shift light **5 SPEEDS READ**

Hey for those of you with 5 speeds and a stock shift light, is the shift light dependant on your RPM and gear? or your SPEED and gear?

its kind of stupid like ill be doing a pretty decent speed and wont really need a whole lot more power and ill be in 3rd gear but it wont tell me to shift, itll keep me in 3rd while i could save like 300 RPMs by going into 4th and yet still have the same momentum (3rd and 4th are retarded 3rd is way to high its like freaking same as 4th)..... then as far as 1st and 2nd go itll tell me to shift before i even hit 2000rpm, wtf? i mean that might be okay but whys it telling me to wait to shift out of 3rd untill 2k? thats just stupid do they thikn the regualr speed limit is like 60? most states its 45.

I guess im just trying to figure out optimum shift points given my gears (3.07s on 32s... soon to be 33s).... At first i thought the lower the RPM the better because its rotating the engine less, thus firing the pistons less, but if the engine is almost bogging or at like 1200 rpm maybe its putting more stress on the engine so its dumping more fuel in and increasing compression? Kinda like how you can floor it and nothing will happen, the butterfly valve on the throttle body is wide open - but is it adding more fuel to the mix as well?

Anyway, i just asked like 5 different questions lol so if you could try to help me out with as many as possible! Any advice or help would be appreciated!:cheers:

i believe it's dependent on rpm and throttle position, but ignore the stupid thing. i want to pull the bulb on mine. shift when it feels ready.

asp387 said:

i believe it's dependent on rpm and throttle position, but ignore the stupid thing. i want to pull the bulb on mine. shift when it feels ready.

Click to expand...

X2
Ignore it...mine comes on in 5th gear sometimes.....I'm just going to pull the stupid bulb

Justin

It's supposed to key you on shift points for "best fuel economy" (it doesn't.) I'm not sure what the signals that drive it are.

Mine used to come on in 5th as well - I say "used to," because last time I changed lights in the IP I just pulled the damned thing. Problem solved.

What model has a shift light for the manual tranny. Ive owned half a dozen and never had a shift light. lol.

I did however install one of those big bling RPM gagues with the light that came on which i set for 5250 rpm but thats just for dragging against V8's

5-90 said:

It's supposed to key you on shift points for "best fuel economy" (it doesn't.) I'm not sure what the signals that drive it are.

Click to expand...

It's typically based on engine vacuum. Which leads to two things:

- when vacuum is reading highest, you're getting the best economy for that speed (least amount of throttle opening).

- lower RPMs does not always equal better economy

It's very possible that 4th gear at 2500 RPM gets you better fuel economy than 5th gear at 2000 RPM. It depends on the load, engine power curve, and a bunch of other funny variables. Basing it on vacuum distills all that down into a single reading, which is simple...more vacuum = better fuel economy.

So I agree it's foolish that the light comes on in 5th gear...mine used to do that...but it's also saying that if you could drop the revs at that point, you'd be doing better on fuel economy.

(installing a vacuum gauge can give the same sort of information)

Jarvis_Pants said:

What model has a shift light for the manual tranny. Ive owned half a dozen and never had a shift light. lol.

I did however install one of those big bling RPM gagues with the light that came on which i set for 5250 rpm but thats just for dragging against V8's

Click to expand...

its not much of a shift light, its an up arrow over on the lt side, I know my 94 has it.

i just ignore the damn thing. between the 4.10's and the 31's it has no idea where its at.

I typically *shift* my Jeep by 2k when I'm trying to conserve fuel.

if you need a light to tell you to shift...sell the jeep, and buy an import.

also, you should be revving WAY HIGHER because you've got 3.07 gears with waaay too big of tires for those gears.

also, did you replace your speedo gear? it's probably wrong by quite a bit.

yea I figured it was a lot of varaibles. The reason i ask is a lot of people tell me they run theirs at liek 2k rpms cruising and shift at like 2500, where as i shift a tlike 2000 and run at like 1200 or so... I just heard on another site also that it is programed to light based on engine rpm, throttle opening, engine load ,and vehicle speed and generally is weighted for best economy.

I guess my main question was about can a car make worse MPGs at lower RPMs if hte engine is trying too hard. I guess ill need a speedo gear to fix this...

Jarvis_Pants said:

What model has a shift light for the manual tranny. Ive owned half a dozen and never had a shift light. lol.

I did however install one of those big bling RPM gagues with the light that came on which i set for 5250 rpm but thats just for dragging against V8's

Click to expand...

Renix era for sure has the light...

My 87 uused to be pukegoat, then somebody swapped in the auto...

running low RPM with high gears and large tires will effectively kill your gas mileage.

It was really for the slush driver that has never had to shift for themselves. That way the poor XJ isn't doing 50 MPH in first with the dummy on his cel asking the dealer should push rods be coming through the hood.
Plus making proper shifting points is important for good smog numbers too.

badron said:

It was really for the slush driver that has never had to shift for themselves. That way the poor XJ isn't doing 50 MPH in first with the dummy on his cel asking the dealer should push rods be coming through the hood.
Plus making proper shifting points is important for good smog numbers too.

Click to expand...

On a 4.0 HO motor the rev limiter would never let you stay in first to 50mph.

The proper shift point isn't what the light tells you... The shift light is probably wrong about 75% of the time.

They're called idiot lights for a reason.

alex22 said:

They're called idiot lights for a reason.

Click to expand...

No Doubt......

emr1101 said:

yea I figured it was a lot of varaibles. The reason i ask is a lot of people tell me they run theirs at liek 2k rpms cruising and shift at like 2500, where as i shift a tlike 2000 and run at like 1200 or so... I just heard on another site also that it is programed to light based on engine rpm, throttle opening, engine load ,and vehicle speed and generally is weighted for best economy.

I guess my main question was about can a car make worse MPGs at lower RPMs if hte engine is trying too hard. I guess ill need a speedo gear to fix this...

Click to expand...

your problem is your running stock gearing(3.07) and 32/33" tires and it sounds like your "lugging" the engine. i highly doubt a speedo gear will fix the problem with the light because the computer doesnt get a signal from the speedometer.

your problem is you have too large of a tire for stock gearing.

unless everone else your comparing yours to is set up exactly like your(gearing, tire size, engine), than your comparing apples to oranges.

In your case, many of us would shift @2500 or higher so that we would'nt be bogging down the engine. I usually keep the revs on mine(3.55s&27") above 2K(I like the 3K sweet spot).

jeepcomj said:

running low RPM with high gears and large tires will effectively kill your gas mileage.

Click to expand...

So basically it isnt good to keep the rpms low? i found out i can just barely touch the pedal if i shift at like 2200 for the earlier gears, maybe 1500 for later ones i thikn this is less stress on the engine. I always wondered, when i do wide open throttle, does it add a proportional amount of gas or is it just not really sucking in a whole lot of air? im refering to like if i floor it the engine is doing a max of like 1300-1500rpm, such as 4th gear or something....?

emr1101 said:

So basically it isnt good to keep the rpms low? i found out i can just barely touch the pedal if i shift at like 2200 for the earlier gears, maybe 1500 for later ones i thikn this is less stress on the engine. I always wondered, when i do wide open throttle, does it add a proportional amount of gas or is it just not really sucking in a whole lot of air? im refering to like if i floor it the engine is doing a max of like 1300-1500rpm, such as 4th gear or something....?

Click to expand...

you must get 5mpg if your flooring it in 4th @ 1300-1500, especially with the tire size and gear ratio your running. do you know how to downshift?

when you floor it, the throttle valve is wide open, so yes it also is sucking in air.

if you want to learn about fuel/air ratio, do a google search on how o2 sensors work.

What I find humorous is my gauge cluster has the "window" for the shift light, but I have an automatic. The same "shift light" idea was used in my friends Dakota, and it really doesn't do much, like was mentioned it would try to tell me to upshift when I was already in 5th.