ZX Diesel Trouble - Any Ideas?

[Negative Creep]

My ZX has suddenly developed an intermittant problem in random stalling when braking under load. The revs drop off which is sometimes enough to stall it but other times it idles roughly for a few seconds before returning to normal. Thing is it's only happened on a few occasions (Saturday night and today) and seemingly only when the engine is fairly cold.So any ideas what it could be? I changed the fuel filter last week and bled the fuel system (didn't seem to be any air in there anyway) but it worked fine for the next few days. It's a bit juddery when lifting off but has been doing that for a while and pulls fine throughout the rest of the rev range. I did think a split vaccuum hose but then surely it would do it all the time? Possibly still air in the system? it's the 1.9 XUD non turbo with a Lucas pump

[Rocket88]

Had this before, but in an old Yank, so may not apply, it was a small split in the feed pipe from rocker cover to the brake servo.

[retrogeezer]

Not sure about ZX's but apparently Mondeos have a speed sensor on the gearbox to keep the revs up under heavy braking. If it fails, then the car will stall so sounds like a similar thing.

[jonkw]

Those 19D ZX's really don't have anything very complicated enough to go wrong, so this sounds like an air in diesel problem. Have a look at the little rubber return pipes between the injectors and the pipe back from the last injector to the return on the diesel pump. These pipes crack and perish over the years and will then draw air. You can replace them will small bore fuel piping.As it was Ok before you changed the diesel filter, maybe double check that the 4 allen bolts on the filter head are all done up nice and tight, then squeeze the rubber primer bulb a few more times, does it go hard? If it doesn't, there air in there or an air leak. The last suspect (although it's pretty rare) is the primer bulb itself. Over the years they can develop small cracks in the rubber due to being squeezed so many times during the course of servicing etc.

[kelvin2008]

does sound like an airleak, being as its diesel it will have a vacum pump on the end of the camshaft direct or v belt driven so Its a separate system unlike a petrol so I cant see how a servo hose leak will stall it as it should run well even without the pump being connected. Or if not air leak on diesel supply side then being as it does it whilst cold maybe the anti stall device connected to the coolant thermostat housing near the diesel injection pump.

[Andrew353w]

Ah ha! I've had a Citroen diesel with this problem and it was an air leak! Mine had one of those "bubbles" you had to squeeze to bleed out the air when you've changed the fuel filter. You knew you'd bled it when the "bubble" goes hard... Mine had a tiny air leak (took ages to find the split in the pipe) and the reason why the engine only stalls at tick-over or over run is because at this time the engine's using very little fuel, and the extra air makes the mixture too weak; when the engine's running normally this little extra bit of air is so little it makes no difference. Go over the pipes again... it's there somewhere! I suppose the brake servo connection to the inlet manifold could have a small leak too.I hope this helps!

[kelvin2008]

There is no brake servo connection to the inlet manifold, its a seperate system with its own vac pump

[Negative Creep]

Ok thanks for all the advice, as you would expect with these things it hasn't done it since. I checked the fuel filter and it's on tight and no obvious splits or leaks in the pipes either. One thing I have noticed is that to get it started after changing the filter I had to pump the bulb until it was solid. Now on startup or whilst running it is squidgy - is it supposed to be like that?Also still getting the slight jerk on lift off despite changing the oil and filters. Any ideas on what that might be?

[kelvin2008]

yes whilst running it will be softer as the fuel return to the tank is now open. Did you bleed all the bleed points starting from the filter to the injectors? still sounds like air getting in somewhere, was the filter a element or a spin on can?

[kelvin2008]

just thought of what I did once to eliminate the fuel filter housing, I bought a half meter long piece of fuel pipe with jubilee clips and bypassed the filter straight from the bulb to the injection pump inlet just to see if it helped. The O ring under the filter housing can leak air once its disturbed but I doubt you took that much apart so just change the top one.

[Negative Creep]

I dropped it into the local garage for them to take a look. The changed the breather pipes, re attached a loose one, cleaned out the engine stop solenoid - and it's still doing it. Now it's stalling so often as to be undriveable which is why I'm here tying this instead of being at work. Other than that they don't know what's causing it, except perhaps water in the fuel tank? I've brimmed it up which had no effect, but maybe the last batch was contaminated?

 

If it helps, I've made a video of what happens, except on these occasions it doesn't stall (taken by a passenger on a private road obviously). You can hear the engine struggling as it drops to about 500rpm, something it's never done before. Is there any sort of idle control or stabilisation valve?

 

http://smg.photobucket.com/albums/v405/ ... 009001.flv

[r.welfare]

Is it only doing it when cold? Your temp gauge (next to the speedo in the vid) seems to indicate otherwise...

 

I think these have a cold-running waxstat thing that keep the revs up until it's warmed. Mine idles at about 1100rpm when cold, lowering to 750-800rpm when hot.

 

I've not owned a Lucas-pumped NA diesel, but on a Bosch-pumped 405 the accelerator cable has a little split pin on it next to a metal bracket which can be moved on the cable's thread (if that makes sense) to change the idle revs (I think it's there to counteract the strength of the return spring on the fuel pump - but I'm no mechanic so might just be spouting turnips there). Might be worth investigating if yours is similar, or if the split pin is missing. The split pin should be where I've put the red circle on the photo below (sorry it's a bit small):

 

[scruff]

Couple of QsDoes it start OK after it has stopped, or does it crank over and over and eventually fire??Does it idle OK or is it really lumpy and struggling??

[Milford Cubicle]

Bloody hell, your engine bay is clean.

[r.welfare]

Not mine! I stole the photo from the Australian website, Autospeed - they did a pretty good series of articles on how to tune the 1.9TD up.Air leaks - my old saloon had an issue with this, being really hard to start in the morning...took a minute of cranking before it would fire, on 3 cylinders initially, with loads of grey smoke. Went onto all 4 after about 30 seconds and would be fine after that - I believe they self-bleed when running? Solved by replacing the primer bulb in the end.I would have thought that any contamination in the fuel would show up in a reluctance to rev, as well?

[Milford Cubicle]

Oh aye, I thought I recognised those red marks on the injection pump.My engine bay is clarted with vegetable oil, it seems to get everywhere during filter changes.The fuel delivery and filter set up on these is a pain in the arse when it goes wrong, there are so many ways for air to get in/fuel to escape. I'm thinking of ditching the standard set up and installing something simpler.

[Negative Creep]

Update time. Friday night on the way to work it ran like a bag of shite, juddering and stalling several times, including approaching a busy roundabout which was fun. Anyway, out of more hope than expectation I tried some of that Dry Fuel stuff (water in the tank maybe) and then went for a 45 minute run on the local A road, not taking my foot off the accelerator for the entire time. Get back into town and it then behaves perfectly.Started it up today and it ran better on the way to work but still stalled a few times. This time the revs didn't seem to drop off though, it just stalled. On the way home from work - you guessed it - didn't misbehave once. Even tried repeatedly to get it to stall by accelerating hard then stopping quickly, but wasn't interested. Now I'm even more confused!