911 Not Starting !!!

[wwest]

I'm puzzled, doesn't this car have a CDI ignition system..??

Both my '78 and '88 do.

So measuring the voltage across the coil would be meaningless unless you're doing it with an O-scope.

CDI modules are a VERY common failure point, especially so if the car has a history of alternator/regulator/battery charging, OVER-CHARGING (smell that "sewer" gas..?) problems.

[scarceller]

84-89 Carrera is not CDI, it's a simple inductive coil setup (old school).

Originally Posted by wwest

I'm puzzled, doesn't this car have a CDI ignition system..??

Both my '78 and '88 do.

So measuring the voltage across the coil would be meaningless unless you're doing it with an O-scope.

CDI modules are a VERY common failure point, especially so if the car has a history of alternator/regulator/battery charging, OVER-CHARGING (smell that "sewer" gas..?) problems.

[wwest]

Originally Posted by JG911

Update

Last night we changed both flywheel sensors and put a new battery on and checked the coil and all working ok there

BUT

It's still not firing,just keeps turning over,rev counter very very slightly bonces,alarm bleeps ok,smell petrol aswell and can hear the fuel pump

Any more ideas please

"..rev-counter very very slightly bounces,..."

Good news, as the rev-counter, tachometer, is driven by the CDI module. At least "some" indication that the CDI module is operational, but at a relatively minor level.

[scarceller]

The 84-89 does not have CDI. The tach pulses are generated by the DME from the flywheel ref sensor. If the tach is bouncing while cranking this is good. The pump will come on when key goes into 'START' and then the pump will remain on after engine starts, the DME will activate the FP and keep it on so long as engine is running.

Originally Posted by wwest

"..rev-counter very very slightly bounces,..."

Good news, as the rev-counter, tachometer, is driven by the CDI module. At least "some" indication that the CDI module is operational, but at a relatively minor level.

[JG911]

Morning Everyone.

Thanks for all the info im passing it onto my friend who is working on the 911.

With reguards the DME i did buy a new 1 last year and it still does the same (not fireing) on my old 1 it said 12v 15a and on the new 1 it says 12v 30a will this make any difference ??

[scarceller]

Where on the DME does it say 12v 30Amp? So long as the 2 DMEs are for a 84-89 Carrera they should work.

But here is the bigger issue: if you have a bad (shorted) coil you will destroy both DMEs! You need to get those 2 DMEs into a known good car to be sure they do still work.

Originally Posted by JG911

Morning Everyone.

Thanks for all the info im passing it onto my friend who is working on the 911.

With reguards the DME i did buy a new 1 last year and it still does the same (not fireing) on my old 1 it said 12v 15a and on the new 1 it says 12v 30a will this make any difference ??

[JG911]

Originally Posted by scarceller

Where on the DME does it say 12v 30Amp? So long as the 2 DMEs are for a 84-89 Carrera they should work.

But here is the bigger issue: if you have a bad (shorted) coil you will destroy both DMEs! You need to get those 2 DMEs into a known good car to be sure they do still work.

It says 12v 15a on the outside casing on the old 1 and it says 12v 30a on the new one i was told the new was for the same year,ill see if my mate can try them both in his SC

[scarceller]

Let's start over on the no-start issue and not assume anything for the moment. When you turn the key to 'RUN' does the IdleControlValve hum and vibrate? If it does then the DME is alive. Test this first.

[JG911]

Originally Posted by scarceller

Let's start over on the no-start issue and not assume anything for the moment. When you turn the key to 'RUN' does the IdleControlValve hum and vibrate? If it does then the DME is alive. Test this first.

Im going to say yes as we can hear a huming from the engine compartment,and we can smell petrol.

[scarceller]

You should not smell any fuel while in 'RUN' the injectors only start fueling when key is in 'START' - please be sure the ICV is humming with key in 'RUN'. I can walk you through diagnostics but it has to be step-by-step (no assumptions).

Also, get a LED test light (from Walmart less than $5.00) this is a 12volt test light but can not have a normal light bulb it MUST be a LED. You will need this type of tester to fully test certain components as we diagnose your problem.

Originally Posted by JG911

Im going to say yes as we can hear a huming from the engine compartment,and we can smell petrol.

[JG911]

ok let me buy a test light and take it from there :-)

[JG911]

Right guys.

We have replaced

Rotor Arm
Dizzy Cap
Battery
DME Relays x 2
Flywheels sensor x 2

Tryed my coil on my friends SC and it starts it fine,but it just keeps turning my engine over.

Any ideas on were to look next ??

Bleedy thing.

[scarceller]

Yes,

Get a LED test light and I can try to help you.

First, when you turn key to 'RUN' do you feel and hear the IdleControlValve? if you do this means the DME is alive and the program code is running.

Let's start here first.

[scarceller]

Originally Posted by JG911

Tryed my coil on my friends SC and it starts it fine,but it just keeps turning my engine over.

Putting a coil from a 84-89 Carrera in a stock SC is not a good idea. The SC is a CDI ignition that hits the coil with 300+volts on the primary side! The Carrera is standard 12vdc ignition and the coil is designed for only 12vdc on the primary, I do not suggest using this coil with the CDI SC system.

[JG911]

Hiya yeh we only tryed it very very quickly and we checked my coil again after wards and it was the same,yes im off this friday so ill get a led tester.

What would you test 1st and what am i looking for ...

[ischmitz]

Originally Posted by JG911

Morning Everyone.

Thanks for all the info im passing it onto my friend who is working on the 911.

With reguards the DME i did buy a new 1 last year and it still does the same (not fireing) on my old 1 it said 12v 15a and on the new 1 it says 12v 30a will this make any difference ??

You are talking about the DME relay. It's a little black plastic box and as the name says it's a double relay driven by the DME. It has the markings you mention.

The DME itself is the large rectangular silver box and that is the culprit. If you buy it that usually sets you back 500 - 1000$ depending on the source. But you can have it checked and repaired. It is what produces the spark by grounding the coil for fractions of a second.

Use the LED test light and measure across the coil while cranking.

Ingo

[scarceller]

Just to be sure, your car is a 84-89 Carrera right?

First test is to see if the ICV is humming with key in run.

Then connect the LED test light across the coils '-' and '+' terminals then crank the engine and the LED light must flicker. If it does not then you don't have coil pulses.

Then disconnect an injector (any one you can get at easily) then connect test light across the 2 pins at the harness side you just disconnected. Again crank engine LED must flicker. If it does not you don't have Injector pulses.

If you find you don't have Ignition or Injector pulses then most likely one of the FlyWheel sensors are not working correctly, either bad, out of adjustment or you could have them reversed, meaning they both have the same style connector so you could have plugged the wrong connector into the sensors (you have them swapped) this can happen if you replace both sensors and did not pay close attention to which one goes where in the bracket that holds them.

So start by ICV humming - then coil pulses - then injector pulses. Let's start here.

[carrera32911]

The car was running fine, parked it in the garage...the next morning it wouldn't start.

Like any self respecting 911 owner, I promptly used my spare DME relay in the glove box and tried to start it without luck. I knew there wasn't any spark since the tach wasn't jumping while trying to start.

Long story short, it was the reference sensor ( 911-606-215-01) that was causing the issue. New reference sensors and we are live again!

[JG911]

Originally Posted by carrera32911

The car was running fine, parked it in the garage...the next morning it wouldn't start.

Like any self respecting 911 owner, I promptly used my spare DME relay in the glove box and tried to start it without luck. I knew there wasn't any spark since the tach wasn't jumping while trying to start.

Long story short, it was the reference sensor ( 911-606-215-01) that was causing the issue. New reference sensors and we are live again!

Thanks dude iv just replaced both sensors and DME relays and battery and rotor arm and cap still no joy

[JG911]

Hiya guys iv just had auto sparky come round to give me his views and he put a very old gadget with lights on the coil and he says the coil is working the wrong way round it's got 12v going to it it just not switching over

On the gadget is was AMPS ON but was off and AMPS OFF mine was on ....

Any ideas or should i now get me LED tester