Ozark Mountain Ranger

So I did the idiot light conversion today and I knew there would be issues with my oil temperature and oil pressure gauge I didn't expect there to be an issue with the tachometer. Having had an idiot lights on this Jeep for the last 23 years I expected my normal shift point from years of listening to the engine to be around 4000 RPMs and was surprised to find that I normally shift somewhere between 2500 and 3000. Is there something additional that I need to change now that I'm running 31s. My XJ has an ax15 and the NP 231 transfer case. I know I need to change the little gear in the trans case in order to reflect the proper speed on my speedometer.

Bugout4x4

It's funny but I found I never even look at a tach anymore. After driving big trucks and all makes and models for so many years there is a natural "feel" that is acquired over time. I am going to bet you have acquired this feel also Sir.

Ozark Mountain Ranger

Yeah I definitely have a feel. That's part of why I think there's something up with the tachometer. When I rev it out in neutral to 4000 to 4500 RPM it sounds like the range I'm at when I shift it on the road under load, but when I shift on the road it says 2500 to 3000.

Bugout4x4

Oh I see, I misunderstood. My fault. You have two different conditions and different readings for each? Wow... Not sure I have seen that before.

Some kind of conflict between the the Cam/Crank sensors maybe? 2500-3000 for a normal shift point sounds right, strange that it is reading different standing still than while driving. I am now super curious with what you find causing this difference. Hope someone can share some insight.

Ozark Mountain Ranger

I'll have to look into it when I replacing the rest of the sensors

SatiricalHen

When I did the swap everything read correctly (just had to get the oil pressure and coolant temp sensors) I'd say you're probably just shifting around 2500-3000 and not really 4000 since a healthy 4.0 is within its power band and very happy shifting at that point.

Ozark Mountain Ranger

So I have thought that needs somebody with much more knowledge about original Jeep equipment to verify this.

1. Is it possible that all ax15 Cherokee's came equipped with idiot lights? I feel like this is a possibility since it seems to be pretty commonplace on vehicles other than sports cars for a manual transmission to be on more base models than they are limited or special editions.

2. If that is the case then wouldn't that mean that most of the gauges that come with a tachometer be meant for it aw4 Cherokee and therefore the readings from the input plug to the gauge might vary between an ax15 equipped a Cherokee and aw4 Cherokee?

I know that the tachometer technically is supposed to be based only on the readings from the crank sensor but if the tack equipped a gauges are meant only for aw4 transmissions then is it possible that the tachometer reading would be a combination reading from the crank sensor and some transmission sensor? I could possibly be overthinking this but knowing that there is a considerable difference between a manual and automatic transmission and that one generally delivers power more efficiently than the other.

I'm going to look at changing my crank sensor when I change the temp and oil pressure sensors but driving it to work this morning under different atmospheric conditions then yesterday it still doesn't feel right.

Tsaani97xj

No difference how the tach reads as far as I know. I swapped the lights to full gauge cluster on a 97 ax15 and had no issues. 4000 rpm on the 4.0 is screaming. Redlines close to 5k iirc. 2500-3000 is moderate shifting and seems accurate to me. Think you are overthinking it and due to the time without the tach youve made an assumption on what youve been reving to and it's stuck in your head. JMO

SatiricalHen

The only thing I could think of that might possibly somehow have caused an issue would be 4 cylinder to 6 cylinder, but still I can't say for certain there is any difference. If the gauge cluster came from a 6 cylinder and you put it in a 6 cylinder it's right unless some broke it somehow. I think you're overthinking it.

Tbone289

+1. I really have to be giving it hell to reach the 4K-5K range. This isn't a high-revving OHC engine. A cheap timing light set with tach is a nice thing to have around to verify.

Bugout4x4

I don't think I have ever taken mine over 3k ever. My subconscious is still in "don't do it" mode from older inline 6 engines where bending long skinny pushrods was pretty easy to do.

Tbone289

I purposefully take it up to ~3.5K on occasion just to exercise the HLAs. 4K definitely doesn't feel "natural" with these and the torque is falling off at that point anyway, after peaking at ~3.6K. I can't believe anyone would normally shift at 4K going by ear. Poor 'ol thing starts to sound like it's going to fly apart in that RPM range. LOL

Thernlund

I have an an AX-15 with an I6 and it came stock with a tach and gauges.

I shift 100% by feel/ear. Looking at the tach, that's right around 2500 or so most of the time. The little shift indicator arrow doesn't like it, but whatever.

Others are right... 4000 rpm is screaming in an I6. I would never go that high unless I absolutely had to for some reason.


-T.

Bugout4x4

Remember the older I 6 engines? They would all get valve float at 3.5k because of the lower rated springs used back then. It was very hard to rev one over 3.5k anyways. My old mind is still stuck in that mode. It really messes me up when I get behind a double overhead cam engine with an 8k redline, I catch myself lugging the hell out of it. I have to regroup and think "motorcycle" to get my mind right. lol

Tbone289

Well, I've driven a few Ford L6's in my time, but they were the 4th-gen stuff (240/300CID) that didn't really have valve float issues. Funny, I'm the opposite as you. I've been driving OHC 4 & 6 cylinders with manuals most of my life with just a few small-block V8s thrown in there, so the 4.0 is somewhat foreign to me. It's strange to be chugging along up a hill with the TC locked at <2K RPM. It's nice to "relax" a bit! hehe