10% MPG Improvement + Better Drivability
CF Veteran
Joined: Aug 2011
Posts: 10,489
Likes: 24
From: Nor-Cal Coast
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
Sorry, I was mistaken. The Neons flow closer to 20% higher flow rate than stock injectors. I flow tested both of them at the same time on the same setup (12 volts, 3 bar pressure, full on for 30 seconds) and the stock injectors averaged 77.7 grams and the Neons averaged 93.0 grams. There was less than 1% measurement variability between the stock injectors.
If the Neons were the same flow rate as stock, you could run them without resetting the ECU.
If the Neons were the same flow rate as stock, you could run them without resetting the ECU.
Also I'm doing a "choppy" experiment. It's been suggested I "reset" my ECU in my 90 Renix Jeep. (did the swap a few weeks ago). Well, I'm going to run a tank or two first, then note any change. Major problem though that freeway trips are rare. Been doing short trips, even just 300 yds!
I'm keeping records and will post results here.
CF Veteran
Joined: Jun 2011
Posts: 2,858
Likes: 1
From: Nor-Cal
Year: 1990
Model: Cherokee
Engine: The venerable 4.0
Originally Posted by DFlintstone
Hi there Notop. Can I assume when you say "Neon's" you are referring to 703's?. (the yard I went to, that day, there where no 703's in Neons!)(actually I looked in more then 10 of them on three visits).
Also I'm doing a "choppy" experiment. It's been suggested I "reset" my ECU in my 90 Renix Jeep. (did the swap a few weeks ago). Well, I'm going to run a tank or two first, then note any change. Major problem though that freeway trips are rare. Been doing short trips, even just 300 yds!
I'm keeping records and will post results here.
CF Veteran
Joined: Aug 2011
Posts: 10,489
Likes: 24
From: Nor-Cal Coast
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
Hey there Chad. Welcome back! Yea, I know. Nagging doubts. I need to look again, but I saw something in the FSM about a memory in the ECU for an 88. Then some of these guys seem to be pretty sure. Then what do I have to loose, not resetting something that doesn't reset? Did you get a Grand?
Senior Member
Joined: Apr 2011
Posts: 813
Likes: 1
From: Lansing, MI
Year: 2000
Model: Cherokee
Engine: 4.0
It may be because you reset the ECU. When you do that, it defaults to a rich setting until it re-learns how your engine runs under different load conditions. The re-learn is based on feedback from the O2 sensor. I have read that it takes up to 50 cold start cycles to perform this before it stabilizes.
Having studied output data from a narrow band O2 sensor like we have, I can tell you it takes a while to hit all of the load conditions and get enough data to make good adjustments. I went through 5 tanks of gas on my Chevelle dialing in the EFI and still only reached 12.5 MPG on the highway. Similar problems to a Jeep: heavy, as aerodynamic as a brick, and an engine/drivetrain that was not designed for fuel economy.
My recomendation to anyone trying these injectors is NOT to reset the ECU UNLESS you are replacing higher flowing injectors (703/784). Swap injectors, start it up, and see how it runs. If it seems lean or the plugs look chaulky white after 30 minutes of driving, then consider resetting the ECU. You can expect it to run rich and get poor gas mileage until it re-learns.
Having studied output data from a narrow band O2 sensor like we have, I can tell you it takes a while to hit all of the load conditions and get enough data to make good adjustments. I went through 5 tanks of gas on my Chevelle dialing in the EFI and still only reached 12.5 MPG on the highway. Similar problems to a Jeep: heavy, as aerodynamic as a brick, and an engine/drivetrain that was not designed for fuel economy.
My recomendation to anyone trying these injectors is NOT to reset the ECU UNLESS you are replacing higher flowing injectors (703/784). Swap injectors, start it up, and see how it runs. If it seems lean or the plugs look chaulky white after 30 minutes of driving, then consider resetting the ECU. You can expect it to run rich and get poor gas mileage until it re-learns.
I upgraded to 784 injectors on my '00 4.0 and reset the ECU, and noticed an immediate drop in fuel mileage. Not a huge one, but it's there.
On subsequent fuel ups, my mileage calculation showed that it's improving, if only slightly. I haven't quite done 50 start up cycles yet, so we'll see.
CF Veteran
Joined: Aug 2011
Posts: 10,489
Likes: 24
From: Nor-Cal Coast
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
Your 2000 has a PCM, not an ECU. Glad it worked out!
EDIT...Oh, drop. Mine runs great. No comment on mileage yet.
(the Renix ECU, last year, 1990, stores no codes, has no light). The extinct DRB II scanner can read live time data, if I have that straight.
EDIT...Oh, drop. Mine runs great. No comment on mileage yet.
(the Renix ECU, last year, 1990, stores no codes, has no light). The extinct DRB II scanner can read live time data, if I have that straight.
Last edited by DFlintstone; Feb 18, 2012 at 05:35 PM.
CF Veteran
Joined: Jun 2011
Posts: 2,858
Likes: 1
From: Nor-Cal
Year: 1990
Model: Cherokee
Engine: The venerable 4.0
Originally Posted by DFlintstone
Hey there Chad. Welcome back! Yea, I know. Nagging doubts. I need to look again, but I saw something in the FSM about a memory in the ECU for an 88. Then some of these guys seem to be pretty sure. Then what do I have to loose, not resetting something that doesn't reset? Did you get a Grand?
Newbie
Joined: Aug 2010
Posts: 25
Likes: 0
From: Sacramento
Year: 1995
Model: Cherokee
Engine: 4.0
I am aware that both Renix and 91-95 run 31 psi at idle and 39 psi at WOT.
And yes there are certain year/engine combos of the neon that dont have 703's and there are other chrysler cars/vans that do have 703's, but the neon seems to be the most often referenced vehicle.
Newbie
Joined: Aug 2010
Posts: 25
Likes: 0
From: Sacramento
Year: 1995
Model: Cherokee
Engine: 4.0
Check these 2 threads for the years/makes of cars to look for, I got mine from 95 neon and 97 sebring:
https://www.cherokeeforum.com/f2/fue...upgrade-34178/
http://www.ausjeepoffroad.com/forum/...ad.php?t=92236
https://www.cherokeeforum.com/f2/fue...upgrade-34178/
http://www.ausjeepoffroad.com/forum/...ad.php?t=92236
CF Veteran
Joined: Aug 2011
Posts: 10,489
Likes: 24
From: Nor-Cal Coast
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
I mention the 43.5 psi or 3 bar because that is what all injectors are tested at as a baseline figure.
I am aware that both Renix and 91-95 run 31 psi at idle and 39 psi at WOT.
And yes there are certain year/engine combos of the neon that dont have 703's and there are other chrysler cars/vans that do have 703's, but the neon seems to be the most often referenced vehicle.
I am aware that both Renix and 91-95 run 31 psi at idle and 39 psi at WOT.
And yes there are certain year/engine combos of the neon that dont have 703's and there are other chrysler cars/vans that do have 703's, but the neon seems to be the most often referenced vehicle.
Partly wanted to be sure somebody didn't see that and change there fuel pump because they thought they had low pressure. Correct, went to 49 in 96.I got skunked on the neon's (that trip in Winsor), Sebring & breeze? My buddy remembers. Wish I remembered the camera.
Thread Starter
Seasoned Member
Joined: Jun 2010
Posts: 448
Likes: 0
From: Charleston, SC
Year: 1990 - 2000
Model: Cherokee
Engine: 4.0
what about these?
http://www.ebay.com/itm/4-0L-JEEP-CH...19427703676644
http://www.ebay.com/itm/4-0L-JEEP-CH...19427703676644
This is very helpful information.
I upgraded to 784 injectors on my '00 4.0 and reset the ECU, and noticed an immediate drop in fuel mileage. Not a huge one, but it's there.
On subsequent fuel ups, my mileage calculation showed that it's improving, if only slightly. I haven't quite done 50 start up cycles yet, so we'll see.
I upgraded to 784 injectors on my '00 4.0 and reset the ECU, and noticed an immediate drop in fuel mileage. Not a huge one, but it's there.
On subsequent fuel ups, my mileage calculation showed that it's improving, if only slightly. I haven't quite done 50 start up cycles yet, so we'll see.
I record date, mileage, gallons, fuel price, and what I did (towing, wheeling, long trip...) and where I filled up (Georgia, Florida, North Carolina...) on every fill-up. It helps explain rises and drops when I go back and look at the data for individual fill-ups. As mentioned, I based my economy improvement data on 3000 miles of driving, and my injector flow data on direct comparison measurements and manufacture's data.
Seasoned Member
Joined: Sep 2009
Posts: 299
Likes: 12
From: Whittier, Ca
Year: 1989
Model: Cherokee
Engine: 4.0L
Liberty injectors
Hello fellow Jeepers.
I put Liberty injectors (OE: 53032701AA, 0280158020) in my 89' 4.0L, Auto AW4, NP242 with 4.10 gears and 31" tires.
I am getting 13mpg city and 18 mpg highway
I'm on my 5th tank and I did reset the computer. Not the results I was looking for. I recently found a shop that rebuilds injectors and the guy told me to clean out my stock injectors and put them back in.
Any other suggestions?
I put Liberty injectors (OE: 53032701AA, 0280158020) in my 89' 4.0L, Auto AW4, NP242 with 4.10 gears and 31" tires.
I am getting 13mpg city and 18 mpg highway
I'm on my 5th tank and I did reset the computer. Not the results I was looking for. I recently found a shop that rebuilds injectors and the guy told me to clean out my stock injectors and put them back in.Any other suggestions?
Thread Starter
Seasoned Member
Joined: Jun 2010
Posts: 448
Likes: 0
From: Charleston, SC
Year: 1990 - 2000
Model: Cherokee
Engine: 4.0
What gas mileage were you getting with the stock injectors?
If you clean them, they may flow better, but I doubt that they will spray any finer than before. They could flow more consistent and provide better idle and throttle response if their flow rates become more closely matched.
18 MPG highway with your tires and gears sounds good. 13 MPG city could be driving habits and the slippage of the auto trans.
If you clean them, they may flow better, but I doubt that they will spray any finer than before. They could flow more consistent and provide better idle and throttle response if their flow rates become more closely matched.
18 MPG highway with your tires and gears sounds good. 13 MPG city could be driving habits and the slippage of the auto trans.
Last edited by notop46; Feb 26, 2012 at 11:08 AM. Reason: added last 2 lines
CF Veteran
Joined: Aug 2011
Posts: 10,489
Likes: 24
From: Nor-Cal Coast
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
A Renix ECU does not have a memory that resets. At least allot of people would be surprised if it did.
So far I'm happy with my 703's. I did only get 12 last tank, but I've gotten almost that low, (12.7) with the old ones. (the original Simmons-Decka where changed 10 years ago). Some of my driving here is even worse than "town driving" though. I did get 17 on a short Hwy. trip, so I know it's not "out to lunch"
One day I'd like to look at readings off a new O2 sensor. Also I saved an article on an adjustable MAP sensor. http://go.jeep-xj.info/HowtoMAPsensor.htm Maybe I'll read it through after I go through my grounds.
After I get a good mileage figure on a longer Hwy trip, I'll leave the battery disconnected overnight, in the name of science!
So far I'm happy with my 703's. I did only get 12 last tank, but I've gotten almost that low, (12.7) with the old ones. (the original Simmons-Decka where changed 10 years ago). Some of my driving here is even worse than "town driving" though. I did get 17 on a short Hwy. trip, so I know it's not "out to lunch"
One day I'd like to look at readings off a new O2 sensor. Also I saved an article on an adjustable MAP sensor. http://go.jeep-xj.info/HowtoMAPsensor.htm Maybe I'll read it through after I go through my grounds.
After I get a good mileage figure on a longer Hwy trip, I'll leave the battery disconnected overnight, in the name of science!
