1990 MJ 4.0 Spark but no fuel

I just bought a 1990 MJ 4.0 yesterday. I have been messing with it this morning and have noticed that the fuel pump doesnt seem to kick on when i turn the key to the ON position. Is there a fuseable link or a relay that would be preventing the pump from getting power?

I cleaned the grounds that everyone talks about on . The owner before me said it drove fine everyday then one day no start. He had it towed home replaced cap, rotor, plugs, and wires, and says he tried to adjust the TPS.

I also just cleaned the throttle body and figured I would try to crank with all the cleaner in the manifold and it fired up for a few seconds. So that reassures my no fuel thoughts.

When I press the schrader valve barely a few drops of fuel come out of the rail.

Can I just connect 12V to the fuel pump to test if it is working?

Any help or advice is appreciated!

The fuel pump shares a ground with the taillight assembly. It's grounded in the drivers side tail light bucket. I can only guess it's that way to prevent the Jeep from driving if the bed flies off?? Who knows. That ground can become corroded, forgotten, or inadvertantly removed if the bed has ever been off.

Any hoo, remove the tail light assembly and look for an obvious ground...or where one should be. It's only a 16ga. wire. Shine it up and re-install.

The other issue not mentioned is the CPS...antoher story. Check that wire, only takes five minutes.

If the CPS is not working properly will it prevent the fuel pump from turning on?

I don't think so..AFAIK it only creates absence of spark.

Removed and cleaned up the CPS today. Seems to be working fine because I have spark. Now I am thinking my fuel pump went out. I can't seem to get it to kick on.

Check for voltage and ground at the fuel pump before you decide it is bad.

Check the fuel pump relay, and female/male contacts, on the passenger side, under the hood. Also check for power at the ballast resistor.

Just avthought on the ballast. When the key is turned on isn't that bypassed to get the prime to start. I removed them from both my 89 XJ so can not remember. He said the fuel pump doesn't kick on with the key. You can bypass the ballast for the heck of it to see though. Switch out the fuel pump relay with a known good one too after checking the ballast. x2 check voltage at the pump. Will need two people but hey turning a key is easy. Can also give it power through the computer plug in under the hood on the passenger side. You will have to look up or may be in the chilton book as to what spot is what on the 2 plug connector.

magimerlin said:

Just avthought on the ballast. When the key is turned on isn't that bypassed to get the prime to start. I removed them from both my 89 XJ so can not remember. He said the fuel pump doesn't kick on with the key. You can bypass the ballast for the heck of it to see though. Switch out the fuel pump relay with a known good one too after checking the ballast. x2 check voltage at the pump. Will need two people but hey turning a key is easy. Can also give it power through the computer plug in under the hood on the passenger side. You will have to look up or may be in the chilton book as to what spot is what on the 2 plug connector.

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I have jumped mine from the battery to the computer diagnostics plug myself, that is the easy way check the pump and main wires to the pump!

On the ballast issue, if the fuel pump has power from the power on timer (ballast resistor bypass) the first few seconds, I would expect to see voltage at the Ballast resistor from the fuel pump, since it should be hot on both wires, if either is hot?

If it doesn't turn out to be an electrical problem, sometimes when a vehicle has been sitting for a long time, the pump will stick. Beating on the tank some with a plastic mallet, might jar it enough to get it going. A low tech solution that has worked out for me in the past.:laugh:

I guess some pumps are masochists?

LOL!

I pulled the pump out of the tank. And then connected it to a battery and it fired right up. So I cleaned the ground on the metal tube assembly and put the pump back together. Plugged it in and it no run when I cycle the key. All I need now is a new piece of fuel line to connect to pump to the pick up assembly. I have to work till 9 but when I get home I hope to get it started.

I got it all put back together and what do you know it started right up! I cleaned a lot of ground in the process of finding the issue. So it could have been a combination or just the single ground on the fuel pump assembly itself. I now have myself a clean fully operating MJ for $1000. Not too bad in my opinion.

score!