Help - Fuel pressure
Discussion
Strange one,
In advance, Sorry for the long post but it takes some explaining.
A little while ago I replaced the std fuel pressure regulator on my 450SE as it was playing up, spoke to Tim Lamont at ACT when sourcing a replacement as to whether it would be worth fitting a rising rate jobie or sticking to the std one, he advised that a rising rate would be ideal for the car, so that's what I fitted, although Tim wasn't able to supply at the time so ended up getting an FSE rising rate reg from RPI. Anyway fitted as instructed and set the base fuel pressure as per the bible 39-40psi/2.7bar. All has seemed well since except that I noticed she takes a little longer to start, a few more turns than with the original reg, also there's always been a niggle in the back of my mind that she didn't feel quite the same, couldn't quite put my finger on it though and as on the whole everything seemed fine I just put it down to the different reg, then the MOT guy mentioned that although the car had passed it seemed to be running a bit lean.
Here's the strange bit, when I set the base pressure I did it without engine running as per the bible and have checked it a few times since and always the same and constant, as I've been doing a few things on the car recently I decided to give everything a once over, so checked the fuel pressure for the first time with the engine running, now initially reads correct as set, and the reg seems to function as it supposed to, in as much as when the throttle is blipped the pressure rises and then drops below when engine on overrun, but a short while after starting the base pressure drops to about 30psi/2bar while idling, now this would almost certainly explain the lean running and probably the longer starting, and my niggling feeling that something wasn't right, but why is this happening?, should I set this reg up with engine running?, maybe it's faulty?, anyone else using one of these or something similar?
Any help, advise, ideas, much appreciated. Rich.
In advance, Sorry for the long post but it takes some explaining.
A little while ago I replaced the std fuel pressure regulator on my 450SE as it was playing up, spoke to Tim Lamont at ACT when sourcing a replacement as to whether it would be worth fitting a rising rate jobie or sticking to the std one, he advised that a rising rate would be ideal for the car, so that's what I fitted, although Tim wasn't able to supply at the time so ended up getting an FSE rising rate reg from RPI. Anyway fitted as instructed and set the base fuel pressure as per the bible 39-40psi/2.7bar. All has seemed well since except that I noticed she takes a little longer to start, a few more turns than with the original reg, also there's always been a niggle in the back of my mind that she didn't feel quite the same, couldn't quite put my finger on it though and as on the whole everything seemed fine I just put it down to the different reg, then the MOT guy mentioned that although the car had passed it seemed to be running a bit lean.
Here's the strange bit, when I set the base pressure I did it without engine running as per the bible and have checked it a few times since and always the same and constant, as I've been doing a few things on the car recently I decided to give everything a once over, so checked the fuel pressure for the first time with the engine running, now initially reads correct as set, and the reg seems to function as it supposed to, in as much as when the throttle is blipped the pressure rises and then drops below when engine on overrun, but a short while after starting the base pressure drops to about 30psi/2bar while idling, now this would almost certainly explain the lean running and probably the longer starting, and my niggling feeling that something wasn't right, but why is this happening?, should I set this reg up with engine running?, maybe it's faulty?, anyone else using one of these or something similar?
Any help, advise, ideas, much appreciated. Rich.
I would say the same as Adam .. up the pressure a bit.
I run mine at 43 psi..
and with the guage fitted the pressure is 43psi at idle but when the engine is reved the pressure drops off a little and on overrun it bounces around a bit until it stabilises.. mine is an FSE but not rising rate as mine is a hotwire only the flappers can use the rising rate.
I run mine at 43 psi..
and with the guage fitted the pressure is 43psi at idle but when the engine is reved the pressure drops off a little and on overrun it bounces around a bit until it stabilises.. mine is an FSE but not rising rate as mine is a hotwire only the flappers can use the rising rate.
Whoaaaaaa
The pressure readings will be based on whatever reference is used. Typically this is the manifold vacuum or atmospheric pressure. If there is a small diameter tube connecting the regulator to the manifold then the pressure readings will vary quite considerably and I would expect them to be low at idle as there will be a considerable vacuum. This reduces the pressure reading. Same thing happens on the overrun when the throttle is shut off.
30 odd lb at idle is not uncommon with a manifold referenced regulator. This is not an indication that the fuel pressure is leaning out. Remove the vacuum link and it should go up. If it doesn't then there is a more fundamental problem like a blocked filter/pipe, dying fuel pump or poor electrical contacts.
The pressure readings will be based on whatever reference is used. Typically this is the manifold vacuum or atmospheric pressure. If there is a small diameter tube connecting the regulator to the manifold then the pressure readings will vary quite considerably and I would expect them to be low at idle as there will be a considerable vacuum. This reduces the pressure reading. Same thing happens on the overrun when the throttle is shut off.
30 odd lb at idle is not uncommon with a manifold referenced regulator. This is not an indication that the fuel pressure is leaning out. Remove the vacuum link and it should go up. If it doesn't then there is a more fundamental problem like a blocked filter/pipe, dying fuel pump or poor electrical contacts.
Ok, thanks guys, plenty of food for thought there, the thing is, I never had these issues with the original std reg, both are vacuum referenced from the plenum and engine is a flapper.
I still have the original reg so may stick it back on and see what I get, I'm not so sure that it was faulty after all, as when doing the additional work found the fuel hoses from fuel rail to injectors to be much worse than I thought which would have counted for the original problem and not the reg. Will also do the stall pressure test for the pump, check that out. Depending on what the original reg says, If all checks out ok, then I'l try tweeking the pressure a little. I'll keep you posted. Thanks again.
I still have the original reg so may stick it back on and see what I get, I'm not so sure that it was faulty after all, as when doing the additional work found the fuel hoses from fuel rail to injectors to be much worse than I thought which would have counted for the original problem and not the reg. Will also do the stall pressure test for the pump, check that out. Depending on what the original reg says, If all checks out ok, then I'l try tweeking the pressure a little. I'll keep you posted. Thanks again.
Edited by Richybaby on Monday 28th January 13:22
If your original regulator was running at higher pressure than it should then the mixture setting would have been set at this pressure.
So when you fitted the FSE that runs at the correct pressure it could run a bit lean.
Have you set the mixture up correctly with the FSE?
What colour are your plugs (Digestive, Rich Tea or Bourbon)?
Russ
So when you fitted the FSE that runs at the correct pressure it could run a bit lean.
Have you set the mixture up correctly with the FSE?
What colour are your plugs (Digestive, Rich Tea or Bourbon)?
Russ
I view these rising rate regulators with deep suspicion. All they do is make the engine run richer as you open the throttle, which is a bad idea unless it was previously running lean.
The fuel pressure should be set relative to the manifold depression. With a conventional 1:1 pressure regulator, if you set the pressure to 2.7 bar with the engine off then as the manifold pressure drops at idle the fuel pressure will drop by the same amount so the fuel pressure will stay 2.7 bat above the manifold. This means you always have a constant 2.7 bar difference across the injectors which the ECU will be assuming in order to meter the fuel.
Since you're now using a 1.7:1 pressure regulator, the fuel pressure changes by 1.7 psi for every 1 psi change in the manifold pressure. You should aim to provide the same fuel pressure at idle (around 2 bar) which means that at full throttle the fuel pressure will rise to about 3.2 bar. Hence when adjusting the fuel pressure with the engine off or the vacuum reference disconnected the pressure you should aim for will be about 3.2 bar.
Surely the instructions for the FSE regulator explained all this?
I wouldn't presume to contradict ACT, but if it was my choice I'd toss the FSE in the bin and buy a decent 1:1 regulator.
The fuel pressure should be set relative to the manifold depression. With a conventional 1:1 pressure regulator, if you set the pressure to 2.7 bar with the engine off then as the manifold pressure drops at idle the fuel pressure will drop by the same amount so the fuel pressure will stay 2.7 bat above the manifold. This means you always have a constant 2.7 bar difference across the injectors which the ECU will be assuming in order to meter the fuel.
Since you're now using a 1.7:1 pressure regulator, the fuel pressure changes by 1.7 psi for every 1 psi change in the manifold pressure. You should aim to provide the same fuel pressure at idle (around 2 bar) which means that at full throttle the fuel pressure will rise to about 3.2 bar. Hence when adjusting the fuel pressure with the engine off or the vacuum reference disconnected the pressure you should aim for will be about 3.2 bar.
Surely the instructions for the FSE regulator explained all this?
I wouldn't presume to contradict ACT, but if it was my choice I'd toss the FSE in the bin and buy a decent 1:1 regulator.
GreenV8S said:
The fuel pressure should be set relative to the manifold depression. With a conventional 1:1 pressure regulator, if you set the pressure to 2.7 bar with the engine off then as the manifold pressure drops at idle the fuel pressure will drop by the same amount so the fuel pressure will stay 2.7 bat above the manifold.
That's why you should set the pressure with the manifold vacuum disconnected.Because the fuel pressure gauge is relative to atmospheric, you want the regulator to reference atmospheric, just while you set it up.
Then when you run the car with the vacuum line back on, at idle you'll see it drop off (to maybe 2.0 bar). This is normal, because the plenum is probably at -0.7 bar at this point, because the throttle is almost shut. So what you're seeing now is normal. The early 2.7 bar you see might be because the EAV is open soon after starting, allowing more air in = higher plenum pressure.
adam quantrill said:
That's why you should set the pressure with the manifold vacuum disconnected.
Because the fuel pressure gauge is relative to atmospheric, you want the regulator to reference atmospheric, just while you set it up
The point I was trying to make is that the goal is to have the same fuel pressure at idle, and then the rising rate regulator will give increased pressure (compared to the standard 1:1 regulator) at full throttle. So if you are setting the pressure with no manifold depression (effectively, under WOT conditions) you will have to set it to a higher pressure, in order to get back to the standard pressure at idle.Because the fuel pressure gauge is relative to atmospheric, you want the regulator to reference atmospheric, just while you set it up
Something to consider is that the ECU on a flapper already has acceleration enrichment circuits controlled by the speed of throttle movement (detected by the throttle pot) and also a full load enrichment circuit which kicks in at anything above 85% full throttle, so the ECU is already capable of significant acceleration and full load enrichment before a rising rate regulator adds even more, based on manifold depression. This makes me wonder if, for efficient fast road use, the extra enrichment offered by RR regulators does no more than empty the fuel tank quicker as well as wash lubrication off the bores creating faster engine wear?
Hi all, in answer to some previous questions:
'No I haven't altered the mixture control for the FSE'
'The destructions that came with the FSE RR reg were very general, basically said how to fit and then to keep adjusting for best results or until your happy'
I haven't had a chance to do any further testing yet, but I think it seems that I have not set the FSE RR reg up appropriately, or at least for a similar pressure to the original. I think I'll put the original reg back on to test the pressures with that for comparison, and take it from there.
Thanks to everyone for your input, I think I now have a much better understanding of what's going on here, and hopefully enough to sort it out. I'll keep you posted.
Cheers, Rich
'No I haven't altered the mixture control for the FSE'
'The destructions that came with the FSE RR reg were very general, basically said how to fit and then to keep adjusting for best results or until your happy'
I haven't had a chance to do any further testing yet, but I think it seems that I have not set the FSE RR reg up appropriately, or at least for a similar pressure to the original. I think I'll put the original reg back on to test the pressures with that for comparison, and take it from there.
Thanks to everyone for your input, I think I now have a much better understanding of what's going on here, and hopefully enough to sort it out. I'll keep you posted.
Cheers, Rich
Ok, did some testing with the original reg, it was set to a higher pressure than that which I had set for the RR Reg, once RR Reg pressure set to similar pressure as original (with engine running), much much better, everything, starting, warm-up, idle, and running, now she is back as I remember her, fierce!
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