Hard starting.. fuel pressure question

[98Chero]

I have a 1990 cherokee 4.0 liter six. Its hard to start but once it gets running it runs fine. I put a fuel pressure gauge on it today and when I turned the key and left it on the gauge read 30 psi and then bleeded down to zero. I started the engine and the fuel pressure stayed at 30 psi, but once i killed the motor it went back to zero. I was thinking that the fuel pressure should stay in the fuel rail for awhile. I was wondering if I have a bad check valve somewhere ? and if so where is it located ?. Im thinking that the fuel pressure is bleeding off somewhere.. maybe in the pressure regulator or the fuel pump area... any help would be greatly appreciated.

 

[O_M_Jeep]

I know on wranglers the pressure regulator is on top of the fuel tank and is usually the culprit in pressure bleed off

 

[carnuck]

Sounds like the regulator is sticking open. Find someone with Amsoil PI fuel system treatment and you may not have to change it.

 

[Jester32]

With the Cherokees there's a tsb for the fuel pump to pick up hose. Also they are bad for injectors leaking down. Replaced two on mine last week.

 

[98Chero]

I went ahead and replaced the fuel pressure regulator today (60 bucks),I wont really know till tomorrow morning when I cold start the engine to see if it improved the starting. even tho the engine is a MFI with injectors it stll does not have any back pressure after you kill the engine... Jester it might be possible that I have a leaky injector(s). Does anybody know if there is a check valve somewhere in the return line or fuel pump assy ?

 

[Jester32]

There is. That's what the tsb is for. The hose leaks fuel back to the tank after the pump. The check valve is in the pump itself

 

[98Chero]

What does TSB stand for ? better yet is there a way the check the TSB valve without removing the gas tank and assy..

 

[carnuck]

TSB = trade service bulletin