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Thread: My goal is to get 25+ mpg from my 99 XJ with 30 x 9.5 R15 ATs Reply to Thread
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  Topic Review (Newest First)
10-19-2019 11:58 PM
42MBGPW
Quote:
Originally Posted by Taylor95 View Post
That is still pretty easy to change the injectors, although I will have to buy the adapters.

21 mpg is good. Seems like it isn't really in that bad of condition. Is the Jeep at stock height?
Except for the Pioneer stereo it's all stock.
10-19-2019 10:02 PM
Taylor95
Quote:
Originally Posted by 42MBGPW View Post
A guess and only a guess is the first mileage check was low due to the ECU having reverted to default map values due to the XJ sitting for several months with a stone dead battery while the later mileage check were greatly and successively improved due to the ECU adapting the map.

I had to run it this last couple of days. A mix of city grid lock crawl and freeway shenanigans at 60 to 72 mph with some hill climbs thrown in for good measure and the occasional WOT to slice/jump/merge or dodge kamikaze drivers. Average gas mileage over 490 miles traveled was 21 mpg. No doubt it will improve with installation of the new new distributor, tune up parts, cleaning up the grounds and a front end alignment.

The results of my best of my research on 12 hole injectors is Bosch Pn# 028015616 / Interchange Part Number 822-11170 is what we're after. Apparently Ford used these in the 2.0 and 2.3 liter Focus from 2003 to 2007 and in V-8 engines in other years. As always verify before going to the parts store or wrecking yard.

They do take EV6 style injector wiring harness connectors so either EV1 to EV6 adapters will be required or the existing EV1 connectors will need to be replaced with EV6 for use in our 4.0 engines.
That is still pretty easy to change the injectors, although I will have to buy the adapters.

21 mpg is good. Seems like it isn't really in that bad of condition. Is the Jeep at stock height?
10-18-2019 06:04 PM
42MBGPW
Quote:
Originally Posted by Firedrive View Post
It took two weeks, but I’ve now read this entire thread.
Thanks to the OP for keeping it updated and going for so long.
You did better and faster than I did.


Quote:
Originally Posted by Taylor95 View Post
Well, you definitely have some room for improvement! Good luck! I was able to get about 21 mpg consistently over the summer, so I'm sure you could do even better with your 4x2. Additional things I have done are hood vents, a 62 mm throttle body, and a mild performance catback exhaust. Let us know how the 12 hole injectors work and where you got them. I currently have the neon injectors, and they work great. I might swap to 12 hole ones though if they are good.
A guess and only a guess is the first mileage check was low due to the ECU having reverted to default map values due to the XJ sitting for several months with a stone dead battery while the later mileage check were greatly and successively improved due to the ECU adapting the map.

I had to run it this last couple of days. A mix of city grid lock crawl and freeway shenanigans at 60 to 72 mph with some hill climbs thrown in for good measure and the occasional WOT to slice/jump/merge or dodge kamikaze drivers. Average gas mileage over 490 miles traveled was 21 mpg. No doubt it will improve with installation of the new new distributor, tune up parts, cleaning up the grounds and a front end alignment.

The results of my best of my research on 12 hole injectors is Bosch Pn# 028015616 / Interchange Part Number 822-11170 is what we're after. Apparently Ford used these in the 2.0 and 2.3 liter Focus from 2003 to 2007 and in V-8 engines in other years. As always verify before going to the parts store or wrecking yard.

They do take EV6 style injector wiring harness connectors so either EV1 to EV6 adapters will be required or the existing EV1 connectors will need to be replaced with EV6 for use in our 4.0 engines.
10-18-2019 09:55 AM
Taylor95
Quote:
Originally Posted by 42MBGPW View Post
95 Cherokee Sport 4.0, 5sp, 2WD, P/S, P/B, A/C.

Battery replaced. Rear wheel cylinders replaced. Wiper blades and one headlight replaced. Water pump replaced. Cooling system flushed. Idler pulley replaced. Fluids changed. Engine oil synthetic 10w30. Trans oil Castrol synthetic MTF. Synthetic rear diff oil.
New distributor, rotor, brass contact cap, wires and copper plugs and four cans of Seafoam on hand ready and waiting for install on the next available weekend. Fan clutch is bad. Will likely throw a used one on in order to buy time until full electric fans can be done.
Next parts order: NO-OX-ID, materials to custom make 2/0 ga battery and ground cables, NTK O2 sensor, hot coil, fatty wires and iridium plugs. Have found a decent source for 12 hole Bosch 0280156161 injectors. Shopping around for an exhaust shop that can fab a high quality no dent down pipe.

Considering an "economy" aka "RV grind" aka torquer cam at some point primarily because I bought the XJ for general purpose use, parts hauling and towing.

Averaged 13MPG on the half tank of gas that was in the tank when we drove it home. Not surprised since it needs a tune up very badly and the fan clutch is dragging and the gas was of unknown age. Dumped in a whole can of Seafoam and tanked up with fresh 87 octane E-10.
Well, you definitely have some room for improvement! Good luck! I was able to get about 21 mpg consistently over the summer, so I'm sure you could do even better with your 4x2. Additional things I have done are hood vents, a 62 mm throttle body, and a mild performance catback exhaust. Let us know how the 12 hole injectors work and where you got them. I currently have the neon injectors, and they work great. I might swap to 12 hole ones though if they are good.

Quote:
Originally Posted by Firedrive View Post
It took two weeks, but I’ve now read this entire thread.
Thanks to the OP for keeping it updated and going for so long.
That is impressive. You would have got a lot of good information from reading all of that. What kind of jeep do you have?
10-17-2019 07:39 PM
Firedrive It took two weeks, but I’ve now read this entire thread.
Thanks to the OP for keeping it updated and going for so long.
10-15-2019 01:09 AM
42MBGPW 95 Cherokee Sport 4.0, 5sp, 2WD, P/S, P/B, A/C.

Battery replaced. Rear wheel cylinders replaced. Wiper blades and one headlight replaced. Water pump replaced. Cooling system flushed. Idler pulley replaced. Fluids changed. Engine oil synthetic 10w30. Trans oil Castrol synthetic MTF. Synthetic rear diff oil.
New distributor, rotor, brass contact cap, wires and copper plugs and four cans of Seafoam on hand ready and waiting for install on the next available weekend. Fan clutch is bad. Will likely throw a used one on in order to buy time until full electric fans can be done.
Next parts order: NO-OX-ID, materials to custom make 2/0 ga battery and ground cables, NTK O2 sensor, hot coil, fatty wires and iridium plugs. Have found a decent source for 12 hole Bosch 0280156161 injectors. Shopping around for an exhaust shop that can fab a high quality no dent down pipe.

Considering an "economy" aka "RV grind" aka torquer cam at some point primarily because I bought the XJ for general purpose use, parts hauling and towing.

Averaged 13MPG on the half tank of gas that was in the tank when we drove it home. Not surprised since it needs a tune up very badly and the fan clutch is dragging and the gas was of unknown age. Dumped in a whole can of Seafoam and tanked up with fresh 87 octane E-10.
09-30-2019 09:09 PM
Taylor95 That sounds like a good idea. If you do mostly highway driving I get it would boost your average mpg by about 5%.
09-30-2019 04:04 AM
42MBGPW I wasn't talking about removing. I was talking about a power steering pump clutch to deactivate the pump above town speeds. It takes between 5 and 8 horsepower to operate the average power steering system. Reducing parasitic power consumption can't be a bad thing.
07-28-2019 10:18 AM
Taylor95 I don't think you'll get a lot from removing the ps pump.
The best thing you can do is buy a scangauge on your 96 or 97+ jeep. It shows you real time fuel usage. That was good for maybe 2 mpg above what I was getting before.
I get 21-22 mpg from my normal driving. Just highway gets me 23-24 mpg.
07-27-2019 01:55 PM
42MBGPW Above 35 mph what do we need power steering for ?

Old school Mopar York RV2 AC compressors had the same shaft taper as the the old school Mopar power steering pump. Back in the day more than a couple guys hung an AC clutch on an extra power steering pump and used that to provide hydraulic power for the snow plows on their pick up trucks.

I see no disadvantages to taking the Cherokees power steering pump out of play above 35 mph. That would be several hp worth of parasitic load reduced for a couple weekends worth of puttering around the shop.
07-27-2019 01:01 PM
42MBGPW I need to keep the 4.0 in it for towing and hauling.
02-12-2019 10:15 AM
Taylor95 If you hypermile your 2wd 5 speed then I'm sure you could average 30 mpg highway without much effort. I'm sure you could do even better if your engine is a 2.5l 4 cyl.
02-10-2019 11:11 PM
42MBGPW I'm still following this thread. The Flattie and the XJ 2 door aren't going anywhere. I need a comfortable and economical utility and tow wagon for general purpose, road trips and parts running. Picked up a 2WD 5 speed four door XJ. With the full Charley3+ mod suite it shouldn't be to hard to crack 27 mpg highway.
12-07-2018 06:59 PM
KF4SQB
Quote:
Originally Posted by Charley3
I don't know if what you said about alternators is correct or not. You might be correct. I'm not sure. There are plenty of other people who say the opposite.
Yes, I'm correct. The load on an alternator or generator is based on electrical load on the device. You have two primary things to look at when looking at such a setup: voltage, and current. There are actually more issues involved, but those two are all you need to know in most "typical" applications. Voltage is a constant (for a given system). For an automotive system, that voltage is 12 volts. This actually varies, and in practice is closer to 13.8 volts, but we say 12 for simplicity's sake. For voltage, an alternator (or generator) will put out what it is rated at, until the current rating is exceeded, at which point the voltage starts to "sag". Within the normal current range of the alternator, the voltage doesn't change very much. Current, however, is totally dependent upon the load. For example, a "typical" headlight bulb for our XJs is 55 watts at high beam, which draws approximately 4.6 amps (per headlight) at 12 volts. A 100 watt off-road light, on the other hand, will draw around 8.3 amps, at the same 12 volts. With an automotive alternator, or any other type of "rotating electricity producer", the more current draw placed on the alternator, the harder it is to turn. There may actually be a extremely tiny difference in how much power is required to turn, from my earlier example, a 1000 amp unit, as opposed to a 90 amp unit, but this difference will be entirely dependent upon the size of the rotor in the larger unit, NOT upon the rated current output, and will be a tiny fraction of a HP with both units pulling the same load. Ever been around a small-engine driven generator, or a welder with standard 120 volt plugs on it, while it was being used to power tools? Pay attention the next time you are. You will notice that the more load applied to the system, the harder the engine driving it has to work. Try it yourself. Start a power tool with a fairly large motor, like a large chop saw, and listen to the generator, then continue to listen as someone else starts another large motor plugged into it. It should be very obvious when the second load is added in, as the engine will "load up" more, and obviously have to work harder than it did with only one load. Obviously, this is why the bigger the generator, the bigger the engine turning it. Vehicle alternators work exactly the same way. The more power you try to get out, the more you have to put in to make it happen. Alternators are very similar to ignition coils, as they only put out what is required of them, no more, and the less required of them, the easier they are to turn. Kindly send anyone who disputes this to me, and I will gladly make them look like idiots! Oh, by the way, yes, I am an electrician, and have been working on everything from component level electronics, up to power lines, and everything in between, for many years. Cheers!
12-02-2018 11:42 PM
Charley3
Quote:
Originally Posted by KF4SQB View Post
Charley3, excellent write-up! However, I feel the need to offer corrections on a couple of misconceptions I noticed.

#1-High-output alternator: a high-output alternator WILL NOT reduce fuel mileage, unless there is actually more load on it. An alternator rated at, say, 90 amps will have very close to the same mechanical load as, for an extreme example, a 1000 amp alternator, if they both only have the same 50 amp load on them. The "turning resistance" of an alternator is directly related to the actual load on it, NOT the rated output.
I don't know if what you said about alternators is correct or not. You might be correct. I'm not sure. There are plenty of other people who say the opposite. In any case, my stock alternator is adequate is more than adequate for the job. So I left alternator stock.

Quote:
Originally Posted by KF4SQB View Post
2-High-output ignition coil: ignition coils are lazy. I mean all of them; stock units, and aftermarket "high output" models alike. What I mean by "lazy" is that a coil will only put out what it needs to. Put the highest voltage, most expensive coil that any manufacturer makes on a stock plug gap, and you will see no difference what so ever. If a stock gap requires, as an example, 15,000 volts to arc over, then that is what the coil will supply to it. I don't care if the coil is only capable of 15,000 volts, or if it is capable of 1.5 million volts, it will only deliver 15,000 volts to the plug to arc it over. "Hotter" coils DO NOT equate to a "hotter" spark, unless you have increased the gap of your plugs. With that being said, yes, I do realize that you HAVE increased gap of plugs. My point is that you very well may have saved yourself some money by not upgrading the coil. Yes, it may be necessary, but it also may not, depending on how much wider you made the gap over stock. Most stock coils are capable of around 30,000 volts, although they usually never come close to that level in "normal" operation. Looking at Summit Racing, most of the MSD brand "high-output" coils they have look to be no more than 45,000 volts output. Only half again as much as a stock coil, and, same as a stock coil, will only deliver what is needed. Cheers!
You may have a point regarding coil, but my stock coil was going bad and needed replacement. The new coil fixed an intermittant miss in the engine during idle. That type of miss is very common amongst low and high mileage Cherokees. The better coil fixed it. So I needed to replace my coil anyway.

You just helped me have an ephiphany. Stock coil puts out 30,000 volts and stock plug gap is 0.035. So math tells me an MSD coil with 45,000 volts should work well with 0.052 gap. So I wish I'd tried 0.050 gap when I owned the Jeep.

P.S. - I used 89 octane gas with 0.045 gap because 89 worked best for me with 0.045 gap. I wonder if 89 would work best with 0.050 gap? Probably, though it might prefer 91 octane with 0.050 gap. Dunno, and I'll never know since I recently sold the Jeep. I sure wish I would have tried 0.050 gap.
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