Slow to accelerate?

[kawaboy13]

I feel like my 4.0 is somewhat underpowered. I see back in its day, the comanche pushed more horsepower than the other brands. But, maybe its because of the power today that I feel this way. It's a standard so it has some get up. But in 3, 4, and 5 gear, I feel like the truck is slow to accelerate. If you punch it on a new truck, it'll jump. But in the comanche, it'll just ease up. Is this normal to be able to put the pedal down and it not reall accelerate hard?

[Incommando]

stock tire size? Gearing? Miles on the truck? How long since a good tune-up? Renix or HO?

 

No, by modern standards the 4.0 is not a powerhouse. But it is no slouch, either, thanks to the light weight of the MJ/XJ.

[kawaboy13]

Not sure if it's had a tune-up. Its got 165K on it. It has 3.08's. It is the renix motor.Ant the tires are a couple inches taller than stock.

[Incommando]

A renix had 177 hp, and your engine is now beyond the life expectancy of the avaerage engine. Your effective gear ratio is now probably a pathetic 2.80:1 or so. Put shorter tires on it, re-gear, or down shift that badboy. :D But first you need to do a complete tune-up so that you are starting with as good a baseline as possible.

[mnkyboy]

The problem is the gearing,regearing should make it pretty peppy

[Pete M]

and when they say "regearing", they mean swapping in an axle with better gearing. it can cost 600 to regear an axle and you should never ever sink that much money into a Dana 35. 3.55 gears are found behind the most common XJ package out there; 4.0L+auto.

 

also make sure your air filter and your cat are not clogged.

[Geonovast]

Doesn't hurt to sink the couple bucks into a cap, rotor, plugs, and wires either. Fuel filter and a bottle of injector cleaner are also good ideas.

[87MJJeep]

Doesn't hurt to sink the couple bucks into a cap, rotor, plugs, and wires either. Fuel filter and a bottle of injector cleaner are also good ideas.

 

Does anyone that puts a lot of miles on their Comanche have any advice on what brand of parts to get or to avoid? (cap, rotor, plugs, and wires)

 

Is there anything else ignition-related to replace during a tune up?

[mkbruin]

DO NOT get the Bosch +4 plugs, or any of the other gimmicy things. Stick with a good quality regular platnum plug for the best spark and best bang for your buck.

 

Before doing the tune-up, start with a can of sea-foam or MCCC. You do not want to do this after new plugs, because it can foul the plug.

 

Rotor/Cap shouldn't be that big a deal... anything new will be noticably better than 25 year old factory parts.

 

FLUID CHANGE. Complete. Radiator flush. F/R Differentials. T-case. Transmission. Engine. For engine, we use Valvoline High Mileage syn blend 10-30 in all our cars. Its low-cost (20 bucks/change at Wally mart) so 3k-5k mile changes are easy on the wallet. We have a '01 caravan with 230k miles on it with zero issues, and its seen HEAVY tow duty (about 50k of the 230k is with a maxed out trailer weight.)

[87MJJeep]

Thanks for the help! I kinda figured anything new is better than what's in there. I didn't have Seafoam on the agenda, but it had crossed my mind. Thanks for the alert to do that before changing plugs!

 

I'm crushed, I wanted to put a set of Splitfires in there. j/k!

 

Thanks for the advice to get platinum. I didn't know if that was advisable or regular style were fine.

[Geonovast]

Generally platinums are ill advised for the 2.5 and 4.0. You'll be just fine with NGK or Champion coppers.

[87MJJeep]

Generally platinums are ill advised for the 2.5 and 4.0. You'll be just fine with NGK or Champion coppers.

 

Thanks! That'll save a few pennies! Is the consensus that Factory spec gap and heat range is best?

[mkbruin]

Generally platinums are ill advised for the 2.5 and 4.0. You'll be just fine with NGK or Champion coppers.

 

Can you elaborate? Why are they ill-advised? I have never heard that anywhere for any vehicle....

[Geonovast]

There's something about our motors that can cause the platinum tips to break off, which can cause severe damage to the piston and cylinder wall.

 

The chances of that happening are pretty low, but platinums give no noticeable gain in power or mileage, so why chance it?

[87MJJeep]

There's something about our motors that can cause the platinum tips to break off, which can cause severe damage to the piston and cylinder wall.

 

The chances of that happening are pretty low, but platinums give no noticeable gain in power or mileage, so why chance it?

 

 

Agreed!

[Pete M]

we've had a couple members who experienced a loss of power when switching to platinums. don't remember which kind of tip though.

[Herc]

In my vehicles I've used either champion plugs, or NGK V-Groove the NGK's were another dollar a pair but they have always run great and slightly better mileage. As for what gap to run them at yeah factory gap which is .35 IIRC.

[87MJJeep]

Thanks guys!

[Geonovast]

In my vehicles I've used either champion plugs, or NGK V-Groove the NGK's were another dollar a pair but they have always run great and slightly better mileage. As for what gap to run them at yeah factory gap which is .35 IIRC.

 

Surely you mean .035" :yes:

[87MJJeep]

In my vehicles I've used either champion plugs, or NGK V-Groove the NGK's were another dollar a pair but they have always run great and slightly better mileage. As for what gap to run them at yeah factory gap which is .35 IIRC.

 

Surely you mean .035" :yes:

 

 

LOL I think I'll try 0.35". I'll lean out the A/F mixture and run several coils in parallel. 100 mpg, here I come! :rotf:

[Herc]

Yup .035 (missed the zero there) or thirty five thousandths of an inch, anything is better than the .062 my plugs were at in the Comanche when I bought it!!

[Dirteatr717]

Surely were not driving "fast" trucks but the 3.07 gearing doesn't help and a tuneup and new air filter will make a noticeable difference... Also tryputting a few dollars of expensive gas in your tank :popcorn: