Occasional stalling when flashing main beam
 

This is an odd one, although I'm sure I've seen it mentioned before somewhere. My 940 2.3 lpt sometimes stalls if I flash the main beam headlights. It doesn't do it all the time, and especially not when I try to make it do it to check why.

I've checked the obvious battery connections and under bonnet earth points, and all seems ok.

Any ideas on a possible reason and / or cure ?

If memory serves correctly, there's a multiple earth point behind the left hand headlamp that is shared by the headlamps and the ignition module which is hidden by the air cleaner.

Could be worth checking this by removing the screw/bolt that secures it, cleaning all connections with emery cloth or similar, refitting it and then covering in silicon grease or vaseline or similar to protect it. Also check the security of any crimped connections on the wiring, an ok looking crimp might be failing/failed internally so the "tug test" comes into play - hold the terminal and tug the wire to see if there's excess movement (it could be the wire is broken inside the insulation) or if the wire comes clean out of the crimp.

Hopefully that should see you right, it sounds like a borderline eareth fault that you won't find by visual inspection alone. ;) :D

Thanks for that. I noticed a few times when it's happened, the stereo presets disappear as well, as if there's a brief but total failure of power somewhere.

In that case you also need to check all the connections to/from the battery including all earths as well as feeds. Don't forget the longer leads that run from the battery to the starter, battery to chassis earths and any others you can find.

I had a look at that and they're all fine. (I removed and cleaned them anway, just in case). I cleaned the battery terminals as well while I was there, but the problem is still there, but not all the time. Are there any earths or other major power connections inside the car that could be loose, for example, behind the dash / instrument binnacle ? I think I remember seeing some earths once when I replaced a duff speedo on an older 940, but it was a few years ago so I couldn't be sure.

Another thought I had is this. Over the winter, the battery went flat a few times, especially when I didn't use the car for more than a few days. The odd thing was, when I jump started it, the radio presets had all been lost, just like what still happens if I flash the main beams and the car stalls.
I thought I'd better ask on here first, in case anyone else has ever had this problem, and to save me having to start pulling the car to bits unnecessarily.

Just to clarify, are you saying when the engine stalls because you've flashed the headlights the memory for the radio is lost?

Also a diagnostic question or two :

If the headlamps are on (i.e. dipped beam) and you operate the headlight flasher, does it still stall?

Have you replaced any fuses in the fusebox at any point? I'm referring to the fusebox behind the ashtray that can be slid out for access.

Last diagnostic question, bit strange but bear with me, is the action of the flasher switch nice and positive or a bit "woolly round the edges"?

Yes. But it only happens occasionally, as with any annoying problem when attempting to diagnose it.

Yes, but not every time. It makes things slightly uncertain, for example if you want to flash to let someone out of a junction you never know if the car's going to cut out. I'd say it only does it one time in 10, but it's so random. When I try to see if will happen again when I'm somewhere it wouldn't cause a problem if it stalled, it never does it,

No.

[quote]
Seems fine, although I can check it again now you've mentioned it.

I've just remembered another thing which may or may not be related to this. The dashboard light dimmer switch stopped working a few months ago, and now, if you start the car at night, the are no dashboard lights at all, and they gradually come on and get up to normal brightness, but it takes about 4 or 5 minutes of driving first.

After a lot of long, hard thought, checking diagrams, double checking them and then checking them again, everything is pointing to the headlight main beam/flasher relay in the fuse box. Not necessarily the relay itself but the earth that comes from terminal 85 on it. That should go to a common earth somewhere on the fusebox (it's shown as having a lot of connections so possibly a bar of some description, could be slightly hidden with just connectors plugged into it) which appears to then have a separate earth cable from there to a body mounted earth nearby.

The instrument lights also earth out through the same point as the headlight main/flash relay coil and thanks to the magic of back-feeds, could be enough to upset the relay coil that switches the fuel injectors on. If i've got the other bits right then that relay is commonly known as the Radio Suppression Relay which is a fairly well-known cause of non-starting and/or cutting out.

In this case though it seems a bad earth is responsible for knocking that relay out.

Normally at this point i'd be pretty sure of my ideas and have 99% certainty of having found the problem. However as this one is intermittent for one thing and secondly it's a strange, "not clearly defined" fault (nothing wrong with what you've said, it's just the fault doesn't seem to have clear times when it happens) and thirdly it's "remote diagnosis" there is a chance i haven't got it right.

That said we're not going to know until you pull the fusebox out and make sure the earths are good and that the fusebox goes back correctly into its slides.

Good luck and let me know how it goes! ;) :D

Thanks for all your input on this. I've been so busy recently that I've not had chance to check the relays. It did it again tonight, but instead of actually cutting out, it nearly cut out, but then carried on for a few miles first, then cut out. In it's death throes, it tried to die a few times, and the ABS light came on. Also, there was some interference noise through the stereo speakers. Once it had stalled and I restarted it, it was fine. I was able to use the main beam for the rest of the evening with no problems. I'll have a look at it this week.

Have you checked the alternator is charging correctly? It may be an intermittent fault on the brush pack (with the voltage regulator built into it). Try to get a multi meter on it and get someone to put heavy loads on the alternator (high beams, radio etc) to see what the voltage does when it cuts out.

Also check the signal wire that runs to the alternator (smaller wire which references battery voltage).