Where the heck is it?

The ballast resistor relay on a 1991 Cherokee. It may be back feeding into computer with the fuel pump relay and we have all sorts of weird problems.

If you are talking about the one for the fuel pump,it is in the engine compartment on the driver's side fender. it is white and rectangle shaped with 2 wires running into it.

That isn't a relay, thats a ballast resistor.

Never had to replace that dang thing.. what does it do?

Okay, checked a buddies FSM. Basically what the ballast resistor does is slows down the speed at which your fuel pump runs, therefore decreasing noise, as well as increasing the life of the pump. The only time you need its full output is when the Jeep hits WOT, and therefore the ECM kicks on the bypass. Well we are getting some sort of back feed through to the computer so that when the fuel pump is on, the injectors won't fire, but if you pressurize the fuel rail, then pull the fuel pump relay, it will run till its out of pressure. The ballast resistor bypass relay is the next place we expect it to back feed from. It is located by the coolant bottle sorta below the Power Distribution Center. I know from memory it has been removed on the jeep, but may have something wrong with the wiring.

Mich88XJ said:

The ballast resistor relay on a 1991 Cherokee. It may be back feeding into computer with the fuel pump relay and we have all sorts of weird problems.

Click to expand...

The ballast resistor is where he said. The relay is in the PDC. Which is it you want?

FYI... from an elctronics tech point of view,....been doin it for over a decade now,.... Resistors rarely go bad...these are just like any resistor, except they are made of a ceramic material,...and made to dissapate heat. as opposed to the little carbon guys soldered to curcuitboards...Im not sure what the resistance on this particular one is supposed to be,...but they dont "short".. they will "open" though...meaning break..and totally halt current flow...a little thing anyone learns in a basic electronics class is that they just dont short...

If it is opened, an Ohm check, or "resistance check" will bring you some ohm value. It should be well within a certain set Ohm value.+/- 5 to 20% All that info should be in the code printed on it.I havent looked at mine and im too lazy to walk outside right now and look under the hood.It may be some code you need a reference book for.They do that sometimes...
If its opened itll be "OL" on some digital meters. Meaning "Open Leads"
OR itll give you an infinite symbol...usually not change at all....

I see a lot of "blame the resistor" posts on here. They can cause issues, but not very often.I would put my hard earned $$ on a relay any day. Moving parts fail WAY before a simple ceramic device designed to turn current flow into heat...Which is what it does....Resistors slow down electrons by giving them a chokepoint (think of when they shut down a lane or two on a freeway)....and this causes friction.A product of friction is heat...(all three lanes are forced to merge into one lane, and people[electrons] get mad, thats friction, and heat..haha....and traffic moves slower.)

So until next lesson on basic electronics....where well discuss the Hole flow theory......