I'm sure this is a topic that has been discussed before, but I really don't have time to read up on it.
The Jeep is a 94, 4.0L, 5 speed. It has been running fine and getting pretty decent mileage. About a week ago, I started it (warm start) and it idled extremely low and actually died. I was able to restart it immediately after and go about my business.
Yesterday, after making several short trips, I went to start the Jeep and wasn't able to get it going. The engine turns over just fine, and I initially could hear one or two cylinders occasionally firing. After a minute or so (off and on, not continuous) of trying to start it, I gave up. I checked for spark, and that is not a problem. It ran just fine when I parked it, so I know its not a compression issue.
All signs right now point to a fuel issue. When I turn the key to "on" I can hear clicking from up front (relays I assume). The check engine light comes on for a few seconds and then goes back out. I do not think that I can hear the fuel pump. I have no interior in the Jeep, and my tailgate is currently off so I would imagine that the fuel pump should be easy to hear. I have only had the Jeep for a few weeks so I am not familiar with it's usual start-up sounds but I swear I remember distinctly hearing the fuel pump before.
The only thing I have checked so far has been the check valve on the fuel rail. With the key in the "on" position, the valve initially gave a little spurt, then nothing. I swapped the fuel pump relay with the horn relay, and the engine still acts the same. I still need to check for power to the fuel pump.
My main question is, given the info, if I have power to the fuel pump can I safely assume that the pump is the only possible problem? If anything else is likely, please let me know what else to check.
My roomate has a compressor but I am not sure if he has a spray nozzle for it.
I just check power to what I think are the wires going to the fuel pump. I can't check it after I initially turn the key, but after the ignition has been on for a while, I get 5 volts on one of the wires. Is that right?
seems a little low. i would think 9v minimum. i have never heard of this being done,but some of the guys were talking about gunk in the fuel tank clogging the filter that is part of the fuel pump. i was thinking maybe a very low pressure applied to the fuel line, toward the tank to loosen up any possible clog.
TREAT EVERY STRESSFUL SITUATION AS A DOG WOULD.
IF YOU CAN'T EAT IT OR PLAY WITH IT,
JUST PEE ON IT AND WALK AWAY.
I don't know about blowing air back. Its a good idea but because I don't even hear the pump kick on I don't think it will help too much. How hard is it to drop the tank? Do I need anything special to remove the pump once the tank is down? Do I need to drain the tank completely, or can I deal with it when it has gas in it? I think I will start removing the skid plate now.
take a multimeter and check your amperage readings before and after the fuel pump relay. make sure though that you have the switch side of the relay and not the magnet side which the ecm controls. you should see a low amperage going into the relay and a higher amperage coming out to the fuel pump.
btw: to check amperage the multimeter has to be in series with the circuit.
if all else fails and you dont want to change the fuel pump yet, do an open circuit test. meaning check voltage at multiple spots in the circuit and if you find that you have the correct voltage through the circuit then change the pump!
im not sure if the fuel pump runs off of 5 vref, if it does than 5v is correct. hope this helps.
Unfortunately i am pretty sure that my multimeter only reads A/C amps. It is the kind that clamps around a wire and gets the amps from the field. I am going to drop the tank before my next class (hopefully) and check voltage at the pump.
Removing the tank is fairly easy as long as there is not a lot of fuel in it. I dropped mine by myslef and changed the fuel pump out. I cannot remember any special tools that were needed. A hydralic floor jack will make the reinstall a lot eeasier though.
Hey, just to update the thread, I did end up changing the fuel pump and it fired right up.
Is there an easy way to drain the tank? I couldn't get a hose down the fill neck. I had to drop the tank with about 2/3rds of a tank in it. I was lucky enough that the fuel was below the level of the pump, and i drained about 5 gallons when I had the pump out.
The only problem I had getting it out was that the trailer hitch sticks out about a 1/2" over the tank shield. Wouldn't have been a problem if the tank was empty.
Just as an FYI, I was getting intermittent no starts after running like you describe, including the clicking and dim idiot lights. After a few minutes, it would start right up. The fix was simple, clean the battery terminals. They didn't look bad, but I disconnected them, wire brushed them inside and out, and the problem disappeared just like that.