406 GLX - 2.1l TD R-reg - engine hunting/pulsing

Hope someone can help with this or at least point me in the right direction.

Got a problem with my car where the revs suddenly start to rise and then the engine "pulses" or "hunts" between 1500 and 1900 revs. It can happen if I'm at a set of lights without touching the accelerator. At tick-over the revs are pretty much correct and it's never stalled (not without my help anyway! LOL). I can find the bite with the clutch and that pulls the revs back down to normal but once I press the clutch in the revs go back to the pulsing bit.

Sometimes I can be driving along and if the revs drop down to around the pulsing area (around 1700-1800) the car starts to kangaroo a little because the engine tries to maintain the 1700 revs. Sometimes that can be quite a strong pull and others the engine will happily drop below that level.

I just don't know where to turn first. I don't know if it's a valve problem somewhere or maybe a flow sensor problem? It can't be a sticking accelerator cable because it can happen even when I'm not touching the accelerator. The air filter has been changed and so has the fuel filter.

Any ideas would be very much appreciated. I'm a designer and just haven't a clue where to look. If it's fixable without going to a garage then I'll definately try and do it myself (not THAT useless LOL).

Daz

Reply to
Darren
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sounds like a flow sensor or fuel pump not keeping up with the feed for the engine,

Reply to
Chris
*snip*

Someone at the parts place mentioned a flow sensor when I was buying the fuel filter. Are they expensive and can they be fitted at home or is it a dealer job?

Just finished trawling through 3 years worth of posts in here (giganews retention is HUGE! lol) and read a post about a dirty idle valve causing pulsing revs too. Is that a possiblity? Where is it for me to clean? God I feel dumb! LOL. I think I need to get a Haynes Manual! lol

Thanks

Daz

Reply to
Darren

It might be worth checking for small amounts of air getting into the fuel lines between the injection pump and the tank, perhaps through a fuel filter seal or a worn o-ring on a banjo union if that model has any. If I remember correctly this can be unnoticeable at higher rpm but cause instability at idle.

J
Reply to
johntyers

Hi J That may well be worth looking into. It only seems to start playing up once the engine has been running for maybe 5 mins so things will hav started to warm up by then so if there are any gaps for the air to get in they would be much more likely to open once warm.

Now I have to go and get a Haynes from somewhere cos I have no idea what a banjo union is! LOL I'll also wait until it's starting to pulse then I'll go round the fuel path in the engine compartment and see if covering things drops the revs back to normal. That may help track down any air leaks. If there's a point where air is getting in, would I see a drop or two of fuel getting out??

Thanks for that

Daz

Reply to
Darren

Darren wrote: . That may help

Unlikely. If a section of clear tubing could be inserted in the inlet side of the injection pump you could look for air bubbles in it but if you're not sure take it to a specialist because diesel fuel under pressure can penetrate the skin and kill.

J
Reply to
johntyers

Wow OK. I think the problem IS air getting in somewhere. There's a clearish section of tubing that goes from around the priming bulb-pump thing to the fuel filter tank and I could see little bubbles of air flowing through it. Just don't know where they are getting in. I think I'm going to have to take it to someone who actually know what they are doing rather than trying to do it myself. At least there's a good chance of being able to narrow it down and fix it pretty quickly now (hopefully).

Daz

Reply to
Darren

The dangerous high pressure is between the pump and injectors, and the pipes are metal, all other pipes are low pressure, supply and return, quite right to point this out though J, The most common places that cause air ingress with this engine,

1, The primer bulb its self, (take it out and by-pass it) about £10 - £12 for new part 2, large "O" ring situated under the plastic fuel filter bowl, (remove filter, 13mm bolt in bottom of bowl, lift bowl and seal up with silicone or replace "O" ring can be about £5 - £6 from dealer ,, a bit expensive for what it is ?? these are two of the easier , quickies to attack first , These are tips I got from this NG a few years ago, and they worked for me ?? HTH Fitzy
Reply to
Fitzy

*snip*

Thanks Fitzy It's got a chance of being the primer bulb then. The air bubbles seem to be going towards the fuel filter tank. Hopefully it's that cos it's nice a cheap to fix and I can do it myself! LOL

I'll give it a whirl at the weekend.

Daz

Reply to
Darren

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