wgebb

Hey guys,

Today I was testing my fuel system ('96, 4.0L) by checking the pressure at the rail. I think I've isolated my problem to the fuel pressure regulator, because I have a slow drop-off of pressure. Without ever starting the car, turned the key on and off until pressure reached 40 psi, then after 20 minutes it dropped to 35 psi. After 40 minutes it was down to 30psi, and after 2 hours it was down to 20psi. I then pulled the fuel rail off with the injectors still attached, ran the pump until it pressured up, but saw no leakage from any injector onto the paper towels I had underneath them.

Now for my questions. When I bled the fuel pressure gauge, the fuel came out yellow. My fuel filter is new, replaced less than 100 miles ago. Yellow, like pee, fuel at the rail - is this just due to dirty lines?

Also, I'm looking to replace my fuel pump, and would love some input on what brand to go with or where to get one from.

NewbJeep

Fuel is pee yellow, you're good there.

Bosch or direct factory replacement have received high acclaim. Don't buy Airtex unless you like spending money and time replacing parts.

If you're not bleeding from your injectors then the drop in pressure is most likely your check valve. On the '96, I'm not sure if it's in the fuel pump assembly like on my '98. If you're pressed for time/money, the poor man's prime will get you by. Turn the key to on (not run) and let it prime, then turn off. Repeat two to three times and then run. Engine should pop off without problems. Did you check your pressure while the engine was running at normal temp? What was it?

Your test of pulling the injectors and priming the pump was a bold move. Be careful with tests like that when you're messing with fuel. Fires are not friends of Jeeps... or people.

cruiser54

It's really not that bad.

But, get some BG 44K and add it to a full tank of gas. Drive til it's 1/2 tank and fill with gas again. Drive it til 1/8 tank before refueling.

NewbJeep

Will this free things up? I'm getting kind of annoyed with the poor man's prime. (Sorry for hijack, OP)

cruiser54

It certainly won't hurt.....

NewbJeep

Right on, thanks!

cruiser54

Let us know how it works.

Cane

since 96 is a funky year, the fuel pressure regulator was a 96-only part and is pretty hard to find. if you can find a new one and you're ready to pay the price, fine, but you could go try and get the regulator itself at a junkyard.

wgebb

I did not check pressure while engine was running. I haven't been able to get it to start. After a poor man's prime, sometimes it will start but die immediately after it fires, even if I'm throttled up. Before this week, I could get it to start but it would die intermittently when idling, after reaching operating temp. The fuel pressure drop made me think it was a problem with the check valve, but now since I have crank no start condition I'm worried that the fuel pump/regulator is not the underlying issue.

Also, the fuel pressure regulator is located in the fuel pump assembly for the '96.

wgebb

Update: Today I swapped my ECU for a computer I pulled off a '96 at the junkyard. The Jeep started right up, on the first crank. I ran fuel pressure test again. This time, primed to 40 psi and it stayed there after 20 minutes of sitting. and constant 48psi while engine running at idle.

Really confusing for me. I had a pressure drop just a few days ago. Now I don't, and the only thing that changed was the ECU, which I don't believe is the underlying problem because I put the junkyard computer in it a few weeks ago, and it did not fix my issues - engine will stall/die sometimes, without warning, when I reach operating temp.

wgebb

I'm going to pull my fuel filter and see what it looks like, it's new so the fuel should be clean in there. If it's dirty then I'll get my gas tank cleaned, maybe that's what has been the trouble.

wgebb

Update: The fuel on the tank side of the filter was clear. A bit of sediment but nothing too bad. I drove the Jeep 40 miles on the freeway 2 nights ago, no issues. Things were looking up, I planned to take it out today and try to drive around 80 miles in the hot weather.

It started right up, I left it idling while I ran inside to grab something, and when I came back out it was not running. Crank, no start. I pulled the center boot off the dizzy to check for spark. Crank, no spark. So maybe the new ignition coil is bad. Wrong, because after this I pulled a plug, got spark, and it started right up. Thanked my friend for turning the key, got in the vehicle and it started right up, but died less than 2 seconds after ignition. Back to crank no start.

This problem must be electrical, right? Bad fuel pump would not give these systems. What could explain the intermittent spark issues? (BTW crank sensor is new, Mopar part. CPS is new too, unknown brand)

wyrick

I recently had similar symptoms on my 95. Yes my fuel pressure bleeds off the same. While driving it would occasionally stall, and when the engine had power again it surged forward. If I was at idle and it stalled it would sometimes try to keep running. I cleaned all my grounds, replaced my regulator just because and assumed I was fine. Was on the highway and it started acting up, this time the stalls were lasting a few seconds. until finally it died for good a few blocks from home. It wouldn't start, had the test lamp out knowing the coil is powered from the ASD relay and grounded from the ECM. Had one of those 'why didn't I think of this before' moments and swapped the AC relay with the ASD relay and it fired right up.
So you may consider trying that.

wgebb

Wow, that must have been fantastic. Just tried it, with no luck. Thank you for the input though.

wyrick

Thanks, it would have been a lot more fantastic had I thought to try it before 3-4 downstream detonations in my new exhaust!
Do you own a 12v test lamp? if so grab a wiring diagram off the internet if you don't have one and trace power upstream of the coil. If the coil doesn't have power, make sure the ASD relay is getting power, ect. You can also reverse the polarity of the test lamp and check ground.
No one likes it when I give that advice but it works when it's a matter of power/no power.