Fox Xtremely high fuel consumption

Noobz347 · Apr 12, 2026

I dunno about you but I get that kind of mileage because of my foot and an addiction to blower whine.

I also think I run a little rich at cruise.

PonyGTrider · Apr 12, 2026

Noobz347 said:
I dunno about you but I get that kind of mileage because of my foot and an addiction to blower whine.

I also think I run a little rich at cruise.

Well with a blower it justifies the hit on fuel economy because of the demand but on a NA set up it is not justified specially when I tried different styles of driving, that is going easy on the throttle or being aggressive doesn’t make any difference too much fuel gone.

Thank you

PonyGTrider · Apr 12, 2026

SORRY, I HAVE TO ASK THIS QUESTION:
There is a sensor not too many people talk about and who knows maybe this is my problem!
I’ve read that a failing BAP sensor not always triggers the check engine and don’t always produce an error code in the ECU. One of the symptoms of a failing BAP sensor is a high fuel consumption.
Dos anyone in here had that sensor failing? And how do you test it without a frequency tester?
This BAP sensor communicates with the MAF sensor to do the appropriate air speed and density to adjust fuel/Air mixture. I hope this is the root of my issues but must have some expertise from all of you plus how to test it.

Thank you all so much!!!

Noobz347 · Apr 12, 2026

In your case, it only registers ambient air pressure during startup.

PonyGTrider · Apr 12, 2026

Noobz347 said:
In your case, it only registers ambient air pressure during startup.

So are saying that if I unplug that thing will only affect me during startup and the MAF and computer will disregard the signal from this barometric pressure sensor? Now I’m more confused…

Noobz347 · Apr 12, 2026

PonyGTrider said:
So are saying that if I unplug that thing will only affect me during startup and the MAF and computer will disregard the signal from this barometric pressure sensor? Now I’m more confused…

It references air pressure at startup so it knows which cold fuel table to go to.

Once you're warmed up and in closed loop, the HEGO and other sensors make that determination.

PonyGTrider · Apr 12, 2026

Noobz347 said:
It references air pressure at startup so it knows which cold fuel table to go to.

Once you're warmed up and in closed loop, the HEGO and other sensors make that determination.

Ok I got you,
Now one question just arises
Is that BAP sensor a specific part number per vehicle year?
My question is because I removed the BAP sensor from my 90 GT and the Part Number is E7EF-9F479-A2A
But when I did a google search AI suggested part number:

Ford OEM Number: E7FZ-12A644-A
Engineering Number: E7EF-12A644-A1A or
A2A
LMR Part Number: LRS-12644A

Is there any difference if I use either one or this could be the root of the extremely high fuel consumption?

Thank you much for the help!

PonyGTrider · Apr 12, 2026

This is what AI suggested when I asked
On a 90 mustang GT will a failing or wrong BAP sensor always cause an error code or will it induce an extremely poor fuel economy?

No, a failing or incorrect Barometric Pressure (BAP) sensor on a 1990 Mustang GT (5.0L) will not always trigger an error code (Check Engine Light), but it will frequently cause poor fuel economy, idle issues, or a rich running condition.
The 1990 Mustang GT uses a Mass Air Flow (MAF) system, where the BAP sensor communicates the ambient air density to the Electronic Control Assembly (ECA/ECU) to calculate fuel injection and spark timing.
LMR.com +2
Here is a breakdown of why it may not trigger a code and its impact on fuel economy:

1. Will a Failing/Wrong BAP Sensor Always Cause a Code?

No, not always: A BAP sensor can be "lazy," "drifting," or partially inaccurate, sending incorrect voltage readings that are still within the pre-programmed "range" of the computer. If the computer believes the voltage is plausible, it will not set a code.
"Wrong" Sensor Issue: Using a MAP sensor (intended for Speed Density) in place of a BAP sensor (for Mass Air), or vice-versa, can cause the car to run poorly or flood (rich condition) without necessarily showing a check engine light, because the computer is operating on false altitude/pressure data.
Common Codes (When they do appear):If the sensor fails completely, the computer may detect a voltage that is too high or too low, leading to Code 22 (BP sensor out of range).

2. Will it Always Cause Poor Fuel Economy?

High Probability: A failing BAP sensor often tricks the computer into thinking the car is at a higher altitude (lower air density). To compensate, the computer restricts fuel. However, more often, a faulty sensor causes the engine to default to an overly rich air-fuel ratio.
Symptoms: This results in excessive fuel consumption, black smoke from the exhaust, "lumpy" or erratic idle, and spark plugs fouling.
Performance Issues: A bad BAP sensor can cause the car to fall into a "limp mode," causing sluggish performance and hesitation.
YouTube +4

3. Diagnosis and Context for 1990 Mustang GT

Location: The BAP sensor is located on the firewall, behind the engine, often near the passenger side, usually identified by a 3-pin connector and no vacuum line attached (unlike a MAP sensor).
Testing: If you suspect a problem, you must use a multimeter to check the voltage output to see if it corresponds to your current atmospheric pressure.
Other Causes: Because the BAP sensor is rarely the only cause of poor fuel economy, you should also inspect the Mass Air Flow (MAF) sensor, oxygen sensors, and check for vacuum leaks.
LMR.com +4

Summary: The 1990 Ford ECU is not as sophisticated as modern OBD2 systems, making it highly possible to have a faulty BAP sensor that makes the car run very rich (poor MPG) without a Check Engine Light.

Will it make sense and by using the correct BAP sensor might help solving my poor fuel economy?????

Please comment, thank you

nickyb · Apr 12, 2026

Who is this AL guy giving you that info?

PonyGTrider · Apr 12, 2026

nickyb said:
Who is this AL guy giving you that info?

Is not a guy, it is a compilation of postings regarding a specific subject and AI makes a suggestion based on those inputs.
I just post it to see all you guys reactions and your agreements and disagreements. All of this in good fate.

Thank you

Noobz347 · Apr 12, 2026

There are different part numbers however, I converted to MAF from SD and am still using the same MAP/BAP. The only difference for me is that the vacuum line had to removed so the sensor is in open air.

86HO5.0 · Apr 13, 2026

One thing I've found AI is good for is misinformation.

PonyGTrider · Apr 13, 2026

Noobz347 said:
There are different part numbers however, I converted to MAF from SD and am still using the same MAP/BAP. The only difference for me is that the vacuum line had to removed so the sensor is in open air.

Ok but the two sensors with different part number send different frequency signal enough to require me to have the specific sensor for my 90 GT with manual transmission or it doesn’t matter? Do I have the wrong sensor?

Thank you

PonyGTrider · Apr 13, 2026

Well apparently those two BAP sensors are interchangeable so what else could be causing to affect my fuel economy?

I’ve done everything I know and all that was suggested and I see no improvements.

One thing that I still don’t have too clear is with regard to my injectors. How could it affect my MPG if I’m using 19lb? Are they maxed out and are over fueling?

I’m running out of options here

nickyb · Apr 13, 2026

PonyGTrider said:
Not a chance, my ride stays in a closed garage.

Thank you

Who has access to that garage?

86HO5.0 · Apr 13, 2026

PonyGTrider said:
Well apparently those two BAP sensors are interchangeable so what else could be causing to affect my fuel economy?

I’ve done everything I know and all that was suggested and I see no improvements.

One thing that I still don’t have too clear is with regard to my injectors. How could it affect my MPG if I’m using 19lb? Are they maxed out and are over fueling?

I’m running out of options here

Your injectors aren't causing the poor MPG issue. Something else is causing it.

A wideband would be a great diagnostic tool.

Noobz347 · Apr 13, 2026

A tune may be in your future.

AeroCoupe · Apr 13, 2026

I know you said the speedo is calibrated correctly but is it possible that the odometer is having issues? Just wondering if it is not recording enough miles and you are actually driving more miles than the odometer is recording.

PonyGTrider · Apr 13, 2026

nickyb said:
Who has access to that garage?

Just me

LILCBRA · Apr 13, 2026

One thing I didn't see mentioned anywhere was ignition timing. Might sound silly, but are the wires routed correctly and is timing set properly?

Fox Xtremely high fuel consumption

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

PonyGTrider

PonyGTrider

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

PonyGTrider

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

PonyGTrider

PonyGTrider

nickyb

I gotta say i never painted my nuts, Never Ever

PonyGTrider

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

86HO5.0

Active Member

PonyGTrider

PonyGTrider

nickyb

I gotta say i never painted my nuts, Never Ever

86HO5.0

Active Member

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

AeroCoupe

lube between the nut and the face. I know my lubes

PonyGTrider

LILCBRA

I wish I didn't have all of these balls in the air

Similar threads

Fox Xtremely high fuel consumption

Stangnet Facilities Maint Tech... Er... Janitor

Stangnet Facilities Maint Tech... Er... Janitor

Stangnet Facilities Maint Tech... Er... Janitor

I gotta say i never painted my nuts, Never Ever

Stangnet Facilities Maint Tech... Er... Janitor

Active Member

I gotta say i never painted my nuts, Never Ever

Active Member

Stangnet Facilities Maint Tech... Er... Janitor

lube between the nut and the face. I know my lubes

I wish I didn't have all of these balls in the air

Similar threads

Privacy & Transparency

Privacy & Transparency