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Several Engine/Fuel Upgrades - All at Once Better?

bzauche

NAXJA Forum User
Location
Dahlonega, GA
Hey all,

Quick question. I am planning on doing several upgrades in the next few weeks, in order to hopefully gain back a few MPG's (and maybe a little power too), that I will be able to take advantage of for the whole summer. I am planning:

Cowl Air Intake
Bored Throttle Body
784 Injectors
Replace all 4 o2 sensors (don't have record of them ever being changed)

Would it be best to do all of these the same day, so the computer only has to re-learn its fuel settings once?

Also, what is the best way to reset the ECU?
 
All at once or one by one, doesn't matter.

This very simple procedure will erase the 1996-2001 “Adaptive Memory” stored inside the PCM and allow a new “Adaptive Memory” to be developed.

After performing this procedure the 1996-2001 PCM will re-learn and store into Adaptive Memory your engines performance characteristics.

Please perform these steps exactly as they are written, in the order they are written. This will cause the adaptive memory in the PCM to be erased and cause the PCM to go into Fast Learn Mode adaptive mode.

Disconnect the POSITIVE battery Terminal and touch it to ground ( not the battery negative terminal ) for 30 seconds. The engine block or the A/C compressor pump will work as a ground. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory).

Reconnect the Battery Cable
Turn Ignition Switch to the “On” position but DO NOT start the engine
Turn Headlight “On”
Turn Headlights “Off”
Turn Ignition Key “Off”


The PCM Adaptive memory has now been flashed, or erased from the PCM.

When you start the engine it will be running off a set of pre-programmed tables that come with the PCM from the factory.

When you get the engine up to operating temperature the PCM will start to collect data for the “Adaptive Memory”.

The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.
 
All at once or one by one, doesn't matter.

This very simple procedure will erase the 1996-2001 “Adaptive Memory” stored inside the PCM and allow a new “Adaptive Memory” to be developed.

After performing this procedure the 1996-2001 PCM will re-learn and store into Adaptive Memory your engines performance characteristics.

Please perform these steps exactly as they are written, in the order they are written. This will cause the adaptive memory in the PCM to be erased and cause the PCM to go into Fast Learn Mode adaptive mode.

Disconnect the POSITIVE battery Terminal and touch it to ground ( not the battery negative terminal ) for 30 seconds. The engine block or the A/C compressor pump will work as a ground. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory).

Reconnect the Battery Cable
Turn Ignition Switch to the “On” position but DO NOT start the engine
Turn Headlight “On”
Turn Headlights “Off”
Turn Ignition Key “Off”


The PCM Adaptive memory has now been flashed, or erased from the PCM.

When you start the engine it will be running off a set of pre-programmed tables that come with the PCM from the factory.

When you get the engine up to operating temperature the PCM will start to collect data for the “Adaptive Memory”.

The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.

Thanks man!
 
How will a bored throttle body or new O2 sensors get you better mileage?

I'd save all the money. IF this stuff got you a touch better mileage (which I doubt), it would take a long time to recover your costs. But, I guess doing something will make you feel better, and this is the internet.
 
O2 sensors helped with my MPG. im getting around 14 now. but i had to replace them to pass emissions and it cost be around $150 i think to replace them all. itd take me forever to earn that money back in fuel costs in going from 11MPG to 14MPG
 
How will a bored throttle body or new O2 sensors get you better mileage?

I'd save all the money. IF this stuff got you a touch better mileage (which I doubt), it would take a long time to recover your costs. But, I guess doing something will make you feel better, and this is the internet.

From all of the records that I have from the PO, the o2 sensors have never been replaced, so at 165k, I'm pretty sure it would be a good idea to replace them. Am I wrong?

I'm not trying to say that this is a set-in-stone plan, I'm just trying to get opinions.

Might as well be dissapointed all at once
Gears are the best bang/buck

I'm sure gears would be a great investment, but I'm not in that position right now. I'm running 3.55's with 245/26/75 (barely a skinny 31"), and to me, the XJ doesn't feel sluggish at all. It's my DD, and I do a decent amount of highway driving, and my RPM's are about 2200 when I hit 70mph. (corrected speedo)

Also, once I graduate and get a real job, I want to get something else as my DD, and have the XJ strictly as a toy. When that day comes, I am probably going to want to get bigger tires, so I was planning on waiting to regear until then.
 
You didn't say what year, but if the O2 sensor is bad it will throw a code. The comment above said he didn't pass smog and needed an O2 sensor, so that makes sense. Sensors are not wear items like timing belts or tires. If they work, they work. You could change the starter and alternator, just in case, since they're old. :)

Internet comments about mileage, and a lot of other things, can't be verified, and everyone has different ways of figuring what they're doing. Most like to say things work, since they spent the money.
 
It's not a bad idea to change the o2's, DIY TB bore(bottom), cai, catback.

That's what I thought. It's not like these things are super, super expensive either. I want to do axle upgrades last (unless something breaks), that way I'll know what size tires I'm at, what gears I need, lockers, etc...

You didn't say what year, but if the O2 sensor is bad it will throw a code. The comment above said he didn't pass smog and needed an O2 sensor, so that makes sense. Sensors are not wear items like timing belts or tires. If they work, they work. You could change the starter and alternator, just in case, since they're old. :)

Internet comments about mileage, and a lot of other things, can't be verified, and everyone has different ways of figuring what they're doing. Most like to say things work, since they spent the money.

It's an '01, so I know the computer is "recent" enough to throw the code. I had thought that o2 sensors could be bad even if it wasn't throwing codes, etc...I guess I'm wrong. I know there are 4 on my XJ, but which ones have to do with the gas mixture? If I wasn't going to replace all 4, I'd probably want to at least replace the ones that have to do with the gas mixture.

I don't know if that's sarcasm or not (about the starter and alternator), but the starter was replaced in February, but I think the alternator is still stock. I don't see how that would affect performance though...my alternator runs just fine.

I know everyone gets it in their head that, "I'm spending money on upgrades, so I KNOW they will help my mileage. How couldn't they?" But I figured that these upgrades/replacements that I'm doing might actually do something. I know about throttle body spacers and programmers, and how much those don't do anything, etc...
 
It's an '01, so I know the computer is "recent" enough to throw the code. I had thought that o2 sensors could be bad even if it wasn't throwing codes, etc...I guess I'm wrong. I know there are 4 on my XJ, but which ones have to do with the gas mixture? If I wasn't going to replace all 4, I'd probably want to at least replace the ones that have to do with the gas mixture.

Don't listen to this:
You didn't say what year, but if the O2 sensor is bad it will throw a code. The comment above said he didn't pass smog and needed an O2 sensor, so that makes sense. Sensors are not wear items like timing belts or tires. If they work, they work.

That's really the opposite of the truth. O2's lose response time gradually over time which makes the air/fuel ratios to become, sloppy, for lack of a better term. You're essentially right about the O2 sensors being bad but not throwing a code. They may not be "bad" enough to cause enough of an issue for the computer to care about, but they can still certainly be "bad" enough to affect your mileage. And the ones you want to replace for the purposes of mileage are your "upstream" O2's which are the first, or upper two. If to your knowledge, they've never been changed, then it's time to replace them.
 
Noticed virtually no difference with a bored TB here.
The issue really is that the 4.0 is a tractor motor. Bulletproof and reliable to be sure, but the top end design is so antiquated, there's not a whole lot to be gained from bolt ons. The best thing yo can do is keep it running properly, and get a gas sipper for your short trips.
 
Typical O2 sensor service life is about 100-150,000 miles. As already explained, they loose their ability to switch as quickly and can lower your mpg's yet still not trigger a CEL.

An unexplained drop in your gas mpg's of 30-40% should make you question your O2 sensors condition and to test them for proper function.


The Jeep 4.0L is old school and responds well to standard hot-roding techniques: cat-back exhaust, header, K&N type filter and/or cold air intake. A bored throttle body increases throttle response at low rpm's with the HO engine, and make the AW-4 downshift more quickly.
 
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Don't listen to this:

That's really the opposite of the truth. O2's lose response time gradually over time which makes the air/fuel ratios to become, sloppy, for lack of a better term. You're essentially right about the O2 sensors being bad but not throwing a code. They may not be "bad" enough to cause enough of an issue for the computer to care about, but they can still certainly be "bad" enough to affect your mileage. And the ones you want to replace for the purposes of mileage are your "upstream" O2's which are the first, or upper two. If to your knowledge, they've never been changed, then it's time to replace them.

Thanks for backing me up! I'll probably just do the upstream 2 then.

Noticed virtually no difference with a bored TB here.
The issue really is that the 4.0 is a tractor motor. Bulletproof and reliable to be sure, but the top end design is so antiquated, there's not a whole lot to be gained from bolt ons. The best thing yo can do is keep it running properly, and get a gas sipper for your short trips.

The bored throttle body is probably the last thing I'd purchase out of the group. I might start with the CAI, injectors, and o2 sensors, and see how it runs after all of that. I can't afford to get a 2nd car right now...just finishing up my junior year in college so that's a couple years away.

Typical O2 sensor service life is about 100-150,000 miles. As already explained, they loose their ability to switch as quickly and can lower your mpg's yet still not trigger a CEL.

An unexplained drop in your gas mpg's of 30-40% should make you question your O2 sensors condition and to test them for proper function.


The Jeep 4.0L is old school and responds well to standard hot-roding techniques: cat-back exhaust, header, K&N type filter and/or cold air intake. A bored throttle body increases throttle response at low rpm's with the HO engine, and make the AW-4 downshift more quickly.

I am planning on changing the two upstream sensors. Recently, I've been getting about 200 miles to a tank (10-11mpg), and I'm only running skinny 31's on 3.5" of lift, and I don't drive it like a race car. I'm not expecting a huge jump in MPG's, but getting it back to 14-15ish would be wonderful.
 
BTW, I own an automotive repair shop. We regularly fix cars/Jeeps (most of them inexpensively) after customers have replaced a bunch of sensors and parts because of what they read about it on the internet, yet it didn't resolve their problem. Whatever your opinion or concern is, if you ask, you will get confirmation on the internet. How valuable is that info? Depends on how important your opinion is to you.

Yes, I was being sarcastic about the starter and alternator.

If you want to really know if you need to replace an old O2 sensor, if you lived close to us, you could swing by and we could put the lab scope on the O2 sensors and watch the output and tell you if it's switching slowly or improperly. We won't replace an O2 sensor unless we verify that it's not switching properly. There's certainly nothing wrong with getting new parts, but it's nice to know they're needed.
 
I don't own a shop, but I have been diagnosing cars in one my entire " adult" life, and I agree with the statement that o2 sensors age and lose their ability to accurately monitor exhaust gas. I also agree that throwing parts at a car based on other peoples internet diagnosis is a waste of time, money and effort. Sometimes its worth letting a reputable pro check it out for the cost of shop time, to keep from throwing money away, and to get an accurate diagnosis of the real problem.
 
If you are getting that kind of mileage there is way more wrong than your o2 sensors. I would be thinking injectors and sparks. My 2dr auto gets a pretty solid 17 with bumpers and tools. I got a solid 15 with my 4door stick on 35s. Even with 3.07s I just didn't use fifth.
 
Don't listen to this:

That's really the opposite of the truth. O2's lose response time gradually over time which makes the air/fuel ratios to become, sloppy, for lack of a better term. You're essentially right about the O2 sensors being bad but not throwing a code. They may not be "bad" enough to cause enough of an issue for the computer to care about, but they can still certainly be "bad" enough to affect your mileage. And the ones you want to replace for the purposes of mileage are your "upstream" O2's which are the first, or upper two. If to your knowledge, they've never been changed, then it's time to replace them.
I've heard this about o2's as well...
 
If you are getting that kind of mileage there is way more wrong than your o2 sensors. I would be thinking injectors and sparks. My 2dr auto gets a pretty solid 17 with bumpers and tools. I got a solid 15 with my 4door stick on 35s. Even with 3.07s I just didn't use fifth.
...And you must be traveling on flat ground with no wind resistance
 
BTW, I own an automotive repair shop. We regularly fix cars/Jeeps (most of them inexpensively) after customers have replaced a bunch of sensors and parts because of what they read about it on the internet, yet it didn't resolve their problem. Whatever your opinion or concern is, if you ask, you will get confirmation on the internet. How valuable is that info? Depends on how important your opinion is to you.

Yes, I was being sarcastic about the starter and alternator.

If you want to really know if you need to replace an old O2 sensor, if you lived close to us, you could swing by and we could put the lab scope on the O2 sensors and watch the output and tell you if it's switching slowly or improperly. We won't replace an O2 sensor unless we verify that it's not switching properly. There's certainly nothing wrong with getting new parts, but it's nice to know they're needed.

I thank you for the offer, but unfortunately I am on the other side of the country. I think that, for the price, it's a logical thing to do, especially if they've never been changed.

If you are getting that kind of mileage there is way more wrong than your o2 sensors. I would be thinking injectors and sparks. My 2dr auto gets a pretty solid 17 with bumpers and tools. I got a solid 15 with my 4door stick on 35s. Even with 3.07s I just didn't use fifth.

That's what I thought. I will be doing 784 injectors with all of this other stuff. Spark plugs were replaced about 1000 miles ago.
 
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