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did putting a check valve on my fuel rail cause starting problems?
HELP..... I'm wondering if I created this problem. I added a check valve at the back of the fuel rail where the fuel line goes in because Jeep doesn't like to start after it sits for a few days. I assumed the fuel was draining back into the tank somehow and a check valve would prevent that.
It started fine a few times after I installed it yesterday. Started fine to go to the doctor today. After the appointment, it won't start. Crank but no fire. Huh. Weird. It's never done that before. Ever. So I test fuel pressure at the schrader valve on the other rail and there's plenty squirting out. Then it starts right up. Then I go to the grocery story, get my junk, come out and same thing - just cranks and won't fire. I burp the schrader valve again and it fires right up.
Does the fuel rail need to be able to relieve pressure? I don't know anything about how these systems without a separate return line work.
How hard would it be to move the check valve back in the system? Do you have room to move the line up and connect directly to the rails while moving the check valve closer to the pump?
How hard would it be to move the check valve back in the system? Do you have room to move the line up and connect directly to the rails while moving the check valve closer to the pump?
Not hard. I believe the fittings in and out of my Bosch filter located on the frame above the rear axle are AN6.
I'd try giving that a shot first. The theory being that after you shut it off, you still have fuel in the rail, however everything from the check valve to the pump bleeds down and still takes time to build a pressure head. Since it would cost nothing but a little bit of time, I'd test it out.
No it should not stall or stop your car. I've used them for years to hold pressure
Well I moved the check valve off the fuel rail and behind the fuel filter that is mounted above the rear axle. Still won't start when its warm unless I burp the test port. I guess I need to go take it off.
Are you running a return line? Where's your pressure regulator? Are you running boost reference? What injectors? What's the outside temperature when this happens?
This might be the best theft prevention I've ever seen.
No return line. The OEM Jeep fuel pump has a built-in regulator. It's supposed to be 58 PSI. I'm showing 60 PSI with my gauge. OEM L92 flex fuel injectors - 12609749. I don't know what "boost reference" is. It's about 65 outside right now.
I was able to replicate the problem. Warm the engine up. Close hood and let it idle for 10 minutes. Turn engine off and leave it for 15 minute. Turn key and the fuel pressure gauge spikes. I assume this is vapor lock?
Perfect, I was going to suggest doing a pressure check.
When idling just before you shut it off, what is the pressure?
And then after sitting 15 minutes, but before you try to start it, what is the pressure?
Perfect, I was going to suggest doing a pressure check.
When idling just before you shut it off, what is the pressure?
And then after sitting 15 minutes, but before you try to start it, what is the pressure?
^^^This.
What year Jeep? I'm curious about the pump/regulator setup.
Last edited by 93Z2871805; 10-08-2020 at 06:09 PM.
With KOEO (Key On Engine Off) does your power to the pump work the same way as that on the Fbody. With KOEN the pump primes the system, then quits after three seconds. Priming allows for a quick start. No reason why it should not start almost instantly if primed at 58 PSI the first three seconds.
Have you checked fuel pressure on KOEN after 2 to three days when you state it starts hard? I would try to fix the no-start on prime issue and remove the check valve.
IMO one shouldn't expect that the fuel lines should be under 58 PSI for days on end.
How old is the intank fuel regulator? A C5 combination fuel filter/regulator should work with your system. This modification requires that you remove the in-tank fuel regulator. Periodic filter replacement means that the regulator is replaced simultaneously when the C5 filter is replaced. So no need to worry about an in-tank fuel pressure regulator failing after years of use.
Last edited by dlandsvZ28; 10-09-2020 at 09:37 AM.
When a vehicle is fully warmed up the underhood temperatures get really high. The increased fuel temp causes expansion, but the regulator (when running) is maintaining the pressure. Remember if the vehicle is idling very little of the fuel is leaving, so the volume in rail starts to absorb a lot of heat. Once the engine is shut off, temperatures continue to increase over the first several minutes, causing more expansion as the fuel in the rail continues to absorb all the heat. So the pressure may actually increase slightly (depending on how high the temps get) for those first few minutes, but this normally would be only a few PSI, not anywhere near pegging a fuel pressure gauge.
Vapor is also forming the rail, which can bleed off more readily past any internal seals (like the tank check valve or regulator). As things cool again and return to outside temperatures, the fuel contracts and some volume has dissipated as well. The net effect is after a couple hours sitting, the pressure can be reduced to half, and continues to drop (albeit at a decreasing rate over time).
My suspicion is somehow the OPs system is accumulating much more pressure than it should be either right before shut-off or during cranking. So much that it's spiking high enough that the injectors can't even open off battery voltage. And the check valve is preventing it from bleeding down.
"So the pressure may actually increase slightly (depending on how high the temps get) for those first few minutes, but this normally would be only a few PSI, not anywhere near pegging a fuel pressure gauge".
Looks like considerably more than a few, assuming that gauge is correct.
"My suspicion is somehow the OPs system is accumulating much more pressure than it should be either right before shut-off or during cranking".
The filter/reg is right at 58-60psi. If that's the case, and the check valve is holding over 100, during cranking, the filter/reg bypass is dumping 100% back to the tank.
If the engine hasn't shut down, the system is operating normal, and no excessive psi should be created.
10-06-2020, 07:58 PM
did putting a check valve on my fuel rail cause starting problems? 
