Ignition problems with a Volvo 940

[PhilipS28]

I have owned my Volvo 940 for 28 years and it has,until now,been utterly reliable. It has now developed an elusive ignition fault.

Power can suddenly be lost, with the engine briefly cutting out and then restarting, causing shunting in the transmission Although the engine is turning over the rev counter drops to zero and fuel/air mixture explodes in the silencer, causing a large hole to be created in the latter. Checks around the engine have not found any loose connections in the ignition circuit. Any ideas?

[LPTJoe]

Crank position sensor?

[Laird Scooby]

First thought is exactly what Joe has suggested but given the ambient temperature, the second thought has to be ignition amplifier module.

This is located on the left hand inner wing behind the headlamp. Remove the plug, the two screws that secure it and remove. Clean the aluminium rear face of it with something non-abrasive and polish to a high finish. Do likewise with where the aluminium mates with the inner wing.

Once both are clean, smear some heatsink compound/thermal transfer paste on the aluminium face of the rear of the module and as you refit it, wiggle it around to spread the paste evenly.

Coat the screws in the same stuff for added heat transfer and refit them, then the plug.

Also worth checking are coil connections to make sure they are clean and tight, don't forget the bracket that holds the coil, this should be clean inside and where the coil fits inside the bracket, clean as well, likewise the area where the coil bolts to the inner wing.
Also check the HT leads but this sounds more like an LT than HT problem.

[Dirty Rooster]

Originally Posted by PhilipS28

... the rev counter drops to zero ...

Crank position sensor.

Replaceable with just a 10mm spanner and an oily right arm.

[Laird Scooby]

Originally Posted by Dirty Rooster

Crank position sensor.

Replaceable with just a 10mm spanner and an oily right arm.

An overheating ignition amplfier module will cause the same symptoms - it shuts itself down to prevent permanent damage then restarts when it's cooled.

Given the current heatwave that is also worth checking as detailed above.

[aardvarkash10]

with Dave on this from previous experience. Replace the CPS and the amplifier. Its not a lot extra in cost and its done and dusted in less than half an hour.

While you are at it, invest in a flat (not offset) 10mm racheting ring spanner. It will make fitting the CPS a doddle.

[Laird Scooby]

Where have been hiding Ash, did you hibernate for winter?

[aardvarkash10]

every second weekend at the mountain snowboarding, and the last two weeks doing an avalanche and back-country course in the South Island...

I'm about ready for an assault on Everest - us kiwis are good at that.

And chores. She has lots of chores for me.

[monkeh]

If the rev counter just drops like a stone when it dies, It'll be the CPS.
Fried wiring due to its location.
Other options are a bad solder joint on the fuel pump but that will cause the rev counter to show revs when the car dies.
The few Volvo redblocks I have owned over the years have had CPS and fuel pump relay issues but never ignition amps. Made a point of pinching a few when I was at a scrappie, Never needed them. They were just expensive paperweights.

[Laird Scooby]

Originally Posted by aardvarkash10

every second weekend at the mountain snowboarding, and the last two weeks doing an avalanche and back-country course in the South Island...

I'm about ready for an assault on Everest - us kiwis are good at that.

And chores. She has lots of chores for me.

Sort of hibernation then - not in your usual habitat!