I am having an interesting battle with my Zed at the moment and would appreciate any advice from those with the necessary tech knowledge. A little after it reaches running temp, my fuel pressue drops to about 20psi and of course it starts faltering. I have put in a new fuel pump, replaced the fuel filter, tried the FPCU bypass, and checked the pressure regulator and dampener all to no avail. When it is cold or even below operating temp, the pressure is holding at about 41psi, so I am convinced it is not a problem wiht the fuel system itself. I seem to recall reading somewhere that if there is a break in either the wiring from the temp sensor, or a fault in that part of the ECU then it can cause similar problems. I have only just loaded Datascan onto my laptop tonight so it wont be until nextweek that I can check that. Tech gurus any advice please.................:zlove:
if its holding pressure id say that the reg/dampner are not leaking. it could be the injector orings themselves!!.. how long does it hold pressure for?
Have you tried replacing the FPR? I reckon that's what it will be. If you are leaking enough fuel through your injector o-rings to drop the fuel pressure to 20psi then I reckon it would be so rich it wouldn't run.
Thanks for that Chripsy. I have not replaced the FPR but there is no leakage into the vacuum side. Also would that not be a stable fault rather than one that comes into play when it gets up to operating temp? I really don't think it is the O rings as that would be present all the time also. I am convinced that it must be ECU related but need someone with greater tech knowlegde than me to confirm or make suggestions. Tony
hows your fuel pump? has it been replaced. if not the 2 inch hose could be faulty, also TTs run a pressure release valve intank. they can fail. and then you have 2 start looking at the rear fuel lines. fuel pump oring. gass filler orings... all fun stuff !!!
If the fuel temp sensor is faulty it will jack up the fuel pressure by increasing the pump speed to full.
Fuel pump is brand new, filter is new, temp sensors were replaced about twelve months ago with new units. Dampener repalced about twelve months ago, no evidence of any leak from the FPR. Don't think it is the pressure relief valve becasue once it has cooled down the pump primes straight back up to 41psi. I seem to recall reading somewhere (have searched but can't find it again) if the temp sensor or wiring is faulty then the ECU will cut back on the fuel pressure.
Worth checking once you get consult working. Try disconnecting it and see if that helps (1 wire off the injector rail). That should increase the pressure, IIRC from what K-Zed told me on the side of the road 3 years ago Erik had trouble on his vert with hot starting due to a dodgy FPR that wasn't leaking.
Sounds like you have eliminated the usual suspects (FPR, pump, dampner etc). PS: What are the symptoms of this low fuel pressure? Are you sure the guage is accurate? Now, the fuel temp sensor / ECu connection has an impact on fuel pressure but I would think not that much to drop it down to 20PSI ... also checked the fuel hose at the front between the fuel rails for leaks? Sounds like you have eliminated the usual suspects. It may be a leaky injector which is dumping fuel which will reduce overall fuel pressure. When you next get this problem, I'd check out all the spark plugs to see if any are distinctly wet... Another test is to do a continuity test with a multimeter across the two terminals of each injector. You are looking for around 12Ohms or less.
Fuel pressure guage is new and purchased to try and sort this problem. Car drives normal and with normal power until fuel pressure drops. This occurred after about five kms driving, after letting it reach operating temp before starting off. No smell of fuel in the engine bay and no dampness at any of the connections. Will not prime up to 41 psi until it has cooled down below normal temp, then it is straight up to pressure as soon as key is turned.
That's correct, but I did not have the pressure guage when I did the bypass, but symptoms were the same.
Id still check voltage at your pump when the problem surfaces. Using logic, the loss in pressure has to be due to either a decrease in the supplied pressure (the pump) or a loss in the system, ie leaking system. The only place you could have a leak that big and not have evidence is to the fuel return via the regulator. If the system was leaking that much through an injector seal or hose connection etc , there would be fuel as evidence. Have you noticed and unnatural suction at the fuel cap when you undo it ie its not venting properly and the build up of negative pressure is loading the pump. Try it with out a fuel cap or very lose. Although we have seen a tank crushed by something like this, if your tank was full it may have different results and not even give you much indication when you undo the cap, maybe try a run with a lose or no cap, and take corners gently as not to throw fuel every where. I know you asked the guru's, but I thought I would put some ideas up anyway. Good luck.
ECU can't adjust fuel pressure, especially with the FPCU bypassed. If the seal in the FPR is on the way out it can leak once it gets warm and won't hold as much pressure on the pump side, it will allow too much into the return pipe. Swap it out with a known good one and test it. I agree with Chrispy Cat, highly likely the FPR. Also regarding o-rings and any other seals, heat plays a massive part in a failing seal. They can loose their structure and expand when heated to a point where they will not seal as well, this is 90% how injector o-rings fail, they swell up, generally starts when warm, and then eventually when cold.
When I open the cap to refuel the TT there is a lot of suction. This maybe an issue and certainly worthy of trying it with a loose cap. But how would it pressure up again once it had cooled if the vacuum in the tank was not released? I think the FPR is worthy of further inspection. I will take the one off the N/A and try it on the weekend. Thanks to all for their input. Gurus or not your help is appreciated. It ain't over yet....:zlove: Tony
