Map voltage and fuel use.

[rainman2]

Hello,
Mine is chewing the gas.
The Ngk Oxy sensor is 30,000 Km old
and according to the scanner, it is switching high to low consistently, as you would expect.
Temp sender is working correctly as is the Intake air sender. TPS appears good, smooth/ within spec.
The cat is not blocked
I don't think there is any exhaust leaks, I've looked/ felt/ smelt can't detect any leaks
3 different Map sensors read the same, all good second-hand units.

The only thing i can see is the map Sensor, at warm idle, it reads 1.2- 1.3 volts and reads 4.8 with the engine off. According to the manual specification is warm idle 1.5-2.1 volts, and 4-5 volts with the engine off.

Could this cause excessive fuel use, it runs fine it is just getting bad mileage and the wideband suggests its always running rich.

If the voltage is low how do i fix it

[Cummins90]

What do you have? Year make model auto/standard?
What mods do you have? What mpg are you getting and how are you calculating it?

[Cheromaniac]

x2
Plus, which injectors are you using and at what fuel pressure?

[rainman2]

Sorry,
I thought that would come up as i filled it out in my profile.
95 obd1 xj cherokee 4.6l comp cam 232.
45/38psi fuel pressure running through neon 703 injectors.
AUTO,32"tyres 4:10 ratios
MPG atm: 22l per 100km / 11 mpg
usually, it runs 16l/100km.
its always been rich at WOT but usually pretty good just driving around.

[Cheromaniac]

Reduce the fuel pressure by 2psi and see how it goes.

[Cummins90]

It runs rich at WOT, which I assume means you have a wideband? My 95 would drop to 12.5 as it hit open loop above 3200rpm. I was never sure if that's what the ecm was programmed to target or if the ecm just would not remap the open loop fuel table while using slightly bigger injectors. I have seen evidence of the obd2 ecm change open loop fuel tables.

[rainman2]

yes have wideband ATM.
My understanding is with OBD1 there is no learning at greater than 80% throttle position its all factory memory in open loop north of there.

[rainman2]

Turns out #5 &#6 injectors were swapped around. FFS.
Map still reads the same.
Just got 16.4 mpg with 32" muds and a 4.5" lift.
AFR at wot is 12.6. this is with 42psi on the rail. and 703 "neon" injectors. '95 obd1 XJ, auto.

[Cheromaniac]

Sounds like you have it pretty well dialed in. A WOT A/F ratio of 12.6 is still slightly rich so you could drop the fuel pressure to 41psi and leave it there.

[rainman2]

yes, 40 psi gave me 13.1, but i think i will leave it where it is, don't spend much time at wot.
The extra fuel will add a bit of a buffer for pinging on 40*c+ Days.