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Motor running lean

JohnAllen

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Okay so my problem started when I increased my air flow to the motor. My first solution was to go with larger injectors. So I went with 19 lb injectors. She's still running lean. Everything has been fault checked, all the sensors and regulators, and they all check out good. There are no vacuum leaks anywhere, it has been fully checked by spraying starting fluid all around the outside of the motor and has been pressurized with smoke to see if it leaks and no leaks anywhere. So I'm wanting to know if I need to increase my fuel pressure at the rail. Just checked it today and at idle it's at 35 lb and wide open throttle is 41 lb.
 


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Blmpkn

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How do you know it's running lean?
 

JohnAllen

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How do you know it's running lean?
When it's under load at a higher speed it'll stutter so I checked the code and it pulled up the motor is running lean.
 

RonD

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Engine will ping/knock if its actually running lean
Same as it will smoke if its running rich

So lean and rich codes are NOT what most people think
These are related to computers calculations

Were there TWO lean codes, left and right Bank both?
What were exact codes, all of them.

Define "increased air flow"

What about the exhaust system?
 

JohnAllen

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Engine will ping/knock if its actually running lean
Same as it will smoke if its running rich

So lean and rich codes are NOT what most people think
These are related to computers calculations

Were there TWO lean codes, left and right Bank both?
What were exact codes, all of them.

Define "increased air flow"

What about the exhaust system?
I'll have to find the notebook that those codes are in. My check engine light recently blowed so I can't get the flash codes off of it anymore until I get it replaced. By increased airflow I took the larger throttle body off of the earlier 2.9s and put on this truck. That's why I put the 19 lb fuel injectors on it thinking that would equal everything out. But I just found out tonight that when I unplug my fuel pressure regulator and trick it into thinking it's wide open throttle to keep the 41 lb of fuel pressure on the rail she idles a lot smoother. Then when I hook it back up like it's supposed to be it's a rough idle again sounding like it has a very small cam in it.
 

RonD

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Different throttle body wouldn't need larger injectors, switch them back to the 14lb/hour
Injectors are not like Jets, the computer can easily adjust fuel flow to more air flow unless you are using turbo or super chargers, even a bigger cam wouldn't need bigger injectors in most Speed Density systems
Change O2 sensor if its more than 12 year old, that will cause lean code, false lean

Your FPR(fuel pressure regulator) is leaking fuel into its vacuum line and its being sucked into the engine, which caused rough running
Engine will run exactly the same with 30-40psi, or 41psi
Not enough of a difference to cause rough running
OR
If you didn't plug the vacuum line when you unplugged it, then extra air was making it run smoother

Computer has no fuel pressure sensor, it assumes 30-40psi then adjusts injector open time based on O2 feedback and MAP sensor vacuum level(in a 2.9l)
Check MAP sensor vacuum line makes sure there are no cracks, that can also cause false lean
Leaking exhaust manifold will cause false lean as will partially clocked exhaust

Check vacuum level in the intake at idle, 18-21" is expected, MAP sensor is the LOAD sensor for speed density, low vacuum can cause all sorts of issues
 

JohnAllen

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Different throttle body wouldn't need larger injectors, switch them back to the 14lb/hour
Injectors are not like Jets, the computer can easily adjust fuel flow to more air flow unless you are using turbo or super chargers, even a bigger cam wouldn't need bigger injectors in most Speed Density systems
Change O2 sensor if its more than 12 year old, that will cause lean code, false lean

Your FPR(fuel pressure regulator) is leaking fuel into its vacuum line and its being sucked into the engine, which caused rough running
Engine will run exactly the same with 30-40psi, or 41psi
Not enough of a difference to cause rough running
OR
If you didn't plug the vacuum line when you unplugged it, then extra air was making it run smoother

Computer has no fuel pressure sensor, it assumes 30-40psi then adjusts injector open time based on O2 feedback and MAP sensor vacuum level(in a 2.9l)
Check MAP sensor vacuum line makes sure there are no cracks, that can also cause false lean
Leaking exhaust manifold will cause false lean as will partially clocked exhaust

Check vacuum level in the intake at idle, 18-21" is expected, MAP sensor is the LOAD sensor for speed density, low vacuum can cause all sorts of issues
All sensors are brand new and has been checked to make sure they are not faulty that's everything from the map sensor to the O2 sensor and all vacuum hoses have been replaced. As I stated before there are no vacuum leaks anywhere on this motor. It has been thoroughly tested at a couple of shops for that. The throttle body that I'm running has a larger bore and butterfly valve then the one that originally came on it. The bore of the throttle body that is on mine is basically the same as that which is on the 4.0. and the fuel pressure regulator has been checked there is no fuel coming through the vacuum line. I got the lean code after the throttle body was put on with a higher flow air filter. The injectors were put on after the lean code was already present. And they did help the drivability of the truck after they were installed.
 

JohnAllen

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33x10.50r15
Different throttle body wouldn't need larger injectors, switch them back to the 14lb/hour
Injectors are not like Jets, the computer can easily adjust fuel flow to more air flow unless you are using turbo or super chargers, even a bigger cam wouldn't need bigger injectors in most Speed Density systems
Change O2 sensor if its more than 12 year old, that will cause lean code, false lean

Your FPR(fuel pressure regulator) is leaking fuel into its vacuum line and its being sucked into the engine, which caused rough running
Engine will run exactly the same with 30-40psi, or 41psi
Not enough of a difference to cause rough running
OR
If you didn't plug the vacuum line when you unplugged it, then extra air was making it run smoother

Computer has no fuel pressure sensor, it assumes 30-40psi then adjusts injector open time based on O2 feedback and MAP sensor vacuum level(in a 2.9l)
Check MAP sensor vacuum line makes sure there are no cracks, that can also cause false lean
Leaking exhaust manifold will cause false lean as will partially clocked exhaust

Check vacuum level in the intake at idle, 18-21" is expected, MAP sensor is the LOAD sensor for speed density, low vacuum can cause all sorts of issues
Also I did plug up the hole for the vacuum line to the fuel pressure regulator. And the exhaust is brand new and has been double checked for clogs and it's still all good.
 

RonD

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Then your 14lb/hr injectors were most likely going bad, clogged up
The 19lb/hr may be closer to 17lb/hr which is why its not running too rich

Its still a 2.9 LITER engine, which means at WOT it can only pull in 2.9 Liters of air every 2 RPM, unless you force more air in, i.e. turbo or super charger
The stock intake can restrict some air flow at WOT making it a 2.7 LITER, lol
But would still be enough fuel flow for 2.9 liters

2.9l is 140horsepower
Six 14lb/hr injectors would be OK up to 200horsepower, 225hp most likely
19lb/hr are for 200+ up to about 300hp

I think there is another reason for the Lean code, not fuel related
 

gaz

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JohnAllen,

While this T/B may have increased the air flow, it's not above the 2.9's ability to use or properly meter the fuel, you more effectively, reduced an engineered restriction; RonD is correct.

I used two 2.9's, both with the larger throttle body from 1987 2.9L's, they not only run perfect with stock injectors, they are doing it through full race ported heads/intakes at approximately 11.5:1 compression and out headers into a 2½" single.

Replace 14# injectors then reevaluate.
 
Last edited:

JohnAllen

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1989
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6"
Tire Size
33x10.50r15
Then your 14lb/hr injectors were most likely going bad, clogged up
The 19lb/hr may be closer to 17lb/hr which is why its not running too rich

Its still a 2.9 LITER engine, which means at WOT it can only pull in 2.9 Liters of air every 2 RPM, unless you force more air in, i.e. turbo or super charger
The stock intake can restrict some air flow at WOT making it a 2.7 LITER, lol
But would still be enough fuel flow for 2.9 liters

2.9l is 140horsepower
Six 14lb/hr injectors would be OK up to 200horsepower, 225hp most likely
19lb/hr are for 200+ up to about 300hp

I think there is another reason for the Lean code, not fuel related
Then I don't know what it could be bc like I've said.everything else fuel and air related has been checked and double checked.its all good. They're getting the right voltage readings and mechanically working as it should.
 

JohnAllen

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33x10.50r15
JohnAllen,

While this T/B may have increased the air flow, it's not above the 2.9's ability to use or properly meter the fuel, you more effectively, reduced an engineered restriction; RonD is correct.

I used two 2.9's, both with the larger throttle body from 1987 2.9L's, they not only run perfect with stock injectors, they are doing it through full race ported heads/intakes at approximately 11.5:1 compression and out headers into a 2½" single.

Replace 14# injectors then reevaluate.
By reducing the restriction on any given object, aren't you there by increasing the flow of that object, there for increasing the volume at which that object is moving?
Also, how would putting larger injectors cause it to run lean? Shouldn't it instead cause it to run rich with the extra fuel going in?
Like I've said. This problem started after I put that throttle body on it, and then I got it to run better under load with the larger injectors. The 14lb injectors was checked way before I decided to go with larger one, and the 14lb injectors was working perfectly.
So, with all other related components checking out good, and no vac leaks anywhere, and a brand new ECM, what could be causing this?
 

JohnAllen

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Tire Size
33x10.50r15
JohnAllen,

While this T/B may have increased the air flow, it's not above the 2.9's ability to use or properly meter the fuel, you more effectively, reduced an engineered restriction; RonD is correct.

I used two 2.9's, both with the larger throttle body from 1987 2.9L's, they not only run perfect with stock injectors, they are doing it through full race ported heads/intakes at approximately 11.5:1 compression and out headers into a 2½" single.

Replace 14# injectors then reevaluate.
Mind you, I'm not trying to be a smart ass here, I'm just wanting a clear understanding of what's going on. I've had this girl for 17 years now and have replaced and/or upgraded with new parts, completely rebuilt, and overhauled everything from the radiator to the rear disk brake conversion. And I'm about tired of throwing money at the dang truck.
KIMG0254.JPG
 

gaz

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Ranger 32", BII 28.5"
JohnAllen,

A 86-87 2.9L t/b is larger but nowhere near a 4.0L's t/b.

If you want your 2.9L to run well, use the stock rated injectors with the 86-87 T/B, then start troubleshooting.

RonD is 100% on the money; the t/b and 14# injectors are not your problem. For the minimal amount of effort, put the original T/B and stock injectors back on and retest. If it runs correctly, then make only 1 change at a time to determine the fault (just keep those 19# in a box in a different room).
 

JohnAllen

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1989
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4WD
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6"
Tire Size
33x10.50r15
JohnAllen,

A 86-87 2.9L t/b is larger but nowhere near a 4.0L's t/b.

If you want your 2.9L to run well, use the stock rated injectors with the 86-87 T/B, then start troubleshooting.

RonD is 100% on the money; the t/b and 14# injectors are not your problem. For the minimal amount of effort, put the original T/B and stock injectors back on and retest. If it runs correctly, then make only 1 change at a time to determine the fault (just keep those 19# in a box in a different room).
The throttle body on the 86 and 87 is 58mm and an oe throttle body for a 4.0 is also 58mm. I've looked that up because I'm planning on doing a mass airflow conversion on this truck soon and was needing to know what style mass air flow sensor I needed. And I've compared my throttle body to the throttle body on my 1995 Ford ranger with a 4.0. They are the same size bore.
Quick question, why did the 86 and 87 have two fuel pumps? Was it to help the engine keep more fuel volume to the rail? And I will look up the size injectors for the 86 and 87 just to see what size they are and test your theory, even though injectors aren't cheap. I'm just tired of throwing money at this dang truck.
 

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