Strange revs behaviour - with video

[Phil Peters]

Hi all,

Maurice has developed a bit of an 'interesting' characteristic over the last few days which I'm hoping some of you more experienced BXers might be able to help diagnose.

The car is a diesel with manual gearbox and the issue happens when driving during gear change. My other half was using the car for work this morning but turned around and came home again reporting that the car had cut out numerous times at junctions etc.

I then took the car out for a spin to see what was going on. Here's a brief video shot on my phone showing the symptoms. You'll see me accelerate from first to second gear and then take the car out of gear at about 1,750rpm. The rev counter plummets down to around 250rpm and bounces back up to tickover again. I'm pretty sure the car's never done this before.



My initial thought was that it was something electrical but having tested the battery, it's showing 13V on the multimeter.

We've been for another blast round the block in it just now (other half behind the wheel again) and while it didn't cut out, there's still this issue with the revs

Any ideas of what to check would be much appreciated. We're heading down south to visit family in a few hours but I need to know the car is going to be able to hack a 200+ mile round trip up and down the M40.

Cheers,

Phil

[Phil Peters]

Just spotted this thread by hvanman, symptoms sound very similar.

Did you ever get to the bottom of this issue hvanman?

[mat_fenwick]

I can't tell from the video whether the engine revs follow the needle, but it doesn't look like it from the speed the needle falls. I think Hvanman's problem was engine actually cutting out.

Yours looks to be simply the rev counter sensor failing - I would expect it to get worse, especially when warm. It may be possible that it's simply shifted position, but more likely that it needs replacing. It's not an uncommon fault.

[ghaddon1701]

Anti stall set incorrectly? Or gone out of adjustment somehow?

[mat_fenwick]

reporting that the car had cut out numerous times at junctions etc.

Sorry, I missed this part Ignore my suggestion about the rev counter sensor!

[Phil Peters]

Thanks for the responses so far guys. A couple of things worth checking there, for sure.

Hopefully after some further investigation next week we'll be able to figure out what's causing it.

[KevR]

Anti stall set incorrectly? Or gone out of adjustment somehow?

Or the anti-stall lever's seized onto the shaft it shares with the cold start lever - small shaft at the pulley end of the pump. Both levers should be able to move independently on the shaft but they end up sticking. Quite common on the CAV/Roto Diesel pumps - easy to sort out, just lube the pivots and move the levers 'til they move freely and independently.

[Phil Peters]

Many thanks for this Kev, I'll check out the movement on the levers today and see if they're okay.

Cheers,

Phil

[Phil Peters]

A quick update on this issue for anyone following along at home...

I followed KevR's advice and had a look at the anti-stall and cold start levers. They seemed a bit stiff so I cleaned them up and lubricated the pivots which did free them up a bit. Unfortunately, the problem still persisted when I took the car out for a test drive.

The car was booked in for cambelt and waterpump change anyway so while it was in the garage last week I asked them to check out the stalling issue. When the car was returned the guys said they'd "adjusted the choke" - I assume they mean the fast idle control. For a short while this seemed to have cured the problem but then it reappeared again just as before, culminating in a nightmare journey back into Leamington from Birmingham on Saturday night with the car stalling at each and every junction once we were off the motorway.

I had a bit of a think about this yesterday. The car can be re-started immediately after it stalls so I'm still leaning towards it being a fuelling issue rather than an electrical issue. ghaddon1701's suggestion that the anti-stall has somehow gone out of adjustment would seem to fit with the symptoms. Does anyone know what could cause this? Possibly worn cables stretching?

There's an engine deceleration test described in the workshop manual as follows:

Bring engine speed at 3000 rpm, then release the accelerator lever :
- in case the deceleration is too fast, (engine often stalling), unscrew stop-screw by 1/4 turn.
- in case the deceleration is too slow, (poor engine braking), screw up stop-screw by 1/4 turn.

I love the translation of the workshop manual; you pretty much have to read it with a French accent.

When I get chance this week, I'll run through this test procedure and also check the anti-stall adjustment settings as per the manual.

[Phil Peters]

Just had a couple of minutes at lunch time to stick my head under the bonnet again. I noticed this piece had come adrift:



It was lodged in one of the small recesses at the front of the pump (photo robbed off the internet and subsequently circled):



Out of interest, what do these things do?

[Defender110]

It is a lead seal that is fitted at the factory to stop the factory settings being tampered with. If this was removed a warranty claim would be void.

[ghaddon1701]

It was probably attached to the engine max speed adjustment screw. You can see it attached on the image. Above and to the right of your red circle. Going back to the anti stall adjustment. To set properly you need a set of feeler guages and a 3mm allen key or piece of wire/rod of the same thickness. The procedure is explained in the haynes manual.

Regards Graham

[peanuts]

Hi - does the engine start from cold normally? I was thinking about fuel related issues, filter replacement for example. Other thing that crossed my mind was the fuel solonoid. I've had a faulty one before now although granted it's odd that the car starts and goes okay at speed. Perhaps take the plunger out of the middle, run the car and see if it stalls. You would have the stall the engine to stop again but it might rule that bit out.

Have you checked all the hoses and pipework? when it is running at low speeds does it feel lumpy or like it has a misfire? Several possibly silly questions there but it might inspire something!

[citsncycles]

If the stop solenoid is similar to that fitted to the carb on my GS, then it could be this - when that failed last year it would start ok and drive fine above 1500rpm as the fuel flow would push the plunger back, but below that speed the plunger would close and the car would stall.

[Phil Peters]

I was on my way to the petrol station last night after work and I remembered that when I used to own an XUD engined Pug 306 TDS some years ago, I put some diesel fuel system cleaner in the tank every now and then as preventative maintenance. I later sold the car and bought a Reliant Scimitar but the Pug was running like a champ on 180k miles when I sold it. In hindsight, possibly the only car I've ever regretted selling, and certainly an influence on buying the BX further down the line. Anyway, I digress...

I realised I hadn't put any fuel system cleaner in the BX since I bought the car last summer so I added some to the tank when I filled up. After an 80 mile round trip last night, the stalling symptoms seem to be significantly reduced and - dare I say it - maybe even solved. Perhaps this is due to one of the following:

• a) Joy of joys, fuel system cleaner has done its job shifted some dirt out of the fuel system somewhere.
  
  b) There was water in the existing diesel which has now been diluted by the full tank of fresh fuel and actually nothing to do with hard earned spondoolies squandered on fuel system cleaner.
  
  c) This car is French and is therefore at liberty to do as it pleases, when it pleases. Owner should know better than to be fooled by temporary Gallic compliance on M40. Issue is still there and still needs sorting.

That being the case, I'm still going to run the anti-stall test and adjustment on the diesel pump on Saturday to make sure that everything is set up as it should be. Earlier this week I put together a home-made 'kit' for testing the anti-stall comprising of a piece of 3mm rod and a small length of 3mm flat bar, both in 304 stainless steel. Having assembled the kit, I might as well actually see some use out of it!