Post lockdown problem
 

Hi everyone, my ancient 940 2.3 LPT (97 MY) has been sitting idle for these past month(s).
Started it yesterday and whilst it started on the button, it's only running on 3 cylinders! Natch, it was running fine before lockdown.
Pulled leads and it's #1 that's doing nothing.
Checked for spark - yes, good spark.
I pulled the injector plugs on #1 and #2 and tested for voltage on the 2 pins with ignition on. #1 showing 11.98V on one and 0.48V on t'other. #2 is showing 11.98V on both.
So from that I assume something is amiss but I have no experience on Fuel Injection and am a bit unsure how to proceed now.
Any suggestions, please?
Thanks.
Andy

The fuel ECU pulls the ground side down to zero to actuate the injector, the 12V is permanent (via the radio supression fuel relay).

All the injector leads are connected in paralell, they should all show identical voltages, and should both show close to 12V if you have at least 1 injector coil still attached.

Seems you have a faulty loom.

Swap the injectors about, you might have a blocked injector. It's a bit of a messy job, especially if the fuel rail is still pressurised (release the pressure using the valve found at the bottom of the fuel rail). You could also check the resistance of each injector. Assuming you have the original 0 280 150 804 injectors, resistance should between 2-3 ohms per injector.

If you're going to remove the injectors, it would be worth flashing a torch into the tops of them to see if the filter basket looks clogged.

Ah, that might be the problem. You've just jogged my memory that I had to throw out a pesky field mouse from BOTH of my Volvos. Chucked him out of the bonnet lining on the 940 and the cheeky s*d moved into the V70.
I left the linngs out and then had to suffer clouds of steam from water evaporating on the bonnet when it rained and I was stopped in traffic.
Will investigate with a torch. He/She might be back as a result of the lockdown.
Just to clarify - should both injector plug wires show the same Voltage when grounding them via the Voltmeter or at least the same Voltages for each separate lead wire IYSWIM?

Thanks for that. Will check wiring first as it seems it might be a more fruitful avenue given the history.

Do this simple test - find a short length of wire and bare the ends. Remove injector plugs #1 & #2 and feed one end of the jumper cable (the one you've just bared the ends on) into the grey connector on #1 and the other end into the grey connector on #2 then refit the plugs on the injectors.
Start it up and see if it's back on all 4 pots. If so, there's either dirt on the connector inside the injector plug on the one with the low reading or a break in the cable.

It will help you narrow down the problem more quickly anyway.

I'm liking that idea - brilliant (and easy to do). Will give it a go tomorrow.
Thank you.

You're welcome, hopefully it gives a few ponters as to where the problem lies. :thumbs_up:

Not sure what you mean, You are not grounding the wires via the multmeter in voltage mode. The multimeter is measuring the voltage difference between 2 points, it doesn't conduct any significant current. Don't ever use current mode if you don't know how to use it, it will just blow the meter.

So with multimeter in voltage mode between chassis ground and either injector pin it should show both as near 12V. An injector just like an open ended coil with 12V at one side. The other side will also be at 12V also because there is no current runing though it. (Vdrop=IR)

If you unplug all the injectors you will see 12V only one 1 pin of the connector, the other side I'm not sure what it will be at because it connected to an open collector output of a power electronic stage in the ECU, it could be at any voltage when its not trying to actuate the injector.

If it's open collector Tony, it will be in high impedance state so there won't be any voltage on it with the injectors unplugged. Could also be they used MOSFET output stages in which case it will still be high impedance but will switch the injectors quicker with fewer worries about hysteresis.

The +12V will be on the pin with the green wire on the injector plug.