Rhys Chalmers Posted April 30, 2023 Share Posted April 30, 2023 Hey ya'll! My wonderful MJ died on the road last September and sat at home unloved for the winter, so it's time to get it running again. This is what I've done/discovered so far. I replaced the fuel pump since it no longer primed when I turned on the ignition and assumed that was the problem. Fuel gauge has never worked and it turns out the floater on the old pump had broken off, so I hope the new one will let me know how much gas I have. I refreshed the ground behind the tail light following cruiser's instructions, and will eventually relocate the ground to the fuel filter, but the ground is now good. I ordered the big 7 from jeepcables.com and will be doing that this week. I've determined the fuel pump relay is good and cleaned the connections. I've gone through the grounds and discovered the the braided line from the engine the chassis is gone! Could this be a possible fix? The fuel pump is definitely good when I use a probe and give it direct power. Basically I'm at a bit of a loss as where to look next. The engine cranks just fine but the fuel pump is not getting any power even to prime it when I turn on the Ignition. Maybe a fuseable link? I'm going to put in a proper fuse/relay box from a 90's cherokee in there eventually, but I just want the thing running again so I can at least move it/work on it in the garage when the weather is bad. Any help is appreciated :) If you need more info ask away and I'll do my best to answer Goddamm Renix jeeps man... Link to comment Share on other sites More sharing options...
Ωhm Posted April 30, 2023 Share Posted April 30, 2023 YR? ENG? TRANS? Link to comment Share on other sites More sharing options...
Rhys Chalmers Posted April 30, 2023 Author Share Posted April 30, 2023 1987 4.0 ax15 trans Link to comment Share on other sites More sharing options...
Ωhm Posted April 30, 2023 Share Posted April 30, 2023 Using a voltmeter or 12vdc testlight (preferred) check for Battery_Voltage_(B+) on the following pins (use battery_negative terminal for ground): D1_5: B+ (Hot at all times) D1_6: At KEY ON only (B+ (Hot for 2-3 seconds)). D2_4: B+ (Hot during KEY ON and Hot during CRANK). Link to comment Share on other sites More sharing options...
Rhys Chalmers Posted April 30, 2023 Author Share Posted April 30, 2023 Thank you so much! I was wondering what those yellow things were for. I'll check these in the am Link to comment Share on other sites More sharing options...
Rhys Chalmers Posted May 1, 2023 Author Share Posted May 1, 2023 So I got the gumption to do it tonight after I got home from work. D1_5 is hot and has power. D1_6 is hot for a few seconds with ignition on D2_4 has power with ignition and crank Link to comment Share on other sites More sharing options...
Ωhm Posted May 1, 2023 Share Posted May 1, 2023 Good readings. Fusible link seems good. If your equipped with a Fuel Pump Ballast Resistor, bypass it (use a jumper wire). Try starting vehicle again. Link to comment Share on other sites More sharing options...
Rhys Chalmers Posted May 1, 2023 Author Share Posted May 1, 2023 Ok so... I'm not sure what's going on here but it's a nightmare. Theres a connector just hanging out. I don't know what the EF-8933002298 is (this engine has been swapped from a cherokee so it may have something to do with that) and all of the red wires seem to be part of the auxiliary light system. Link to comment Share on other sites More sharing options...
Ωhm Posted May 1, 2023 Share Posted May 1, 2023 Early 4.0L came with no Fuel Pump Ballast Resistor. Link to comment Share on other sites More sharing options...
Rhys Chalmers Posted May 1, 2023 Author Share Posted May 1, 2023 So this morning after getting rid of the auxiliary light wires this is what I'm looking at. As you can see I no longer have the fuel pump ballast resistor. Where should I look next? Link to comment Share on other sites More sharing options...
Big_Mark Posted May 1, 2023 Share Posted May 1, 2023 In my case I installed a new fuel pump and sending gauge assembly. After lots of diagnosis I ended up pulling the assembly and discovered the output hose between the fuel pump and the fuel line had slipped off. So what was happening to me was the pump was working but it was sending most of the fuel back into the tank. I know it's a PITA but you may want to pull out your sending gauge / fuel pump assembly to make sure everything is in place. Link to comment Share on other sites More sharing options...
Ωhm Posted May 1, 2023 Share Posted May 1, 2023 Under the dash, near the Parking Brake, locate connector C157. While CRANKING vehicle over, check for voltage on pin C157_F (ORN) (IP Harness side). Link to comment Share on other sites More sharing options...
Rhys Chalmers Posted May 1, 2023 Author Share Posted May 1, 2023 @Big_Mark I've actually encountered this problem already. It was indeed a PITA but i took out the pump and the connection had slipped off like you described. When i put it all back together i tested the pump with a probe while in the tank to make sure it was still connected. I'm going to check the c157 connection now like this other person said and get back to ya. Ya'll are so helpful ❤️ Link to comment Share on other sites More sharing options...
Rhys Chalmers Posted May 1, 2023 Author Share Posted May 1, 2023 So... I've tested for voltage on both connectors since I was not sure which end I should test. The female side of the connector (I think it's the harness side) on c157F has power with ignition on but DOES NOT have power while cranking. Male side (the one shown in your picture) has no power with ignition or cranking but that's the pump side of the harness, right? Link to comment Share on other sites More sharing options...
Ωhm Posted May 1, 2023 Share Posted May 1, 2023 3 hours ago, Rhys Chalmers said: Male side (the one shown in your picture) has no power with ignition or cranking but that's the pump side of the harness, right? That is correct. 3 hours ago, Rhys Chalmers said: The female side of the connector (I think it's the harness side) on c157F has power with ignition on With voltmeter connected, turn KEY ON, NO CRANK does your voltage reading timeout after 2-3 seconds? Link to comment Share on other sites More sharing options...
Rhys Chalmers Posted May 1, 2023 Author Share Posted May 1, 2023 I will check when I get home from work tonight Link to comment Share on other sites More sharing options...
Rhys Chalmers Posted May 2, 2023 Author Share Posted May 2, 2023 I went in with a probe to get a proper voltage reading and here are the results. There is 12 volt power for 2 to 3 seconds then it drops to zero on CRANK ONLY There is about 9 to 10 volts DURING CRANK. It turns out there is indeed power during crank. The cheap test light I used at first just wouldn't light up. So I have power up to this point. What's next? Link to comment Share on other sites More sharing options...
Ωhm Posted May 2, 2023 Share Posted May 2, 2023 1 hour ago, Rhys Chalmers said: The cheap test light I used at first just wouldn't light up. This could be telling us something. But not yet. 1 hour ago, Rhys Chalmers said: So I have power up to this point. What's next? Now, easy for me to say, reconnect C157, then disconnect C139 at the Fuel Pump. Perform the same test on C139_C (ORN) (vehicle side of the harness). Link to comment Share on other sites More sharing options...
Rhys Chalmers Posted May 2, 2023 Author Share Posted May 2, 2023 That connector is gone so I had to cut and strip wires to do this test. Same result as before. 12 volts for 2 to 3 seconds then nothing. About 10 volts during crank so there is power! When I ground the fuel pump directly to the negative terminal on the battery, and the power is coming through the harness, the pump primes finally! That leads me to believe it's still not getting ground. I hooked up both the harness and fuel pump negative cables to an eyelet terminal and put it on the fuel filter bolt thinking that would finally ground it...but still no luck. It's not getting a good ground. I'm still wondering if the engine is simply not grounded to the chasis? Like I said in the first post, the braided cable that goes from the cylinder head to the chasis is missing entirely. My cables from jeepcables.com came in today so I have a replacement to put on tomorrow. I am giving up until morning as I am defeated and it's now pouring outside! Is there something else I'm missing? I'm not sure but I'm so darn close! Link to comment Share on other sites More sharing options...
cruiser54 Posted May 2, 2023 Share Posted May 2, 2023 Might be time to do the fuel pump ground mod? Even a temporary one for diagnostic purposes? What kind of connectors were used on the cobbled up connections at the fuel pump? Link to comment Share on other sites More sharing options...
Rhys Chalmers Posted May 2, 2023 Author Share Posted May 2, 2023 Update! Not fully successful but some progress. Here's what I've got. I installed a new ground wire from the bat negative to a radiator mount bolt on the front. I installed a new cable going from the driver side firewall to an intake manifold bolt instead of the cylinder head bolt (do all three need to be connected?). I then did the fuel pump ground upgrade while I was under the truck. @cruiser54When i installed the fuel pump there were zero connectors going from the harness to the pump. It was all crimp connected, so when I installed the new one I used solder and seal connectors that use a heat gun. Not as good as soldering, but still better than crimp connectors. Plus soldering next a fuel tank is not ideal. So...with everything connected the fuel pump primes! YAAAAY! The truck turns over but now won't start...BOOOOO! But still, progress What confuses me is the truck ran briefly last night when I used a direct ground from the battery to the pump. I threw fresh gas in today and now it primes, cranks, but won't start! I'm running out of ideas but am refusing to give up Link to comment Share on other sites More sharing options...
Rhys Chalmers Posted May 2, 2023 Author Share Posted May 2, 2023 ITS ALIVE! After priming the pump a million times it's back! I've released it from the swamp it was in and gave it a test drive. God what a good feeling! I can't thank yall enough for the continued help. Still lots to do but this site rocks! Link to comment Share on other sites More sharing options...
cruiser54 Posted May 2, 2023 Share Posted May 2, 2023 YAY! Way to stick with it. Link to comment Share on other sites More sharing options...
Big_Mark Posted May 2, 2023 Share Posted May 2, 2023 3 hours ago, Rhys Chalmers said: ITS ALIVE! After priming the pump a million times it's back! I've released it from the swamp it was in and gave it a test drive. God what a good feeling! I can't thank yall enough for the continued help. Still lots to do but this site rocks! Great job! These things require tenacity! To make sure I didn't run into the slippery hose issue again, I secured the pump to the bracket with hose clamps as shown below So far so good and trail tested! Link to comment Share on other sites More sharing options...
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