Fuel pump

What is the difference between a 1990 fuel pump assembly and a 1991 fuel pump assembly. From what I can tell the pump itself is same part number but the whole assembly is a different number

maybe someone with more knowledge on the assembly can chime in but i know that the original Bosch pump can still be bought although not at the dealer because its discontinued.

Good luck finding the assembly.

Spectra and airtex are junk all around so id try to stay away from them(unfortunately they seem to be the only ones who offer the assembly in my experience ymmv)

i vaguely remember the newer ones at some point went to a "returnless" fuel system but im not too sure what years.
that may be the difference you are asking about...
Could also do with the sending unit...

95% sure the polarity on the fuel gauge sender was reversed in 91. On the fuel pump side of the connector, the dark green/red wire is the fuel pump, the dark blue is the sender and the black is ground. The sender and the pump ground are spliced together somewhere on the pump assembly.

The Renix sender is 0 ohms to 88 ohms, the higher the resistance the higher the fuel level reads at the gauge. I believe in 91 they reversed that. But I'm not sure of the max resistance reading, if it is the same or not.

There may also be some difference in how they mount, I've never swapped one out on a 91. Though in some post-Renix models I did notice the tanks were different.

the sending unit polarity is what i was trying to remember...good on ya 8mud

Bought my first XJ off a friend. As I was driving away I said to myself, "Sweet, full tank of gas". A couple days later I said "Man, this thing gets great gas mileage". A couple days layer it dies on me. No fuel pressure. "Crap, need a new fuel pump and the tank is full." Get the parts and tear into it. Remove the straps and as I'm lowering the jack I realize that the tank is empty. Can't remember if I replaced the pump or not, that may be the one sitting on my shelf. Told my buddy the story and he's like "All yeah, I forgot to tell you..."

hey we've all been there...but sorry that is funny.