Is this normal fuel pressure loss?

[Bowhunter]

The Jeep was difficult to start due to a leaking check valve in the fuel pump. It would also not start at all after a 10-20 mile trip when it was hot outside. After it cooled for 30 or so min it would then start with a few cranks of the key. I then tried installing design engineering’s fuel rail and injectors insulator kit. Made no noticeable difference

I then replaced the fuel pump and the Jeep starts very well now. But I took it for a 20 mile trip last week when it was hot outside. Once I parked it, I tried starting it about 5 min later. Same thing, would crank and everything would sound good except it wouldn’t fire. My thoughts are the heat from the motor after a longer trip cooks the fuel in the fuel rail to a vapor and vapor locks.

So today I barrowed a fuel tester and on key cycle, the pressure shoots up to about 47lbs and then will lose about 1lb of pressure per minute for the first few minutes and then hold at about 38lbs. I stopped the testing after 15 minutes

Sound like normal fuel pressure loss or do I have leaky injectors?

 

[Bowhunter]

Update, 37 minutes after the one key cycle and the pressure is at 23lbs

 

[TJ4Jim]

It is perfectly normal for the pressure to bleed off as it cools down, as long as she starts properly when cold it should not be an issue.

 

[Jerry Bransford]

Mine doesn't leak down significantly even after being parked over 2 months. I started it a week ago and it started instantly (!) which actually kind of surprised me.

Bowhunter did you also replace the fuel pressure regulator when replacing the fuel pump? It too has a valve that can leak though its effects are normally pretty fast to happen. Slower effects are usually from the fuel pump.

 

[Bowhunter]

It is perfectly normal for the pressure to bleed off as it cools down, as long as she starts properly when cold it should not be an issue.

Starts awesome when it’s cold. But when it’s hot outside and I drive for 20 miles (about 30 minutes) and I shut the Jeep off and let it sit for a few min, Jeep won’t start till it cools downs . If I do a short trip or drive early in the morning, turn the Jeep off, it will fire back up no issues

 

[Bowhunter]

Mine doesn't leak down significantly even after being parked over 2 months. I started it a week ago and it started instantly (!) which actually kind of surprised me.

Bowhunter did you also replace the fuel pressure regulator when replacing the fuel pump? It too has a valve that can leak though its effects are normally pretty fast to happen. Slower effects are usually from the fuel pump.

Hey Jerry,I replaced the entire fuel assembly with a Delphi unit. The bleed off before I replaced the fuel pump was very significant and quick

 

[Bowhunter]

Update:

got a more trust worthy fuel pressure tester.

in 15 min I lost 4lbs, in 40min I lost 8 lbs(from 46lbs to 38lbs).

is it possible for the engine heat after a longer drive to be so intense that it cooks the fuel in the rail and injections within a few minutes of sitting when it’s has good fuel pressure?

note, fuel pressure with Jeep on is 58 psi. When shutting it off, fuel pressure holds well at 52-54lbs for 5 or so min essentially losing no pressure (it instantly goes from 58 to 54lbs when you turn the engine off). No idea how the engine is hard to start when the fuel pressure is good, the rail and injectiors are insulated and the starter, plugs and battery are good. Any ideas??

 

[TJ4Jim]

Update:

got a more trust worthy fuel pressure tester.

in 15 min I lost 4lbs, in 40min I lost 8 lbs(from 46lbs to 38lbs).

is it possible for the engine heat after a longer drive to be so intense that it cooks the fuel in the rail and injections within a few minutes of sitting when it’s has good fuel pressure?

note, fuel pressure with Jeep on is 58 psi. When shutting it off, fuel pressure holds well at 52-54lbs for 5 or so min essentially losing no pressure (it instantly goes from 58 to 54lbs when you turn the engine off). No idea how the engine is hard to start when the fuel pressure is good, the rail and injectiors are insulated and the starter, plugs and battery are good. Any ideas??

Clearly something is going on, just for giggles and shitz try a test ride and when she is warmed up shut her down and open the hood and see if she will start after a few minutes.. Also you may want to try without the insulation on the rail.

Fuel pressure is good, no apparent issues.