RedMJ Posted October 6, 2019 Share Posted October 6, 2019 Hey guys so I have a 1988 Jeep Comanche with a 2.5....so long story short I swap the motor to a 4.0 but Now I'm having issues with the fuel and pump. 1997 fuel pump doesn’t fit in my gas tank. Anyone please help thanks in advance Link to comment Share on other sites More sharing options...
87MJTIM Posted October 6, 2019 Share Posted October 6, 2019 97 fuel pump??? That must have come from an XJ. Did they tell you the pump/sending units face the opposite direction in an XJ? There is a reason it doesn't fit: because it DOESN'T fit! Link to comment Share on other sites More sharing options...
Dzimm Posted October 6, 2019 Share Posted October 6, 2019 What fuel tank are you running and are you fully 97+ swapped as in dash and electrical are all 97+? I'm going to assume yes based on the dash shape in your picture. On my full 97+ swap I run a 22 gallon fuel tank and pump assembly from a 98 Dodge Dakota. Tank needs very minor modification to clear a frame brace and the pump wiring will splice directly into the 97+ XJ wiring and the gauge will read correctly and everything works as it should. My build thread covers this, link in my sig. To use the factory MJ tank you would need to do some custom work since the 97+ XJ fuel pump goes into the top of the tank and the depth won't be correct so the gauge won't read correctly. Link to comment Share on other sites More sharing options...
RedMJ Posted October 6, 2019 Author Share Posted October 6, 2019 1 hour ago, Dzimm said: What fuel tank are you running and are you fully 97+ swapped as in dash and electrical are all 97+? I'm going to assume yes based on the dash shape in your picture. On my full 97+ swap I run a 22 gallon fuel tank and pump assembly from a 98 Dodge Dakota. Tank needs very minor modification to clear a frame brace and the pump wiring will splice directly into the 97+ XJ wiring and the gauge will read correctly and everything works as it should. My build thread covers this, link in my sig. To use the factory MJ tank you would need to do some custom work since the 97+ XJ fuel pump goes into the top of the tank and the depth won't be correct so the gauge won't read correctly. What model did you get the fuel pump and tank out of ? Was it 1998 3.9 v6?u got pictures of how u did it Link to comment Share on other sites More sharing options...
RedMJ Posted October 6, 2019 Author Share Posted October 6, 2019 1 minute ago, RedMJ said: What model did you get the fuel pump and tank out of ? Was it 1998 3.9 v6?u got pictures of how u did it Dzimm yes i do have a complete swap. The only issues I have right now is my fuel pump it runs and all but my fuel psi pressure is at 36-39 and i struggle to turn it on and it also lags when I give it gas. By any chance do you have pictures you can post Link to comment Share on other sites More sharing options...
RedMJ Posted October 6, 2019 Author Share Posted October 6, 2019 3 hours ago, 87MJTIM said: 97 fuel pump??? That must have come from an XJ. Did they tell you the pump/sending units face the opposite direction in an XJ? There is a reason it doesn't fit: because it DOESN'T fit! Yea the Mj gas tank has the pump on the side and the Xj pump is top of the tank and the sending units are different.What I want to know is if anyone has change the tank from the Mj in order to make Xj pump fit and work? Link to comment Share on other sites More sharing options...
Dzimm Posted October 6, 2019 Share Posted October 6, 2019 7 minutes ago, RedMJ said: What model did you get the fuel pump and tank out of ? Was it 1998 3.9 v6?u got pictures of how u did it I misspoke before, mine came from a 99 but any Dakota of that timeframe should have the same setup. Not sure what model, I think they all either had the 18 gal or 22 gal. The 18 will fit the MJ without modification, the 22 gal requires a dent to clear a frame bracket, torch and 2x4 works for it, just be careful not to melt a hole in the tank. The Dakota pump assembly provides the proper fuel pressure you will need, again not sure which model it came from but I only found one option when searching so they may all use the same. I also forgot to mention, the 97+ XJ fuel straps work perfect in the MJ with the Dakota tank, just need to straighten then rebend them. Part way down the first page of my thread posted below you will see the fuel tank pictures with the dent and a description of how I did it. I don't know if I have pictures of it installed but I can take some tomorrow if I need to. Link to comment Share on other sites More sharing options...
Dzimm Posted October 6, 2019 Share Posted October 6, 2019 9 minutes ago, RedMJ said: Yea the Mj gas tank has the pump on the side and the Xj pump is top of the tank and the sending units are different.What I want to know is if anyone has change the tank from the Mj in order to make Xj pump fit and work? My initial guess is they just rewired to use the factory MJ pump, which won't provide a working fuel gauge nor the proper fuel pressure. That needs to get taken out. Link to comment Share on other sites More sharing options...
Dzimm Posted October 6, 2019 Share Posted October 6, 2019 Also forgot to mention, if you get an older (early-mid 90s) 22gal Dakota tank, it has a different shape to the rear that clears the rear axle a little better, the late 90s 22gal sits within an inch or so of the rear diff. Link to comment Share on other sites More sharing options...
RedMJ Posted October 6, 2019 Author Share Posted October 6, 2019 12 hours ago, Dzimm said: Also forgot to mention, if you get an older (early-mid 90s) 22gal Dakota tank, it has a different shape to the rear that clears the rear axle a little better, the late 90s 22gal sits within an inch or so of the rear diff. I’m checking my local pick your part I found a 1990 and a 1998 Dakota right now Link to comment Share on other sites More sharing options...
Dzimm Posted October 6, 2019 Share Posted October 6, 2019 32 minutes ago, RedMJ said: I’m checking my local pick your part I found a 1990 and a 1998 Dakota right now Not sure how far back you can go. 90 might be too old. As long as it's the plastic tank that looks the same as the pictures it should work. You will want the later fuel pump tho. Link to comment Share on other sites More sharing options...
RedMJ Posted October 6, 2019 Author Share Posted October 6, 2019 Why do you say that? Maybe I can get the newer gas tank and hopefully change the sending units Link to comment Share on other sites More sharing options...
RedMJ Posted October 6, 2019 Author Share Posted October 6, 2019 36 minutes ago, Dzimm said: Not sure how far back you can go. 90 might be too old. As long as it's the plastic tank that looks the same as the pictures it should work. You will want the later fuel pump tho. Out of what year did you do your swap?mine is a 1997 Jeep Cherokee from what I know the fuel regulator is in the fuel pump right?? 1996 and lower the regulator is next to the fuel rail ? I’m I right??? Link to comment Share on other sites More sharing options...
Dzimm Posted October 6, 2019 Share Posted October 6, 2019 7 minutes ago, RedMJ said: Out of what year did you do your swap?mine is a 1997 Jeep Cherokee from what I know the fuel regulator is in the fuel pump right?? 1996 and lower the regulator is next to the fuel rail ? I’m I right??? You are correct. The 97-01 XJ stuff is all the same. As far as I know the 96-early 00s Dakota pumps are all the same as well. My Dakota tank and pump was from a 99. Get the later 90s pump and if you can the mid 90s tank for the extra axle clearance otherwise a late 90s Dakota tank is fine, just close to the axle in a swb MJ. No matter what 22 gal Dakota tank you get, you will need to make the clearance for the frame brace towards the front. The 18 gal fits without modification iirc. As for the wiring, I will post the diagrams of both plugs and you'll just need to splice them together. If you can, get the body side of the Dakota fuel pump harness so if you need to swap the Dakota pump later, it's a direct plug and play. Link to comment Share on other sites More sharing options...
Dzimm Posted October 6, 2019 Share Posted October 6, 2019 Here are the wiring diagrams. Dakota: XJ  Just cut and match the wires. Also here is a thread that talks more details about using the Dakota tank and well as what some others have done to make it work. The way I did it is simpler imo. Link to comment Share on other sites More sharing options...
RedMJ Posted October 7, 2019 Author Share Posted October 7, 2019 21 hours ago, Dzimm said: Here are the wiring diagrams. Dakota: XJ  Just cut and match the wires. Also here is a thread that talks more details about using the Dakota tank and well as what some others have done to make it work. The way I did it is simpler imo. I think my Comanche still has the old wiring with only 3 cables Link to comment Share on other sites More sharing options...
Dzimm Posted October 7, 2019 Share Posted October 7, 2019 Just now, RedMJ said: I think my Comanche still has the old wiring with only 3 cables You'll need to follow that back and see where it's spliced into the XJ harness. I'm guessing it will be under the driver's seat where the MJ pigtail ends. Link to comment Share on other sites More sharing options...
RedMJ Posted October 7, 2019 Author Share Posted October 7, 2019 25 minutes ago, Dzimm said: You'll need to follow that back and see where it's spliced into the XJ harness. I'm guessing it will be under the driver's seat where the MJ pigtail ends. If i get the Dakota gas tank n pump will it work with my 1988 comanche plug or would I need to change it to a 1997 plug? Link to comment Share on other sites More sharing options...
Dzimm Posted October 7, 2019 Share Posted October 7, 2019 16 minutes ago, RedMJ said: If i get the Dakota gas tank n pump will it work with my 1988 comanche plug or would I need to change it to a 1997 plug? You'll need to cut the plug off and splice the wires together, or get the plug from the Dakota harness and replace the one on the MJ so it's removable. You will need all 4 wires tho so trace it back to the XJ harness and splice there. Link to comment Share on other sites More sharing options...
RedMJ Posted October 11, 2019 Author Share Posted October 11, 2019 On 10/7/2019 at 10:34 AM, Dzimm said: You'll need to cut the plug off and splice the wires together, or get the plug from the Dakota harness and replace the one on the MJ so it's removable. You will need all 4 wires tho so trace it back to the XJ harness and splice there. Is your Mj short bed or long bed?? Link to comment Share on other sites More sharing options...
Dzimm Posted October 11, 2019 Share Posted October 11, 2019 Just now, RedMJ said: Is your Mj short bed or long bed?? Short bed. I will be able to get you some pictures now. My fuel pump died last night so I'm gonna be pulling the tank. Link to comment Share on other sites More sharing options...
RedMJ Posted October 11, 2019 Author Share Posted October 11, 2019 49 minutes ago, Dzimm said: Short bed. I will be able to get you some pictures now. My fuel pump died last night so I'm gonna be pulling the tank. Please man can you I will appreciate it ! I also wanted to ask you of what year is your motor out of ? Link to comment Share on other sites More sharing options...
Dzimm Posted October 11, 2019 Share Posted October 11, 2019 I can't be for sure exactly as I got the motor as a unit in the truck. I'm pretty sure the block and head are original 90 but the valve cover and intake manifold are off a 00-01 and the exhaust manifold is also the HO style. Electronically it's all 97+ though. Link to comment Share on other sites More sharing options...
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