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90 comanche pioneer 2.5 fuel pump questions

Old 01-07-2016, 07:36 PM
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Default 90 comanche pioneer 2.5 fuel pump questions

Previously, last 2 winters i just parked my jeep cause i couldn't figure out why wouldn't run when it was under 40 degrees or so. I had another vehicle, and just plain forgot to fix in the summer, worked a lot of hours... anyway she quit on the way home yesterday and i noticed the fuel pump and gauge were both not working and no prime with the key. Anyway get a very breif shot of power to the pump wire at the pump, but not the 2 sec prime... like half sec if that and pump dont come on. Pump works fine hotted @ battery. The number 6 ecu diagnostic output thingy gets the same .5 second 12v flicker. Anyways driving me crazy cuz my girl dont like me driving her pos blazer.... sorry would be more descipt but not on computer, hate these touch screens. Thanks in advance, any and all. Great forum here been reading for years.
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Old 01-07-2016, 08:08 PM
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Oh yeah and the voltage drops down to something really low. And i have looked and looked i cannot locate ballast resistor. Driver side is dominated by white plastic tanks.
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Old 01-08-2016, 06:49 PM
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Double check the fuel pump ground behind the driver side tail light...
The 2.5s don't have a ballast resister...
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Old 01-09-2016, 11:52 AM
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Yeah look for corrosion or loose wires maybe a short
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Old 01-09-2016, 11:55 AM
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Did you do a voltage drop test on the battery it's self?
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Old 01-10-2016, 06:55 AM
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Yes ive tested the battery voltage and ground. It seems like im not getting enough power from the front, imagine its the computer, but weird the fuel gauge and pump go exact same time. Thank you ill quit looking for the ballast. Thanks guys
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Old 01-10-2016, 07:06 AM
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Also how long will a fuel pump last if i just hook it to the key switch?
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Old 01-12-2016, 06:39 PM
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Sometimes the wires inside the tank for the pump can come loose enough to not draw power to the pump...
Try pulling the sending unit out and make sure the wires are tight at the connections...
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Old 01-12-2016, 06:40 PM
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Make sure NOT to damage the sending unit itself because new replacements are non existent and used ones are even harder to find...
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Old 01-13-2016, 09:50 AM
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The sender and pump are fine, corroded as all get out, but the connections carry power fine. Up front and at the harness directly in front of the tank, the power isnt right. Im not getting that "key on prime". The shot of 12v i get is really short, .5 second or less.


And yeah, i tried getting the whole assembly when i suspected the pump. I couldn't get a sender. Thanks for the help. Still leaning towards the ecu or ecu connections but it is 4f out, im gonna have to get in someones garage before i keep jacking around this dog.

Last edited by Bdecker9; 01-13-2016 at 09:55 AM. Reason: Forgot to say.
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Old 01-19-2016, 06:12 AM
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Originally Posted by 88whitecomanche View Post
Make sure NOT to damage the sending unit itself because new replacements are non existent and used ones are even harder to find...
.http://comancheclub.com/topic/22442-...der-with-pump/

Last edited by freegdr; 01-19-2016 at 06:30 AM.
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Old 02-02-2016, 09:07 PM
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Sorry been internet-less, man its been a bear to work on this, pretty much in an open field. Last 2 days were good, but spent the them working on a pos blazer... waste of time, think i could've had this jeep at least drivable. ...im just curious, been reading this fsm looking for what the ignition switch controls... anyways just really bothering me gauge and pump went same time.... been staring @ wiring diagrams all day. Would found what was looking for if it wasn't pdf on a tablet or if i had a printer.

I found a couple of splices im gonna check, but im nit holding my breath they had continuity from the eng bay to the plug by tank. Ground was goo behind tail light ... working on uprgade. Wow this is crazy. I always get one of a kind problems. Still nred to check ecu, and im really curious about the ignition but just guessing. Come on jeep gods. Im gonna check other gauges and stuff tomorrow, weather permitting

Thnx all again!
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Old 02-02-2016, 09:40 PM
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Only thing gauge work by being grounded as pump operates on 12 volt current ...https://www.cherokeeforum.com/f2/fue...problem-40410/

Last edited by freegdr; 02-02-2016 at 09:42 PM.
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Old 02-02-2016, 11:07 PM
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The ground is good, still gonna update for good measure. ..
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Old 02-03-2016, 02:21 AM
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Originally Posted by Bdecker9 View Post
The ground is good, still gonna update for good measure. ..
Ground for sending units different from ground to pump. As fuel level change so does ohms of ground to gauge sorta like a dimmer switch for a light. Have switched in good known relay ?

Last edited by freegdr; 02-03-2016 at 02:27 AM.
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