fuel pressure problem?

[89cherokee]

I have an 89 cherokee with a 4.0 engine. I read several threads in the forum about fuel pressure and regulators. Here's my problem...the jeep would start and idle, but stall as soon as the gas pedal was touched. I hooked up the pressure gage to the connection and it read 28 PSI with the vacuum hose detached ...and 28 PSI with the regulator vacuum hose attached (it should have increased 8 psi) So I replaced the regulator...no change. I replaced the fuel filter earlier today. Could the fuel pump relay cause this? Or is the fuel pump the problem? Any suggestions would be greatly appreciated.

 

[89cherokee]

I did the bleed down test...as soon as I shut off the engine it bleeds to zero. No waiting 30 minutes to watch it drop 20 PSI...right to zero...whew!

 

[Bounty__Hunter]

Exactly the symptoms I had on my '88 4.0L, and it was a bad fuel pump. The pressure should have increased like you described, but the pump can't keep up.

 

[89cherokee]

Thanks Bounty Hunter...I needed a definitive answer. Now, the next question is... do I need to drain the fuel tank? I know to disconnect the battery and avoid metal tools that spark...but empty the gas tank?
Thanks again for your help.

 

[Bounty__Hunter]

You don't have to, but the tank is easier to lower with less fuel in it.

Can't remember if you have to lower the tank on an XJ to change the pump or not, my MJ can be changed with the tank in place.

 

[dropseys]

Thats affirmative on lowering the tank on XJ's.

 

[89cherokee]

Dropseys, I read in the manual where dropping the tank ended with the 1988 model. I looked under the car and it sure appeared to be a straight remove and replace. By the way, on a scale of 0-10 with 10 being stinking dangerous, how tough is this repair? Also the parts guy at pep boys asked which pump I had, Bosch or Waldo (something like that?) and I said "I'd like the Bosch" and he says "no you need to see whcih one you have, they're not interchangeable". Any thoughts on that? I thought I had brand name choice, but he seems to think I need to replace the same brand pump...a little strange thought I.

 

[89cherokee]

Done Big thanks to bounty hunter (bad fuel pump) and dropseys (had to drop the tank) for their diagnosis. You go guys!

Notes to future fuel pump changers...check the bolts that hold the gas tank straps, you might need to replace them. I was unable to get the nuts loose, and I had to hacksaw through the bolts and buy new ones from the dealer ($15 each). Getting the lock ring off was a challenge too. I would never have been able to change the pump with the tank in the car. Good luck to anyone else changing the pump....its do-able. And thanks again to the jeepz forum.