Ian C Posted December 20, 2012 Share Posted December 20, 2012 So I'm wondering, the fuel system is supposed to retain pressurisation when the engine isn't running, to make it faster and easier to start the next time, right? Does anyone know how this actually happens, because I'd have thought it'd just drain back into the tank down the return line. I ask as I'm still rummaging around trying to work out what's going on with my hot start problem, and a lack of fuel pressure seems like one of the possible causes. Mine drains down slowly, although interestingly a lot faster when the engine is hot... Is there some mechanism inside a FPR that stops it draining down when fuel isn't flowing? I've checked for leaky injectors and a failure of the non return valve on the fuel pump, all is okay there. Oddly, though, I clamped off the fuel return line at the fuel tank and the pressure still slowly drained away, so I'm very confused now -Ian Quote Link to comment Share on other sites More sharing options...
JamieP Posted December 20, 2012 Share Posted December 20, 2012 Non return valve on top of the pumps is the normal? thats how mine was, dont remember anything else, try upping the pressure and see if any leaks appear? Quote Link to comment Share on other sites More sharing options...
Ian C Posted December 20, 2012 Author Share Posted December 20, 2012 Well that's the thing, I've pulled the pump out the tank and tried blowing down the non return valve and not a squeak - it's stopping any flow in that direction. Nothing's leaking out as I'd smell it in the garage (which does of course stink of fuel at the moment hah), plus it'd fly out when the system was pressurised. I'd have thought it'd be siphoning down the return line but I double clamped it and it still slowly lost pressure, the speed of which didn't change when I unclamped it again. Odd. The pressure must be going somewhere. I checked the injectors while swapping the spark plugs. I ran up the fuel system by bridging +B and FP in the diag port, then had a look down the bores for wetness and smell. Nothing. I even turned the engine over by spanner to open up all the valves and checked again. Really I'm wondering if it should hold pressure and how much for how long is normal. And should this change if the engine bay is hot, something I'll verify happens with mine when I next get the chance. Quote Link to comment Share on other sites More sharing options...
Andy Blyth Posted December 20, 2012 Share Posted December 20, 2012 The pressure is held at one end by the non-return valve in the supply line and at the other by the FPR in the return line. The FPR is always trying to hold the fuel rail pressure at the setpoint pressure. If there is no flow from the pump (i.e. it is turned off) then the FPR will be fully closed, which has the effect of holding the pressure in the fuel rail. Note that with some aftermarket FPRs (Aeromotive is one example), even when the FPR is "fully closed" there will be some internal leakage within the valve. This means that the fuel rail pressure will drop to zero within minutes. Quote Link to comment Share on other sites More sharing options...
Ian C Posted December 20, 2012 Author Share Posted December 20, 2012 Aeromotive is what I have. Perhaps this is one of the reasons CW doesn't like them If it's contributing to hot start issue, neither will I. Having said that, 6yr old NGK plugs probably weren't helping Quote Link to comment Share on other sites More sharing options...
David P Posted December 20, 2012 Share Posted December 20, 2012 (edited) There's no fuel pressure retained for cold start, yet you haven't mentioned a problem there. If you haven't done so already, I'd be changing the crank position sensor. Edited December 20, 2012 by David P (see edit history) Quote Link to comment Share on other sites More sharing options...
Ian C Posted December 21, 2012 Author Share Posted December 21, 2012 Cold start is fine, might take a few turnovers (zero fuel pressure and the ancient plugs probably weren't helping with that) but it starts from cold every time on first attempt. It's been like this for about 3 years so if it was the CPS I'd have expected it to fully give up the ghost by now I'm trying out several things to figure it out, one of which was fuel pressure retention, then I realised I didn't really know how that worked seeing as the FPR should in theory let fuel drain back into the tank. Seems like it does with an Aeromotive, which might be at least exacerbating the problem. I haven't tested it with the new plugs in yet, been a bit ill, so hopefully it was that. The old ones all had a gap of .9 to 1.0mm oops, yet it didn't misfire under boost Quote Link to comment Share on other sites More sharing options...
dandan Posted December 21, 2012 Share Posted December 21, 2012 The return line isn't "connected" to the high pressure part of the fuel line or rail, unless the pressure in the rail is above the setting of the FPR - that's just a function of the fact it holds the preset pressure. With the engine off, the FPR will be closed and nothing should go back down the return line (ignoring leakage in the FPR). What happens if you put the ignition on and wait for five seconds before you crank? Or better still, turn the ignition on for 5secs, then off very briefly and back on again, give it another 5secs before cranking. If it starts then you have been struggling with not enough fuel in the rail when cranking. Quote Link to comment Share on other sites More sharing options...
Ian C Posted December 21, 2012 Author Share Posted December 21, 2012 The return line isn't "connected" to the high pressure part of the fuel line or rail, unless the pressure in the rail is above the setting of the FPR - that's just a function of the fact it holds the preset pressure. With the engine off, the FPR will be closed and nothing should go back down the return line (ignoring leakage in the FPR). Yep, getting my head around that now Seems like the Aeromotive slowly drains the pressure out when cold, and rapidly does it when warm. Stupid thing. What happens if you put the ignition on and wait for five seconds before you crank? Or better still, turn the ignition on for 5secs, then off very briefly and back on again, give it another 5secs before cranking. If it starts then you have been struggling with not enough fuel in the rail when cranking. Well, the behaviour is, I'll try and start it after filling up with fuel, and it'll turn, sputter briefly, then sort of change noise to a turning-over-and-making-no-attempt-to-catch thang. Hard to describe. Once it does that, I can forget it, it's not going to start no matter what I do until I key off and let all the electrics power down. If then I turn it to pos2 and wait for all the electrics to fire up and leave it for a few seconds, chances are it'll start fine. If I try too fast again, chances are it won't. So it is indeed probably something to do with fuel line pressure, which gets all cocked up when the engine is hot and the pressure isn't there to start with. Just keying it to spin up the pump (I can hear it in the cabin so I know when it happens) and then trying again doesn't seem to sort it, though Also, keying ON doesn't actually spin up the pump, so why waiting a few seconds helps I've no idea. I did blame the EMu to start with but I'm not convinced now. It's annoying as it dents my faith in the car, even though it'll always start eventually. And an unsolved problem bugs me of course I tried datalogging what's going on with the E-Manage, but it's a bit crap at anything pre-running engine. It looks like the injector prime pulse doesn't happen when it fails to start and sounds odd, but that might just be it not recording stuff properly Oh for a Syvecs, or at least the money for one Quote Link to comment Share on other sites More sharing options...
mellonman Posted December 21, 2012 Share Posted December 21, 2012 i had a very similar thing with my AEM fic, turned out to be the firmware and more exact irt, any who FYI my fpr drops its preasure within seconds but it still starts first time hot or cold but if left for a hour takes slighly longer to catch Quote Link to comment Share on other sites More sharing options...
Scooter Posted December 21, 2012 Share Posted December 21, 2012 can you not do that bridging of the diagnostic port in order to fully prime the fuel system from the engine bay? that should at least rule out the fuel pressure. Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted December 21, 2012 Share Posted December 21, 2012 I have seen this on several different cars, which are according to the manual supposed to retain fuel pressure, but non of the have, i suspect its solely down to the FPR not having a good enough seal once the fuel pump is not running to compensate, the seal is only affected by a BB on a conical seat, so i doubt its going to be that effective unless its been ground. Quote Link to comment Share on other sites More sharing options...
Ian C Posted December 21, 2012 Author Share Posted December 21, 2012 can you not do that bridging of the diagnostic port in order to fully prime the fuel system from the engine bay? that should at least rule out the fuel pressure. That's one of the tests I've got lined up next Take that, fuel pressure! Quote Link to comment Share on other sites More sharing options...
CanisLupus Posted December 21, 2012 Share Posted December 21, 2012 I have a similiar problem also running the EMU and Aeromotive FPR. Switching the injector scaling helps for the starting issue. For example 440 -> 600 switched to 440 ->500 and the car starts without a problem. I also had in mind it's pressure related, boiling the fuel in the rail when not under pressure but leaving the pump running prior to starting(even for extended periods) didn't help. Maybe that helps Quote Link to comment Share on other sites More sharing options...
Ian C Posted December 21, 2012 Author Share Posted December 21, 2012 The injector scaling is a disaster zone that I don't go anywhere near, so it's not that I tried pulling fuel and adding fuel, none of that sorted it, plus if it was that it surely wouldn't consistently start on the second attempt after leaving it on for a few seconds... I'll see how running the pump manually does next chance I get, if it makes no difference I'll try a more scientific approach with altering fuelling for startup. Quote Link to comment Share on other sites More sharing options...
mellonman Posted December 22, 2012 Share Posted December 22, 2012 also a thing to check , at the cranking rpm at psia (absolute psi ) this can be half way up your map so timimng maybe pulled there when not needed at cranking Quote Link to comment Share on other sites More sharing options...
CanisLupus Posted December 22, 2012 Share Posted December 22, 2012 The injector scaling is a disaster zone that I don't go anywhere near, so it's not that I tried pulling fuel and adding fuel, none of that sorted it, plus if it was that it surely wouldn't consistently start on the second attempt after leaving it on for a few seconds... I'll see how running the pump manually does next chance I get, if it makes no difference I'll try a more scientific approach with altering fuelling for startup. Maybe a whise choice not to. I think i'll reconsider using it and just tune the map without ^^ Hope it helps you running the pump longer my problem is not solved with it Quote Link to comment Share on other sites More sharing options...
Ian C Posted December 23, 2012 Author Share Posted December 23, 2012 Even with the gauge registering 39psi of fuel in the system it still did the hissy fit. Ri ront row Seeing as it always starts second time if you wait about 10 seconds, I'm starting to lose interest in sorting it It's probably an e-manage quirk, I've run out of other things it can be, really. On the plus side, I finally changed the browny/black sock filter on the fuel pump And it cold starts and warms up better, and idles smoothly with new plugs and a tweak to the cam timings (4deg advance on exhaust, 2deg retard on intake). I think it's mildly helped spool on the turbo as well - it should do theoretically but my datalogs were a bit inconclusive. Still goes well though Quote Link to comment Share on other sites More sharing options...
TBDevelopments Posted December 24, 2012 Share Posted December 24, 2012 even with the regulator not retaining any line pressure the pump is activated on 2nd stage ignition anyway and only takes a split second to re-pressurize the lines, so by the time you start cranking its up to full pressure anyway. Even if it isn't a could of rotations of the engine it soon will be. Used SX and Aeromotive regulators on all my build cars and never had an issue, its one of the few regulators i highly recommend over any other brand. Tim Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted December 24, 2012 Share Posted December 24, 2012 a tweak to the cam timings (4deg advance on exhaust, 2deg retard on intake). I think it's mildly helped spool on the turbo as well - it should do theoretically but my datalogs were a bit inconclusive. Still goes well though I ran my exhaust cam advanced, no change to inlet though, and i noticed better spool (GT4088) also pretty low EGTs compared to others. Quote Link to comment Share on other sites More sharing options...
secondjump Posted December 31, 2012 Share Posted December 31, 2012 Even with the gauge registering 39psi of fuel in the system it still did the hissy fit. Ri ront row Seeing as it always starts second time if you wait about 10 seconds, I'm starting to lose interest in sorting it It's probably an e-manage quirk Ian, not sure if this helps...mine always did exactly the same. i'd go into the garage to pay for fuel and return knowing that she would fire up on cue on the second turn of the key. If I turned the car off and back on within a minute then it would fire on first turn, i also never had an issue starting from cold. Quote Link to comment Share on other sites More sharing options...
DJT88 Posted April 1, 2013 Share Posted April 1, 2013 Reviving this old thread... Been having a similar kind of problem, but don't have an E-manage, but a piggyback HKS fcon-s though. First try at warm starting is difficult, but second attempt almost instant success. :S Cold start needs 1-2 seconds. Might change fuel filter and pump soon, as I don't know how old they are. Ian, did you get it fixed eventually? Quote Link to comment Share on other sites More sharing options...
Ian C Posted April 1, 2013 Author Share Posted April 1, 2013 Not yet I've got an oscilloscope now to watch exactly what the injectors do when it has trouble starting, see if I can figure out exactly what's different to make it not start. The cold weather and other priorities at home have precluded me digging around at this yet though. I'm fairly sure it didn't do this when I first went to the setup I've got now, which means it's fixable. Quote Link to comment Share on other sites More sharing options...
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