940 se injectors not firing (LH 2.4)

  • Thread starter Thread starter Bilko
  • Start date Start date
B

Bilko

Hi

This car died on the motorway a couple of weeks ago and has been dead since.

Some info...

- The car won't start but cranks.

- I am getting spark which will jump 1/4 inch when tested against the block
so I assume the problem must be fuel delivery.

- The fuel pump runs.

- The FI relay activates.

- The radio suppressor relay activates.

- The wiring from the injectors to the ECU pin 18 (injector signal) pin is
OK.

- The supply and ground voltages at the relevant ECU pins are OK.

- The other pin of the injectors is getting 12v via the radio suppressor
relay.

- I removed a spark plug and held a cotton bud in the cylinder as the engine
was cranked -- there was no sign of fuel on it. Also, I used a long
screwdriver as a stethoscope to listen at an injector... I couldn't detect
any clicking.

- When I crank the engine the voltage read across the pins of all injectors
remains 0.0v so it looks like the pulse signal from the computer isn't
working.


All I can think of is a bad ECU... anything else I'm missing?

Any advice would be welcome.


Thanks

Bilko
 
Yeah the series resistor pack for the injectors would seem to have become
disconnected somewhere.

Cheers, Peter.

: Hi
:
: This car died on the motorway a couple of weeks ago and has been dead since.
:
: Some info...
:
: - The car won't start but cranks.
:
: - I am getting spark which will jump 1/4 inch when tested against the block
: so I assume the problem must be fuel delivery.
:
: - The fuel pump runs.
:
: - The FI relay activates.
:
: - The radio suppressor relay activates.
:
: - The wiring from the injectors to the ECU pin 18 (injector signal) pin is
: OK.
:
: - The supply and ground voltages at the relevant ECU pins are OK.
:
: - The other pin of the injectors is getting 12v via the radio suppressor
: relay.
:
: - I removed a spark plug and held a cotton bud in the cylinder as the engine
: was cranked -- there was no sign of fuel on it. Also, I used a long
: screwdriver as a stethoscope to listen at an injector... I couldn't detect
: any clicking.
:
: - When I crank the engine the voltage read across the pins of all injectors
: remains 0.0v so it looks like the pulse signal from the computer isn't
: working.
:
:
: All I can think of is a bad ECU... anything else I'm missing?
:
: Any advice would be welcome.
:
:
: Thanks
:
: Bilko
:
:
:
:
:
 
--


Peter Milnes said:
Yeah the series resistor pack for the injectors would seem to have become
disconnected somewhere.

Cheers, Peter.
Click to expand...

Thanks for the suggestion, but this 940 is a non-turbo and doesn't have a
resistor in series with the injectors. The +ve feed for the injectors comes
direct from the suppressor relay.


Thanks

Bilko
 
Tony Stanley said:
The crank sensor may have something to do with it. Not sure exactly, I had
thought it didn't switch on the pump until it got crank pulses, but that was
in a much older car with analogue injection control (B200E 360 GLT).
Disabling injectors is a much better way in a more up-to-date car, so the
fuel can build pressure a few seconds before it gets crank signal. Having
said that my 940 Turbo seems to take a while to build fuel pressure (much
longer than the 360).
Click to expand...

--

I forgot to mention in my original post that I'm getting an engine speed
signal to the FI ecu (pin1 ~6v when cranking) from the EZK ignition unit so
I don't think it's the RPM sensor.


Thanks for the input.

Bilko
 
Bilko said:
Hi

This car died on the motorway a couple of weeks ago and has been dead
Click to expand...
since.

Check the ballast resistor pack on the drivers side (i think) suspension
turret.

Tim..
 
Bilko said:
Hi

This car died on the motorway a couple of weeks ago and has been dead
Click to expand...
since.

PS. You may not have a ballast reistor pack on this engine, some have, some
haven;t- fingers b4 brain syndrome!

With the igntion on, and fuel pump primed, try grounding the injectors to
ecu line to earth for a secord or so, then crank. If the engine fires you
know spark and fuel pressure is fine, and 12v to the injectors is ok.

Then check very carefully all the ecu earth's.
 
Tim.. said:
since.

PS. You may not have a ballast reistor pack on this engine, some have, some
haven;t- fingers b4 brain syndrome!

With the igntion on, and fuel pump primed, try grounding the injectors to
ecu line to earth for a secord or so, then crank. If the engine fires you
know spark and fuel pressure is fine, and 12v to the injectors is ok.

Then check very carefully all the ecu earth's.
Click to expand...

No this car doesn't have ballast resistors -- it uses high impedance
injectors.

I'll try as you suggest and see how it goes.
 
[email protected] by Bilko dropped his wrench, scratched his head and
mumbled,
Tim, I grounded the injector wire and they clicked as expected. When I
turned the key the engine fired briefly.

I rechecked the ECU grounds and they were OK.

I also rechecked the engine speed signal by reading pin 1 with the crank
sensor disconnected (0 volts) and with the crank sensor connected (5.4
volts).

Apart from a dodgy crank sensor signal, do you know of any other faulty
input that would make the computer shut down the injectors?


Thanks

Bilko
Click to expand...

Since the auxiliary fan relay and the radio suppression relay have the
same P/N you can swap them and see if there's a difference. If you ground
the fan relay at the radiator switch through a test light, the fan will
run with the key on--easy way to check both relays for operation.

If that fails I'm afraid the control unit has left the building. That's
the only thing left that generates an injector pulse.

Bob
 
If that fails I'm afraid the control unit has left the building. That's
the only thing left that generates an injector pulse.

Bob
Click to expand...

Yes, looks like you may be right and the ECU itself is the problem.

Tried everything else I could think of that would stop the injectors
pulsing -- no RPM signal, bad wiring, faulty injectors, bad suppression
relay, bad ECU supply or grounds, erroneous WOT signal from TPS putting the
ECU in "clean start" (flooded engine) mode...

Luckily it's not my car... it's the father-in-law's. I think he's out at
the moment looking for a car with a carburettor.... :-)


Cheers

Bilko
 
Bilko said:
Yes, looks like you may be right and the ECU itself is the problem.

Tried everything else I could think of that would stop the injectors
pulsing -- no RPM signal, bad wiring, faulty injectors, bad suppression
relay, bad ECU supply or grounds, erroneous WOT signal from TPS putting the
ECU in "clean start" (flooded engine) mode...

Luckily it's not my car... it's the father-in-law's. I think he's out at
the moment looking for a car with a carburettor.... :-)
Click to expand...

Apols for not being online lately- blasted Lovsan virus bolloxing my pooter!

Sounds like you have successfully eradicated any other fault with the car
and it does point to an ECU failure.Makes a refreshing change that someone
takes a logical approach to fault finding rather than just automatically
blaming the ecu!!

It would be worth having ATP check your ecu on their bench testers local to
you. http://www.atpelectronics.co.uk just to be sure. This costs £35 which
is discounted if your ecu is faulty and you order a reconned or new one from
them.

Tim..
 
Tim.. said:
Sounds like you have successfully eradicated any other fault with the car
and it does point to an ECU failure.Makes a refreshing change that someone
takes a logical approach to fault finding rather than just automatically
blaming the ecu!!
Click to expand...

Just to let you all know it was indeed the ECU that was at fault.

A free replacement was procured from a scrap car, plugged it in and the
beast came to life with the first turn of the key... :-D


Cheers

Bilko

--
 
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