snakedoc67 Posted July 18, 2015 Share Posted July 18, 2015 Finally got my 87 4.0 back together this week but when I turn my key to on the fuel pump does not run. I've tested the fuel pump by running a jumper from the battery and it will run and provide pressure to the fuel rail. I've checked the relays and can feel them opening and closing when power is applied, also I have used a battery tester to confirm the base is getting 12V from the battery. Starter works fine, and the plugs and wires are new. I parked the truck last Aug for a radiator replacement and while it was apart decided to fix some other things such as worn power steering hoses, etc and clean up the engine bay. On the passenger side, most of the wires were exposed so I cleaned them up and put new wirelooms on them, and pulled out the support for the relays to clean, repaint and reinstall. I also took out my C101 to clean and reinstall as that wire harness was shot as well. When I rebuilt the C101 harness, I ended up using the injector harness out of an 88 parts truck. As I was reinstalling the wiring onto the back of the C101, I had not wrote down which wire went where and I came up with an extra one that did not have a counterpart on the injector side, nor could I tell where it went from pictures I had taken when I first bought the truck. IIRC it was a blue wire with red stripe, but will take a look later on to make sure. Trying to figure out any additional ideas, I've looked thru the forum here to see what I could find. Link to comment Share on other sites More sharing options...
HOrnbrod Posted July 18, 2015 Share Posted July 18, 2015 Got a ballast resistor on it? If so try jumpering across it. Link to comment Share on other sites More sharing options...
87MJTIM Posted July 18, 2015 Share Posted July 18, 2015 87s did not have the ballast resistor. Link to comment Share on other sites More sharing options...
Rockfrog Posted July 18, 2015 Share Posted July 18, 2015 But many did have them added as a factory TSB ... due to "noisy fuel pumps" so it is possible. Link to comment Share on other sites More sharing options...
87MJTIM Posted July 18, 2015 Share Posted July 18, 2015 do you think it is too late for mine? :) Link to comment Share on other sites More sharing options...
HOrnbrod Posted July 18, 2015 Share Posted July 18, 2015 87s did not have the ballast resistor. Confucius says: Nothing is written stone when referring to Jeeps. Link to comment Share on other sites More sharing options...
snakedoc67 Posted July 18, 2015 Author Share Posted July 18, 2015 that is true when applied to jeeps but no ballast resistor on mine. I do have a few in the garage that I pulled off JY ones thinking I was supposed to have one. lol Link to comment Share on other sites More sharing options...
fiatslug87 Posted July 18, 2015 Share Posted July 18, 2015 I had an issue with the fuel pump working intermittently, turned out to be the harness connector up by the front driver side kick panel being loose. Link to comment Share on other sites More sharing options...
Marine1Texas Posted July 19, 2015 Share Posted July 19, 2015 I have a fuel pump Ballast Resistor up front on driver side near air box. Mine came factory that way. I replaced it about 2 years ago because it broke in half. I know on start it bypasses it. I would check connection, could be some corroded connector. Link to comment Share on other sites More sharing options...
Pete M Posted July 19, 2015 Share Posted July 19, 2015 the ballast resistor is bypassed by the computer at startup. if it's bad, the truck would start, then die after a couple seconds. the pump only gets fuel for a second or 2 if the key is turned to "run". once fuel pressure is reached, it shuts off. (and may not turn on at all if fuel pressure if already reached) the pump gets power for the entirety of time that the key is turned to "start". if you can disconnect the starter, you can have someone turn the key to "start" and check the pump then. Link to comment Share on other sites More sharing options...
Marine1Texas Posted July 19, 2015 Share Posted July 19, 2015 If your not getting any prime, Remember check ground being left rear tail lamp it is connected to pumps negative line. Always make sure the connection points are good and not corroded. The pump gets power from two locations. The relay supplies both locations for prime and full time running. The yellow wire that supplies power to open relay, also passes thru to the ECM. ( you said relay is working, but good to use volt meter to check) So your see the yellow wire on relay plug also attached to a orange/black wire which go's to the ECM. It is the ECM'S job to prime the pump. (this is the pass thru for prime) It plugs in to port A5 the 6th wire from the end of ecm. You can remove ecm turn ignition on and check voltage. if voltage is good then you need to check positive wire that go's from ecm to fuel pump. It is a solid orange wire right next to the orange/black wire. it go's directly to the fuel pump. Now that is a long wire so your need to find a easy way to test that the current is going thru the wire. If wire voltage is good and connections are good on pump side you have a ECM issue. Now if your getting prime and not a continue power for pump you need to check the red wire on the relay, that connects to the starter. if voltage is good and relay is working as it should you then need to check that solid orange wire that go's from relay to ECM. again you can remove ECM and test the wire. The wire from relay will be the 4th wire from end. don't mix up with other three orange wires they are all side by side on ECM 4,5,6. now if voltage is good then you have a ECM issue. Link to comment Share on other sites More sharing options...
Marine1Texas Posted July 19, 2015 Share Posted July 19, 2015 This is a pdf of wiring http://oljeep.com/gw/elec/cherokee/91076b23.pdf Link to comment Share on other sites More sharing options...
Incommando Posted July 19, 2015 Share Posted July 19, 2015 87s did not have the ballast resistor. Confucius says: Nothing is written stone when referring to Jeeps. Truer words were never posted Link to comment Share on other sites More sharing options...
snakedoc67 Posted July 23, 2015 Author Share Posted July 23, 2015 Noriyori_Kudo, thanks for the help with the colors. Spent half of a day taking down the ECM but I was expecting that to be a pain and I learned quite a bit about it. After ruling out the ECM and all points after that, it ended up being the following: the wires had not been fully engaged when I reinstalled the relays bases a few months ago and pulled loose. Now the fuel pump works as it should. Link to comment Share on other sites More sharing options...
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