Fuel shut off valve/solenoid

[topgear]

Hi there,
As most of you probably know ive been having rough running problems with my 1.6 VDP for about a year now, lumpy after the first ten minutes of running, and revs dropping and fluctuating, also a dramatic increase in the use of fuel...

... I have replaced the vacuum switch, and the Stepper motor O rings, the latter seemed to make a difference for a while concerning Miles Per Gallon, however it was still running rough.

... Today i adjusted the carb, mixture and fast idle - but the revs are still fluctuating.. i thought id try a little experiment, and i took both wires off the fuel shut off valve to see what happened, whilst the engine was running... It made no difference at all, which leads me to believe this is faulty! Am i right? Could this be the problem, or at least part of the problem? It says in the Haynes manual that this being faulty can attribute to the factor or increased fuel use! I have also smelt a little petrol for the past year or so when starting up, or switching off after a long run, just occasionally.

Your thoughts on this would be much appreciate.. would you reccomend me getting a new fuel shut off valve? where would the best place be to get one of these, and it is as easy as it looks to replace it?

Many thanks!
Topgear...

[advantage_d]

As I understand it the fuel shut off solonoid only operates when certain conditions are met, accelerator pedal switch is closed(foot off the pedal), revs in excess of 1300 rpm, air temerature above 6 deg centigrade and water temperature above 80deg c. It only operates for 5 cycles at half second intervals.

It does not operate as a fuel shot off valve to prevent overunning only as an economy device.

Hope this is some help.

[topgear]

Hi,

Many thanks for your reply.. that is useful to know, thank you.

How do i test whether its faulty or not? how about doing the same test as you would on the radiator thermostat, and joining the wires together with a piece of wire? Or is that a big no,no?

[SimonR]

Hi Topgear, I'm afraid that I can't offer much help but I think I'm in the same boat with my VP S-Series - it's probably actually worse than yours. I'll describe the symptoms below:

It starts fine and the revs immediately rise to about 1500 and then about 3-5 seconds later drop right down again and it nearly stalls, just as the battery light begins to come on it seems to correct itself and it repeats this cycle about 3 or 4 times. After about 30 seconds it seems to be running more smoothly but even then if I try to move it I have to get the revs very high otherwise as soon as I lift the clutch it cuts out - as if there's no power. Over the next ten or so minutes the tendency to cut out becomes reduced and the engine gets *a lot* smoother and far more powerful as it warms up.

My S-Series is still 'lumpy' when warm tho, I put this down to the fact that I changed the head over to unleaded and never changed the ECU to an unleaded one. It's running on optimax so maybe that wouldn't make any difference. What fuel are you running your VP on?

I, too, wondered if it was the overrun fuel cut off valve so I changed it and that made no difference.

I think that part of the problem with my car is that the fuel mixture is very weak - I had problems with a bunch of monkeys and their emissions test equipment at my local MOT test station so got my mechanic to make it very lean to pass. However if it is just weak mixture then I'd expect the engine to have these problems all the time, rather than just when cold.

Topgear - have you tried a different ECU? Could that be screwing up your timing?

[E_T_V]

No No....

To test simply unscrew it (yes it is that easy if you can get teh screw out) and put 12v across its terminals. if it moves smoothly it works. if it sticks it doesn't. I've always found the best thing is to just disconnect it all together. As said it only really works to save a little fuel (and I mean a little) when using engine braking down a hill for example. If it was stuck closed you'd soon know as the car wouldn't start. Try just disconnecting it and taping the connectors away from each other as they'll be live at some point. Doubt that'll be your problem though.

Is it an S series lump? If so just check the connections to the crank position sensor (on the front near the starter motor but on the engine side, ours had an intermittant contact which took ages to trace. Also try blowing out the vacuum tubes as sometimes fuel vapour can condense leaving a small blockage in the pipe.

Does it run well when you give it some welly i.e., is it just an idle problem? Or does it play up all the time. If it is all the time check for water in the carb. Only a tiny droplet is enough to cause havoc.

Also check the vacuum hose to the air flap thingy that selects hot or cold air. disconnect it at the engine end and suck the pipe. you shouldn't be able to suck much through it but the flap should move as you apply more negative pressure (I think it is that way round - I can't really remember what you have to remove to see it but I think it is just the bonnet to filter air intake pipe) if the valve is leaking, or infact any of those damn vacuum tubes it upsets it no-end.


Hope some of this might help

Cheers

Dan

[E_T_V]

Good point about the weak mixture. Weak mixtures cause hunting (cycling from high to low revs). Is the steppermotor richening up the mixture enough when cold? I remember that some o-rings swell and cause the steppermotor to stick. Might be worth just a check that it is still free to move. Also check the ambient air temberature sensor - behind one of the headlights from what I remember - the black chip thingy you have to disconnect and bridge with a certain resistance to tune the mixture up properly. I remember a mechanics face as he twiddled the screw on the top of the carb to try and lean up the mixture as it was failing the emisions test without following the correct proceedure. His face was a picture as he turned the screw it was ok for a second or two and then the car compensated itself back to where it was. I can't remember the exact proceedure but the Haynes will tell you. Also might be worth checking the timing is somewhere near where it should be.

Hope this helps too.

Cheers

Dan

[Wonko_The_Sane]

To test the electrics for the shutoff solenoid, disconnect it, and remove one of your indicators. Remove the blue bulb holder and disconnect it, and then plug that into the shutoff valve wires.

Start the engine, and use the throttle linkage at the carburettor to raise the idle speed above 1500rpm, without touching the accelerator pedal in the car. There is a contact on the accelerator that closes when the pedal is "at rest".

When the engine hits 1500rpm or so, the ECU reads the switch as closed and assumes an overrun condition, so it pulses power to the solenoid wires. The length of the power application depends on the engine speed-the higher the speed, the longer the duration of the power pulse.

Since you have a bulb connected instead of the solenoid, you should see the bulb flashing if it works. If it does, the system's OK. If not, check the wires at the accelerator. Mine were disconnected.

To check the solenoid itself shut the engine off, and use a spanner/wrench to undo the hex hut with the terminals on, on the bottom of the solenoid. You can then remove the moving part of the solenoid without disturbing the bit that fits on the carb body.

Plug the terminals on the removed solenoid mechanism into the wires vacated by the bulb unit on the indicators, and flick on the hazards.

If the solenoid "guts" are OK, you'll see it moving back and forth in time with the indicators.

While I had mine off, I wire wooled it to clean it and get a smooth action, and I cleaned up the rubber valve with boot polish to make it smooth and supple again. I then blasted it with WD40 and refitted it.

I tested it with a 12V bench pack, and powered it up with the ingine idling..sure enough it killed the engine..:) Good enough to tell me it works..:laugh: If you don't have one, I suppose an alternative would be to connect the horn wires to the solenoid and press the horn with the engine running to see if it dies when you hold the horn button in. Who said Maestros didn't have built in testing equipment? :laugh:

I no longer have the ECU connected personally, so my shutoff valve will become manual controlled soon as an additional "engine killer". Stealth immobilisation..;)

[e692wtt]

You may have changed the vacuum switch previously, but is the one that's on the carb at the present time faulty? Pull it off and suck through the 'hole' that the vacuum pipe to the carb goes onto - if you can suck air in, the vacuum switch has failed. And try the whole of the vacuum pipe from the vacuum switch to the carb to the ecu for integrity (suck on the vacuum pipe at the point where it meets the vacuum switch when connected, block the 'hole' that mounts onto the carb, and suck... don't blow, or you may damage the ecu). If any leaks, find and seal them.

The vacuum switch mounts on the side of the carb opposite to where the 'overrun fuel cut off' valve/switch goes, ie on the driver's side of the carb.

The other other Rich.:)

[topgear]

Hi all,

Many thanks for your replies and interest, and very useful information. Much appreciated!
Ive checked all hoses, tested the fuel shut off solenoid ( great test) and also the carb vacuum switch.. all ok.. so ive adjusted the mixture to the book, and its running a lot smoother now. and MPG is touching 40 now!!! Bit different to the 15 - 20 i was getting! So, looks like the O rings were the first problem, and since adjusting the mixture.. its all fine again! Also found that Optimax and Castrol additive has done wonders to performace and economy at the same time! Even if it is 78p a litre compares to 72p for premium unleaded! Its worth it!

Thanks again,
:-)