KatahGii Posted February 17, 2020 Share Posted February 17, 2020 Ok so I have replaced the fuel pump and redone the ground and it still won’t work. It’s a brand new pump and the relay is kicking on. And I can’t figure out what it is. The wiring in the cab looks brand new. I followed it as far into the foot well as I could see. Here is a pic of my fuse box maybe something is missing I can’t see and these 4 wires that aren’t connected to anything. Idk where they go to maybe someone can help. Link to comment Share on other sites More sharing options...
Pete M Posted February 17, 2020 Share Posted February 17, 2020 have you checked for power at the pump? have you supplied 12v straight to the pump to verify that it does indeed function? Link to comment Share on other sites More sharing options...
KatahGii Posted February 18, 2020 Author Share Posted February 18, 2020 3 hours ago, Pete M said: have you checked for power at the pump? have you supplied 12v straight to the pump to verify that it does indeed function? No no power. I assumed it was the firing to the pump but it all looks good someone told me to redo the ground and it might work so I did and still no dice. I didn’t check the pump I’m kinda just assuming since it was brand new it would be good. Link to comment Share on other sites More sharing options...
Pete M Posted February 18, 2020 Share Posted February 18, 2020 people have bought them DOA so it never hurts to check. when are you checking for power? the 12v is only sent for a few seconds after turning the key to run and then while the engine is cranking. if you pull the starter relay so the engine doesn't crank, you can have someone turn the key to start and be sure power is being sent. Link to comment Share on other sites More sharing options...
KatahGii Posted February 18, 2020 Author Share Posted February 18, 2020 24 minutes ago, Pete M said: people have bought them DOA so it never hurts to check. when are you checking for power? the 12v is only sent for a few seconds after turning the key to run and then while the engine is cranking. if you pull the starter relay so the engine doesn't crank, you can have someone turn the key to start and be sure power is being sent. I’m checking for power at the harness side of the pump connector. what are your recommendations on checking for power and checking if the pump is functional? Link to comment Share on other sites More sharing options...
Pete M Posted February 18, 2020 Share Posted February 18, 2020 the where is ok, but when are you checking for power? Link to comment Share on other sites More sharing options...
KatahGii Posted February 18, 2020 Author Share Posted February 18, 2020 Just now, Pete M said: the where is ok, but when are you checking for power? I have my leads in when my friend turns the key so I’m reading from before the key is turned and then to the 3rd click of the key so right before you turn the key to start the engine. Link to comment Share on other sites More sharing options...
Pete M Posted February 18, 2020 Share Posted February 18, 2020 I think you should pull the relay and check for constant power. someone back me up on this, but I think if you jumper 30 to 87 then the fuel pump should get power. 30 is always hot and 87 goes to the pump. I think. Link to comment Share on other sites More sharing options...
Ωhm Posted February 18, 2020 Share Posted February 18, 2020 Using a voltmeter or testlight check for B+ on the following pins: D1_5: B+ (Hot at all times) D1_6: KEY ON (B+ (For 2-3 seconds)) or CRANKING (B+ (Hot during CRANK)). Link to comment Share on other sites More sharing options...
KatahGii Posted February 18, 2020 Author Share Posted February 18, 2020 1 hour ago, Ωhm said: Using a voltmeter or testlight check for B+ on the following pins: D1_5: B+ (Hot at all times) D1_6: KEY ON (B+ (For 2-3 seconds)) or CRANKING (B+ (Hot during CRANK)). Are these the connectors in the diagram? Link to comment Share on other sites More sharing options...
eaglescout526 Posted February 18, 2020 Share Posted February 18, 2020 Yes those are them. 87-90 have them on the pass fender. Link to comment Share on other sites More sharing options...
GrizzzzBear Posted February 20, 2020 Share Posted February 20, 2020 Fuel Pump Ballast Resistor?? That was my Issue. Link to comment Share on other sites More sharing options...
jdog Posted February 20, 2020 Share Posted February 20, 2020 Glad to hear you got it fixed Stock 1988 swb 4.0 ax15 np 231. Link to comment Share on other sites More sharing options...
Comanche man Don Posted February 21, 2020 Share Posted February 21, 2020 Have you checked the fuel tank ballast sensor? Located under the hood on the driver side fender. If this thing is bad your fuel pump will not kick on. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 21, 2020 Share Posted February 21, 2020 I'm glad to see you guys are using my photos!! That's what they're there for. Link to comment Share on other sites More sharing options...
Comanche man Don Posted February 21, 2020 Share Posted February 21, 2020 Haha it’s your photo for real? That’s pretty cool Link to comment Share on other sites More sharing options...
87MJTIM Posted February 21, 2020 Share Posted February 21, 2020 1 hour ago, cruiser54 said: I'm glad to see you guys are using my photos!! That's what they're there for. You get a 5% royalty for every dollar I collect. 5% * $0 = $0 Link to comment Share on other sites More sharing options...
cruiser54 Posted February 21, 2020 Share Posted February 21, 2020 4 hours ago, 87MJTIM said: You get a 5% royalty for every dollar I collect. 5% * $0 = $0 Nice to know you've got my back!! LOL. Use that stuff!!! Link to comment Share on other sites More sharing options...
cruiser54 Posted February 21, 2020 Share Posted February 21, 2020 5 hours ago, Comanche man Don said: Haha it’s your photo for real? That’s pretty cool Both of them. The one Pete posted also. Link to comment Share on other sites More sharing options...
Eagle Posted February 21, 2020 Share Posted February 21, 2020 On 2/17/2020 at 9:27 PM, KatahGii said: I have my leads in when my friend turns the key so I’m reading from before the key is turned and then to the 3rd click of the key so right before you turn the key to start the engine. THIRD click is START, IIRC. First click is from locked to OFF, second click is RUN, third click is START. You should be testing in the RUN position. Link to comment Share on other sites More sharing options...
KatahGii Posted February 21, 2020 Author Share Posted February 21, 2020 1 hour ago, Eagle said: THIRD click is START, IIRC. First click is from locked to OFF, second click is RUN, third click is START. You should be testing in the RUN position. Well I feel stupid now *facepalm. I’ll check that out now thanks! Link to comment Share on other sites More sharing options...
Rich4.0L Posted August 22, 2020 Share Posted August 22, 2020 Howdy, working on a 1990 MJ 4.0 . Fuel pumps work outside but only getting 6.5 volts best I can tell at harness. Learned a lot here all ready and will be checking grounds. One comment above stated a faulty ballast resistor would prevent the fuel pump from kicking on. My understanding was the resistor was not in play during the starting process, only after the engine was running. Was hoping someone could shed some light on this. My problem seems intermittent. Through the harness, with the key the pump in a Jug worked fine. 5 min later nothing. Just found this forum. Probably because even as a farm truck it never stopped b4. Very helpful,good knowledge. Thanks. Rich Link to comment Share on other sites More sharing options...
Pete M Posted August 22, 2020 Share Posted August 22, 2020 have you worked through all of Cruiser's renic tips yet? I do believe one of them is for adding a ground near the fuel pump. could also be a bad pump, or a failing harness inside the tank. Link to comment Share on other sites More sharing options...
Ωhm Posted August 22, 2020 Share Posted August 22, 2020 12 hours ago, Rich4.0L said: My understanding was the resistor was not in play during the starting process, only after the engine was running. Was hoping someone could shed some light on this. Kinda of TRUE. Its in play only in the sense that it supplies ≈9-10vdc (voltage drop across ballast resistor) during engine RUN and CRANK (Fuel Pump Relay is ON). Now during engine CRANK the Starter Relay terminal (BAL) is wired to bypass the ballast resistor and supply direct battery voltage to fuel pump. During engine CRANK higher voltage wins. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 22, 2020 Share Posted August 22, 2020 Bypass it in about 10 seconds and see what happens. Go to my website and complete Tips 1,3,4 and 5. Link to comment Share on other sites More sharing options...
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