Electrical problem 940

[Laird Scooby]

Originally Posted by Ammorack

Smart solution to work from the injector and fuel system. I have ordered that noid light kit. But In the meantime. What else is there to check? It takes a while for my noid light to arrive. So it can be other components to check for? I removed that random cables with those two fuses on positive terminal.

Peel back the rubber boot on one of the injector connectors. Put your multimeter +ve (red) probe in there on the green wire and the black one (-ve) to a good known earth. Switch the ignition on, Record the voltage.

Start the car and record the voltage again. Bring the revs up to 3000rpm and again check the voltage.

Depending on your model you may or may not have an injector resistor pack. Either way, with only the ignition on, you should get near battery voltage. If you don't have the resistor pack, it should follow battery voltage fairly closely when running.
If you do have the resistor pack, the voltage will vary slightly with engine speed as you're measuring at a midway point between the battery +ve and earth and the injectors are being switched on and off - most multimeters can't respond quickly enough to display the pulses so give an average value. This isn't a substitute for the NOID test, it's a different test altogether to ensure you have a feed to the injectors.

Other than that, it's a waiting game on the NOID light which is why i asked quite early in the thread if you had one.

[Ammorack]

Originally Posted by Laird Scooby

Peel back the rubber boot on one of the injector connectors. Put your multimeter +ve (red) probe in there on the green wire and the black one (-ve) to a good known earth. Switch the ignition on, Record the voltage.

Start the car and record the voltage again. Bring the revs up to 3000rpm and again check the voltage.

Depending on your model you may or may not have an injector resistor pack. Either way, with only the ignition on, you should get near battery voltage. If you don't have the resistor pack, it should follow battery voltage fairly closely when running.
If you do have the resistor pack, the voltage will vary slightly with engine speed as you're measuring at a midway point between the battery +ve and earth and the injectors are being switched on and off - most multimeters can't respond quickly enough to display the pulses so give an average value. This isn't a substitute for the NOID test, it's a different test altogether to ensure you have a feed to the injectors.

Other than that, it's a waiting game on the NOID light which is why i asked quite early in the thread if you had one.

If one of the injectors shows a bad reading? Does that mean a bad harness or relay, or pcm?

[Laird Scooby]

Originally Posted by Ammorack

If one of the injectors shows a bad reading? Does that mean a bad harness or relay, or pcm?

No, that's not what you're testing for there. You're testing for the supply to the injectors.

Doesn't matter which one you test, they all have the same supply. The thing that might be causing a problem is the RSR - Radio Suppression Relay - that said some of the last cars didn't have one but it's still worth checking you have a feed to the injectors.

The NOID light will show up a bad PCM as you put it or a bad ECU as we say here. It may also show a wiring harness fault but we'll get to that later.

[nutco]

The thing that might be causing a problem is the RSR - Radio Suppression Relay - that said some of the last cars didn't have one but it's still worth checking you have a feed to the injectors.

Mine is a feb 1998 940 lpt and I have a Radio Suppression Relay located on the inner wing just above the battery

[aardvarkash10]

easiest way to test the RSR is to bypass it.

OTTOMH, I don't recall the plug pattern - Dave may beat me to it.

You'll need a short length of electrical wire, bared back at each end. No other tool required.

[Laird Scooby]

Originally Posted by aardvarkash10

easiest way to test the RSR is to bypass it.

OTTOMH, I don't recall the plug pattern - Dave may beat me to it.

You'll need a short length of electrical wire, bared back at each end. No other tool required.

The two large round pin holes are the switched power and power in Ash - don't remember myself which way round it is.

As the problem seems to occur at a certain engine speed and some late 940s had a two-speed fuel ECU controlled electric cooling fan and others had a single speed fed from a relay identical to the RSR, i was trying to find a test to cover the eninge speed and the RSR without potentially gtting the RSR and single speed cooling fan relay mixed up.

Mine are side by side on the coolant expansion tank and knowing what Volvo were like for changing things.................

[aardvarkash10]

heer we go.

Unplug the relay and use your piece of wire to connect the RED wire to the RED/GREEN wire. Check for the 3,000rpm fault.

If its still there, the relay is NOT the problem. Refit the plug.

If the problem is gone, remove the link wire and let us know. Do Nothing Else.

[Ammorack]

Originally Posted by nutco

The thing that might be causing a problem is the RSR - Radio Suppression Relay - that said some of the last cars didn't have one but it's still worth checking you have a feed to the injectors.

Mine is a feb 1998 940 lpt and I have a Radio Suppression Relay located on the inner wing just above the battery

That’s where I’ve got mine aswell. I unplugged it and the car wouldn’t start. So I guess it works?

[Ammorack]

Originally Posted by aardvarkash10

heer we go.

Unplug the relay and use your piece of wire to connect the RED wire to the RED/GREEN wire. Check for the 3,000rpm fault.

If its still there, the relay is NOT the problem. Refit the plug.

If the problem is gone, remove the link wire and let us know. Do Nothing Else.

Will do!!

[Ammorack]

Originally Posted by aardvarkash10

heer we go.

Unplug the relay and use your piece of wire to connect the RED wire to the RED/GREEN wire. Check for the 3,000rpm fault.

If its still there, the relay is NOT the problem. Refit the plug.

If the problem is gone, remove the link wire and let us know. Do Nothing Else.

I used a piece of cable from the 12v+ Red wire to red and green wire. It fired up. When I connected that wire to those pins. Something happened. Injectors opened? It’s still rough and revs to 3000rpm. I must mention. Owners before me have been behind the dashboard and harness to cut wires for any reason. No idea. I find cut wires. Everywhere.
But the 3000rpm is