Xantia V6 fuel pressure regulator upgrade.

[Stickyfinger]

ahhh.....you see I am a cheap bugger, I did not pay for next day

[Mandrake]

So I fitted it to the car this afternoon and it seems to be working. I tested both the old and new regulator with my fuel pressure gauge with the vacuum line disconnected - the old one measured 2.9 bars, the new one measures 3.4 bars. The fact that both readings are slightly low (with one regulator being brand new) suggests the small discrepancy is probably in my £30 fuel gauge...

To test that the fuel pump still has sufficient delivery under the higher operating pressure you floor the accelerator from idle (without over-revving) with the vacuum line disconnected - if the pump is up to the job the pressure should stay exactly the same without any sag - which it did. It's a good idea to test this as volume delivery of the pump drops off quite a bit as the fuel pump motor wears with age and also drops quite a lot with increased pressure, however there should still be sufficient headroom in pump delivery unless it is faulty or badly worn. (In which case it needed replacing anyway)

I also did a static pressure drop test where the engine is run then switched off and you monitor the pressure for any drop over about 10 minutes - no drop at all was observed.

I tried to go for a test drive but about 2 minutes into the journey a heavy hail stone downpour started out of nowhere (WTF ? ) and I got stuck in rush hour traffic - as I'm off work at the moment I had completely forgotten I was setting out at peak hour on a working day... Wost possible time for any sort of test drive, so I wasn't able to do more than about 30mph in small bursts.

Also swapping the regulator is difficult without disconnecting the battery for safety reasons (which resets the engine ECU clearing all learnt fuel trim and knock retard data) as well as disturbing the front fuel rail/injectors, ignition wires and multi-connector. So it will probably take a couple of days use for the engine to settle down and the ECU to adapt to the new operating conditions before any conclusions can be drawn.

I'll report the results in my blog in a week or so after I've had time to drive the car normally for a while and it has settled in...

[Mandrake]

Other things are currently being discussed in my blog so rather than derail that conversation with unrelated stuff I'll report results back here.

In short, I'm very happy with the change of fuel pressure regulator. There is a very definite improvement in performance, just like I remember when I did the same thing to my old V6.

I always felt the foot to the floor acceleration of this V6 wasn't as good as the last one I had, and I did have both cars together for a week before selling the old one, alternating driving both cars, so it's not just a case of rose coloured memory. Of course by that time the old V6 already had the raised fuel pressure, so technically it was an unfair test.

I have a regular "test road" that is isolated and out of the way which consists of a relatively steep incline a couple of miles long with a roundabout at the bottom that I use for evaluation of "foot to the floor" performance...I can tell by the speed I get to at a certain point how well the car is performing. Needless to say after this change it is now reaching a significantly higher speed by the same milestone, on the first attempt, more than it has ever managed before on previous runs.

At lower speeds under more normal driving conditions the engine does feel quite a bit more eager and willing with better throttle response, and more importantly it performs more consistently now. Previously its performance did vary somewhat from day to day, also depending on temperature (worse on hot days) but now its pretty consistent nearly all the time.

I was bracing myself for worse fuel consumption but at least on the one fill I've done since it has actually improved - well, improved from 18.4MPG to 20.6MPG.

However that is under my usual cold engine, short milk run grind where I could never reach or get above 20MPG before. And I did nothing to change my driving style, if anything I've been giving the throttle a squirt fairly regularly to test its responsiveness and yet got a better result than ever before. So at the very least it doesn't seem to have hurt MPG.

While this seems counter intuitive it is easy to explain - a leaner mixture only gives better fuel consumption up to a point, if you go too far you'll either get a lean misfire under load which of course will both waste a lot of fuel and reduce performance, or it will make the engine more prone to pinking under certain conditions like hot running. And because this engine runs at 10.5/1 compression ratio it is more prone to this than some engines.

You don't actually hear the engine pink because the ECU is so fast at detecting knocking and immediately reduces the ignition advance (up to a maximum of 12 degrees on this engine) to prevent the knocking. (You can hear it knock if you disconnect the knock sensor though) But losing timing advance hurts the performance quite a lot as you're still burning the same amount of fuel per revolution but getting less mechanical work from the combustion because it fired too late in the stroke.

So making the mixture slightly richer - if it prevents pinking and resultant loss of timing advance can actually give a net improvement in efficiency in theory.

Anyway, for the £20 including postage it cost me for the regulator I think its a worthwhile tweak to get a little bit more performance out of this engine, especially in these days of Ethanol blended petrol - fitting the regulator can be done without removing the upper intake manifold but it is somewhat fiddly since you're trying to lift up the left hand end of the front fuel rail only and remove the regulator which comes out the bottom of the fuel rail and also has the vacuum hose attached at a difficult to reach location at the bottom. But it can be done if you are careful.

[DHallworth]

Haven't been on FCF in a while now and have just seen your thread. I've jumped on the band wagon and ordered this as well, hopefully it turns up before Wetherby and I can get it fitted before giving the car a good run!

How easy is it to fit, Simon? Where on the V6 is it? (I'm just being lazy and not going to look tbh!)

David.

[Mandrake]

Haven't been on FCF in a while now and have just seen your thread. I've jumped on the band wagon and ordered this as well, hopefully it turns up before Wetherby and I can get it fitted before giving the car a good run!

How easy is it to fit, Simon? Where on the V6 is it? (I'm just being lazy and not going to look tbh!)

David.

Hi David,

Looking into the engine bay, it's under the left hand end of the front fuel injector rail in front of the upper inlet manifold, which in turn is below the horizontal rectangular cable conduit under the top of the plastic engine cover. Of the two fuel lines that come over the timing belt cover the one that is most towards the front of the car goes down directly on top of where the fuel pressure regulator is, and connects to its overflow spigot - that should give you some idea. It's a bit of a fiddly job and you have to be careful not to break the vacuum hose. (which seems surprisingly resilient actually - I haven't managed to break one yet) I would allow about an hour for the job due to it being a bit fiddly and awkward in places.

Here is a guide of how to do the job:

1) First drain any pressure from the fuel rail and also make sure the fuel pump is disabled. This is important because the ECU will actually operate the fuel pump a few times after the engine is switched off! You don't want this to happen when you have the fuel line disconnected. The way I do this is run the engine then pull out the fuse for the fuel pump while its still running - it is F9 in the under bonnet fuse box by the battery. When you pull the fuse the engine should keep running for a few seconds but then start to sputter and then stall. If it does that you have the right fuse and the fuel rail pressure is now gone. I leave this fuse out for the remainder of the job which allows me to still use central locking etc without any risk of the pump running with disconnected fuel lines.

2) Remove the top plastic engine cover, disconnect the spark plug leads and lift them away as far back as the front edge of the upper inlet manifold guide strip. (The manifold won't come out but the horizontal plastic wiring guide that the wires clip onto at right angles will need to lift up quite a bit) Release the clip that holds the hydraulic pump feed hose where it goes past the oil filler cap which allows the rectangular plastic wiring conduit to lift up a bit higher.

3) Remove the 4 allen bolts that hold the black plastic wiring conduit that runs along the edge of the front of the inlet manifold - the one that has the two ECU earth wires that come out and bolt onto the cambox. Disconnect those two earth wires as well. (Ideally you should disconnect the battery or engine ECU before doing this) The fuel rail is below this black plastic wiring guide but to be able to lift it far enough out of the way you need to do a few more things - unplug the low voltage plug on the left hand end of the coil pack, disconnect the slide lock connector on the left hand side of the inlet manifold next to the small vacuum hose and thread the connector between the two fuel lines to get it free. (Unclip the fuel lines on the timing belt cover to make this easier) You also want to remove the bolt in the engine mount that clamps the round cable conduit. After doing all of these you will be able to lift the plastic cable guide up far enough to get at what's underneath.

4) The fuel rail itself has 3 Allen bolts holding it down onto the lower manifold. Two are accessed through holes in the steel frame so a 3/8" drive Allen bit probably won't work unless it has a long tip due to fouling in the hole it must pass through. (I had to use an Allen attachment on a screwdriver handle that had a sufficiently slim shank - the bolts aren't that tight and can be done with a large diameter screwdriver handle) Once you lift this up a little disconnect the front fuel line from the end of the fuel rail by squeezing the two locking buttons and pulling. Be careful of the vacuum hose that is attached to the bottom of fuel pressure regulator - it has pre-formed bends and is routed in such a way that you can't remove it without removing the inlet manifold! (Designed by the Bureau de-bastards ) You don't want to break this plastic hose as it would be a right ball-ache to replace it.

5) To remove the regulator first remove the large circlip at the base that faces backwards with some long nose pliers, then use a small pointy tipped posi/phillips screwdriver - just give it a good push into the hole of the spigot where you removed the fuel line and it will push the regulator right out. It may be quite tight. It's probably a good idea to disconnect the vacuum hose off the bottom of the regulator with some long nose pliers first, or you may find you can't do that until the regulator is free. Manoeuvring the regulator out, releasing the vacuum hose all while holding the wiring guide and fuel rail up out of the way and then getting the new one back in seems nearly impossible but its just one of those fiddly jobs that you will find is actually possible when it looks like it isn't

"Reassembly is the reverse of the above". To get the new regulator to go in I'd put a good wipe of lithium grease on both o-rings on the regulator, it's quite a tight fit with new o-rings and you don't have much room to work when you're trying to squeeze it back into the rail, all whilst trying to avoid breaking the vacuum tube! You have to get the hose for the vacuum line started on the regulator before you squeeze it into the rail with your fingers. Also make sure you grease the fuel rail return spigot before you push the click lock fuel hose back onto it so that it doesn't leak.

Hope that helps.

If you have a fuel pressure gauge and want to verify the pressure after the job the Schraeder valve is on the right hand end of the front fuel rail - remove the air filter box to get at it, and you may need to remove one bolt from the cruise control bellows bracket and tilt it to clear your pressure gauge fitting. Pressure should be tested with the vacuum line temporarily disconnected.

By the way don't panic if the engine has a little bit of difficulty starting and misfires for a minute or two after reassembly! I panicked a bit with mine because it had quite a bad misfire for about the first minute of running after reassembly but I later realised this is due to the fuel rail being completely drained down and the regulator removed, leading to air pockets being trapped in the fuel rail that take some time to disperse - until they do one or more cylinders won't be firing as some injectors will be firing blanks. Just hold it at 2000 for a couple of minutes and it will clear up as the air pockets disappear from the rail.

Edit: fixed the fuse number (F9 not F14) and added some extra steps I forgot about.

[Stickyfinger]

Nice one Simon....Wiki that will you.

[DHallworth]

Thanks Simon,

I've ordered a regulator, however, it's saying at present they don't know when it'll be delivered. Ho hum...

David.

[Mandrake]

That's a shame. Did it list out of stock when you ordered ?

When are you going to weatherby ?

[DHallworth]

Yea, it said delivery date unknown when I ordered it.

Erm... Wetherby is next weekend. I'll be heading down on Friday morning (20th May) and heading back up Sunday afternoon.

David.

[Mandrake]

Just checked that Amazon listing and it says back in stock on the 20th of May. DOH! Looks like you won't be getting it in time

I also often seem to have this kind of bad luck when ordering car parts trying to get them before a specific date...

[DHallworth]

It's happened again!

Ordered rear discs and pads for the Activa from Citroen. Was quoted today for delivery to the dealer, went to get them and they're on back order.

If they're not in by Wednesday then it won't be getting genuine.

David.

[DHallworth]

Have had an email now saying that it'll be delivered on 21st May. At least we're heading in the right direction.

David.

[Stickyfinger]

It is a bloody fiddly job to do, the hardest part being getting the vacuum pipe off/on the regulator ....

Filled with Shell V power nitro 99ron)........umm, well it is quite a big difference, pulls much better lower down the rev range. Not really tried anything but short busts but it felt better above 4k revs as well, will see another time.

[xantia_v6]

I have ordered a pair of these (one for the XM and one for the Xantia). At least that gives me free postage...

Would it be reasonable to assume that these (or equivalent higher pressure regulators) would be just as effective on other petrol engines of the era?

[Deanxm]

Im wondering if the effect of higher pressure is greater fuel delivery (which i doubt) or better atomisation, the ecu must be getting the mixture right at the stock rail pressure or it would be running lean on the stock setup which would be compensated for.

Im thinking of doing the same with my old 8v XU10 lump but the thinking behind this was primarily to delete the external regulator which is an expensive beast to buy and difficult to track down, fitting a TCt rail would mean using a rail with an integral regulator, tidier, cheaper and now the issue has been raised higher rail pressure.

Im just interested in the science behind why you are seing gains from running higher rail presssure as i dont think it will be squirting more fuel in.

D