940 Advice on fuel problems

[940phil]

I have a 940 2.3 LPT estate, 130,000 miles, I've owned it 21 years from brand new.

About a year ago had intermittent problems with it stalling, refusing to start, etc. Pretty sure I traced this to the fuel pump relay. I dis-assembled the relay, gave the armature contacts a good cleaning with 2500 grit paper, and returned it to service, where it has behaved fine since.

Roll forward to 3 days ago and it stopped again - same symptoms as before, just stalls unexpectedly and refuses to start. I pulled the relay again, gave it a thump and a good telling off, but nothing will get it started again.

When I turn the ignition on I can hear the relay operate and also can hear the/a fuel pump operate for about 3-seconds, but still no life when I crank it.

I understand there are two pumps, a lift pump in the tank and a high pressure pump in line under the car. I presume 940's had this dual pump arrangement right up to their last year of manufacture?

As I can hear a pump run when I switch the ignition on, I'm assuming one of them works.

So to my question, at last: Are both pumps powered in the same way, or does the lift pump operate separately? If one pump goes intermittent, will it still run, or are both essential? Any suggestions where I should look first?

After 21 years this car owes me nothing, and almost any repair is economically unsound. But it still drives like the day I bought it (well, when I can start it anyway) and I'm damned if I'm giving up on it without a good crack at trying to diagnose and resolve this.

Grateful for any help and advice.

[ThePurplePanther]

Have you checked the pressure in the fuel rail (there is a valve with a dust cap on it on the rail)?

That is where i'd start - make sure it is a fuel problem.

PP

[aardvarkash10]

are you SURE its a fuel problem?

When the engine dies , does the tacho immediately drop to zero, even as the engine is spinning down? If so, its MOST likely ignition

As you crank the engine, is the tacho "pulsing" If not, its MOST likely ignition.

[Laird Scooby]

I know what the other two are getting at with checking the tacho etc and agree you need to narrow it down to ignition or fuel.

Try squirting some Ezi-Start in the air intake while an assistant tries starting it. If it fires, it's almost certainly petrol.

It could be condensation in the tank, built up over the 21 years you've owned it. Adding 2L of meths to about 4 gallons or less of fuel already in the tank will remove the condensation.

https://www.toolstation.com/shop/p99550?searchstr=methy

Also worth doing the pressure check to make sure both pumps are running and yes, it will matter if one or the other isn't running. Usually you get warning signs of it happening though, strange noises coming from a pump, holding back and sometimes a few other symptoms.

My first guess would be condensation in the tank, second guess would be the Crank Position Sensor (mounted on the bell housing near the cylinder head) not giving the ignition signal needed to fire the engine. Third would be the fuel pump relay but if you've recently revived it, probably not but worth checking again.

[940phil]

Many thanks for the really helpful responses.

If my understanding is correct this very late model 940 may only have one pump, located in the tank. I need to have a look underneath in daylight to check.

Last night I tried fitting a new cheapie pump relay, just for good measure, and no difference. I am also quite sure I can hear the pump run every time I turn the ignition on. But just for good measure I opened the access cover and whacked the filler/level/pump assembly on the tank a few times. Still no sign of life.

So I am now beginning to doubt my initial diagnosis, and wonder if it is in fact an ignition issue rather than a fuel supply issue.

Next I will try blipping the Schrader valve on the supply rail and see if there's pressure there.

When it stopped there was no warning, it was running fine, then suddenly nothing and the dashboard lit up like a branch of Dixons. I didn't notice if the tacho fell straight to 0 or not.

I had the car taken home on a truck, and a few hours later it started and ran perfectly.

I then (pretty stupidly) took the car for a drive. After about 3 miles it stalled again. But started 10 seconds later. I then got another 1,000 Metres before it stopped again, and hasn't gone since.

Dose this sound characteristic of the crankshaft sensor giving out, because I wouldn't expect the ignition coil or any electronics to come and go in this way?

Unfortunately it is now parked about half a mile from my house, so I am trying to diagnose this in the road. If I get no further with it I will arrange to tow it home and do some more thorough diagnosis there.

Good advice about the condensation, but there was absolutely no hint of a problem prior to this - no misfiring or loss of power etc. Just went straight from running like a dream to being a nightmare...

[ThePurplePanther]

Were you turning hard or braking hard when it died?

Just thinking out loud could be a loose plug or dodgy earth - might explain the intermittent nature of it. Might be worth going around as many sensor plugs as you can and unplugging - good squirt of contact cleaner - work the plug in and out a few times to really clean the contact and see if this helps.

Oh, and have you checked the battery voltage and if the alternator is producing sufficient charging power? Also is the alternator belt tight?

Just want to rule out the obvious and easy to diagnose - i know how fun it is trying to do all this guff at the road side (esp in this weather)

Good luck

PP

[mocambique-amazone]

Hi Phil, nightmare.... this isn't the right word!
After 21 years this car will tell you: I need some care ;-)

1997 is with one pump
This pump will die suddenly, the schrader valve is the "to check point"
Flywheel sensor: Yes! it's prone to not live 21 years. If this is the first one, lucky guy
Did the car ever got a new fuel filter?


"After 21 years this car owes me nothing, and almost any repair is economically unsound"

No, I think totally different to you. If you won't change your mind, make a gift to me and I will fly to the United Kingdom (it's still allowed till march of next year, who knows what will be after) and be a proud owner of a 1997, hape to drive him to Germany.

kindly, Kay

[GreenBrick]

I think I have a spare crank sensor you can have for the cost of postage, if you want me to dig it out..?

[Laird Scooby]

Originally Posted by 940phil

Dose this sound characteristic of the crankshaft sensor giving out, because I wouldn't expect the ignition coil or any electronics to come and go in this way?

Strangely enough, yes. I've not had one go but from what i understand they're in a prime position to get covered in leaked engine oil (from the rocker cover) which then rots the insulation. This can cause short circuits between the signal wires and in some cases, the wires break.
As things cool down, the wires move and all of a sudden, you can start the car again. As you rightly say, electronic stuff usually works or doesn't but a heat-related fault can have you guessing for a long time!

Also a funny one i did have on one of mine, similar symptoms but the fuseholder was to blame. It had got hot at some point and burned.
Every time it got hot afterwards, the increased resistance from the hot contacts meant the fuel pump stopped.

Pulling the fuse and refitting it effected a temporary cure, i later rewired it onto a new separate fuseholder.

On my next 740, i thought i would check that as it had been a problem with the last one - someone had already been in there and done similar.

This was 14 ish years ago, at that time my 740s would have been a similar age to your 940 now so could be a similar problem. Strangely this problem only seemed to effect some fuseboxes, others were fine. Perhaps different fusebox manufacturers?

Certainly worth checking the fuseholder, also the fuse for a hairline fracture which may well give similar symptoms - remove the fuse and hold it up to the light to see. Worth checking the crank sensor as well, if only to eliminate it from the process.

I'm with our friend in Germany - well worth investigating and fixing! While the car may owe you nothing after 21 years, it's worth a lot more than nothing and for the sake of a few quid in diagnostics materials and/or components to fix it could happily go for another 21 years.

[940phil]

Had another quick look last night, but the failing light and snow (and the cold) limited my stamina to spend much time on it.

When I crank it the tacho doesn't blip at all. Does that point to the crankshaft sensor? In 21 years I have never noticed if the tacho normally pulses when the car is cranked (other than that fuel pump relay problem a year ago it started on its first spin of the starter every single time)

I tried waggling the wire to the sensor just to see if that made a difference, but zilch.

Purple Panther - not braking or turning. Just driving along a dead straight road at about 35mph, not a hint of trouble in the 20 min long journey prior to that.

Both the times it stalled when I stupidly took it for a drive, the same is true, straight road, cruising along, then suddenly no power.

Next time I go I'll check for fuel pressure at the schrader valve on the fuel rail