Hi guys,

I Did a long colorado camping trip with the jeep well loaded with cooler, chairs, tent, all that jaz.......

anyhow the big passes had this thing puffing like crazy, 30mph at best. I know not to expect much power with this combo, but does that seem normal to have the jeep slow down to 30mph chugging hills?
Shes got 256200, with engine #2 and the stock cat, straight pipe/Header, bosch 4 holes.


Does this sound normal or should I check anything in particular?


thank you in advance, Hopefully everyone had a great 4th!

 

Seems normal , tractor mills don't make much power or go fast.

Thats why I went 4.88 gears so I can comfortably go slow.

That said I wonder if tps sensor could be fiddled with alittle. I think holes would have to be slotted alittle similar to the oval holes in renix tps sensor.

Probably isn't recommended but might be able to adjust powerband alittle. Tweak drive repeat.

 

Thank you for the reply Evan. Thats an interesting thought on the TPS. This engine has never kicked into the overdrive type power band as smoothly as my old one. I know thats the not the engine that does this, but its just never felt the same. The 99 engine was just smoother. Ive adjusted the kickdown a few times since the swap, I have to mash the hell out of the gas to get the od to kick in sometimes.


I choose 456s to keep it a bit more street drivable and not have the rpms through the roof.




Im sure none of the steels weight helps on the highway passes either. She has noooooooo guts going over Vail pass or anything alike, terribly low on power and runs hot lol.

 

You would have to double check your ratios with a calculator, but I have read a few times that high altitude can cause a significant power loss in these units, cant remember the fix (if there was one)

I only have 30s on stock 3.55, but mine flys up any hill, but altitude is under 3000ft, always drops to 2nd if you really floor it

 

Yes tps settings from factory are set at max power at sea level. The air fuel ratio from theyre degrades but the mechanical connection the throttle body has with the tps sensor is fixed.
It may not make a ton of difference but I adjusted my renix tps and was surprised to instantly pick up a cleaner idle quicker rev and much better rev down.
I believe the seat of the pants dyno also reads an improvement in acceleration
i didn't set the tps with a volt meter I just winged it blips on the throttle and listening to idle. Ounce the ho tps is modified it to can be adjusted and verified with a volt meter if a guys worried if within specs or not. Atleast I think it can become adjustable i havent looked at it super close

 

I read a deal about slotting the mounting holes of a cps, small timing advance 🤔. Along w/adjustable map sensor, can run a bit more timing &fuel. A possibility for ya. R

 

Agree with EvanM that 4.88s is probably a better choice when running 35s. That is what I am running with a 5 speed.
That said, your perfomance climbing passes while loaded with camping gear is not at all unusual. Keep in mind there is 3% less oxygen with each 1,000 ft of elevation gain.
Climbing any 10,000'+ pass like Vail, Hoosier, Cumberland, & others is going to be a slow uphill slog. Especially if there is a long curvy uphill approach like up Coal Bank & Molas out of Durango.
You can tweak your motor a bit if you want, but having spent a lot of time in CO with two different XJs, just have a lot of patience climbing. Better to go with the flow rather than try to hammer down & have something blow.

 

System is likely over fueled at elevation

 

Hopefully you are locked out of OD while towing? You can install a performance CPS but you will need to run premium fuel while loaded, midgrade unloaded.

If you haven't installed a fairly large trans cooler downstream of the factory cooler now is the time to do it.

An Efan control toggle is also a good option if your vehicle speed has decreased that much. Dont install one that backfeeds voltage into the ecu (Ksuspension).

For the 99 ECU you can test your tps to ensure that is has the correct sweep voltage, don't modify it.

​​​​​​Although oxygen content decreases in relation to elevation the feedback loop data from the o2 sensor will command a lower pulse duration of the injectors. In short the ECU will remap the modified fuel table to keep the AFR at factory target.

Advanced CPS

 

Yes that is the intention to tweak afr as needed.

Keeps us from having to change jets or fiddle with mixture screws.

But I do not believe it to be perfect much better than a carb . But could still be fiddled with if a person wanted. Gains may or may not be made

 

There are no accelerator pumps, jets, or mixture screws involved tho. The TPS signal should be correct but left alone in the sbec2 and JTEC applications.

The JTEC commands closed loop fueling in about 1.5 minutes after cold soak start up. The adjustment range is much greater than its given credit for as well. Like the time I started a stock ecu up on 36lbs injectors. It ran as is if the map sensor was unplugged with roughly a 10.5afr. As soon as closed loop was available the afr was stable at 14.7 and dithering.

 

I might be missing something here, but how can moving the crank sensor adjust my timing. Its just a hall effect sensor reading the flex plate right? I know some adjust them up and down to get them to read, but not to advance/retard timing, afaik.
As for the TPS is there a chart for reading the sweep of this adjustment or would this be done monitoring tuning?

 

no difference in 3rd vs Od other than Rpm bouncing into od too often, it slugs up either way.

ive never seen anyone running a performance dizzy& sensor if thats what you mean, i see the crank sensor you show but im not understanding that, the flex plate doesnt change.


the E fan toggle is a great idea, i have a stock upcountry trans cooler, ive always intended to add a bigger one. In regards to the tps testing I can look at it again for the hey of it, its a mopar sensor this time. When my naps tps was acting up ( water related- theyre fine otherwise) and I read it with an analog VM Before replacing it.

 

wouldnt i be loosing power with 488s? In my mind it would be running through gears quicker(good), but eventually screaming higher rpms once its slugging hills?


lord if only a hemi could appear in my jeep overnight.

I really wish someone had video of a stroker on 35s driving passes like this, im ignorant but skeptical of the power one woukd really gain?

 

Crank sensor should set timing if you don't have a distributor. Cam position sets fuel. At least it's that way in the distributorless 4.0 if I recall.

Lower gears, colder air, maybe some roller rockers. There's honestly not much you can do without getting into forced induction or getting into the internals of the 4.0. if you want more power you could talk with Russ Pottinger about a new cam and a ported head. Beyond that it's serious surgery or a pit of money. Just upgrading the cams on these engines isn't as easy as it should be. A $300 cam and lifters turn into $100 or so in machine work for the spring seats and the valves and then another $300 for the actual valves and springs. With gaskets and a timing set you are looking at close to a grand for maybe what I'd guess are no more than 20-30hp. If you have a stroker then those mods make more sense, but on an otherwise stock engine I have no idea.