yankeedoodoo Posted May 19, 2003 Share Posted May 19, 2003 A few of us are finding that @ wide open throttle our fuel pressure is dropping: mine drops from 42 to around 24. A similar 200HP zetec exeriences a 6-8psi drop. We think that the injectors are correctly sized and the fuel pumps are pumping plenty of fuel. Any thoughts, guidance or experience on this would be very much appreciated. It didn't stop us from enjoying a 250+ mile mountain blat this weekend with three 7s and a nicely turned out Birkin. One dedicated 7er introduced us to 3 great and empty mountain roads we'd never seen. I'd never seen a zetec with Webers before saturday. Thank you very much for all thoughts and wisdom imparted ❗ Link to comment Share on other sites More sharing options...
AMMO Posted May 19, 2003 Share Posted May 19, 2003 Yankeedoodoo That's a big pressure drop. When and how does it happen? What fuel regulator do you have? Is your fuel pump in the tank? AMMO Link to comment Share on other sites More sharing options...
AMMO Posted May 19, 2003 Share Posted May 19, 2003 Yankeedoodoo I'm in the process of fitting a fuel swirl pot so this does not happen. The idea is that a low pressure pump feeds the swirl pot, this in turn feeds the high pressure pump. Any excess fuel from the regulator is also fed to the swirl pot. The swirl pot has a return to the tank. This is to ensure that the high pressure pump is always fed with a head of fuel. It avoids problems under heavy cornering where the tank pickup can become uncovered. AMMO Edited by - ammo on 19 May 2003 06:33:10 Link to comment Share on other sites More sharing options...
stevefoster Posted May 19, 2003 Share Posted May 19, 2003 Do you know it is surge or is the pump flagging? I used the in tank pump with some concern on the track. It's Arnie old tank and pump the one he had before trying to bag tank it. Anyway I have had no problems and run pretty low on fuel. I aim to finish the races with 2-3 lts to spare and fill it up from the known empty state using a dipstick to know how much fuel I have in the tank. I have not yet had problems. Chessons drift would be the high speed higish G corner where it would occur. I run a wideband O2 meter and any coughing would be accompanied by a high too lean number on the display instantly. I tested the pumps ability to cope by removing the throttle bodies still connected to the fuelling system. Placing them face down over a suitable bowl and connecting all the injectors to permanently on and seeing if the pump could cope with all guns blazing. It did. If it is surge then the above is all pretty irrelevant. My racing pics, 7 DIY, race prep. Updated often here Photo's of the year here Hants (North) and Berkshire Area club site here Link to comment Share on other sites More sharing options...
julians Posted May 19, 2003 Share Posted May 19, 2003 As an aside (but vaguely related), I noticed on my 2.0 zetec on injection that the cylinder closest to the start of the fuel rail is running rich (black plugs), but as you go further away down the fuel rail (towards cylinder 4) it gets progressivly leaner with the plug in number 4 cylinder being fairly white. I presume this is due to a drop in fuel pressure across the rail. Is this normal and is it something I should be bothered about ( I presume not since the engine has done about 8000miles like this so far) Link to comment Share on other sites More sharing options...
Chelspeed Posted May 19, 2003 Share Posted May 19, 2003 Julians - This is a red herring. Pressure is controlled by the fuel pressure regulator which is after the 4th injector. Everything upstream of the regulator, ie between the pump and the regulator, will be at effectively identical pressure. If the mixtures are different from pot to pot then look for something else, it won't be anything to do with fuel pressure variations. Link to comment Share on other sites More sharing options...
Peter Carmichael Posted May 19, 2003 Share Posted May 19, 2003 What is being used to measure the pressure drop? Is it causing the engine to misfire. If it isn't misfiring then the pressure is still OK and the pressure measuring device is a worry gauge. Link to comment Share on other sites More sharing options...
yankeedoodoo Posted May 20, 2003 Author Share Posted May 20, 2003 The zetec was not misfiring when this was observed. It was discovered while programming the pectel ecu on the Mustang dyno. Somewhere around 6000 rpms the FP started to drop and continued to drop up to redline above 7000. We just programmed around it on the fuel curve using the wideband lambda to arrive at a reasonable mixture. It actually generated the maximum observed horsepower under that condtion. The FP regulator is made by Aeromotive. My friend has a similar problem with a home built fuel injection system and an sds ecu---also observed while on dyno. Any thoughts about a cure or dangers running the motor in this way?? Thank you for all your responses ❗ Link to comment Share on other sites More sharing options...
Chelspeed Posted May 20, 2003 Share Posted May 20, 2003 If it was mapped with this variation and the mixtures were OK even with the very low fuel pressure at wot then it should be OK I guess. But here's a big but..... but only if the fuel pressure variation with revs stays the same every time on the dyno and on the track. Fuel pressure should ideally stay constant over the full range of operation, closed to full throttle, 0 to full revs. That's what the fuel pressure regulator (FPR) is designed to do, no matter what fuel the engines taking the FPR will vent just the right amount of fuel back to the tank to maintain the pressure in the fuel rail at the required pressure. If the fuel pump doesn't have sufficient capacity, either it's always been too small or it's gradually wearing out or otherwise giving up, then at high fuel demands from the engine the fuel pump will be going flat out, the FPR will be closed but there's still not enough fuel from the pump to maintain the pressure. That sounds to me like what you're seeing, except that if it was, then opening the injectors longer to maintain the correct mixture wouldn't work, it would just take more and more fuel from the fuel rail and pressure would still not be maintained or more likely fall further. If the FPR isn't up to the job then...... hmmmm.....I guess either the fuel pressure will be too high at tickover, FPR too small to pass enough fuel back to the tank when the engine is consuming the minimum amount, or the pressure will fluctuate randomly, FPR can't control properly. Can't think of a mechanism where the FPR could cause falling fuel pressure at high engine fuel demands as that's when the FPR is doing the least work. If the fuel lines are too small, if a filter is too small or blocked then you'll be getting pressure drop between the pump and the fuel rail. At low fuel demands from the engine the FPR will bleed fuel back to the tank, the pump will be seeing close to closed valve head and I would think total flow through the system will be at a minimum so pressure drop across the above components will be low. At high fuel demands the FPR will close in to hold pressure but the total flow from the pump will be at a maximum so the pressure drop across these components will be at it's highest which could cause low pressure at the fuel rail. Do you have a filter after the pump? Have you changed it recently? Can you read pressure both sides of it? So back to the but above. If the fuel pump isn't up to the job then I would think it should always behave the same, fuel pressure will always drop by the same amount at the same throttle setting and revs on the road and on the dyno (provided of course that the same fuel system is used on the dyno....), and if you've mapped it to keep acceptable mixtures then it'll be OK. But if the pump isn't keeping the pressure 'cos it's 3/4 knackered then it'll be getting worser and worser as time goes on and the fuel pressure at throttle site 15 and 9000rpm might have been OK on the dyno but won't be on the track now and next month will be even worse. If the pipes are too small then it'll be the same as the pump being too small. If the filters blocked then it'll be getting more and more blocked so it'll be getting worse and worse. All in all I think I'd try and restore constant fuel pressure if at all possible and, in the meantime, I'd be keeping a very close eye on fuel pressure on the track, ideally by logging as it'll be dropping just at the time when you're putting 110% concentration into looking where you're going..... Link to comment Share on other sites More sharing options...
yankeedoodoo Posted May 20, 2003 Author Share Posted May 20, 2003 The FP is the standard in the tank SLR unit, whatever that may be. We are thinking that it may not be pumping enough at higher rpms and I may eventually replace the tank and unit with something more trackworthy. The symptom on the dyno was consistent so we feel like the map compensates for it in an adequate manner. But it does make me a bit nervous ❗ Link to comment Share on other sites More sharing options...
stevefoster Posted May 21, 2003 Share Posted May 21, 2003 Do the flow test with all 4 injectors open and see what pressure you get on the rail. That is equal to a bit more than max power delivery as far as the pump/pressure reg are concerned. It takes about 0.5hr to do as I described above. Make sure there are no sparks or naked ladies (old flames ) about 😬 My racing pics, 7 DIY, race prep. Updated often here Photo's of the year here Hants (North) and Berkshire Area club site here Link to comment Share on other sites More sharing options...
Mike Biddle Posted May 22, 2003 Share Posted May 22, 2003 Yankee, I had this problem recently, and cured it by fitting the uprated fuel pump as fitted to the R 500. Mike. Link to comment Share on other sites More sharing options...
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