1999 Xantia HDI Wandering fuel pressure

[Chris570]

Seems to be a trend here, so lets carry it on!

Ok so my 110HDi has an interesting fault. Every now and then (3 times so far) the engine has failed to start and by that I mean you turn they key, it fires and then cuts out after maybe 2 combustion cycles. If you then try to restart the engine will spin over (plenty fast enough to start) but even after 10-15 seconds it won't start, doesn't even try. If you then turn the key back and wait a few seconds and try again, she'll fire after 4-5 compressions, which is the normal amount of time. Oh and you can hear the lift pump running on the failed starts as well.

Now that's the scenario, now for some added extras to help solve this.

I'm pretty sure she's down on power by about 20% ish.
The car will sometime 'surge' while driving (almost like it's running out of fuel) but only very gently (imaging a very small trailer on the back)
MPG is the same
Once running she doesn't miss a beat and idles spot on, no clattering.
Only run on BP Ultimate fuel
Current mileage is 249k
Injector flow correction rates are within 2 points of each other on the Lexia.
On idle the fuel pressure sits at 298bar but will wander by about 20 bar either side of that quite often.
At 2400rpm the fuel pressure will vary by about 60 bar
At 3000rpm the fuel pressure will vary by about 80-90 bar.

Those last 2 lines are from memory so may not be exact but the trend is what I've seen.

The HDi hasn't been on the Lexia for at least 60k so my memory is vague but I don't seem to recall the fuel pressure wandering so much if at all and I'm thinking this could be the cause of the problems. The injector flow rates also haven't changed in the 60k, if anything they are slightly tighter to each other now than they were.

My thoughts are the Fuel Pressure Regulator is going west but what are your thoughts?

I'd like to see this car make 300k

[Peter.N.]

I would suspect the pressure regulator on the HP pump, these seem to cause all manor of problems although its usually caused by the filter on it becoming obstructed. Its only held in with two screws and a connector, you will see the filter on the end when you remove it, looks like a stainless steel tube, if it has shards of metal sticking out of it your in tank pump is failing.

I have never been able to successfully clean one of these filters but as not all regulators have them I removed the one from mine and it works fine now, the easiest thing to do is grind the end off, making sure you get rid of any swarf. If it does have metal . 'whiskers' make sure you change the lift pump first.

Peter

[Chris570]

I would suspect the pressure regulator on the HP pump, these seem to cause all manor of problems although its usually caused by the filter on it becoming obstructed. Its only held in with two screws and a connector, you will see the filter on the end when you remove it, looks like a stainless steel tube, if it has shards of metal sticking out of it your in tank pump is failing.

I have never been able to successfully clean one of these filters but as not all regulators have them I removed the one from mine and it works fine now, the easiest thing to do is grind the end off, making sure you get rid of any swarf. If it does have metal . 'whiskers' make sure you change the lift pump first.

Peter

I'm glad you're of the same thinking then.

I have a spare lift pump anyway so that can be swapped if required.

Would you suggest popping the regulator out and having a quick look and removing the filter?

[Peter.N.]

If you have a spare pump just swap the regulators over, much easier than changing the pump, shouldn't take more than 10 or 15 minutes. The screws will either be torx or allen. I think you have to remove the filter, wasn't all that long ago I did it but my memory is not good, if you do its quite easy - I can remember that.

Peter

[citroenxm]

Wont be lift pump chris.. they work or dont. So dont waste time there..

recent service? I had this on a 406.. turned out to be a weak seal on the fuel filter allowing a slight run back of fuel.

Theres enough to start it inthe rail but it cant supply enough to keep the engine going so stalls. While cranking again its priming and building up pressure again till correct then goes... because its all primed.. there is allowed tolerances for pressurereadings... there has to be. Its impossible to have a dead set reading.

Id be looking at low side pipes and fuel filter house first. Is the water drain pipe dry? They do leak and will allow fuel out too check that first..

[DickieG]

Don't forget there is also a pressure sensor on the fuel rail which is exposed to the elements and can suffer a poor connection.

[Chris570]

Now there are some good thoughts!

I have a replacement FPR on my desk now (but as usual after clearing the non related faults on the lexia the car is driving normally) (If anyone cares the faults were an EGR low pressure fault and a cylinder sync problem which was when the engine was at 83 degrees and 2000 odd rpm)

The fuel filter was changed about 20k ago so nothing new there. The drain is as dry as a bone.

Mr G of Dickieness might have a point though, the car used to have a tuning box that was put inline with the Pressure sensor at the point of the join on the front of the engine. Certainly worth a looksie.

[CitroJim]

Chris, I'd be ever so tempted to do an injector leakoff test at some point just for peace of mind and rule out for sure it's not a leaky injector just pulling the rail pressure just below the start/run threshold.

At least it's one thing less to consider.

[Chris570]

A little update here....

Now at 252k and on Monday the engine cut out approaching a roundabout (clutch down changing down a gear). The engine started easily enough and then drove ok for the rest of the day. The "tugging" was getting worse and so on Wednesday the FPR was swapped for another one. The original FPR had no filter on the end but the replacement did.

On idle the pressure wanders by about 5 bar and at 600 bar it wanders by about 50. These figures are tighter than before and the car is driving a lot better now with the power right back up. The "tugging" has gone now as well.

It seems that this has solved the issue, or at least was a fault that contributed to it.

My question though is should the pressure wander like it does?

[CitroJim]

Chris, it's good to hear the replacement FPR seems to have resolved the issue. Fingers crossed it really has..

Gosh it was a bit of a 'mare to swap though