Topic: fuel filter swap

[sharpxmen]

People keep getting the models confused and it could be because of me so let me go back to step one.

2.5 YJ 1990 was the original engine - everything else on it is for the 2.5 minus the engine, trans, t-case

donor 1988 cherokee, I have the engie from that - a Ax15 and new Tcase.

So radiator, exhaust, fuel system (tank, filter, pump) is off a 2.5 1990 YJ.

how thick is your radiator? the 2.5 came with 2 different rads, 1 was the same as the 4.0 and the actual 2.5 one which was 5/8'' thick core (if i recall correctly) - if you have the latter then you need to replace it with a 4.0 one which is a thicker core

[bammerman]

I know it is a single core radiator.  If I take a picture would that help?  Not sure how to measure it.  Oh one more thing if you all know.  If I got a 4.2 fuel pump would it be the same as one for a 4.0 roughly?  I was told the 4.2 will fit in a 2.5 gas tank.

[Jeffy]

I know it is a single core radiator.  If I take a picture would that help?  Not sure how to measure it.  Oh one more thing if you all know.  If I got a 4.2 fuel pump would it be the same as one for a 4.0 roughly?  I was told the 4.2 will fit in a 2.5 gas tank.

The 2.5L YJ and the 4.2L YJ as well as the 4.0L YJ all use pretty much the same exhaust.  There is no difference other then the exhaust manifold and down pipe.

The 2.5L will usually have a 1 core or 2 core radiator.  A 4.0L will have a 3 core normally.

The 4.2L is a carbureted engine and does not need as high fuel pressure.  Also the 4.2L uses a mechanical fuel pump.

[Jeffy]

Oh and just use the YJ's fuel filter.

[sharpxmen]

I know it is a single core radiator.  If I take a picture would that help?  Not sure how to measure it.  Oh one more thing if you all know.  If I got a 4.2 fuel pump would it be the same as one for a 4.0 roughly?  I was told the 4.2 will fit in a 2.5 gas tank.

i think even the thin ones are 2 core - depending on the year you can even have a thick 1 core radiator (1.5'' or 1.75'' can't recall, I've seen them in the late TJs) - just different manufacturer

it's the thickness of the core that matters most, so like i said, if you have the thin core rad that was exclusive on the 2.5L you need to swap it with a 4.0 radiator.

[Jeffy]

The easiest way to tell is to look at the core covers and the lower tank.  If there is a 1/2" gap where the core stops short then it's a 2.5L core.  The 4.0L core will cover the tank.

My OE radiator was a single core but it was a long tube.  My newer  radiator is a twin core but the cores are shorter so there is no real difference.

[sharpxmen]

The easiest way to tell is to look at the core covers and the lower tank.  If there is a 1/2" gap where the core stops short then it's a 2.5L core.  The 4.0L core will cover the tank.

My OE radiator was a single core but it was a long tube.  My newer  radiator is a twin core but the cores are shorter so there is no real difference.

yep, that's pretty much it (the visual check).
i think all the aftermarket ones are thick, at least i could only find 1 part number for both 2.5 and 4.0 when i looked but it is better to clarify the core thickness if he purchases one online (could be NOS in which case could still be a thin core).

[chardrc]

have you checked the fuel pressure at the rail when running to see if the tbi pump is keeping up? stock exhaust on the 4.ol xj's wasn't that big, no bigger than the exhaust on my 90 2.5l although everything behind the cat was replaced before i got it, so i wouldn't worry about exhaust much (although opening it up wouldn't hurt).

[bammerman]

So ya'll think a 2.5 fuel pump will be enough for the 4.0?  Also here are a few pictures.
radiator.  Also to the fan question it is blowing inward - that is a piece of paper in the picture


Think the fan is only 16" maybe that is why.  I know it is getting hot proved it today... Also my mech said there was little to no fuel pressure at all.  Said my fuel pump looked corroded

[bammerman]

My new cold air intake with crap parts from autozone and new custom bracket

(just wanted something working to cover tbi, will upgrade later)

[chardrc]

Also my mech said there was little to no fuel pressure at all

well there is a big problem. time to swap fuel pumps.

[bammerman]

well there is a big problem. time to swap fuel pumps.

Thats my issue, the drive home it was sputtering and backfiring (i think)

do I get a new gas tank and a 4.0 fuel pump (not what I want to do) or can the 2.5 (90 YJ one) push enough fuel to work with a 4.0 (88 cherokee engine).

[Jeffy]

Thats my issue, the drive home it was sputtering and backfiring (i think)

do I get a new gas tank and a 4.0 fuel pump (not what I want to do) or can the 2.5 (90 YJ one) push enough fuel to work with a 4.0 (88 cherokee engine).

Someone has the PSI specs for the 2.5L TBI fuel pump.  I remember it being lower then the MPFI fuel pump.  If it was me, I'd remove the intake pump and add an aftermarket inline pump.

[bammerman]

Someone has the PSI specs for the 2.5L TBI fuel pump.  I remember it being lower then the MPFI fuel pump.  If it was me, I'd remove the intake pump and add an aftermarket inline pump.

Oh jeez, if we were talking about hacking computers or network security I could follow ya jeffy, I am lack their of without pictures or explanations :D

[sharpxmen]

tbi pump won't work on mpfi, the tbi is meant for lot lower pressure

i can't tell what that piece of paper does in that picture, the way you have installed the fan it should push thru the rad (put the paper on the other side and make sure it's blowing towards the engine

but if you're running lean that can be the reason it's getting hot.