start the engine the metre read 4.5 volts.

And iv just put a new DME relay on.

[ischmitz]

that's a different story - while you crank there will be a complex wave pattern on the coil and a DVM is not sufficient to tell you what is going on. Depending on the mark and model of your DVM you'll see some reading. It depends on the time constant of the meter.

It is easier to check for spark with an old spark plug connected to one of the spark plug connectors. Also, a timing light can be helpful to see if the sparks are timed right (reference sensor check).

Then it is on to the fuel. You need an LED test light to check for fuel pulses. And of course make sure there is fuel pressure in the rails.

Ingo

[JG911]

Sounds like iv got to get a auto electriction out then ....