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92 xj 4.0 Hard starting since outside temps are warm?

C

cjben

NAXJA Forum User
Location
Illinois
since the temps here in Illinois have been in the 50's my xj has decided to take it's sweet time cranking over before it starts. I am talking 15-20 seconds before it starts. it runs fine after the engine has started. seems like anyhting below 40 degrees out,the engine will start in 5 seconds or less. I am talking about the 1st start of the day. If I start the engine after it has been sitting less than 5 minutes or so,it starts right up. seems like if I leave it sit for 10 minutes or longer after the engine has reached normal operating temp,it is back to the long crank time again. I need some ideas what could be causing this. i have replaced the plugs,wires,dist cap,rotor,air and fuel filters all in the last 3,000 miles. 92 xj 4.0 5 speed 174,000 miles. thanks for the help....Ben
 
Fuel pressure regulator?? Also, try letting your fuel pump prime fully before starting. (you can hear it when you turn the key)
 
logdog, the FPR is a possibility. where is it located on my 92? and i do cycle the ignition key twice before I start the engine to prime the fuel pump,doesn't seem to make much of a difference in the crank times when I do this. thanks,Ben
 
how hard is the FPR to replace? I think i may swap it out just to see if that makes a difference. Any truth to what i have heard about the 4.0 engine having to have oil pressure before it starts? if this is true,that could be part of my problem also. thanks for the help,Ben
 
cjben said:
how hard is the FPR to replace? I think i may swap it out just to see if that makes a difference. Any truth to what i have heard about the 4.0 engine having to have oil pressure before it starts?
Click to expand...

No, that's a load o' cobblers. The oil pump generates some oil pressure while the engine's cranking over but it's only after the engine fires up that it reaches its maximum.
It sounds like your fuel pump check valve could be bleeding off fuel pressure from the injector rail when the engine's standing for a long time. Turn the ignition to the "on" position just once and leave it there for a few seconds before starting the engine. It it starts much faster, the fuel pump check valve is probably at fault. You can confirm this by checking the fuel pressure at the injector rail.
 
I tested fuel pressure tonight after work. I have 31 psi when the engine is running. I noticed after I shut the engine off,and cycled the pump by turning the key on,that it jumps to 40 psi real quick,then goes down to zero real quick. I let the jeep set for 2 hours,then went back and cycled the key without starting the engine. the 1st 2 cycles,the gauge didn't even move. on the 3rd cycle,it moved to about 15 psi,then went back to zero. I don't know what this means,but I don't think this is normal,is it? I was under the impression that there should be fuel pressure all the time when the key is on and the fuel pump primed. if this isn't normal,what would be causing the fuel pressure to do this? sorry for the simple questions,but this is the 1st fuel injected vehicle that I have owned that I have had a fuel pressure related problem with. thanks for the help!!!!....Ben
 
The FPR is on the front of the fuel rail, and has a vacume hose attatched to it. Disconnect the vacume hose and hold your finger over the opening on the regulator, have someone turn the key. If there is no difference in starting, you have bad vacume or the regulator is bad. While the hose is off, hold your finger over the hose and turn the key again. Feel for a small amount of suction. If you dont feel any, you have a clog in the line. If you feel it, replace the regulator.

I had the same problem, and this worked for me on my '92.
 
nobody around to help me tonight. how high should the fuel pressure go up if i unplug the vaccum line from the FPR? I unplugged it and the pressure went up to 39 pounds. thanks again,Ben
 
39 is where it should be. What was the pressure before you unplugged it? If its working properly, it should be between 30 and 35 psi
 
logdog,the pressure with it plugged up and running was 31. guess I should be looking at the possibility of it being the fuel pump,huh? :(
 
After starting and then turning off the motor the system should hold fuel pressure. After 30 minutes the drop should not exceed 20 psi, so if you are running at 35 psi, you should still have around 15 psi after standing for 1/2 hour.
 
the system does not hold pressure after I shut it off. if I cycle the pump without starting the motor after I shut it off,it will jump up to 40 psi,then go down to zero very quickly. what do i need to replace to fix this?
 
sounds like your pump is fine. might be worth pulling the pump and checking the small section of hose at the pump outlet. This hose was rotted on my 89 and allowed press to bleed. I changed the pump anyway but prob did not need to. Also if you do have your pump out change the inlet screen $6 at autozone.
 
if I do have to pull the pump to fix the problem,I am going to replace it. I don't want to have to do the job twice.
 
Like Dr Dyno said, the check valve in the fuel pump is probably bleeding the pressure down. Just replace the pump. Its cheap and easy.
 
do I need to drop the tank to change the fuel pump? any tips or tricks to make this job easier would be appreciated...thanks,Ben
 
Nope. The fuel pump on a 92 is mounted on the front of the gas tank. All you need is a flat screwdriver, hammer and a pair of pliers. There is a lock ring you need to remove. Then the whole thing should come out. There is a rubber isolator on the bottom of the fuel pump that keeps it from moving around in the tank, so when you intall the new pump, make sure the isolator is seated properly. The whole process should not take more than 30 minutes.
 
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