98 4.0l in a 91

HotRodP71 · May 17, 2016

Hell everyone,
new to the site, bought my second Ranger. It is a 91 4.0l auto, bought it CHEAP with the notorious "tick". Thinking i could just replace the push rods and rocker arms, I quickly found out my problems are much more serious.... Long story short, I need an engine. I bought one at a junk yard, so this question may be a bit late, but will a 98 4.0l work in a 91?? I would assume so, just wondering if there are any things I should be aware of. I know the 98 has an EGR setup that is not present on the '91, I was going to re-use my intake. I just read that the exhaust ports are different, so I was just going to use the 98 manifolds and delete the EGR tube.

Any info is MUCH appreciated!

cp2295 · May 17, 2016

I know the motor mounts will work just fine since the 98 block has all 3 gens of ranger mounts drilled, so youre good there. I dont think there should be an issue using your intake and deleting the egr valve. Only thing i can think of too to swap over is your old cam sensor (or buy a new one for a 91) since they have a different style sensor.

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HotRodP71 · May 17, 2016

Cool, thanks for the input! I forgot to mention that i am also aware that I must use the '91 flex plate/flywheel.

adsm08 · May 17, 2016

No, you will have to use a 98+ flywheel/flex plate. 90-97 had a 6-bolt crank. 98+ has an 8-bolt crank.

If you snag an engine from a manual trans vehicle I have a 98+ flex plate, but I need a manual trans flywheel for an 8-bolt crank.

cp2295 · May 17, 2016

Good point adsm forgot about that make sure u grab that plate!!!

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HotRodP71 · May 17, 2016

Wait.... So my trans won't work?? If thats the case, it's for sale...

RonD · May 17, 2016

Your 4.0l trans will work.
'91 engine will have a crank with 6 bolts for flywheel(or flexplate)
'98 engine will have 8 bolt crank for flywheel(or flexplate)
So not interchangeable

You need the flywheel(manual trans) or flexplate(automatic) for a '98

If you have an automatic and get a flywheel with the '98 engine, adsm08 said he would trade you.

Yes, the '98 has high velocity exhaust ports, that was to heat up cat converter faster for lower emission on cold starts, so yes use the '98 exhaust manifolds

HotRodP71 · May 19, 2016

Okay, so I have the engine mostly prepped for install. Got a flex plate for a 98 on it's way from summit. The only question I have at this point is, is there a difference between the injectors used on a return style fuel system vs a return-less style fuel system? In other words, should I use the injectors off of the 91 or use the current units on the 98 motor? I would assume the 98 units would work.... Just making sure!

Again, thanks for any info!

RonD · May 19, 2016

Should be 21lbs/hr injectors on both.

Fuel rail, of course, needs to be changed to return style use

adsm08 · May 19, 2016

Extremely early 4.0s had a different flow rate. Since yours is a 91 I would use your original injectors.

HotRodP71 · May 19, 2016

Yeah thats what I decided to do, just to be safe. I got o-ring kits to install, since the original ones were more like hard plastic rather than rubber....

recutright · May 27, 2016

hows your install coming along? I have a customer who wants the same thing done to his ranger. 97 expo 4.0l into 90 2.9l ranger. I didn't know the crank had 8 bolts til now. so I need to find a 8 bolt flex plate. ADSM08, I do have an 8 bolt flywheel if you still want to trade?

HotRodP71 · Jun 4, 2016

I've pretty much got all the parts, but have run into a snag, we have removed all of the trans mating bolts (6 total) And the trans is SOLD to the engine. We have also removed the four torque converter bolts as well, kind of at a loss here. It is solid as a rock, and weve double triple quadruple checked to make sure they're all out.

As always I do appreciate any info guys, thanks!

recutright · Jun 8, 2016

the damn dowel pins get corroded and like to stick. if its on a lift just rock the trans a bit and they should come loose. if its on the ground, jack the trans up as far as you can, then place a jack stand with a wood block under the engine oil pan and lower the trans. it wont go fat but it should give you a small gap between the motor and trans.

98 4.0l in a 91

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