Xantia V6 fuel pressure regulator upgrade.

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Re: Xantia V6 fuel pressure regulator upgrade.

Post by Mandrake »

xantia_v6 wrote: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?
I think it's highly dependent on the engine, and how smart (or dumb) the ECU is, and I wouldn't like to speculate too far beyond the ES9J4.

I think it works on this engine precisely because the ECU is pretty "dumb" by modern standards. Most ECU's these days have long term fuel trim and short term fuel trim. The short term fuel trim is from immediate feedback from the oxygen sensor and is only used in closed loop mode (oxygen sensor in active use) while the long term fuel trim is learnt over time based on the short term fuel trim being out for a long period of time, and applies in both open and closed loop modes.

For example say that the engine is running lean at idle due to Ethanol. When the oxygen sensor is warmed up it will notice this and the ECU will quickly make a correction to the short term fuel trim of say +5%. If you have long term fuel trim then this 5% short term trim being permanently required at idle would eventually (it takes a few minutes or more) cause the long term fuel trim to creep up to 5% while the short term creeps back down to 0%. The job of the long term fuel trim is to bring the short term to 0%. In open loop mode only long term fuel trim is used, in closed loop mode they are added together.

However what I've noticed on the ES9J4, is that it behaves as if it doesn't have a long term fuel trim memory! (Or if it does, it doesn't work very well) An example of this is in the above example it should learn 5% long term fuel trim for idle, then the next time you start the car, the long term fuel trim should cause the idle mixture to be correct before the oxygen sensor warms up and starts working (which takes 90 seconds) but it doesn't! :?

Before the fuel pressure change it consistently starts up and idles lean until the oxygen sensor warms up and starts making corrections. (Both my V6's have done this) You can see this by monitoring the oxygen sensor output on a scope. Generally in open loop mode the engine should err on the side of running slightly rich, but you can see from the oxygen sensor output as it starts to warm (but before it starts switching) that it starts off somewhat lean. After the pressure change it starts of slightly rich before it starts switching. I have noticed an improvement in initial running during a cold start as well.

It seems like it only has short term fuel trim. If this is true then it means any time you are in open loop mode (including idling for the first minute or so while the oxygen sensor warms up, WOT, or momentarily when you press the throttle) it is using pre-calculated fuelling calculations which don't include anything "learnt" by the oxygen sensor. So if there is a systemic error in mixture due to say Ethanol the open loop mixture will always be a bit leaner than it ought to be.
Deanxm wrote: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.
See above. In closed loop mode the ECU will compensate for the increased fuel pressure by reducing injector firing times. Closed loop mode is active when idling (but only after the initial 90 second warm up time of the heated oxygen sensor - idle will be richer now during that initial warm up) and when holding a steady rpm at a light to moderate throttle, eg cruise. So an emissions test is not affected by this change as the test is performed at idle and a steady 2500 rpm under no load.

Open loop mode occurs during initial startup, during WOT or high load, and momentarily every time you press the throttle, especially from idle.

Those that remember carburettors will remember the throttle pump that gives a squirt of fuel when you press the throttle, without it the sudden increase in air flow without an increase in petrol will cause a lean hesitation/stumble, especially if you press the throttle quickly from idle.

On a fuel injected car that same function is provided by the throttle position sensor. Every time the ECU sees the TPS open further, especially if it moves quickly it instantly drops into open loop mode and gives a large pre-calculated squirt of fuel to prevent a stumble. After about a second if you hold the throttle steady it will go back to closed loop again using the oxygen sensor, unless the throttle is open enough to constitute a heavy load - if its a heavy load it will stay in open loop.

If you increase the fuel pressure you increase the fuelling in open loop mode, basically. So WOT will be richer, initial startup and idle will be a little richer for about the first 90 seconds, and the "throttle pump" like squirt of fuel that you get every time you press the throttle will also be a little richer. Mixture during warmed up idle and cruise will be exactly the same as before.

Going from 3 bars to 3.5 in theory will make open loop mode about 8% richer, whilst E10 petrol should in theory make the car run about 5% too lean, so it is over compensating a little bit, but on the other hand Citroen probably tune the engine on the economy side anyway, so you're getting a little bit more performance than standard at the expense of slightly less economy - but because its only richer during acceleration it shouldn't affect cruise MPG significantly.

Hope that explains what's going on. Your point about atomisation is a good one - I believe that an increase in pressure will improve fuel atomisation as well (up to a point) and its probably no accident that a lot of cars use 3.5 bars or even 4.0 bars as their standard fuel pressure. They actually seem to be more common than 3.0 bars from what I have seen.
Simon

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Re: Xantia V6 fuel pressure regulator upgrade.

Post by Mandrake »

Stickyfinger wrote: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.
Are you saying the Shell V power made a difference, what were you running it on before ? Or are you saying that the fuel pressure made a difference then the fuel change made a further difference ?

The fuels I've found the ES9J4 likes best are Shell V-Power, Tesco Momentum, BP Ultimate, probably in that order, even though Momentum is known to have 5% Ethanol in it in some parts of the country. (I don't know if BP or Shell use any Ethanol in theirs, I don't think they say) Because I'm a miser at the moment I've actually been running on Tesco Momentum for the last few months with no complaints - it's the same price as the 95 RON Shell...

Fuels it doesn't like are any 95 and especially Asda 95, and surprisingly it doesn't seem to like Esso's high RON (97 ?) Premium fuel either. A new Esso opened up just down the road from home so I tried it but within about 20 miles I noticed the car wasn't happy with quite a noticeable loss in power and "willingness" for lack of a better term. (This was long before I changed the fuel pressure)

Performance remained down significantly for the rest of the tank to the point where I started to think it could be something else wrong like an ignition problem. (I didn't immediately connect the change with the petrol as those 20 miles were spread out over a few days) I ran it down to about 10 litres left and filled it with Tesco Momentum, literally within a few miles it started to perk up again and after about 20 miles it was back to normal! Go figure.... I'm actually wondering if there was some containment in the fuel as it was a brand new station that had only just opened. Or maybe they had accidentally sold mislabelled 95. Whatever it was, it did not like it.
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Re: Xantia V6 fuel pressure regulator upgrade.

Post by Stickyfinger »

Hi, and let me say....Great THREAD !

I am saying the pressure regulator made the biggest difference, and that it has got better now with another £30 top up of V-Power.

I have used tanks of V Power before the port matching/flow work and fitting the new regulator and the car always remained a little "slow response". It improved in pick up with the previous physical work to the induction system however the difference now is better torque/power low down [it seems].
I like to think the changes I have made all add up to better running/power delivery. The engine is running soother under quick acceleration and it is pulling better in a lower rev range. All in all a better car now from when I started messing with the induction.

It would be good to drive a car without the induction work but with a new regulator and see if they can be compared
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Re: Xantia V6 fuel pressure regulator upgrade.

Post by Mandrake »

Glad to hear it seems to make a difference for you as well and that it's not just my imagination... :-D

I was just driving the car yesterday thinking to myself "boy does this thing feel nippy lately"... It's not just raw acceleration but more so responsiveness to the throttle that I notice. Previously it would sometimes experience a little bit of "throttle lag" at certain rpm ranges where the power wouldn't kick in right away... and not all the time either. It seems to have sharpened up the throttle response quite a bit and the performance overall seems more consistent and uniform than it was before.

In my case I've done a direct comparison of fuel pressure change on two Xantia V6's now, and got good results on both.

The only induction work this car has had since I got it is a new air filter, the throttle plate was cleaned (although not to the degree you have done!) and the idle control valve was removed and unseized/cleaned, as it was totally seized when I got the car, and that work was all done over a year ago. Also I run nothing but high octane fuel and tend to stick to either Shell V-Power or Tesco Momentum, so I don't have different fuel types as an uncontrolled variable in my comparisons.

I'm not surprised that you see most of the change low down, I do too. This engine gets good low down torque (234Nm at 2000 rpm!) from having a high 10.5/1 compression ratio, specially designed inlet manifold and plenty of timing advance. (which is crucial for low down grunt) Of course this means it needs 98+ octane fuel due to this. Anything that causes the engine to start knicking will be detected by the ECU which will pull out timing advance - up to 12 degrees in a worst case scenario, which would cause a massive power loss low down.

Lower octane fuel and lean mixtures will both trigger knocking when the engine is hot and under load, this instantly causes the ECU to pull the timing back a few degrees until it stops knocking. It happens so quickly (just a few engine revolutions) that you don't even hear it knock, you just notice a loss of power. So anything that you can do to prevent it from knocking and pulling back the timing will improve the performance. (Or technically will prevent the performance from being degraded)

The power loss on 95 RON is really obvious but I always felt that even on 99 octane I was still seeing some "fluctuations" in the performance mostly at the bottom end, my gut feeling is that the mixture was too lean and was just on the verge of triggering some timing reduction during acceleration - so sometimes it ran at full advance and sometimes it pulled the timing back a bit, probably dependent on how hot the engine/engine bay/weather was, as it always seemed to run better on cold days.

The intention behind making the open loop mixture a little bit richer was to push it back over the threshold in the other direction so that it doesn't knock at all on 99 octane and thus can run at full timing advance all the time, even with the leaning effect of an Ethanol blend to allow for.
Simon

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Re: Xantia V6 fuel pressure regulator upgrade.

Post by Deanxm »

Very good thread indeed.

The stumble you get with sudden applications of throttle from idle is what my 8v XU suffers with and i was hoping higher fuel pressure would help this (very minor) issue. I did have a failing fuel pump with very low delivery pressure (1bar) and was getting vapour lock on hot restarts after sitting 10 mins or so but also VERY stumbly when pulling away and general poor performance.

While we are talking high Octane fuel i find this old dinosaur of an engine runs silky smooth on high octane at idle and runs smoother under load but is tuned for 95 and doesnt have a knock sensor so has no way of compensating with ignition timing to make use of the higher octane.

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Re: Xantia V6 fuel pressure regulator upgrade.

Post by Stickyfinger »

just as it is interesting....V6 C5 Carlsson

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Re: Xantia V6 fuel pressure regulator upgrade.

Post by xantia_v6 »

I think that the visible modifications in the photo are an LPG kit, not necessarily by Carlsson. I don't think that they ever did much more than a re-map and cosmetics on the C5.
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Re: Xantia V6 fuel pressure regulator upgrade.

Post by Stickyfinger »

all C5x7 owners take note.....bonnet lift rams :)
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Re: Xantia V6 fuel pressure regulator upgrade.

Post by white exec »

Citroen have a long tradition of running their petrol engines as lean as they can get away with. With the mention of carburettors, I recall a brand new leased BX16TRS we had in 1989. Had a monumental flat spot when attempting to pull away with anything other than light throttle. Citroen (under warranty) refused to either acknowledge the problem, or fix it. Eventually, the week before expiry of 1-year warranty, we gave them an ultimatum - replace the carburettor (again), replace the engine, or replace the car. They responded by immediately fitting a set of Peugeot carb jets (from Peugeot's version of the same engine), with the result that the car then went like a rocket - wheel spin on tap, but -2mpg. Apparently Citroen had tuned the carb for economy; Peugeot had done it for performance, with their heavier car.

Going back a tad further, I remember that S.U. carburettors never suffered from weak or flat spots (provided you kept the dashpot filled). When you opened the throttle, the piston rose, and immediately delivered increased fuelling at the correct mixture. I became somewhat expert in tuning these, whether singles, twins or triples. No daft squirty pumps!
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Re: Xantia V6 fuel pressure regulator upgrade.

Post by xantia_v6 »

white exec wrote: Going back a tad further, I remember that S.U. carburettors never suffered from weak or flat spots. When you opened the throttle, the piston rose, and immediately delivered increased fuelling at the correct mixture. I became somewhat expert in tuning these, whether singles, twins or triples. No daft squirty pumps!
Just for historical accuracy, the acceleration enrichment on an SU actually works the opposite way. When you open the throttle, the increased airflow tries to raise the piston, but the oil filled damper resists, holding the piston down, which increases the vacuum at the jet, causing more fuel to be sucked up.

On most SU equipped cars, the enrichment was more than sufficient and for around town use, you could get 1 MPG or so economy improvement by using 5W oil in the damper.
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Re: Xantia V6 fuel pressure regulator upgrade.

Post by Stickyfinger »

for info: Do we know if the ECU is mapped the same on the Citroen.V6 vrs the Pug.V6 cars ?
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Re: Xantia V6 fuel pressure regulator upgrade.

Post by white exec »

xantia_v6 wrote:On most SU equipped cars, the enrichment was more than sufficient and for around town use, you could get 1 MPG or so economy improvement by using 5W oil in the damper.
Yes, dead right on the enrichment and damping procedure.

Do remember that choice of oil made a real difference. Most (Rover-Leyland) owner's manuals advised topping the dashpot with "engine oil", which in those days meant 20W-50. This was far too heavy for the job, and far better results could be obtained by using a less viscous oil, like Castrolite. Some even used brake fluid (perhaps not a good idea) or ATF (fine). 3-in-1 was an absolute no-no, as in those days it turned to varnish! S.U. actually offered an oil themselves (which no-one knew about or bought), which was probably SAE 5.

With a light oil in there, most S.U.s gobbled it up, though, necessitating topping up at least monthly. Many drivers ran around for years with the dashpot(s) empty.

Down in the workshop there's still a neon timing light, a Carbalancer, and a 'diagnostic' dwell/multimeter. Also remember fitting Electronize electronic ignition to several P6's and Dolomite, together with my own contactless mod for the distributor, based on a V3 proximity sensor from RS. Everyone else used Lumenition.
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Re: Xantia V6 fuel pressure regulator upgrade.

Post by Mandrake »

Deanxm wrote:Very good thread indeed.

The stumble you get with sudden applications of throttle from idle is what my 8v XU suffers with and i was hoping higher fuel pressure would help this (very minor) issue. I did have a failing fuel pump with very low delivery pressure (1bar) and was getting vapour lock on hot restarts after sitting 10 mins or so but also VERY stumbly when pulling away and general poor performance.
A stumble with sudden application of throttle from idle can be caused by many things, which I would check before raising the fuel pressure....

1) Secondary ignition problem such as worn out spark plug leads or faulty coil - if the coil/leads (assuming it has leads) can't deliver a high enough voltage it may run fine under moderate throttle but you'll get a misfire under high cylinder pressure, (due to the spark jumping somewhere other than the spark plug electrode, such as outside the engine!) and wide throttle at low RPM gives near maximum cylinder pressures. So when you snap the throttle open suddenly you get an ignition misfire. If this is the cause you would probably notice some loss of WOT acceleration as well though as it would tend to misfire there too.

2) A throttle position sensor with a dead spot near the idle position. The TPS is simply a potentiometer, and anyone who has owned an old stereo amp will be familiar with "scratchy volume control" syndrome when the control gets old and wears out. This can happen to a TPS as well and in fact is more likely to occur than on a stereo amp because carbon film potentiometers wear out a lot faster when subjected to DC voltage/current (as they are when used as a TPS as they are varying a 5v DC voltage) compared to when they are passing an AC signal, as they are in an amplifier.

The ECU relies on seeing an instant increase in voltage from the TPS the instant you start pressing the throttle from idle, a dead spot near the idle position can cause the voltage to drop to zero momentarily - the ECU responds to this by leaning the mixture instead of richening it! As soon as you pass the bad bit of the potentiometer it starts working again and the mixture returns to what it should be, hence a stumble/flat spot. Some cars may use "wire wound" potentiometers which don't suffer as much when used with DC but they also aren't as precise, so I think carbon film types are still more common.

3) The idle control valve can also cause a stumble when you floor the throttle from idle, on some engines. On the ES9J4 the idle control valve is a two coil permanent magnet rotary type which can turn 90 degrees to open or close a valve, what often happens to them when they age is (a) the magnet loses its strength, possibly due to heat and shock (b) the bearings at each end wear out and become loose.

The combination of these factors means that the ECU can't control the valve very well - the movement of the ICV tends to "overshoot" a lot - the ECU commands it to move from 20% to 60% but it swings well past there to say 90% then swings back and forth a bit until it steadies itself. The loose bearings and lack of motor strength prevent it from being pulled quickly and effectively to the desired position.

At idle the valve is open a small amount to regulate the idle speed, when you floor the throttle the ECU also commands the ICV to open fairly wide (about 60% or so) however if the ICV is worn out as above it opens too much momentarily which can make it slightly leaner than anticipated.

Both my V6's have suffered from an intermittent flat spot when opening the throttle quickly from idle - the first one I had was much worse and funnily enough the ICV on that was very sloppy and worn, and it also did have a tendency for the idle speed to under and overshoot - for example if you revved the engine then when it came back down it would dip below the correct idle before recovering. (The V6 I have now doesn't do this) I believe the ICV was to blame but wasn't able to prove it as getting a replacement is near impossible and second hand units off old engines are probably also worn out. There was a good thread about the ICV issues of the ES9J4 over on the 406 coupe forum.

Cleaning the throttle plate helped the most with minimising this stumble from idle but it didn't eliminate it, bumping the fuel pressure up has also helped a bit but also hasn't eliminated it, although it is very minor now. After trying lots of things to eliminate it on two different cars now I suspect it may be a bit of a characteristic of the engine when it gets old, possibly related to the ICV wearing out so I don't worry about it much.
While we are talking high Octane fuel i find this old dinosaur of an engine runs silky smooth on high octane at idle and runs smoother under load but is tuned for 95 and doesnt have a knock sensor so has no way of compensating with ignition timing to make use of the higher octane.
But as discussed earlier, higher octane fuel typically has less or no Ethanol compared to 95 RON, so whilst your car can't make use of the higher octane itself, it may be responding favourably to the reduction in Ethanol.
Simon

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Re: Xantia V6 fuel pressure regulator upgrade.

Post by Mandrake »

Stickyfinger wrote:for info: Do we know if the ECU is mapped the same on the Citroen.V6 vrs the Pug.V6 cars ?
I don't think there is a difference but the way to check that would be to see if the engine ECU has the same part number for Citroen and Peugeot...

There is a difference in ECU for the ES9J4 between Automatic and Manual Gearboxes though, apparently the mapping around the idle region is a bit different as a few people have reported that using an Automatic ECU in a manual Activa V6 conversion (such as David's) can result in hesitation when accelerating from idle. Makes sense when you consider launching from stationary is a very different load for the engine on a manual gearbox with a clutch than an auto with a torque converter!

Also the Automatic ECU communicates with the gearbox ECU and has extra programming for that, whilst the manual ECU has no gearbox ECU to communicate with...
Last edited by Mandrake on 19 May 2016, 09:53, edited 1 time in total.
Simon

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Re: Xantia V6 fuel pressure regulator upgrade.

Post by Deanxm »

Ive been all over the management system, TPS is fine, ICV new and at great exense for the big Bosch units (did make some differnce to idle stability) plugs new NKG, leads are old but good, coil pack fairly new as is the Ignition amp, throttle body doesnt get dirty at all but all the tiny air passages from the crank breather etc have been cleaned because after 24 years there was some dry crusty bits in them. Its just a bit of a stumble if you dab the throttle too hard when pulling away and not all the time these days, most people wouldnt notice. Off topic for this thread anyway.
I will be fitting a tct rail with integral reg for other reasons, it wont hurt to up the pressure and suck it and see, it either helps, makes no difference or makes it worse and there is only one way to find out, after 24 years a strip down and clean of the injectors would probably help more though, maybe.

I didnt think about the Ethanol content, are we sure they dont use ethanol in high octane fuel? i would guess they cant as its got a lower calorific value and would compromise the claimed benifits of premium unleaded but are they not forced to use a certain % of renewable ethanol in the fuel by some directive?.

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