DAGAD Posted March 13 Share Posted March 13 we have an '87 comanche short bed with a 1996 drivetrain, electrical, dash, etc. We have rigged up the in-tank fuel regulator required for the '96 to the original 1987 pump and sending unit in the original '87 tank. The jeep ran for a bit but has now stopped. There is no fuel at the rail despite hearing the pump turn on. The gas gage never did work since the swap. We are looking for solutions: a working gas gage and a reliable, quiet pump. I've heard the 1996 pumps are great (smaller and quieter). The aftermarket, oe style fuel tanks are advertised as replacements for 86-92, despite the 1991, and 1992 having very different pumps. The 1992 comanche fuel pumps/sending units (entire assembly) on Amazon are different than the 87s and and are advertised as working in both the xj AND mj tanks. We purchased the 1992 mj/xj sending unit on Amazon but are likely sending it back because it looks like it's not made for our '87 fuel tank. the 1992 sending unit float and screen point toward the front of the jeep, not the back like the 1987 sending unit. The 1996 sending unit appears to be the same shape and also has a float that points toward the front of the jeep just like the 1992. The 1987 tank (I can confirm) has the ballast at the back of the tank and it seems the 87 float and fuel screen likely sit in the ballast. This youtube video by "major weakness" shows a 1991 tank with a ballast at the back of the tank despite a float and screen assembly that point toward the front of the vehicle but the pump and sending unit work great??? Here is the video name: Fuel Tank and Filler Hose Replacement Jeep Comanche MJ #jeepmj #jeepcomanche Can I purchase an aftermarket mj fuel tank and put in a 1996 fuel pump assembly w/o modifications to the xj sending unit? I'm willing to modify, but if I'm purchasing new items regardless, it seems superior to complete the 1996 drivetrain with an oe style pump/sending unit/regulator. Cost is $100 for an MJ fuel tank and $200 for 1996 pump/sending unit. Old fuel tank is full of garbage (old pieces of fuel hose, etc) but does not leak - If the new tank works, I was considering mounting the old tank on the passenger side for a dual tank setup in the future. Link to comment Share on other sites More sharing options...
Ωhm Posted March 13 Share Posted March 13 7 hours ago, DAGAD said: The gas gage never did work since the swap. We are looking for solutions: a working gas gage This place claims they can help you. MeterMatch Fuel Gauge Interface Module Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted March 13 Share Posted March 13 MTS sells new MJ specific fuel tank sending units. https://www.mtscompany.com/sendingunits.htm The bare sending unit is part number JPSU-7. You would need to modify the pump mount but the sending unit does work. I have one in my truck Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted March 13 Share Posted March 13 The difference between the Cherokee and Comanche sending units is the Cherokee sending unit goes to the right and the Comanche goes to the left. According to Rock Auto all 87-92 Comanches used the same fuel pump. The Cherokee changed to the turbine style pumps in 94. The 94-95 Cherokee fuel sending units are not available any where. But you can get a 96 sending unit assembly Crown Automotive Part #: 5003869AA. But because it is for a Cherokee it won't drop in to your tank. Link to comment Share on other sites More sharing options...
DAGAD Posted March 13 Author Share Posted March 13 Sweet. Thanks Ohm. That is one solution to the gas gage problem. This mj has been sitting since the '96 swap about ten years ago - I think I'm going to replace the sending unit regardless as I'm hoping to be a part of a 1000+ mile trip this summer that is going to push the jeep. If I end up replacing the sending unit with a one not compatible with the dash - I guess I can spend another $90 to get a working gas gauge :-) I'm really need info on if the aftermarket gas tanks that look OEM are different inside making them able to accommodate either style pump. If they are the same - I'd love to hear from someone who has run an early xj style pump (forward facing float and screen) in the mj fuel tank. One other person on here said it can work but requires mods. . . Link to comment Share on other sites More sharing options...
DAGAD Posted March 13 Author Share Posted March 13 @Eagle_SX4 thanks for the reply - especially to a stranger/new member:-) The MTS units are all the same size and shape - even the 91 and 92 units. The parts store and amazon show a an overlap of xj and mj units for 91 and 92. You are correct, the float and strainer point toward the front of the vehicle (right) if it's an xj unit. The youtube video referenced above clearly shows an right (forward) turning fuel pump in an MJ tank. I'm wondering if the after market tanks are specifically made to accept either direction pumps? The crown unit you referenced is the one I'm considering. The MTS JPSU-7 will have different ohms on the sender and not interface with my gauge cluster w/o the meter match solution shared by ohm. I'd really like the xj unit to work in the mj style tank - just like the youtube video shows. . . has anybody tried this? Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted March 13 Share Posted March 13 The problem with running a Cherokee sending unit in a Comanche tank is the pickup won't get to the bottom because the sump is in the way. You would need to remove and relocate the sump for it to work properly. There was a Cherokee sending unit in my truck when I bought it. It ran fine when the tank was full but I could never use all of the gas because the pick up was in the wrong. place. I think what you might need to do is combine an MJ specific hanger with the newer 96 pump/regulator/sending unit. So that it matches the location of the stock left side sending unit. Link to comment Share on other sites More sharing options...
gogmorgo Posted March 13 Share Posted March 13 Prior to MTS building fuel sending units there were a few people who used the parts off an XJ sending unit to refurbish their MJ assembly. I also recall a thread where someone simply modified the XJ unit to point the correct direction/depth. The ‘91-‘96 clusters are interchangeable so if you got an MTS sending unit for a ‘91/‘92 MJ and modified it the same way as the one you have it should read the fuel level correctly on the ‘96 fuel gauge. From experience if you start having fuel delivery issues shortly after installing a new fuel pump and you can hear the pump running, if it’s not out of gas it usually means something came apart inside the tank and either it’s not sucking fuel from the bottom of the tank anymore or else it’s just pumping it straight back into the tank. If your modifications included using some fuel line in the tank, make sure it’s submersible fuel line. The regular fuel injection line is only fuel safe on the inside and the outer layers start breaking down when submerged. Link to comment Share on other sites More sharing options...
DAGAD Posted March 14 Author Share Posted March 14 @gogmorgo Thanks - regarding what you said: 19 hours ago, gogmorgo said: From experience if you start having fuel delivery issues shortly after installing a new fuel pump and you can hear the pump running, if it’s not out of gas it usually means something came apart inside the tank and either it’s not sucking fuel from the bottom of the tank anymore or else it’s just pumping it straight back into the tank. This pump worked >10 yrs ago, sat unusued for a long time, and then worked again when we put a battery in the truck. but it never ran longer than 20 min because the cooling fans aren't working. We did consider something coming apart in the tank - but that wasn't the case when I pulled it out. The hoses in there certainly weren't "submersible" though. They were really rough. that's helpful to know the 91-96 clusters are the same. I noticed there is a bump in the middle of the sump at the bottom of the tank - it looks like a little perch for the pump to sit on. If that's the case, the strainer/pickup doesn't quite reach the bottom of the tank anyway. I have to wonder how different it is to put a cherokee/right facing pump in there if it doesn't rest on the bottom of the tank regardless. Perhaps the perch helps keep the strainer from falling off? I'll be sure to report back on what we finally do so this info can be on the interwebs for others to find later:-) Link to comment Share on other sites More sharing options...
wombat Posted March 19 Share Posted March 19 I was just browsing MTS's sight. Seems they make the factory replacement stuff, but nothing to help if you have done a 96+ swap. Id love to keep a single port fuel rail. looks like i would have to hodge podge some components together to make that work. Link to comment Share on other sites More sharing options...
The86manche Posted March 19 Share Posted March 19 15 hours ago, wombat said: I was just browsing MTS's sight. Seems they make the factory replacement stuff, but nothing to help if you have done a 96+ swap. Id love to keep a single port fuel rail. looks like i would have to hodge podge some components together to make that work. Could you not use the 92 ho pump they sell and just cap off the pumps return port? Link to comment Share on other sites More sharing options...
DAGAD Posted March 21 Author Share Posted March 21 the new '92 xj-style pump does not fit in my 1987 mj tank - the pickup hits the sump/baffle and it won't install. Also the '92 pump sending unit does not work with my 1996 dash (though I heard they are supposed to work). I plugged it in and moved the float with no change to my gas gauge. (could this be a grounding problem?) I finally found on here what I was looking for thanks to @Swampy- He has an older project similar to ours. 1996 drivetrain into a comanche. it turns out at least some of the aftermarket tanks don't have a sump/baffle, so the xj sending units work. I'll check and if they don't reach the bottom of the tank, I think I can modify it easily to get there. Link to comment Share on other sites More sharing options...
DAGAD Posted March 21 Author Share Posted March 21 @wombat My dad wants to do what you suggested - change out the fuel rail - purchase a 1990 pump and sending unit, and at the same time switch out the computer to a 1995 so that there isn't an emissions code from the fuel tank. I'm not even sure the 95 computer will plug into the 96 harness? My goal is all 1996 (or newer) - so I think I need a charcoal canister looped back on itself so the sensor can have something to plug into?? Link to comment Share on other sites More sharing options...
The86manche Posted March 21 Share Posted March 21 3 hours ago, DAGAD said: the new '92 xj-style pump does not fit in my 1987 mj tank - the pickup hits the sump/baffle and it won't install. Also the '92 pump sending unit does not work with my 1996 dash (though I heard they are supposed to work). I plugged it in and moved the float with no change to my gas gauge. (could this be a grounding problem?) I finally found on here what I was looking for thanks to @Swampy- He has an older project similar to ours. 1996 drivetrain into a comanche. it turns out at least some of the aftermarket tanks don't have a sump/baffle, so the xj sending units work. I'll check and if they don't reach the bottom of the tank, I think I can modify it easily to get there. Mts sells mj ho sending units. That's what I meant, not the xj sending unit I was aware they don't fit unless you modify Part number jpsu-7(18g) and jpsu-7p (23g) Link to comment Share on other sites More sharing options...
ghetdjc320 Posted March 22 Share Posted March 22 Goodness sakes there is a lot of confusion here. First of all, XJ and MJ sending units are not the same despite how many companies market them as such. The MJ tank has a small splash pan the pump and strainer sit in that is towards the rear of the tank. I've seen XJ sending units used but they will be oriented to the front of the tank and won't have any baffling. MTS makes an original MJ style sending unit that fits MJ tanks. The fuel gauge level sensor changed resistance ranges in the HO years (91-92) but the Renix and early model HO 4.0 pumps are the same. The 96+ setup runs a higher system psi and no return line (which is not a pump return line but rather a tank return line). You can run an aftermarket pump and modify it to fit the MJ sending unit. Turbine pumps are the newer tech and much smaller and more efficient than the old rotary vane style pumps. You can easily add an external regulator to provide either a dead head (return less) or return style fuel supply at whatever pressure you need provided the pump can support it. Most of the old rotary vane style pumps can’t consistently provide the necessary volume at the higher 96+ pressure requirements. So using a later style turbine pump is a good idea but requires some mods to the sending unit to work well. I'm personally running the DW200 pump on a modded MTS sending unit but there are plenty of other options. Link to comment Share on other sites More sharing options...
Swampy Posted March 23 Share Posted March 23 On 3/21/2024 at 8:48 AM, DAGAD said: the new '92 xj-style pump does not fit in my 1987 mj tank - the pickup hits the sump/baffle and it won't install. Also the '92 pump sending unit does not work with my 1996 dash (though I heard they are supposed to work). I plugged it in and moved the float with no change to my gas gauge. (could this be a grounding problem?) I finally found on here what I was looking for thanks to @Swampy- He has an older project similar to ours. 1996 drivetrain into a comanche. it turns out at least some of the aftermarket tanks don't have a sump/baffle, so the xj sending units work. I'll check and if they don't reach the bottom of the tank, I think I can modify it easily to get there. Glad my older thread was able to help. You can buy a new tank for an mj 86-87 i believe that does not have the splash pan in the tank. I havent experienced anything bad about not having a splash pan in the truck offroad but i almost always have it over 1/2 tank. I plan to build so custom baffles in the tank evventually Link to comment Share on other sites More sharing options...
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