Hard start when cold ...changed fuel pump did not help

It takes me two tries to get the engine to turn over in the mornings then tries to stall for about 15 seconds. This happens only when the truck has been sitting for several hours. I had this prob b4 on other xj's and it turned out to be the check valve in the fuel pump. I had a spare good pump so I changed it out.

Before I changed it out I took some readings 49psi at idle, 45psi with key on, but it drops pretty quickly with key off prob about 20 psi in 5 minutes. Anyway after changing the pump I have the same problem.

I have NO issues after initial start up, and priming the pump does not do anything. I have no stalling, rough idle, or reduced power. If I try to start it up right after shutting it down it fires no prob. Also the hard to start condition is not like a slow crank, the crank is strong.

I have recenlty done:

plugs, cap, rotor, wires
cleaned TB
cleaned all main body grounds
tested battery (good) and cleaned connections
tested cks/cps (good)
tested tps (good)
IAC (good)
I also check for leaks in the fuel lines and i saw nothing

I am starting to lean towards a leaking fuel injector. I obviously am loosing pressure from somewhere. I also suppose that could give me a flooded out type condition.

Does anyone know the best way to test the fuel injectors for a leak? Or can anyone add any suggestions..


Thanks

Mike


99 sport 4.oL aw4 np231

pull the injectors and rail as an assembly and place each injector in a glass jar (still attached to the rail)-- cycle the key to prime the system. There should be no fuel loss from the injectors-- any loss is a dirty/faulty injector.

Well i took the rail off, pressurized the system and watched it for about an hour. I did not see one drop out of any of the injectors. I'm back to the drawing board. I'm gonna take another pressure reading 2morrow and see what it says again just for grins. I also put some 93 octane and fuel injector cleaner in today just for the heck of it.

I know the fuel pump I installed worked just fine when I took it out of my wrecked 99 xj but I am wondering if something happened to it will it was just sitting there dry.

Geesh havent been this stumped in a while.

Test your coolant temperature sensor--if priming isn't helping then pressure isn't the issue, as it doesn't stumble and run rough then I don't think you have an injector leaking down.

I tested the CTS the resistance values don't seem to be correct. I'm gonna get a new one tonight and see what happens. Thanks for the idea.

Be sure and post up what happens.

Good luck.

Turns out it was the coolant temp sensor. I tested the resistance values and compared them to some numbers I found on line and they were off. The computer thought may xj was 150 degrees when it was sitting all night, therefor the fuel mix was to lean to start up when cold. I was reluctant to think it was the CTS because I just replaced it with a BWD part from Advanced only a few months ago. Turns out that part was crap.

What did the coolant temp gauge on the dash register when cold?

The bad sensor did not have any effect on the temp reading on the dash, another reason I did not suspect the CTS.

That odd. One would expect the dash to say 150* as well.

Yes very odd...it had me going nuts.

Glad you got it squared away.

Good luck.