940 b230ft random engine stalling
 

Hello fellow Volvo guys!

My manuel 93” 940 have developed a new problem....
It just recently started to die out on my when it’s warm. Like I said in the title it comes randomly.
I have tried to trigger it but reving high by babying the throttle, easing into it, flat out at low rpm but no results, it took it like a champ. I can drive for a long distance on the freeway no problem...

The times it died for me: when shifting from 2nd to 3rd, putting in reverse and even cruising in 3rd and 4th, top of 2nd doing a pull.

The first times it did it, it started up fairly quick but the last couple of times I had to wait a few minutes before it fired back up, It does stutter sometimes when it fails to start... when it drives there is no noticeable difference and pulls and drives smooth.

When it dies the rpm gauge drops to 0 and when I give it a little gas(when still rolling in 2nd or 3rd) it make this “nice” backfire pop so I’m guessing it is not the fuel but the igniting might be the problem? sometimes when Rolling long enough the rpm gauge goes back up to whatever rpm it should be and the car drives perfectly like nothing happend

I have checked the od relay and fuel pump relay and they look like new inside(pics included).It did however sound the same way when i try to start it without the pump relay as when it dies
Any one have had this problem before and yes i have searched the Forums but couldnt find anyone with the exatct same problem.

Best greetings from Denmark

crank position sensor on the bellhousing behind the cylinder head.

Just replace it. There are about a million threads on this forum on the subject with plenty of advice - I think there is a pictorial how-to as well.

My guess... somewhere a whire losing insulation and grounding randomly.

If you are losing the rev counter (going to 0), and the engine is still turning (say its in gear and slowing down), then you definately have an igntion problem. The rev counter is driven by the back emf from the coil (output driven by ignition amp). The rev counter will work provided the engine is turning, it only needs the crank position for input (via the ignition ECU and amp).

There are 2 common(ish) proiblems

1. crank sensor (CPS)
2. Amp failure on high temps (ignition amplifier)

If you are still getting fuel during the fail condition (from the pop) then it seems the CPS is still working (the fuel ecu would cut the pump if there is no 5v signal from the ignition ECU). If you could connect a light to the fuel pump power then that would confirm it if you see it still lit during fail condition. I have often said a fuel pump power indicator would massively help diagnose these types of problem.

I would therefore go for the ignition amp at this point.

There can be other problems of course, like the coil, but that is more likely to be a complete failure, and these coils are very reliable.

FYI the fuel pump relay can fail in other ways than the solder joints, it does seem a bit underrated for the job and gets too hot. Always carry a spare.

https://youtu.be/36LdJ3cuuLk It doesnt sound anything like this, it doesent hesitate like the one in the video, it just turns and turns and turns but doesn’t start

I try and order one, a relay and a fuel filter and cross my fingers it’s the problem, thank you for your help

Almost certainly the CPS, as Ash said, just order one and renew it. It will cut the fuel supply as well if it's not giving an output. For the cost, it's not worth messing about and will eliminate it from the fault finding if it isn't that. I'll be amazed if it isn't though.

That YouTube video you linked to isn't a definitive indication of a faulty CPS by the way, that one obviously had enough of a contact left to prime the fuel system and cause a spark at the wrong time but it also sounds as if the timing is over-advanced on that one.

I have ordered the parts I’ve mentioned above and hoping its one of them that is faulty “fingers crossed”

Yup. And it stops randomly, and when it stops the tachometer drops like a stone. As you crank it, it doesn't fire and the tacho needle doesn't even flicker.

If you wait a bit - 30 seconds, two minutes, it varies - it will start and run.

Been there, done that, wiped my grease-stained hands on the t-shirt.

Replace the CPS. And the ignition amp as well. Job done in less than half an hour.

The video looks fake to me, he appears to be stopping the starter before it starts. Engine sounds aweful.