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How to test coil "switching"?

P

Parc

New member
Joined
May 22, 2018
Location
Vancouver
Hello,
Trying to track down no spark on '85 245 (again) leaning towards the ICU, have gone through several methods of diagnosis but am not clear on how to do this one step:

Next ground the coil's high tension lead and put a meter on the coil's 12v terminals. No 12v switching? Since most systems apply 12v and switch the ground lead, if there is no 12v at all, check the power lead to the ignition, wiring, fuse etc.
source: https://www.volvoclub.org.uk/faq/ElectricalIgnition.html#CarWontStartIgnitionDiagnosis

If anyone could clarify how exactly to do this test, I would so appreciate it! What I understand is to ground the high tension lead of the coil, put ohm meter + on + terminal and - on - (or vice versa?) and crank the engine. With ignition at || there is no voltage reading, when cranking, there is something like .01. Am I doing this right?

Thanks
 
Parc said:
Hello,
Trying to track down no spark on '85 245 (again) leaning towards the ICU, have gone through several methods of diagnosis but am not clear on how to do this one step:

Next ground the coil's high tension lead and put a meter on the coil's 12v terminals. No 12v switching? Since most systems apply 12v and switch the ground lead, if there is no 12v at all, check the power lead to the ignition, wiring, fuse etc.
source: https://www.volvoclub.org.uk/faq/ElectricalIgnition.html#CarWontStartIgnitionDiagnosis

If anyone could clarify how exactly to do this test, I would so appreciate it! What I understand is to ground the high tension lead of the coil, put ohm meter + on + terminal and - on - (or vice versa?) and crank the engine. With ignition at || there is no voltage reading, when cranking, there is something like .01. Am I doing this right?

Thanks
Click to expand...

No that's not right, and I don't think that excerpt is the best way to explain how to test for proper signal to the coil. Ground the output of the coil (the connection that goes to the distributor) and measure the voltage between terminal 15 and terminal 1 on the coil, while cranking. It should read 9-11V (12V amplitude but it's a pulse not a continuous signal, so your meter won't read the max voltage).

Refer to the green books.
 
Lando said:
No that's not right, and I don't think that excerpt is the best way to explain how to test for proper signal to the coil. Ground the output of the coil (the connection that goes to the distributor) and measure the voltage between terminal 15 and terminal 1 on the coil, while cranking. It should read 9-11V (12V amplitude but it's a pulse not a continuous signal, so your meter won't read the max voltage).

Refer to the green books.
Click to expand...

It is rather confusing. Thanks for clarifying. So I did this test and my reading fluctuates, but it is well below 1V...not what i need but good indicator of something...

Put a test light between coil negative and ground. It should blink. Or use a scope.
Click to expand...

Thanks, I did this test and the light stays full brightness with ig on and cranking, and there is no fluctuation.

So, there is voltage at the coil but no switching. I now understand from the greenbook that the switching is done by the ICU, the hall sensor is new, wires have been repaired/replaces, grounds/connections checked and rechecked. So I think it's time for an ICU...hope my logic holds up
 
Last edited:
85 240 has Chrysler ignition, no?

I've heard the white shielded wire is a weak point on those.
 
Thanks for the input! here's a little more background:
2 months ago there was a no spark, I diagnosed a bad hall sensor, replaced it, and it fired up, but that didn't last long. I then removed the harnesses and their looms and found 6 possible shorting locations (completely bare wires, worn thru shielding, cuts/cracks etc.) I replaced several full length wires connectors and mended others. Cleaned all grounds and it ran great for a month every day. Then it wouldn't start one afternoon. No spark again, power to coil but no switching. New spare coil and spare hall sensor proved ineffective.

I've heard the white shielded wire is a weak point on those.
Click to expand...
Will double check this wire, no white, but possibly the light grey wire from ICU to coil. Also yes, I've never understood what deems it a Chrysler ignition system, would it be the ICU? everything else is bosch.
 
Volvo had a in depth s.b. On this system years a go. What jumped out was they said -replace the harness if removed from the controller. There was another that wanted sleeves added to certain pins. I have a 83 that we changed to 2.2 that is doing the same as yours.
 
good to know, thanks dl242gt.

What jumped out was they said -replace the harness if removed from the controller. There was another that wanted sleeves added to certain pins.
Click to expand...

I read that as well and couldn't square the logic of entirely replacing either component if disconnected (unless maybe pulling it with ignition on). Do you think it had to do with a concern of damage to the pins and receptors themselves, or concern about the circuitry? It almost starts to sound like Douglas Adams had a say in this. I guess I understand the logic of the sleeves which mine has, acting to improve connectivity and sort of stabilize the connector...I also put Burndy Penetrox in there...

Anyhow, will try to source an inexpensive icu and see if that does it. It makes sense to me that 6 shorting sites would probably have caused damage to the computers
 
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