No power when AC is on.

[loke]

I have an '85 XJ. 2.5 engine with a 5 speed manual. Lifted 3" and running 31" TrXus MT's.
When I'm accelerating with the AC off it feels ok, but with the AC on (it's really needed here in Texas) I am being passed by pedestrians and bicycles.

I know my exhaust manifold is leaking (broken bolt), but would this be the reason?
I'm not sure about my gearing as the labels are gone from both differentials.

[cal]

"'85 XJ. 2.5 engine with a 5 speed manual. Lifted 3" and running 31" TrXus MT's"

Thats why. That 85 2.5L only nominally had enough power to get around with stock tires..

[loke]

I know it's not the most powerful engine in the world, but it pulls ok without the AC on. Does the AC really make that much of a difference?

[cracker]

I know it's not the most powerful engine in the world, but it pulls ok without the AC on. Does the AC really make that much of a difference?

Obviously it does ;)

I'm surprised the AC still works

[loke]

Obviously it does ;)

I'm surprised the AC still works

Yeah, I guess I should have expected an answer like that. What I meant was: Is the AC supposed to make that much of a difference? :moon:

[cal]

yes, thats pretty normal behavior. You don't notice it on most vehicles because there is at least /some/ power to spare, but your pushing that little 2.5 as hard as it can work just to go down the street.

[90Pioneer]

Rev it up a few hundred extra rpm than normal before you release the clutch.

[Lawn Cher']

Yeah, I guess I should have expected an answer like that. What I meant was: Is the AC supposed to make that much of a difference?

The AC will drag a significant amount of power off the engine. I notice it in both my turbodiesel Suburban and my wife's '01 XJ, so with as anemic as your XJ is in stock form adding the 31's makes it even worse.

[loke]

So regear? (I don't even dare to ask what recommendation you might have:angel: )

[muddshutter]

It makes that much difference. Even in my Volvo DD, if i am going up a big hill with AC on, it drags. Turn it off, it jets away.

I worked as a Tractor Truck designer for a while and most companies are switching their AC units over to a different sysytem. There would be a generator on or near the engine that would supply electricity to an AC unit w/o ANY load on the engine. Its a better way to get the same result.

You might try regearing, that puts less stress on the engine.

[Lawn Cher']

So regear? (I don't even dare to ask what recommendation you might have:angel: )

You probably already have 3.73 or 4.10

You could go to 4.56 or 4.88 if you put a D44 under the rear, but you'd be better off with repowering altogether. Which, in an '85 probably isn't worth the effort. Maybe just look for a newer one with a 4.0 liter engine.