i have a 1989 cherokee with a rebuilt motor only 1,000 miles ago, and a 5 speed. In town it has tons of power, and does amazing, but on the freeway its all it can do to maintain 75, its pretty much floored all the time to try to maintain speed. it really struggles, especially up hills. It has 235's... i don't know what gearing it has, but man.... its very sluggish. Any ideas? Also, i don't know how much this has to do with anything but sometimes when my cherokee gets to opp. temp, it has less power then when its cold. Also, it doesn't like to idle at 700 rpm.... it kinda goes anywhere between 650-750 rpm, and jumps around. Sometimes when i let off the throttle, the rpm goes close to zero, then it catches itself.... So, any ideas? Its always has this idle problem thing, even with the old motor, but the other stuff is sorta new. Ive sorta had problems with my injectors in the past, so a lot of these problems might be related to injectors? i dunno, thats why i came here haha.... Maybe its just me, ive never driven any other cherokee, so it could possibly be normal to struggle on the freeway haha i don't know. Thanks for any ideas, or comments
-Josh

 

what injectors are you using did you change them or reuse the ones you had before the rebuild

 

Since it was built 1000 miles ago, what is new and what is old??(plugs, wires, fuel injection, air filter ect ect. go thru the list of what is new and old)


as far as idle goes. Mine does the same thing, it sounds normal. As long as it doesnt get to low to where your electronics cut out for a split second then you are fine(every so often mine will do that....).

And with a new motor, you should have new car and rotor, new plug wires and new plugs, i suggest soak cleaning your injectors or getting new ones(reman with Ev6 technology are around 100 shipped. i run them with no issues) your intake chemical cleaned, your TB cleaned, a new air filter and fuel filter. It should have been a big tune up, not just a motor replacement.

like i said, what are the specs on waht you replaced and didnt replace

 

well as far as new stuff goes fuel and spark related, i have new plugs, wires, new cap and rotor, ive had the TB and intake chemically cleaned, i have a new air, and fuel filter.... the only thing i really haven't messed with are my injectors, and fuel pressure regulator. I cleaned my injectors with some cleaner, but thats about it..... they are just the stock ones.... a few use to leak sometimes before the rebuild, but i cleaned them, and put them back on and they haven't leaked at all..... so could injectors be a problem?

 

I'd be inclined to guess you have too much back pressure, maybe from a clogged catalytic converter? Can it hold 75 in fifth gear?

 

Injectors do wear out over time. Most people do not notice tho. If you get an Ev6 style injector you wil notice a bit of fuel econ. increase. and a bit more power. It allows for better atomization. There are many options from remans with new internals or neon injectors to ford injectors

 

Have you increased the tire size?

 

it has a brand new exhaust and cat, but it will hold 75 on flat ground in fifth, even then I have my foot way down on the throttle. but even with the slightest incline I have to shift down and floor it. I think the stock tire size is 215 and I have 235's so I don't know if it would make that big of a difference.

 

IIRC all sticks (mine 2) have 3.07s

 

3.07's? wow, well that would explain a lot haha. Does anyone know where to buy these injectors?

 

i ran 3.07's with with a 265 with no issues at all i could accellerate with in 5th and maintain on hills with 140xxx. There is something else going on here.

Cause with 3.07's and 33's i can maintain 75 in 5th and i have to drop into 4th to pass or go up a hill and then i can realy accelerate!

these are the same injectors that i bought(well a different year). i vouch for them completely on being a legitimate business as well as having a quality product.

http://cgi.ebay.com/ebaymotors/1987-...ht_7147wt_1026

 

i have 3.55 stock

 

3.55 - auto
3.07 - manual

The reason there is a difference is the power loss in the auto tranny has to made up somewhere.

This is also why when you buy gears for bigger tires manual tranny's take the next step up in size.

where an auto might need 4.56's a manual will need 4.10's or the freeway RPMS will be way to high.

 

yeah, i'm thinking something else could be going on. On my old motor i could maintain 75 no problem. I rebuilt my engine, and it has a ton more power around town and everything, it runs amazing, but now it really seems to struggle on the freeway, the only other thing i have changed is it has a 5 inch lift, but still the same tires (for now).... So i don't really know whats going on.... this just doesn't make a whole lot of sense to me.

 

Did a shop rebuild it or did you rebuild it?

also is there a certain power decrease at a certain rpm or just in 5th gear?

Sorry if these are repetitive just scratchin my head to try to help you figure this out man