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No fuel pressure '91 MJ
- Thread starter sharq
- Start date
I'm familiar with Renix fuel systems, I'm going to assume they used the same colors in the harness.
Orange at the pump should be 12V, black is ground, blue (?) sender.
Pump harness grounds to the same place as the taillights, it's a sheetmetal screw behind the tail light, it sucks, when it goes bad the pump doesn't work, it also makes the gauge go screwy.
Do you have a multimeter? You need to check and see that the pump is getting 12V at the plug by the tank.
Orange at the pump should be 12V, black is ground, blue (?) sender.
Pump harness grounds to the same place as the taillights, it's a sheetmetal screw behind the tail light, it sucks, when it goes bad the pump doesn't work, it also makes the gauge go screwy.
Do you have a multimeter? You need to check and see that the pump is getting 12V at the plug by the tank.
joe_peters
NAXJA Forum User
- Location
- Grants Pass, OryGun
Does the pump "prime" when you first turn the key on?
Jumper the wires at the ballast resistor on the driver's side fenderwell--the white ceramic thingy. After that check for 12 volts to the pump at the connector by the tank, and check the ground for continuity.
Jumper the wires at the ballast resistor on the driver's side fenderwell--the white ceramic thingy. After that check for 12 volts to the pump at the connector by the tank, and check the ground for continuity.
the ballast resistor is bypassed when the key is in start, so if it were the ballast resistor it should start, then die immediately when the key goes back to run, well, not immediately, but about 5 seconds. At least that's how the Renix version works.
I've made the assumption that chryco didn't change the wiring harness too much, just the engine harness.
- Location
- Rainy side of Washington
The OBD-I and RENIX 4.0L MPFI fuel senders for the MJ are the same, same connector, everything is the same EXCEPT for the resistance of the gauge sender which goes the opposite direction.
Haven't checked my ground location yet but I'm fairly certain it is also the same.
Haven't checked my ground location yet but I'm fairly certain it is also the same.
joe_peters
NAXJA Forum User
- Location
- Grants Pass, OryGun
Dude! What has been seen, cannot be unseen! That is FUGLY.
you are correct. there are some chemicals to clean the inside of the tank, but I would just scrap it & replace.
- Location
- Rainy side of Washington
JEESUS! :shocked:
That's pretty bad. Even mine was only rusty on the outside.
Good luck finding a new sending unit, any store claiming to have them is lying because their app database is wrong. It's a junkyard part only. your ideal donor vehicle is any 91-up mj, or if you can't find that, 87-90 mpfi equipped 4.0 (was there any other kind? Unsure of early year renix specs) mj. The 87-90 sending unit will fit fine and pump, but the gas gauge will go in reverse. No big deal and someone recently wrote a howto on swapping in a renix fuel gauge in the obd-i cluster that fixes it.
That's pretty bad. Even mine was only rusty on the outside.
Good luck finding a new sending unit, any store claiming to have them is lying because their app database is wrong. It's a junkyard part only. your ideal donor vehicle is any 91-up mj, or if you can't find that, 87-90 mpfi equipped 4.0 (was there any other kind? Unsure of early year renix specs) mj. The 87-90 sending unit will fit fine and pump, but the gas gauge will go in reverse. No big deal and someone recently wrote a howto on swapping in a renix fuel gauge in the obd-i cluster that fixes it.
Thats what i have hear. Ive been to my local junk yard. no luck. theres another one i still need to go to. what about combining parts of a new cherokee unit and the old comanche unit?
In theory you should be able to simply swap the pump out of the sending unit. It looks like it sat for a long time with no fuel in the tank.
I have a good fuel pump and sender in a fuel tank outside. it came from the 23 gallon tank, I don't know what the differences may be. It's also got a Renix fuel sender, but if your sender is good you could cabbage the pump from it.
Best bet is to remove the pump from the sending unit, take some measurements and find one that will fit. AMC wasn't to hip to actually making their own parts, it would be a nice thing for MJ owners to know what universal fuel pump they can use.
The other option would be to remove the internal tank pump, replace it with a piece of hose to complete the pickup and run an external pump. I'm running an aeromotive pump and the 4.0 loves it plenty.
http://www.summitracing.com/parts/AEI-11109/
Rockauto says that Carter P74057 is the correct one for XJ/MJ. It's just a bare fuel pump and some hose, so as long as it fits in the hanger it should work.
As for testing the ground, you need to set your multimeter to "OHMS", ground the black lead to the frame on a clean spot and touch it to the pump ground. Anything over about 5 Ohms is going to indicate a problem. I would really recommend that you take off the drivers tail light and clean/inspect the ground to the body back there anyway, it's usually a problem.
I have a good fuel pump and sender in a fuel tank outside. it came from the 23 gallon tank, I don't know what the differences may be. It's also got a Renix fuel sender, but if your sender is good you could cabbage the pump from it.
Best bet is to remove the pump from the sending unit, take some measurements and find one that will fit. AMC wasn't to hip to actually making their own parts, it would be a nice thing for MJ owners to know what universal fuel pump they can use.
The other option would be to remove the internal tank pump, replace it with a piece of hose to complete the pickup and run an external pump. I'm running an aeromotive pump and the 4.0 loves it plenty.
http://www.summitracing.com/parts/AEI-11109/
Rockauto says that Carter P74057 is the correct one for XJ/MJ. It's just a bare fuel pump and some hose, so as long as it fits in the hanger it should work.
As for testing the ground, you need to set your multimeter to "OHMS", ground the black lead to the frame on a clean spot and touch it to the pump ground. Anything over about 5 Ohms is going to indicate a problem. I would really recommend that you take off the drivers tail light and clean/inspect the ground to the body back there anyway, it's usually a problem.
i dont think the sender is good but i will double check the ground on the pump/sender harness maybe that was the problem with the sender. the ground looks fine though. not loose at all. is the actual sender removable from the assembly?
i do like the idea of an external pump.
removing the sender is a bad idea, they're really fragile. Best bet there is to try and clean the contacts where the little "fingers" are. Sometims you can find new fingers and replace them on the arm and that fixes them.
Did you actually remove the ground behind the taillight and clean it?
Did you actually remove the ground behind the taillight and clean it?
never trust how a ground looks. It's best policy to just take it off, clean both sides to shiny metal and put it back. Takes 5 minutes, you're already there and you know it's good then.
A dab of Ox-Gard or something similar will keep that ground in good shape.
Have you jumped the pump to 12V yet? Since you have the sender/puump out of the tank it's pretty simply. Watch out for squirting fuel, and don't run it more than a second or you'll damage it running it dry. At least then you'll know if the pump is totally hosed or not.
old_man
NAXJA Forum User
- Location
- Loveland, Colorado
If you are going to try and save the tank, drain out all the fuel. Put about two cups of muratic acid in the tank along with about a half gallon of HOT water. Slosh it all around, let it sit a few minutes and repeat the sloshing a couple of times. Rinse out with a water hose somewhere you would like to kill the weeds. Repeat several times until what comes out is clean. Muratic acid is strong so use rubber gloves and safety glasses and make sure you don't get any on you.
Go to www.eastwoodco.com and get some gas tank sealer and coat the inside of the tank.
Go to www.eastwoodco.com and get some gas tank sealer and coat the inside of the tank.
How would i go about jumping the pump? hook it straight to the battery?
What can i do with the contaminated fuel? isnt muratic acid available at pool supply stores?
