Never trust a French fuel gauge / Why my GTi won't start?

[Melchior]

AFAIK the pump runs all the time, I think supplying something like 3 bar pressure to the fuel rail. The injectors open for a set time to inject the amount required, the remaining fuel goes back to the tank. There is a pressure valve on the return end of the rail which controls how much to allow back to the tank - that valve and the pump together ensure constant pressure.

At least that's how I always understood it and how it's been in every other petrol injection car I've owned. Citroen may WELL be different!!

[Melchior]

Not an expert on fuel injection systems, but if the pump runs on pressure it may not run constantly anyway.

Would it be worth trying to clean up the rusty connection (or even replacing it) before bying a complete pump?

Not sure about that, it looks like the terminals on the pump itself are a bit shot. Photo isn't that great but you can see the general mess in that area:

[Way2go]

While the engine was running I could hear and feel the pump running but it was NOT constant. Seemed to be randomly going on and off - more off than on.

Next step - new pump...

???
Then it sounds as if the pump is working normally as the rail is pressurised, it will be commanded to run more frequently by the ECU as higher fuel demand is assessed. I suggest you are chasing the symptom rather than the cause. The cause is likely to be gummed up injectors as mentioned before.

[Melchior]

All 4 gummed up?
But that does not explain no fuel pressure in the feed pipe whilst cranking. When I got it running earlier there was pressure in the pipe whilst the pump was working. Then the engine died and the pipe was soft again.

Would the gumming up be visible if I removed an injector or is it more likely to be deep inside the thing? Just wondering if I can whip one off and have a quick look.

[mat_fenwick]

The pump should run continuously with the engine running - it's not cycled on and off with demand. The fuel needs to be kept circulating otherwise it will heat up and cause gummy deposits. It's not uncommon for people fitting LPG conversions to cut the petrol pump when running on gas, which leads to such problems. The only one I can think of which does regulate the fuel pump dependant on pressure, is the Jaguar S Type and (presumably) related vehicles (and that modulates the pump rather than cycling it on and off).

I do think a temporary feed to the fuel pump would be a good idea to prove/disprove the wiring. Or were you saying earlier that there was voltage across the FP at all times that there should be, but it seemed to cut in and out randomly even when voltage was present?

[Melchior]

The pump should run continuously with the engine running - it's not cycled on and off with demand.

Cheers, that has always been my experience with other types of car / fuel systems.

I do think a temporary feed to the fuel pump would be a good idea to prove/disprove the wiring. Or were you saying earlier that there was voltage across the FP at all times that there should be, but it seemed to cut in and out randomly even when voltage was present?

Yes I'm saying what you think I'm saying (!) i.e. there was good voltage at the times there should have been. I could barely hear it running but could feel it very slightly. Even managed to put my ear up against it and again could barely hear anything, just a bit of a rumble and feel a tiny vibration as it was turning.

When it first started it wouldn't rev much without choking, then after a minute or so it would (but I didn't rev it hard of course, it was stone cold). Deffo wouldn't start again though, matey had gone by that point so I couldn't check the pump voltage/noise but am pretty damn sure it wouldn't have been working.

Better go, the car spares shop closes at 6 and I gotta get the train there.

Thanks all for your help so far...

[Way2go]

All 4 gummed up?

It's possible. I've had that on a BX GTi that was off the road for a period. Don't forget the injector is not a simple on/off device, It has various spray patterns and duty cycles depending upon speed and demand. The metered throughput also needs balancing. All these things can be checked and remedied off the car on an ASNU machine.

But that does not explain no fuel pressure in the feed pipe whilst cranking. When I got it running earlier there was pressure in the pipe whilst the pump was working. Then the engine died and the pipe was soft again.

This is true, there should be pressure while cranking. The pipe should not go soft when the engine dies but remain pressurised for some considerable time. It does seem to indicate that the engine was running after the pump stopped and the injectors use of the residual pressure caused the pipe to go soft followed by engine stop.

I just checked the Haynes diagram 6-circuit V and this confirms that the pump(683) is supplied via the injector relay(734) and that is for multipoint Jetronic. The coils for this relay are in series with a second relay(731) which is under the command of the ECU.

Would the gumming up be visible if I removed an injector or is it more likely to be deep inside the thing? Just wondering if I can whip one off and have a quick look.

This would be difficult to see as its minute particles within the device that clog unless just carbonisation of the pintle caps. You could examine the pintle caps for damage and maybe remove the filters to examine under a magnifier but really this is unlikely to tell you the full story. The ASNU process gives you both the analysis and the cure (Filters, pintle caps & 'O' rings are replaced at the same time).
I had mine done on this car & it not only solved the acute problem I had set out to cure but also a lot of little niggardly problems that I had lived with for some time.

[Melchior]

Well, I have ordered a new pump for just over €100. They are more expensive than I thought but having thought about it I would rather that than an unknown 2nd hand one. With any luck it will arrive in the next few days and I'll fit it after work one day next week and get the car running again

Let's see...

[Melchior]

Pump arrived, I fitted it in the work car park (slightly less freezing weather this time, still NOT good getting petrol on your hands in cold wind) yesterday evening and BOOM! She is running beautifully again Feels more powerful, smoother and no random misfires, I reckon the pump must have been weak for a long time.

While it was laid up, the suspension was left on full height. I was surprised because it was sat for over a week and didn't sink at all. When I drove it this morning, the suspension felt much smoother. There are some bumps near my street which normally shake my bones in the BX (I think due to slightly sticky front struts) but today it soaked them up beautifully! Weird.

Thanks to everyone for your help on this thread, I am really pleased my BX is running again

[mat_fenwick]

Glad all seems to be well again!

While it was laid up, the suspension was left on full height. I was surprised because it was sat for over a week and didn't sink at all.

It will tend to sink less from anything other than normal ride height, as the strut sealing surfaces will be less worn in those positions. I can't think why it rode better, unless it was just pleased to be mended...