DuoWing Posted September 28, 2009 Share Posted September 28, 2009 Hey guys I have an issue with fuel pressure. 76' 280Z. I've swapped my L28ET into it, I've got it wired up. Right now I have the stock 76' 280Z Pump in there. It does run, but getting it started is an effort in itself. Anyway I'll flip the key to on and my Pump does the prime cycle before shutting off. During this time it'll hold pressure. Then once the pump shuts off the pressure will rapidly drop to 0. Sometimes it will slowly drop to 0. Sometimes it will drop about 10-15psi and stay there. I clamped off the return line and the pressure shot way up and stayed there. So I thought it was the regulator. Got a new adjustable regulator that says it's factory set at 40psi. Anyway when the pump is priming the pressure shoots up hits 40psi, then once the pump stops it just slowly drops. I have a pressure gauge on my Pallnet rail. Two other odd things. The pressure dropped, then what I did was to help get more fuel which helps to get the car started, I put vice grips on the return line, but only so it was partially pinched. This helps get the car started. While I had my friend crank it, I watched the gauge. The car was cranking, but it took probably a couple of cranks before I even saw pressure start building on the gauge. Finally when the car is running it seems to idle fine, rev up fine, etc. Except the needle on the pressure gauge will be rapidly shaking like it can't seem to hold steady pressure. I'm thinking it's a fuel pump issue? I can't find leaks anywhere. One other question I have. The 280Z has the line from the tank to the pump, then the pump line runs up into what looks like some sort of regulator then on into the metal line towards the front of the car. I'll have to go grab my Haynes guide, but what is that? I don't seem to remember anything like that on my 280ZX. Should I remove this when I install my Walboro? Quote Link to comment Share on other sites More sharing options...
stravi757 Posted September 28, 2009 Share Posted September 28, 2009 Maybe your fuel filter is clogged up, or your fuel pump is out. I would put the new fuel pump in and see if it fixes the problem. Quote Link to comment Share on other sites More sharing options...
DuoWing Posted September 28, 2009 Author Share Posted September 28, 2009 Forgot to mention that the fuel filter is brand new, but it's possible that it's clogged. I had the tank fully cleaned out, and before I put the tank back in I used a can of kerosene mixed with fuel injector cleaner, and connected the feed line to the return line, and cycled the clean stuff through the pump and through the fuel system straight into a separate can that caught the dirty crap. How well this worked I'm not sure. Quote Link to comment Share on other sites More sharing options...
ktm Posted September 28, 2009 Share Posted September 28, 2009 Sounds normal to me. Aftermarket FPRs are not very good at holding pressure when the car is not running. My Aeromotive A1000-6 FPR drops pressure when the car is turned off and will read 0 within a minute or two. The shaking on the gauge is most likely due to fuel pulses from the fuel pump, except it sounds like you have the stock fuel damper in place which should mitigate the pulses. Your damper may no longer be functional. Quote Link to comment Share on other sites More sharing options...
DeleriousZ Posted September 28, 2009 Share Posted September 28, 2009 Sounds normal to me. Aftermarket FPRs are not very good at holding pressure when the car is not running. My Aeromotive A1000-6 FPR drops pressure when the car is turned off and will read 0 within a minute or two. The shaking on the gauge is most likely due to fuel pulses from the fuel pump, except it sounds like you have the stock fuel damper in place which should mitigate the pulses. Your damper may no longer be functional. I can second this. I have the same regulator and the first few times I primed the fuel system before running the car and it was having a hard time holding pressure. Now that the car has been run for over probably a half hour it holds pressure a lot better after the pump is off. Quote Link to comment Share on other sites More sharing options...
DuoWing Posted September 29, 2009 Author Share Posted September 29, 2009 Alright well today I messed with my car. I cut up the old factory 76' fuel pump bracket to mount my Walboro 255lph or whatever pump. So right now I have a completely refurbished/cleaned out tank. The feed line from my tank to a Fram G3 Filter, into my Walboro, then the walboro into the metal line that runs up to the engine. I took out the old factory fuel damper, which seems to have made no difference as to the shakiness of the needle on the gauge. Anyway from there I have the line running to the engine bay up to the fuel filter, then into my pallnet rail. From there I have a line running out of the pallnet rail back towards the firewall and into my FPR then to the metal return line. As far as I can tell this should be correct. It still doesn't make sense though. The pressure will hit 40, but then drop to 0 really rapidly, in about less than 20 seconds, but if it's as you guys say. Then maybe I have an issue elsewhere. My regulator looks exactly like the Aeromotive, except it's Blue and uses NPT fittings instead of AN fittings. It's by Professional Products or something. Also my Walboro fuel pump is ridiculously quiet. I've always heard people say that the aftermarket pumps are louder. Quote Link to comment Share on other sites More sharing options...
DuoWing Posted October 1, 2009 Author Share Posted October 1, 2009 Am I not able to go back and edit messages after a certain amount of time? Anyway does that stock damper need to be in place? It doesn't have any sort of check valve in it does it? The factory damper I took off I could manage to blow through it both ways so if it had a check valve in that, it no longer is of use. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted October 1, 2009 Share Posted October 1, 2009 The exit of the fuel pump should be a built in check valve. At least the factory pumps had a check valve directly screwed into the pump exit. The damper is not a check valve. I would leave the damper in place if it's not leaking, although it's not absolutely needed. Take your old 76 fuel pump and unscrew the check valve from the pump outlet. 10 bucks says the check valve is stuck open. I take Paypal. The regulator does not hold pressure in the system when the sytem is off. The system is sealed at both ends. At the pump it's sealed by a check valve. At the other end it is sealed by the shut injectors. When you turn off the car, the entire fuel system stabilizes to a hydrostatic pressure and should hold for at least an hour. Mine actually increases by about 4-5psi after a hot shutdown, as the fuel begins to heat up from latent engine heat. Mine will bleed down to zero in about 6 hours, probably due to hose clamps and fitting micro leaks. I run the factory damper and another damper on the fuel rail. It's probably overkill, but you want smooth pressure at the injectors for the best tunability. Try to get a glycerin filled gauge that will dampen the needle movements. If you use a regular gauge, the needle may eventually snap off from the shaking. Quote Link to comment Share on other sites More sharing options...
DuoWing Posted October 2, 2009 Author Share Posted October 2, 2009 The gauge on my pallnet rail is a liquid filled gauge. Did running a damper at the rail help smooth it out? I may do that and run a damper over in the engine bay or right at the rail before or after the filter. The old damper seemed to not be doing anything for me. By the way, what kind of FPR are you running? Quote Link to comment Share on other sites More sharing options...
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