Fuel pressure regulator
Discussion
I guess because the ECU meters all the fuelling under the varying load and throttle openings. If the fuel pressure varied because of inlet pressure it would alter the amount of fuel delivered for any given timed opening of the injectors. Hence introducing a variable that the ECU couldn't account for.
But that has to be wrong for two reasons.
1) The idea of connecting the regulator to MAP, is to make the work easier for the ECU not harder as the ECU probably can't process as fast as the changes to MAP are happening. The ECU can only make decisions on what it knows and doesn't have access to pressure sensors. Its just assuming all this from throttle position and engine revs. That means no account is being made for a non 'ideal' engine.
2) Every other bosch setup in the world connects the tube.
I realise TVR are an innovator, but couldn't I connect the tube and possibly change the regulator for an adjustable type?
1) The idea of connecting the regulator to MAP, is to make the work easier for the ECU not harder as the ECU probably can't process as fast as the changes to MAP are happening. The ECU can only make decisions on what it knows and doesn't have access to pressure sensors. Its just assuming all this from throttle position and engine revs. That means no account is being made for a non 'ideal' engine.
2) Every other bosch setup in the world connects the tube.
I realise TVR are an innovator, but couldn't I connect the tube and possibly change the regulator for an adjustable type?
I don't see why you couldn't connect the regulator to the same manifold pressure signal as the MAP sensor (leap of faith here, I assume it does use a MAP sensor and not mapped totally off the tps?), since that must surely have been taken from a well behaved vacuum source. But if you have enough range on the injectors to cover the whole scale from tickover to full power without the duty cycle getting too low at tickover or too high at full power, then I don't see any strong arguments for or against doing it. Adding or removing the vacuum reference would surely have a huge impact on the lower part of the map, so the chances of fixing a minor fuelling discrepancy by this seems pretty remote, more likely to totally eff things up unless you adjust the map to compensate for the different fuel pressure, but why would you bother?
If it doesn't use a MAP sensor then there may well not be a well behaved vacuum source available, which would be a good reason not to use it iyswim.
If it doesn't use a MAP sensor then there may well not be a well behaved vacuum source available, which would be a good reason not to use it iyswim.
Thank god for your reply, thought I was going to die of boredom again 
No MAP sensor on AJP8. Plenty of places to plug into the inlet vacuum though.
Front what I understand you are right that the majority of its effect will be on slow or mid range running, and its possible the standard map is set for it disconnected.
But the standard map is also know to vastly overfuel in the low and mid range. Most of what jools says he does in low and mid range is to restrict the fuelling.
It might just give me a car that doesn't run, which is why I wonder if someones tried with an alterable regulator.
can't believe I'll be the first to try this though
. Trouble is no one wants to admit to being as stupid as me.
No MAP sensor on AJP8. Plenty of places to plug into the inlet vacuum though.
Front what I understand you are right that the majority of its effect will be on slow or mid range running, and its possible the standard map is set for it disconnected.
But the standard map is also know to vastly overfuel in the low and mid range. Most of what jools says he does in low and mid range is to restrict the fuelling.
It might just give me a car that doesn't run, which is why I wonder if someones tried with an alterable regulator.
can't believe I'll be the first to try this though
. Trouble is no one wants to admit to being as stupid as me.Julian64 said:
No MAP sensor on AJP8. Plenty of places to plug into the inlet vacuum though.
Oh dear, in that case you might need to do a fair bit of work to get a smooth vacuum signal. I think you'd normally connect all the cylinders together via a restrictor to get a smooth signal.
Julian64 said:
its possible the standard map is set for it disconnected.
I think it's absolutely certain to be. You'd get massive overfuelling if the engine was set up to run variable fuel pressure and it was running constant pressure. It may be a bit rich, but surely not by 25%+.
Isn't it just the 4.5 that has a less than optimal map?
Joolz won't map the 4.2 because it doesn't yield much in the way of benefit (unless there have been induction mods or the like)
I can see how an ECU using MAP rather than throttle position could be helped by the fuel regulator being connected to the same pressure source since the ECU would be metering fuel based on the same input as the regulator uses for pressure changes.
But since the ECU is metering based on throttle position it would surely just foul up the metering?
IIRC there is facility in the ECU to adjust the base map based on Manifold pressure but the values in it are the same across the whole map (and not very sensble looking) so it may not even be active in the TVR version of the ECU firmware.
Isn't this one of the unusual things about the AJP? - the fact that throttle position and not manifold pressure is used for the maps. I think its mentioned in the haynes tuning book (the one with the Emerald software) as an unusual setup.
And (also from the same book) doesn't MAP suffer from pressure fluctuations trough the inlet tract?
Given that Joolz now has some new pulse plate induction mod that increases BHP there must be some wave that is being reflected back down the inlet which suggests the Cerb does suffer from such fluctuations.
So TPS should be more consistent? It certainly gives a very snappy throttle on the 4.2 as the injectors are cylinder side of the butterflies and blast the fuel straight (well round a rough bendy casting) at the inlet valve. (JOOLZ - are you there? Do the pulse plates work on the 4.2? )
Joolz won't map the 4.2 because it doesn't yield much in the way of benefit (unless there have been induction mods or the like)
I can see how an ECU using MAP rather than throttle position could be helped by the fuel regulator being connected to the same pressure source since the ECU would be metering fuel based on the same input as the regulator uses for pressure changes.
But since the ECU is metering based on throttle position it would surely just foul up the metering?
IIRC there is facility in the ECU to adjust the base map based on Manifold pressure but the values in it are the same across the whole map (and not very sensble looking) so it may not even be active in the TVR version of the ECU firmware.
Isn't this one of the unusual things about the AJP? - the fact that throttle position and not manifold pressure is used for the maps. I think its mentioned in the haynes tuning book (the one with the Emerald software) as an unusual setup.
And (also from the same book) doesn't MAP suffer from pressure fluctuations trough the inlet tract?
Given that Joolz now has some new pulse plate induction mod that increases BHP there must be some wave that is being reflected back down the inlet which suggests the Cerb does suffer from such fluctuations.
So TPS should be more consistent? It certainly gives a very snappy throttle on the 4.2 as the injectors are cylinder side of the butterflies and blast the fuel straight (well round a rough bendy casting) at the inlet valve. (JOOLZ - are you there? Do the pulse plates work on the 4.2?
) GreenV8S said:
Julian64 said:
No MAP sensor on AJP8. Plenty of places to plug into the inlet vacuum though.
Oh dear, in that case you might need to do a fair bit of work to get a smooth vacuum signal. I think you'd normally connect all the cylinders together via a restrictor to get a smooth signal.
Julian64 said:
its possible the standard map is set for it disconnected.
I think it's absolutely certain to be. You'd get massive overfuelling if the engine was set up to run variable fuel pressure and it was running constant pressure. It may be a bit rich, but surely not by 25%+.
Interesting you should say that, because on the 4.5 all cylinders ARE connected together to provide a smooth vacuum. More than that each cylinder has a screw thread adjustment that could be used to alter how much vacuum each cylinder is contributing to the overall effect
Julian64 said:
Interesting you should say that, because on the 4.5 all cylinders ARE connected together to provide a smooth vacuum. More than that each cylinder has a screw thread adjustment that could be used to alter how much vacuum each cylinder is contributing to the overall effect
What's that vacuum system used for, then? The brake servo is all that's left if you don't have a fuel pressure vac line or dizzy vac advance. Do they feed the breather into that vacuum system?
They go to the big cross pipes thingy on the front of the engine. Feeling a bit blonde as am at work and therefore can't tell you much more at the mo.
I only know because I have the thottle bodies in pieces at the mo for a workover.
Interestingly the bar the throttle butterfiles sit on is a 10mm mild steel, and the screws to hold the butterflies on the rod are standard M4.
I have just bought some 10mm mild steel round from my local B&Q, and some wickedly low profile screws from my local seller.
Did get some strange looks from the B&Q staff when I sat testing the diameter of their poorly machined metal with my micrometer.
I shall be trying to improve on the throttle bar design and making myself a new one, while preserving the old ones just in case.
I only know because I have the thottle bodies in pieces at the mo for a workover.
Interestingly the bar the throttle butterfiles sit on is a 10mm mild steel, and the screws to hold the butterflies on the rod are standard M4.
I have just bought some 10mm mild steel round from my local B&Q, and some wickedly low profile screws from my local seller.
Did get some strange looks from the B&Q staff when I sat testing the diameter of their poorly machined metal with my micrometer.
I shall be trying to improve on the throttle bar design and making myself a new one, while preserving the old ones just in case.
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