fixitman

hello, i recently sold my lifted k5 blazer and baught a 99 cherokee
so far i like it until it started having a problem where when i go to start it sometimes it will just crank likes its not getting gas forever but on the second attepmt to start it will start right up, i was told by a jeeper from work that its a common fuel problem with teh cherokees, what could this be??
thanks

CodeXJ

Mine does it occasionally.

I'm tempted to check to see if there is a check valve on the fuel rail that might be bad, it seems like fuel pressure is bleeding off as it sits.

okcjeeper

Well mine was doing this and ended up being a bad fuel pressure regulator..After replacing that mine starts up pretty quick..

BlueXJ

There are no check valve per the FSM but there is a cure for that. A BMW check valve can be installed. I have seen write-ups about it on other Jeep sites.
It will still crank over a little before starting as that is programmed into the system. The computer needs to see 300 RPM and three pulses from the CPS before it turns on the injectors. During that time period the fuel pump is building pressure in the fuel rail. So it can't be completely eliminated but can be minimized.

SeriousOffroad

Bad checkvalve in the fuel pump assy. Been there, done that.

FWIW I learned the hard way that aftermarket pump assemblies don't last as long as an OEM assy. Suck it up and buy one from a dealer.

BENSONJAS

...or buy a couple from the junkyard. i got a couple from Pick and Pull during their 1/2 off sale for $40 and haven't had a problem with the one in the tank since.

BlueXJ

Frank I have been told that check ball in the pump is not very strong or even designed to hold the 39# of pressure your injectors need. It was designed to keep the pump from losing it's prime while sitting. So the BMW solution may be the better way to go on this. What do you think??

SeriousOffroad

couple of things to consider.
The 97 and up fuel systems run at 49psi.
Since the pump itself is at the very bottom of the pump assy, maintaining a prime inthe pump really isn't an issue. The pump builds pressure almost instantly. Tested mine in a small bucket of water and burst a small rupper test hose....freakin' water went everywhere while I screamed like a little school girl....ya had to be there to appreciate it.

There are a ton and a 1/3 97+ XJ's out there with OEM pump assy's that are still going strong. To me that tells me that the internal checkvalve is good one. Yes they fail from time to time, but many more don't

YMMV.

CodeXJ

I think I'm going to try changing the FPR on mine, first. It's got a new fuel pump as of 10k ago, so it's probably fine. If I'm right in my assumption the FPR is at the end of the fuel rail on the return line, right? It controls how much fuel is sent back to the tank, if it's sticking open then the check-valve in the pump isn't going to be an issue.

It's a pressure leak-down issue for sure, though. Get in the Jeep and turn the key to RUN, but don't START for about 10 seconds, and it'll fire right up every time.

SeriousOffroad

That's not an FPR issue.

CodeXJ

Explain?

I left my book at home, but I didn't think that the return line went through the check valve on the pump, and that the FPR controlled how much fuel was allowed to return to the tank? Or am I totally wrong?

SeriousOffroad

FPR regulates the pressure at the rail. Excess pressure is returned to the tank...BUT the lack of liquid fuel at the rail indicates that the checkvalve is allowing fuel to drain back to the tank.

CodeXJ

I don't know if it's a lack of fuel at the rail, so much as it's a lack of adequate pressure at the rail during startup.

The check valve is built into the pump assembly, right? Can you get to it without dropping the fuel tank?

SeriousOffroad

Time to slap a pressure gauge on the heep and see what is really going on. Don't waste your time fartin' around with maybe's...it gets to be really expensive and time consuming.

Post up your leak down test results and lets see where that takes us. Okie-Dokie?

CodeXJ

Yeah, gonna pick up a gauge this weekend.