Johnfishin1 Posted April 28, 2022 Share Posted April 28, 2022 So I just bought an 86 Comanche X today. Runs off of starting fluid. When I turn the key to start it, the fuel pump relay clicks, but fuel pump doesn't engage. I personally know the previous owner, and they had replaced the fuel pump and fuel sending unit and had it running and driving. It sat for 2 years after that. What do I do to figure out the issue? Link to comment Share on other sites More sharing options...
eaglescout526 Posted April 28, 2022 Share Posted April 28, 2022 I would recommend testing the fuel pump to ensure it still functions. Fuel pumps don’t like to sit in fuel and in turn won't work. They gum up and can just not work at all just from sitting for so long. Link to comment Share on other sites More sharing options...
Johnfishin1 Posted April 28, 2022 Author Share Posted April 28, 2022 19 minutes ago, eaglescout526 said: I would recommend testing the fuel pump to ensure it still functions. Fuel pumps don’t like to sit in fuel and in turn won't work. They gum up and can just not work at all just from sitting for so long. do I have to drop the tank to test? Link to comment Share on other sites More sharing options...
eaglescout526 Posted April 28, 2022 Share Posted April 28, 2022 Nope. Thats the beauty in it. Remove the lock ring and the assembly should come right out. Now judging by the sounds of it, you have the 2.5L 4cyl correct? Link to comment Share on other sites More sharing options...
eaglescout526 Posted April 28, 2022 Share Posted April 28, 2022 So if you crawl underneath, you will see the drive shaft and the fuel tank. The sending unit hoses and wires face the drive shaft. So yeah the lock ring holds it in place. Its an all in one unit which measures how much fuel is in the tank and has the fuel pump attached. No.2 is what holds it in. Link to comment Share on other sites More sharing options...
Johnfishin1 Posted April 28, 2022 Author Share Posted April 28, 2022 Yes I do. Sorry, I didn’t realize the fuel pump was on the side of the tank, I haven’t even been down there yet. Just got all excited Link to comment Share on other sites More sharing options...
Johnfishin1 Posted April 28, 2022 Author Share Posted April 28, 2022 Thank you, that’s a handy diagram! My fuel gauge also doesn’t work, it bounces back and forth… could that be the float in there? Link to comment Share on other sites More sharing options...
eaglescout526 Posted April 28, 2022 Share Posted April 28, 2022 No problem! As for the bouncy gauge, clean your grounds and its also mostly the float in the tank that will do that. I guess you have the idiot light cluster? Link to comment Share on other sites More sharing options...
Johnfishin1 Posted April 28, 2022 Author Share Posted April 28, 2022 The one where you just have the necessities and tons of lights? Yeah. Any easy way to change that? Link to comment Share on other sites More sharing options...
eaglescout526 Posted April 28, 2022 Share Posted April 28, 2022 Yup thats the one. Change form idiot light cluster to a 5/6th or a full? Theres few write ups on it but you need the right year cluster and the sensors for temp and oil. 84-86 have a different speedo connection than the 87-90 clusters but you can swap out the cable to the newer style and use an 87-90 clusters. Otherwise yes that fuel gauge is known to be a bit more sensitive to the fuel sloshing around. Link to comment Share on other sites More sharing options...
Johnfishin1 Posted April 28, 2022 Author Share Posted April 28, 2022 Alright last question for now then I'll check fuel pump tomorrow. Do you have any idea what MPG I should expect to get out of it? I've heard 20 mpg and 20 gpm Link to comment Share on other sites More sharing options...
89 MJ Posted April 28, 2022 Share Posted April 28, 2022 6 hours ago, Johnfishin1 said: Alright last question for now then I'll check fuel pump tomorrow. Do you have any idea what MPG I should expect to get out of it? I've heard 20 mpg and 20 gpm That can truly only be determined by how you drive it. If it’s a 4cyl, 5 speed, 4x4, 16 mpg is probably a safe guess. Link to comment Share on other sites More sharing options...
cruiser54 Posted April 28, 2022 Share Posted April 28, 2022 CRUISER'S MOSTLY RENIX TIPS IMPROVING THE FUEL PUMP GROUND JANUARY 3, 2016 CRUISER54 54 COMMENTS EDIT The fuel pump and fuel tank sending unit ground at a sheet metal screw up behind the spare tire on an XJ, and behind the driver’s taillamp on an MJ. Not only is a sheet metal screw a lousy way to ground things, this ground path is long and travels through some connectors that are prone to corrosion and moisture. Locate the black wire on the HARNESS side of the fuel pump/sender 3 wire connector. Remove a 6″ length of the split loom covering. Strip back about 1/2″ of insulation from the BLACK wire. Take your new ground wire, preferably at least 14 gauge and 12 to 18 inches long as needed, strip it about 3/4″, and wrap it around the exposed part of the harness plug wire.Solder the connection. Tape it up and reinstall the split loom covering. At the other end of your new ground wire, add a crimp on eyelet. Attach the eyelet under a bolt that goes directly into the chassis. Be sure to clean the attaching point til shiny and apply OxGard to the contact surfaces. Link to comment Share on other sites More sharing options...
cruiser54 Posted April 28, 2022 Share Posted April 28, 2022 What do the fuel pump and gauge sender have in common? They share the same GROUND. Behind driver's taillamp. Link to comment Share on other sites More sharing options...
eaglescout526 Posted April 28, 2022 Share Posted April 28, 2022 As 89 MJ said. Just depends on how you drive her. Drive her hard and fast, 16mpg easy. Drive her like a grandma and you might see higher. Link to comment Share on other sites More sharing options...
Johnfishin1 Posted April 29, 2022 Author Share Posted April 29, 2022 So I did take off the fuel pump and tested it at the wiring harness to see if it would work connected to a battery. Sure enough it did not do its job. However I did check everything else everyone listed, and sure enough, those were ALL issues I had. Lol. I found out this poor guy sat for about 15 years total. Within the last 5 years it had a new timing chain, new head gasket, ECU replaced, new distributor cap, rotor, and spark plug wires, that new fuel pump 2 years ago that went bad, a new gas tank, new fuel sending unit, a new clutch, and the front diff was rebuilt supposedly. Now, that being said, in edition to the fuel, I have another issue, the brake pedal goes to the floor. It has some pressure, and sounds like when you push on the pedal air is being pushed somewhere. I've never had that happen before so I'm not sure if that would be the master cylinder or brake booster, but I'm fairly certain it's not a line. Any advice on which one to go for? Attached will be a picture of her, and my vision for her in case anyone wants to stick around for the journey. Lol Link to comment Share on other sites More sharing options...
NC Toy Boy Posted May 3, 2022 Share Posted May 3, 2022 Help Please! Manche Lovers... This Thing is bout to Worry Me!! I have the 89 Pioneer 4.0, 5 Spd..4wd. Recently (March 2022) replaced the Tank and Fuel Pump Assembly... It worked/ ran well when first installed.. This weekend it started acting up. Spun over several times before it cranked a few times. Now it will not crank.... Runs with starter fluid. Now It sometimes sounds like the fuel pump pumps up and shuts off. Tank is fuel of fuel. But very little Pressure and flow at the Schrader Valve on the Fuel rail. What Pins on The Fuel Pump Relay (C216 I think) can I Jump out to ck the pump with the Ignition on. I have tried jumping the Fuel Pump Ballast. Is there a Fuel Pressure switch or just the Regulator and how does that work? Does the Crank Position Sensor control Power to the Fuel Pump? I am getting confused trying to follow the 88 Electrical Troubleshooting Manual posted on this site... Thanks In Advance ! Link to comment Share on other sites More sharing options...
Pete M Posted May 3, 2022 Share Posted May 3, 2022 you can try swapping the relay with one of the others right next to it. Link to comment Share on other sites More sharing options...
Ωhm Posted May 3, 2022 Share Posted May 3, 2022 Remove Fuel Pump Relay. Jumper Pin_1 (Hot at all times) with Pin_4. FP should RUN. Link to comment Share on other sites More sharing options...
NC Toy Boy Posted May 3, 2022 Share Posted May 3, 2022 Ok Gents, I jumped pins 1 and 4 for the pump relay. The Pump runs and I can hear the pump running, I got some fuel flow at the rail, but not a hi pressure squirt when I pressed the Schrader valve. I tried to start it but it did not crank. I jumped the Ballast resister and tried again. No Crank.... I put a spark tester in between the coil and the coil wire. It has spark when I turn it over but still no crank. I put the Pump Relay back in and tried again.... still no crank.... What else could it be??? Link to comment Share on other sites More sharing options...
Pete M Posted May 3, 2022 Share Posted May 3, 2022 might be time to pull the pump and make sure it's all together. did you change out the fuel filter? Link to comment Share on other sites More sharing options...
NC Toy Boy Posted May 4, 2022 Share Posted May 4, 2022 I have picked up a new inline filter... I will change it next.... Link to comment Share on other sites More sharing options...
NC Toy Boy Posted May 5, 2022 Share Posted May 5, 2022 A few more Questions.... What Fuel Pressure should I have at the rail? Does the Fuel Pump Run continuously and the Regulator open/close to keep the pressure in range or does it cycle the pump off/on as needed? Is there a way to test the Fuel Pressure Regulator? Bypass it for testing? Does anyone have a Recommended Brand/Part Number for a Replacement Fuel Pressure Regulator? I have the Fuel Pump assembly recommended from Summit Racing Part# UMWUSEP7072S US Motor Works USEP7072S - US Motor Works In-Tank Fuel Pump Modules... I will be asking them for the specs on the Pump. Also, The Fuel Gage now seems to work backwards ??? When Tank is Full the Gage shows empty and Low Fuel Light burn is on ??? I do remember seeing some discussion on this in other posts.... Link to comment Share on other sites More sharing options...
Pete M Posted May 5, 2022 Share Posted May 5, 2022 while the engine is runnning, the pump is on continuously. if the engine is off, the key turned to "run" should have the pump fire up, then shut off once pressure is reached. if the engine is off (and you've disconnected the starter for these testing purposes) and the key is turned to "Start", the pump should run continuously. if I remember it right. Link to comment Share on other sites More sharing options...
NC Toy Boy Posted May 7, 2022 Share Posted May 7, 2022 I spent some time on this today before the rain started... I unhooked the fuel line before the fuel filter. When I turn the key on the pump runs for about 3 seconds and shuts off. With the Fuel Pump Relay. Jumper Pin_1 (Hot at all times) with Pin_4. The pump runs all the time but still no pressure or flow. I will pull the pump next.... I did get the original pump assembly out of the old tank and connected it to the harness.... Same results.... Pump runs for a few seconds when ignition is turned on and the stops... It does run continuous with the FPR Pins 1 and 4 jumped.... MY Question is.... what turns the pump off when it does not have pressure after 3 seconds???? I have not found anything about how to test the Fuel Pressure Regulator and in appears to only have Vacuum and return fuel lines connected... nothing electrical.. Link to comment Share on other sites More sharing options...
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