FSE rising rate FPR

[4.6_crossbolt]

...I'm assuming that your test process was similar to this:

Yes, but more thorough, as per Rover Workshop Manual. The first test showed that the FPR was where the pressure was being lost, but I carried on and checked to make sure the injectors and the non-return valve at the pump weren't contributing.

1 the pressure on your non standard Efi system may have been set to something other than 35 37 psi but the rest of the process is valid.

I set the system at 36 psi.

2 unless you somehow isolated the FPR, how can you be sure it is not faulty?

I explained at the beginning of the thread that the 'fault', if indeed it is a fault, was in the FPR.

3 the injectors, fuel pump and pipework can all be equally suspicious for losing pressure, after the ignition is switched off.

I'm satisfied that there is no other significant pressure leakage other than at the FPR.

However if your system is running at 35-37 psi and you have an ECU that has acceleration and full load enrichment circuits then the reason for fitting an additional boost, by RR FPR, is somewhat negated.

It would seem so.

If the rapid pressure drop (when ignition is switched off) is a genuine feature of your particular FPR then, as stevieturbo says, may not adversely affect the system when running, because as soon as the fuel pump engages, the pressure build up will fire up the engine with only a short delay.

Yes, I'm inclined to agree, however, my original question has not been answered after all this discussion - viz, is the rapid drop-off of pressure in the fuel rail a feature of the FSE FPR.

Strangely, I think I may have found the answer via one of Stevieturbo's posts.

[stevieturbo]

I do not believe pressure should drop off with the FSE.

[kokkolanpoika]

I and my couple of friend have got leaking FSE regulators. If you but lockpliers on the return line before FSE, pressure will then stay on the line approx +10min?? Our Finnish car forum has got similar topic like this witch mention FSE regulators.. Many have got same issues, even more.
Also they will change pressure if there is cold weather or warm..
I would not recommended FSE to anyone.

I notice that if pressure drops quickly on the line you have to make longer cranking to get engine fire up..

Can you squeeze lockpliers to 100% your return line before FSE, then you can elimante if it is FSE or pump or injectors etc..?

[4.6_crossbolt]

I and my couple of friend have got leaking FSE regulators...Our Finnish car forum has got similar topic like this witch mention FSE regulators.. Many have got same issues, even more.

Right, now that's what I wanted to know, but I have a feeling that it isn't a 'fault' with the FSE unit.

Also they will change pressure if there is cold weather or warm..

I can't say I've noticed that.

I notice that if pressure drops quickly on the line you have to make longer cranking to get engine fire up..

Exactly right, but if the pump is good, it doesn't seem to effect start-up too much.

Can you squeeze lockpliers to 100% your return line before FSE, then you can elimante if it is FSE or pump or injectors etc..?

Yes, that's what I did - there is a test procedure in the SD1 Rover Workshop Manual that will help to pinpoint where the pressure loss is occuring. The only thing is I prefer to use proper hose clamps rather than lockpliers (Molegrips) to avoid damaging the hoses.

[r2d2hp]

AM I right in thinking this item was fitted around 18 years ago, eg when you saw Mark. Could it be its just worn out now and needs replacing.

[4.6_crossbolt]

TBH, rates like that (1:3) are absolutely the last thing you'd want with boost. That's why I dont believe even the 1:1.7 is correct.

Not sure I understand why rates like 1:3 would be the last thing you'd want, as I understand these particular units are marketed for turbo-charged Japanese engines, but I have no experience of turbos and even less about Japanese cars. I do believe the 1:1.7 may be correct - more about this later.

But say a base pressure of 45psi, 20psi boost and 1.7x, you'd be talking almost 80psi fuel pressure...

Not sure I fully understand the maths here, especially where the '20psi boost' comes from, but I take your point that very high pressures are involved - on blipping the throttle I see momentary spikes of 55-60 psi on my SD1. Admittedly, I can't vouch for the absolute accuracy of the gauge!

...that's why I simply dont believe they increase fuel pressure by that ratio, although must admit have never tested one.

A long time ago, when my SD1 VDP EFI was still standard, I had a prolonged period of random engine cut-outs, which eventually was tracked down to an ECU fault and repaired by Mark Adams. During this period I fitted a fuel pressure gauge permanently, connected to the Cold Start spur, to help me better understand the workings of the EFI system. The gauge is still fitted and as a result I'm constantly aware of fuel pressure and the behaviour of my fuel system, hence the observation of the drop in pressure at shut-down.

For reasons of brevity I did not previously describe the movement of the gauge in detail, but what actually happens on switching off the ignition is that the needle drops immediately from 36 psi to about 20 psi and then fades away to zero, sometimes within about 30 seconds, sometimes a bit longer.

If you multiply 20 by 1.7 you get 34, which is not far below the 36 base pressure, which leads me to believe that the rising rate function is working and that the rate is indeed 1:1.7. Agreed, the subsequent slower drop in pressure to zero is faster than the 10.6 psi/minute recommended by the Workshop Manual, but this may still be a feature of the FSE unit.

I'm open to discussion about my logic, and I really would like to hear from someone who has technical knowledge of the FSE rising rate FPR.

[Baracus]

Also they will change pressure if there is cold weather or warm..
I would not recommended FSE to anyone.

Same experience here. I found the base fuel pressure varied all the time without the adjuster knob moving at all, which made mapping not possible until i replaced the FSE. I didn't twig that it varied with temperature though.


It's never explained very well in the FSE literature, but i believe the rising rate bit means that on a change of manifold pressure, the fuel pressure briefly overshoots the change before returning to the correct figure, providing a very crude sort of acceleration enrichment.

[r2d2hp]

The way StevieTurbo explained it to me was that for a supercharged engine you require fuel pressure to rise at the same rate as the boost so the pressure across the injectors stays constant. I am using an FSE based on Stevie’s recommendation and so far no issues but will keep my eye on things now.

[stevieturbo]

but what actually happens on switching off the ignition is that the needle drops immediately from 36 psi to about 20 psi and then fades away to zero, sometimes within about 30 seconds, sometimes a bit longer.

If you multiply 20 by 1.7 you get 34, which is not far below the 36 base pressure, which leads me to believe that the rising rate function is working and that the rate is indeed 1:1.7.

There is no logic in what you are saying. Almost in theory and if the FPR etc was shut, fuel pressure should almost rise on power off, as vac has been removed from the top side of the diaphragm so the FPR will try and increase pressure. Obviously it wont happen because the pump stops though.

The way StevieTurbo explained it to me was that for a supercharged engine you require fuel pressure to rise at the same rate as the boost so the pressure across the injectors stays constant. I am using an FSE based on Stevie’s recommendation and so far no issues but will keep my eye on things now.

Ive said many many times. The factory regulator will do the same job. It already has vac applied to it to reduce pressure under vac conditions, and likewise under boost it will raise pressure.
The actual ratio isnt really that important as long as it is consistent as you'd be tuning fueling electronically anyway.
But 1:1 is typical and makes the most sense.

[4.6_crossbolt]

...I found the base fuel pressure varied all the time without the adjuster knob moving at all...

From this, I guess you're talking about the type with an adjusting knob instead of a screw-driver slot, lock-nut and dome nut. I'm using the later which doesn't vary at all. The setting stays set.

It's never explained very well in the FSE literature, but i believe the rising rate bit means that on a change of manifold pressure, the fuel pressure briefly overshoots the change before returning to the correct figure, providing a very crude sort of acceleration enrichment.

You're right about the lack of information - I've been searching FSE sites all afternoon and even suppliers can't agree. Most say that the fuel pressure rises according to the ratio of 1:1.7, but some say it's the speed of reaction to pressure drop that is faster!

I'm now starting to glaze over with the whole thing, but I've ordered a new replacement (cheap on eBay), so I can compare. Watch this space.

[r2d2hp]

I don’t believe a standard regulator will increase fuel pressure under boost but never been able to check myself. As the ECU cannot increase pressure only injector duration you would soon run into issues if the differential across the injectors was not maintained.
That’s how it was explained to me. Stevie, any comments



Stevie I fitted an FSE based on you advice. If a standard reg would increase pressure with boost why did I bother to make the change. Confused now

[stevieturbo]

I don’t believe a standard regulator will increase fuel pressure under boost but never been able to check myself. As the ECU cannot increase pressure only injector duration you would soon run into issues if the differential across the injectors was not maintained.
That’s how it was explained to me. Stevie, any comments

If you apply pressure to it, it cant do anything but increase rail pressure, in exactly the same way when manifold vacuum is applied, it reduces pressure.

There is nothing special about a "turbo" regulator at all. Turbocharged cars use exactly the same style and often same reg as their n/a counterparts.

The ecu doesnt need to change fuel pressure.

And as long as the regs behaviour is consistent and mapping carried out, any regulator will do.

You could just as easily run a fixed base pressure and tune around that too, with no pressure changes ( and some OEM cars do this, although they use a higher base pressure )

[4.6_crossbolt]

Fitted replacement new FSE regulator and I can now confirm that like the original unit, on switching off the engine the running pressure drops immediately about 10 psi to approximately 25 psi. However, unlike the old unit, the pressure from 25 now very slowly drops off - after twenty minutes it had dropped about 5 psi, whereas before it took less than a couple of minutes to drop to zero.

From this, I conclude that my old unit was, indeed, somewhat worn, although still performing satisfactorily enough that general engine performance was unaffected.

I also noted that although the length of time cranking with old unit was not excessive, with the new regulator it was minimal, the engine starting almost immediately the key was turned.

It remains to be seen how the car now behaves on the road as I haven't had it out of the garage since the gritting.

[DEVONMAN]

Glad to hear that the new FSE is better controlling the drop off in pressure.
Clearly the old unit had a faulty seat on the return valve. Given that it's a metal to metal seal, it dosen't take much for fuel to seep past it.

I'm still curious about the 10psi drop at switch off. Logically the FSE should not cause this as removing manifold vacuum from the unit will effectively tell it to increase pressure although the pump will be now off so no increase will occur.

I note you mention that your pressure gauge is connected to the cold start spur. I assume this spur is at the main fuel rail pressure?

A plausible reason for the 10psi drop is that the return system is overwhelmed at idle conditions. In other words, the return pipe is acting as a restriction and keeping pressure up and taking some control away from the FSE. The small bore of the FSE return connection may have an influence here, together with any restrictions on the return pipe to the tank. Once the engine is working under load and injectors releasing fuel then the FSE will start to take control.
I have two fuel pumps on my car and when I switch one off at idle the fuel pressure drops by a few pounds for the reasons given above.

Grasping at straws here, but some other unlikely but possible explanations.

- your fuel pump allows fuel back at pressures greater than 25psi?
- Could the cold start valve momentarily open at engine switch off?
- Do the injectors keep buzzing for a split second after the fuel pump has stopped(ie flapper still part open.)

With reference to the FSE valve generally, it has 2 diaphragms one of which has an area of 1.7 times the other one. The manifold pressure /vacuum acts on the larger diaphragm and the fuel pushes on the smaller one. This gives the control advantage to the manifold diaphragm and this causes the fuel pressure to change by factor 1.7.

The FSE is useful when compensating on a fixed ECU motors when the owner has fitted an induction kit and a free flow exhaust.
It's a band aid, but has been used with success when set up on the rollers on many 4 pot jap jobbies.

Regards Denis
-

[4.6_crossbolt]

Thanks for the reply, Devonman. Some interesting things to ponder over. The cold start injector spur is connected directly to the main fuel rail and as pressure in a liquid is transmitted equally throughout, I assume the spur, and therefore, the gauge is at the same pressure as the rail.

I'm also curious about the 10 psi drop at switch-off. Such evidence as I have at the moment seems to indicate that it is a feature of the FSE regulator, for some reason. I'm tempted to re-fit the original Rover Fuel Pressure Regulator as an experiment to see what happens.

I take your point about the possible restricting effect of the return line. The other suggestions are interesting - I like the third one best - the injectors pulsing for a split second longer and dumping pressure. The pump is fairly new, but of course, this is no guarantee of perfection. The cold start injector is removed from the system.