Volvo 940 Starts then dies very occasionally

[Dirty Rooster]

I had a good one on evilbay for my previous car, just make sure it's the right type.
you can remove your own easily to check how it looks, and that's good practice for refitting the new one.
My current car still has an OEM which is jammed in tightly, so if it goes bad I'm going to have a right headache.

[Pete940]

LH2.4 does normally require a few rotations before starting, so that might be normal.

With regards to the relay, the white cover clips onto the base so you need to prise it off. You can put a finger on the relay and feel it click when starting - have a gander at the relay testing procedure on the FAQ site.

[Eyebrows123]

Oh sorry, I misread the previous thing regarding the relay. I thought the problem was the solder connections on the board the relay attaches to rather than the relay itself. I'm quite happy dismantling the relay and sorting it out, in fact might crack it open and give it a clean, see if there's any carbon build up over the years.

Also, I don't have a 2.4. I have a petrol 2.3 lpt, I'm pretty sure it takes twice as long to crank over than any other petrol ive seen but it always takes exactly the same amount of time. And with the exception of twice, it has always started.

[TonyS9]

The igniton sensor pattern only has one indicator per rotation before the computer knows where the crank is. Its a bit poor, the renix on the 300 series has 2.

Anyway once it hits this it starts producing sparks and triggering the rev counter, and if there are fuel relay problems you can see the rev counter triggering but no life. I think it may not send rpm info to the fuel computer (to allow fuel) until tdc so that fuel is not dumped into the cyls without spark.

The rpm signal comes from the coil primary low voltage side, but the rev counter triggers from high voltage coil back EMF induced in the primary not the 12V drive signal. Its not 100% indication of spark but close to it. You might want to confirm sparks with some spark checkers on the plugs.

In a good car you should not see the needle move without the engine starting immediately.

[Pete940]

Originally Posted by Eyebrows123

Oh sorry, I misread the previous thing regarding the relay. I thought the problem was the solder connections on the board the relay attaches to rather than the relay itself. I'm quite happy dismantling the relay and sorting it out, in fact might crack it open and give it a clean, see if there's any carbon build up over the years.

Also, I don't have a 2.4. I have a petrol 2.3 lpt, I'm pretty sure it takes twice as long to crank over than any other petrol ive seen but it always takes exactly the same amount of time. And with the exception of twice, it has always started.

That explains it. I wondered if you were talking about the whole relay block.

Lh2.4 is the Bosch engine management system. It's used on all petrol 940's as far as I know.

[Eyebrows123]

Oh apologies, thought you were talking about the 2.4 diesel engine. My bad!

I'm pretty sure mine takes longer than usual as from what I've seen before most people's car will spin over (the rev counter won't budge) and then it'll fire straight up. Mine the rev counter won't budge, then it'll get signal and bounce a few times then start but it doesn't really start with a roar. I'll try video it if possible.

So does the rev counter run off the coil or the ECU? And I've replaced the spark plugs very recently with Volvo ones and the ignition system was only replaced a couple of years ago. Might pop the dizzy cap and have a look in there to see how that's doing. It's just strange that it should take a few more cranks before firing. And the fact that it does exactly the same thing every time.

[Dirty Rooster]

Originally Posted by Eyebrows123

...I'm quite happy dismantling the relay and sorting it out, in fact might crack it open and give it a clean, see if there's any carbon build up over the years.

The relays are cheap on evilbay.
It isn't carbon that kills them, its the solder joints that crack and they can be fixed but buying a new one is easier.

[TonyS9]

Originally Posted by Eyebrows123

So does the rev counter run off the coil or the ECU? And I've replaced the spark plugs very recently with Volvo ones and the ignition system was only replaced a couple of years ago. Might pop the dizzy cap and have a look in there to see how that's doing. It's just strange that it should take a few more cranks before firing. And the fact that it does exactly the same thing every time.

See my post above, I just answered this question. But anyway I agree it seems either HT side or fuel/air leaks, unless its something more mechanical like poor compression.

[Rversteeg]

I found that if the engine for some reason does not pick up immediatly after cold starting and a second start attempt is necessary, you have to press the pedal a bit to start. It seems like the ECU only enriches the fuel mixture on the first start attempt. It makes sense because otherwise the engine might by flooded by multiple start attempts.

[Eyebrows123]

Right, went and did some probing around on the car. I took a couple of videos of it starting, then turned it off, waited 20 seconds and started it again, I have attached the videos, the longer one is the second time. Typically though it seemed to start slightly faster than usual (always the case when the camera is rolling isn't it!). Anyway, wriggled the Crank sensor and it didn't seem to have any effect on the engine running so I'm going to guess it's ok? Another problem I've always had is a squealing sound, you can hear it in the engine on the second video as soon as I rev the engine when standing in front of the bonnet, does anyone know what this could be or do I need to probe around with a stethoscope?

As for the relay, I took it out and took the cover off, it all looked fine and I took a picture.

Good point about the ECU possibly not sending fuel in for a second start, that would explain why the pumping of the accelerator is required. I don't have a compression tester on me but in a couple of months time I might try do one.

Anyway, what do you think about the videos and photo? Or should I just stop worrying about it and live with it?

The first start:

https://drive.google.com/open?id=0B-...3B3UVdpSWJYQU0

The second start:

https://drive.google.com/open?id=0B-...XNyRTlHR1I2M2M

Thanks for all the help so far, really do appreciate it!