All going so well-car just died.

[wayner007]

Well all was going so well but on a trip out tonight in the Porsche the car ran fine for 60 miles but all of a sudden lost all revs and power, as if there was no fuel.
Car turns over but won't start, changed the dme for a spare one, checked for spark and have none! Voltage going into the coil but no spark.
Will check after a few hours kip with another coil I have in the garage but after getting recovered from London by the AA need to get some sleep.
Curious as to why it just died the immobiliser has been by passed now due to being faulty and has started and run all week with no issues.

 

[DivineE]

There seems to be a lot of talk about the crank sensors causing these kinds of problems lately but as there is one for starting, one for running and your car is doing neither I guess that rules that one out. Hmmm no spark. Could the rotor arm have disintegrated inside the cap due to age?

 

[will lyons]

I had exactly the same thing happen to my 87 turbo. In the end after loads of investigation of all the obvious. It turned out to be the ECU.

 

[barks944]

ORIGINAL: DivineE

There seems to be a lot of talk about the crank sensors causing these kinds of problems lately but as there is one for starting, one for running and your car is doing neither I guess that rules that one out.

I don't think thats quite true, the two reference sensors are essential for both starting and running of the engine. The first sensor picks up the starter motor teeth, this signal is used to calculate engine speed (speed sensor). The second detects top dead centre via a screw in the flywheel (reference sensor). Both are essential for the engine to run.

If the tachometer bounces when the engine cranks then the speed sensor is probably ok as the DME outputs the tacho signal after it has worked out the engine speed using the speed sensor.

 

[chrisg]

Barks 944 is spot on, I had an identical problem with the rear Hall sensor on my car - this is the one that picks up on the ring gear teeth. I eventually replaced it but, my suggestion would be:

Try wriggling both of the hall sensors both where the wire goes into the actual sensor (classic failure point) and check that the 3 pin wire/plastic clip where they plug into the main engine loom are secure and fully connected.

If having done that you're still not getting spark or fuel then one of them has probably failed. I had to call out the RAC for this and the chap despite his best efforts couldn't diagnoses the problem - he used a node LED thingy into one of the injectors and got no pulse at cranking nor a spark.

Good luck !

 

[Northern924]

Also have a looks at Clarks it shows how to test the referecne sensor, worked for me with the '24S was the front most BG sensor which is the inportant one for starting the car.

 

[wayner007]

Just checked the ref and speed sensors there fine.
1 Kilo ohm and over a mega ohm on both readings on both sensors.
Checking the coil with another one now.

 

[peanut]

Its important to remember that both your fuel delivery system and your ignition system are both grounded internally within your ECU (providing all the attached sensors are working correctly.)

if your crank sensor is working then i would remove your DME relay and check that you have 12v+ at terminal 30.
(Chance to use your nice new multimeter [])

Terminal 30 of your DME socket is constantly live with ignition on or off.

Next I would remove the DME relay.
Make up a simple 3x way cable (30 amp electrical wire or similar ) and stick 1 wire in terminal 87 one wire in terminal 87b and the the third wire in terminal 30 last .

This will effectivly bypass your ECU fuel delivery control and should start your fuel pump running continuously . It will also by pass the ECU and ground your ignition system for a spark.

If you get no spark at the coil then you have a problem somewhere in your ignition circuit probably supply to the coil from the ignition switch.

 

[barks944]

Does the ignition circuitry go through the DME relay?

 

[peanut]

yes the ECU is powered through DME terminal 87 ,The ignition system is grounded through the ECU .

If the ECU doesn't see 200+rpm engine speed it shuts off the ignition and fuel systems which is why the crank speed sensor is so critical ...and of course a good strong battery to get 200+rpm on cranking

In the event of a fire some of the sensors will trigger the ECU to shut off the fuel pump and ignition system

 

[wayner007]

Right made up a dme that is shorted internally between 87-87b and 30, fuel pump is going and I had 12v at pin 30 at the terminal.
Still no spark have 12v going to the coil but led to believe that doesn't matter as its switched neutral?
Changed the coil for one that reads lower than the other but both in range.
Now at a loss so going to check the control module when I find it that is.
Just done the coil check and had no spark tapping the flying lead to ground even with 12v readings of both legs so looks like a fault between the switch and coil I think.

 

[peanut]

be careful. The low tension ignition system is not grounded to the chassis it is grounded and pulsed internally through the ECU. It is electronic NOT points system
The ECU works on as little as 1v+ and grounding ECU imput/output wires to chassis earth could be harmfull to your ECU.

My suggestion would be to have a little patience and look at the schematic and trace the wiring.

These cars have a very complex fuel delivery and ignition systems and nothing is as straightforward as it seems .Its not a Ford Escort []

Have you a fully charged battery? does it turn the engine over at at least 200+ rpm? if it doesn't your ECU won't pulse your low tension circuit.ie no spark.

 

[peanut]

If your coil checks out ok and the primary connections are sound and thesupply from the ignition switch checks out yet you are getting no secondary voltage from the coil I would test the Ignition Amplifier and its connections.
Your coil primary voltage is controlled by your ECU.
You haven't had a jump start recently have you ? or had any welding done on the car ? or charged the battery without disconnecting it ?
http://www.megamanual.com/ms2/Bosch_124.htm

 

[peanut]

Wayne any luck yet ?

Your coil primary circuit is earthed to chassis via the ignition amplifier (see attached picture)
It is earthed by an electrical switch in the amplifier which is contolled by pulsing from the ECU

i would check you have a good clean earthing point to the amplifier which is probably on the pass side near the headlamp pod

 

[wayner007]

Thanks for the help fellas, peanut had som welding done and had a jump start but since have driven it around for a week with no issues, on the iPhone at the moment but will open the link in a bit, auto electrician comes tomorrow, but will check the amp next.
Had a weekend off this weekend and had a reunion and a Footie doo for my little boy so the car has been left other than sat morning, back on it today though.

 

[wayner007]

Exuse the double post had a route around the only thing I could find was what I thought was something to do with the alarm>

Few more than four wires to could this be it?
The only thing I found by the light pod was the following bunch of wires and an earth>

 

[FistsOfHam]

Argh scotchlocks! I hate those things.

Try prying them open with a screwdriver and checking the connections inside, they're very good at bad connections.

 

[peanut]

By crikey Wayne you've got to clean up those earthing points. []
WARNING

you must disconnect the battery terminal before you put your hand down next to the headlight pods always. If those pods are accidentally triggered you'll loose your hands


Every brown wire that is connected to the bodywork is an essential ground and a poor connection will cause a multitude of problems.

I assumed (maybe wrongly ) that even the early cars would have a ignition amplifier module. I need to check a schematic to verify this.

 

[wayner007]

Cheers for the warning Peanut.
Checked a few things got voltage on the following>
Fuel Pump / DME Relay Primary Supply Voltage pin 30.
Fuel Pump / DME Relay Primary Primary Coil Voltage pin 86.
Fuel Pump / DME Relay Primary Coil Activation pins 18 and 35.
One place I didn't get the full 12vdc was on the Starter Solenoid Signal only got 10.5 vdc but put this down to starting the car dragging it down.
Checked resistance from the coil to the earth point around 10ohms hopefully get that down with a good clean up.
At a loss with the amp though can't find that at all and the only drawing I have shows the dme but no amp.

 

[DivineE]

Seriously whether its the cause this time or not I'd clean up that earth point. mine was half as rusted as that and when I dipped the contacts in acid and polished the contact area with some sand paper I almost doubled the brightness of my headlights. They went from yellow to white and twice as light for the total sum of free[]