Manche757 Posted September 8, 2022 Share Posted September 8, 2022 89Mj, 4.0, 5 speed manual. First time this ever happened. Has been running fine. Came out of grocery store. Engine starts right away and dies smoothly; no sputtering. Starts again easily. Engine zooms but tapers out. Same over and over. Gas tank slightly less than 1/2 tank. Any guess? Link to comment Share on other sites More sharing options...
Ωhm Posted September 8, 2022 Share Posted September 8, 2022 Bypass the fuel pump ballast resistor. @cruiser54 Link to comment Share on other sites More sharing options...
Manche757 Posted September 8, 2022 Author Share Posted September 8, 2022 5 minutes ago, Ωhm said: Bypass the fuel pump ballast resistor. @cruiser54 Pull both wires loose and connect them? Link to comment Share on other sites More sharing options...
Manche757 Posted September 8, 2022 Author Share Posted September 8, 2022 Well, that worked. Before god and the world I would never have figured that out. Happened in front of O'Reilly. They don't carry it. Probably too old. Where should I get one? Link to comment Share on other sites More sharing options...
Ωhm Posted September 8, 2022 Share Posted September 8, 2022 Glad it worked for you. You can get them at a lot of places, I would think. Some will say just leave it bypassed, myself, pick one up and remember your symptom. Link to comment Share on other sites More sharing options...
Manche757 Posted September 8, 2022 Author Share Posted September 8, 2022 Yes, it worked. Thanks Ohm. It saved me from walking home and calling a tow truck in the morning. Anyone know where to get the resistor? Link to comment Share on other sites More sharing options...
Eagle Posted September 8, 2022 Share Posted September 8, 2022 Rock Auto https://www.rockauto.com/en/moreinfo.php?pk=8744632&pt=7052&jsn=891 Link to comment Share on other sites More sharing options...
Minuit Posted September 8, 2022 Share Posted September 8, 2022 Won't hurt a thing to leave it bypassed, unless your fuel pump is noisy enough to bother you. Link to comment Share on other sites More sharing options...
Pete M Posted September 8, 2022 Share Posted September 8, 2022 yup, 87 4.0s didn't have it. it was added in 88 to quiet the pump. (and retrofitted into some 87s) Link to comment Share on other sites More sharing options...
Manche757 Posted September 8, 2022 Author Share Posted September 8, 2022 Ordered from Rock Auto as pointed out by the Pres of the LIMJPS, aka Eagle. $12.92 plus shipping and tax. $17.68 total. 6 day ETA. CC at its best. Accurate, quick and efficient help. Thanks Link to comment Share on other sites More sharing options...
Manche757 Posted September 16, 2022 Author Share Posted September 16, 2022 I installed the Rock Auto part. Engine will start and run at half throttle but cuts off at idle. Wrong sized replacement resistor? Link to comment Share on other sites More sharing options...
Manche757 Posted September 16, 2022 Author Share Posted September 16, 2022 Part gets hot quickly Link to comment Share on other sites More sharing options...
gogmorgo Posted September 17, 2022 Share Posted September 17, 2022 Does it have a resistance value stamped into it? Or can you take an ohm reading? I think the original was supposed to be something like 1.1 or 1.5 amp. I can maybe investigate in the morning if no one else knows the value. It getting super hot makes me think there’s something weird about it. Link to comment Share on other sites More sharing options...
Ωhm Posted September 17, 2022 Share Posted September 17, 2022 On 9/16/2022 at 9:20 AM, Manche757 said: Engine will start and run at half throttle but cuts off at idle. How does the engine start and run when the "NEW" resistor is bypassed? Link to comment Share on other sites More sharing options...
cruiser54 Posted September 17, 2022 Share Posted September 17, 2022 Ditch that POS and do a clean job of wiring the connectors. That resistor was there ONLY because of customer complaints regarding fuel pump noise. That's it. Link to comment Share on other sites More sharing options...
Manche757 Posted September 17, 2022 Author Share Posted September 17, 2022 15 hours ago, gogmorgo said: Does it have a resistance value stamped into it? Or can you take an ohm reading? I think the original was supposed to be something like 1.1 or 1.5 amp. I can maybe investigate in the morning if no one else knows the value. It getting super hot makes me think there’s something weird about it. 1.1 with the ohm symbol is imprinted on the old one. And a string of numbers that I assume are serial numbers. There is no marking at all on the new one. I ordered the one that Eagle's link above shows. The box does not indicate an OHM rating. The box shows the part to be RU38 made by Standard. I went to their site, standardbrand. com. It does not give a rating either but lists it as an "ignition coil resistor". Wrong part maybe? https://www.standardbrand.com/en/ecatalog?part=RU-38 - Ignition Coil Resistor&type=p I went to "CHECK YOUR FIT" and it states that it does not fit an 89 Comanche with 4.0, I Googled what a fuel pump resistor does. I did not find anything MJ specific but there are comments about dropping the voltage from 12amp to 10amps.. That would generate heat of course which the part is intended to dissipate. Link to comment Share on other sites More sharing options...
Manche757 Posted September 17, 2022 Author Share Posted September 17, 2022 2 hours ago, Ωhm said: How does the engine start and run when the "NEW" resistor is bypassed? It starts and will continue if given gas but if it will not idle and shuts off. Multiple tries and it does the samething. Link to comment Share on other sites More sharing options...
Manche757 Posted September 17, 2022 Author Share Posted September 17, 2022 2 hours ago, cruiser54 said: Ditch that POS and do a clean job of wiring the connectors. I read that and thought what is the gentleman from Prescott throwing at me with POS? Power Operating System? WTF does he mean? Ah hah! An expansive sense of humor coming from the rattlesnake state. Link to comment Share on other sites More sharing options...
cruiser54 Posted September 17, 2022 Share Posted September 17, 2022 Gotta love acronyms, eh? Link to comment Share on other sites More sharing options...
Eagle Posted September 18, 2022 Share Posted September 18, 2022 16 hours ago, Manche757 said: I Googled what a fuel pump resistor does. I did not find anything MJ specific but there are comments about dropping the voltage from 12amp to 10amps.. That would generate heat of course which the part is intended to dissipate. Volts, not amps. Quote It starts and will continue if given gas but if it will not idle and shuts off. Multiple tries and it does the samething. If it behaves the same whether the resistor is in the circuit or bypassed, then the problem obviously isn't the resistor. It could be a dirty throttle body, it could be a bad idle air controller -- or it could be something else. Link to comment Share on other sites More sharing options...
Manche757 Posted September 18, 2022 Author Share Posted September 18, 2022 39 minutes ago, Eagle said: Volts, not amps. If it behaves the same whether the resistor is in the circuit or bypassed, then the problem obviously isn't the resistor. It could be a dirty throttle body, it could be a bad idle air controller -- or it could be something else. Yes, volts, not amps. The engine runs as it should when bypassed. Apparently the part is not correct and the correct one is not available. Bypass wins. Link to comment Share on other sites More sharing options...
cruiser54 Posted September 18, 2022 Share Posted September 18, 2022 Hmmmm. what to do..... Link to comment Share on other sites More sharing options...
Eagle Posted September 20, 2022 Share Posted September 20, 2022 On 9/18/2022 at 6:53 AM, Manche757 said: The engine runs as it should when bypassed. Apparently the part is not correct and the correct one is not available. Bypass wins. That's the opposite of what you said above. Agree - just bypass the resistor and move on. Link to comment Share on other sites More sharing options...
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