940 no spark. Power stage issues? Or something else?

[Rversteeg]

Does it run on start-pilot? In that case I would continue looking at the fuel supply.
You said the fuel relay is working, but it actually consists of two relays. The second relay switches the fuel pump via fuse 11. When cranking, do you measure 12V on fuse 11?
Although the in-tank fuel pump of the last series 940 are of an improved design, they can also fail. Mine lasted "only" 430K miles and could only be brought back to life by a smack on the side of the tank.

[Ltom]

I don't have any more start pilot to test, and it's my only car so I'm now stranded unfortunately.

Things I did:

Checking the fuel pump relay:
• Took the cover off the dual fuel pump relay
• Put it back in place with the cover off
• Used an endoscope camera to look at the relay while I started it.
• On ignition on, I see one contact close. On crank I see the other contact close.
• Inspected all solder joints with a and all look good.

Checking fuel pump operation
• I removed the fuel supply at the rail
• With fuse 11 in place, on crank, loads of fuel came out
• With fuse 11 removed, on crank, no fuel came out.

So it seems the fuel pump is working fine?

[Ltom]

I took the king lead off and sparked it against a ground (now it's dark) and I noticed it's very orange, not blue.



Could it be the coil? Or a faulty ground somewhere?
Is there a diagram of grounds to check?

[Rversteeg]

So it seems the fuel pump is working and there is a spark. If you take a spark plug out, does is spark on cranking? Is it wet of fuel?
It could be the fuel injectors are not injecting. They are supposed to have a constant 12V feed from the radio suppression relay via the package of "fire crackers". They inject simultanuously on grounding by the ECU. You should be able to hear them clicking.

You could check the grounding points, but I usually check them by creating a temporarily ground with a wire directly on the battery.

Also worth checking:
http://www.stepbystepvolvo.com/Resou...20No-Start.pdf

[Ltom]

I tested the injectors and they are getting voltage and working correctly.

If I remove a spark plug after cranking, they are wet. If I crank with the spark plug removed I can see (and smell) the fuel mist as well. I think the injectors are fine.

Fortunately I received an in-line spark plug tester in the mail today so I performed the following steps:

1. First, I put the tester on an (inserted) spark plug and plugged the HT lead into it and cranked the engine.
2. I checked this on two cylinders, no light on either so assuming a spark problem upstream.
3. I removed the king lead from the distributor and held it close to a ground and cranked. Orange spark.
4. I put the spark plug tester on the king lead and held that close to a ground. Orange spark plus the tester lit up. Reconnected the king lead as normal.
5. I put the spark plug tester on the end of an HT lead and held it close to a ground. Orange spark + test light.
6. I removed a spark plug, put the spark plug tester on it and connected the HT lead. I held the spark plug against a ground. Spark at plug and test light illuminated. So the test lamp and spark plugs are okay.
7. Reinserted the spark plug into the block with the tester attached. No test light.
8. I tested the resistance between the head and the battery and all earths are okay. I also added a jump lead from the head just in case but same result.

From this I can only assume that the coil is gone and the spark is too weak under the cylinder conditions.

[Rversteeg]

According Volvo factory documentation:
Primary coil (terminals 1 and 15) 0.6 - 0.9 Ohm
Secundary coil (terminal 1 and HT) 6,5 - 6,8 kOhm.
This is valid for B200F/E/K, B230F/FB/K/FT, B204/E?FT/GT B204E/FT/GT and B234F/G.
Volvo OEM p/n 1346071, Bosch p/n ... 131 753.

[Ltom]

Primary coil is measuring at about 0.7 Ohms
Secondary at 7.2 kOhms.

Measuring the primary coil resistance is tricky since the resistance of the multimeters leads is about 0.7 Ohms so I measured 1.4 and subtracted the 0.7 from the leads.

Even though the results are close to nominal, there could still be a problem at load and the spark is too weak. I can't think of a way to check aside from simply replacing the unit.

EDIT
Also, I went back and checked that the top timing mark lines up with TDC on cyl 1. I couldn't be bothered to take all the stuff off to check the lower timing mark but I used an endoscope to look at TDC through the spark plug hole.

[Rversteeg]

There should be a Volvo dealer who probably still has a 940 coil in stock. Twelve years ago, during my vacation in France I had a problem with my 940 that I could not get solved. A local garage tried a lot of the obvious things, all to no avail. At some point I suspected the coil and ordered one at the closest Volvo dealer in Lyon. I felt really bad about it, but I never collected it, as at some point the car was more or less driveable on petrol (it runs on LPG) and Lyon was still at quite distance. The dealer was not happy, as the coil was a special order.

After I returned home I managed to find the culprit. When running on LPG the petrol injectors are switched off. This relay was damaged due to water ingress and the 12V relay feed intermittently found its way to the petrol injectors. It had also damged the LPG computer, throwing in a bunch of strange symptoms to add to the confusion.

[Ltom]

Thanks Rversteeg. My nearest Volvo dealer is still some distance. Nothing was in stock in town and down here older Volvos are quite uncommon so a used part is unlikely.

I've ordered the part from Skandix and I'll update in a few days once it arrives.