Baro Sensor - Ford Powerstroke Diesel Forum
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post #1 of 11 Old 12-27-2018, 06:08 AM Thread Starter
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Baro Sensor

I recently got Forscan and an adapter. I found out through all the tests that Forscan can do that Im in pretty good shape. 2600 PSI HPOP Max 33% IPR WOT. Cylinder contribution and buzz tests good.

One thing I did notice is my baro sensor is reading 5 PSI and my map is reading 14.7 PSI.

I know in illinois baro should be 14.7 psi so that makes sense that KOEO my MAP sensor is reading 14.7.

My question is my BARO sensor is reading 5 even though it should be 14.7 as well. Electrical PIN test shows good Vref. So what negative effects might I notice with a bad BARO sensor. If the BARO reads 5 and Map reads 14.7 will it make it run lean or rich or might there be no change at all?

Also the truck runs great builds 16 PSI boost and my problem is the fuel mileage used to be around 16 MPG now its around 13.5 MPG no smoke.

Thanks in advance.

1995 F250 Ext Cab 2WD E40D, FludDmpr, Rebuilt Injectors, 6337 Intake, CCV Re Route, Cat Delete, E Fuel.

Last edited by StrokerPains; 12-27-2018 at 06:13 AM. Reason: Factual Change
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post #2 of 11 Old 12-27-2018, 06:41 AM
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Hard to say the specific impact of the failed sensor. BARO is used in the mixture calculation and - if it is reading low - the truck is going to run rich. The glow plugs will also be run longer. ...but only up to a point.

As soon as the PCM calls BS on the sensor, it will set a code and use the MAP sensor reading at low idle as the new BARO. ...and then you're pretty much back to normal.

Despite the ambiguity of outcome, the conclusion of all of this is clear. Quit screwing around and replace the damn sensor.

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post #3 of 11 Old 12-27-2018, 09:40 AM
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The barometric pressure sensor has little if anything to do with how the obs 7.3 runs. It became a little more involved with the 99 models. What you are reading is more likely voltage than pressure (analog 5 volts). Diesel engines do not run rich or lean, it's more about how much air is being pushed through them. As for less mpg, winter blend diesel fuel always nets less than summer blend. You can run power service diesel kleen in the white bottle (winter) silver bottle (summer) and get a little mileage back. You should always be using a fuel additive in these older engines anyways because they where not designed to work with today's low sulfur fuel. I'm guessing that with 16psi boost your engine is 100% stock.

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post #4 of 11 Old 12-27-2018, 02:47 PM
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Quote:
Originally Posted by 1Dieselman View Post
The barometric pressure sensor has little if anything to do with how the obs 7.3 runs.
I stand by what I said. The following is from the "Technical Service Bulletin: 1994-1997 Ford 7.3 L Powerstroke – DIT Engine Information" - Reference Number(s): 97-15A-1, Date of Issue: August 4, 1997

https://www.hotshotsecret.com/diagno...gine-info-tsb/

It can also be found in the PC/ED:

Quote:
Barometric Pressure (BARO) Sensor
Signal Functions
The BARO (Barometric Pressure) sensor is a variable capacitance sensor that when supplied with a 5 volt reference signal from the PCM produces a linear analog voltage signal that indicates barometric pressure.

The BARO signal if used to determine altitude to adjust timing and fuel quantity to optimize engine operation and control smoke throughout all altitude conditions.
The BARO signal is one of the variables used to calculate glow plug “ON” time. At higher altitudes, glow plug “ON” time is increased to insure faster clean up of startup smoke.


Fault Detection/Management
A BARO signal that is detected out of range high or low by the PCM will cause the PCM to ignore the BARO signal and use the Manifold Absolute Pressure (MAP) signal sensed at low idle as an indication of barometric pressure. If the MAP signal has also failed, a fixed value of 29.61 In. Hg. (14.6 PSI) is used as the default. The NGS tool will display the PID default value of 29.61 In. Hg. (14.6 PSI) when the BARO system has failed.

Barometric Pressure (BARO) Sensor Fault Detection/Management
NOTE: After removing connectors always check for damaged pins, corrosion, loose terminals etc.

CONNECTOR CHECKS TO GROUND (B-) (CHECK WITH SENSOR CONNECTOR DISCONNECTED AND IGNITION KEY OFF, ALL ACCESSORIES OFF)
Test Points Spec Comments
(1) to Grd. < 5 ohms Resistance to chassis Grd, check w/key off, > than 5 ohms the harness is open.
(2) to Grd. > 1000 ohms Resistance less than 1000 ohms indicates a short to ground.
(3) to Grd. > 1000 ohms Resistance less than 1000 ohms indicates a short to ground.

CONNECTOR VOLTAGE CHECKS (CHECK WITH SENSOR CONNECTOR DISCONNECTED AND IGNITION KEY ON)
Test Points Spec. Comments
(1) to Grd. 0 – .25 volts If greater than .25 volts signal wire is shorted to VRef or battery.
(2) to Grd. 5 Volts +/- .5 VRef check with key ON, if voltage is not spec., see VRef circuit.
(3) to Grd. 0 – .25 volts If greater than .25 volts signal wire is shorted to VRef or battery.

HARNESS RESISTANCE CHECKS (CHECK WITH BREAKOUT BOX INSTALLED ON ENGINE HARNESS ONLY)
Test Points Spec Comments
#91 to (1) < 5 ohms Resistance from sensor connector to 104 pin connector – Signal Ground
#90 to (2) < 5 ohms Resistance from sensor connector to 104 pin connector – VRef
#84 to (3) < 5 ohms Resistance from sensor connector to 104 pin connector – BARO signal

OPERATIONAL VOLTAGE CHECKS (CHECK WITH BREAKOUT BOX INSTALLED IN LINE WITH THE PCM)
Test Points (+) #84 to (-) #91 kPa Comments
Voltage In. Hg.
4.89 31.0905 105 High atmospheric pressure
4.6 29.61 100 Normal atmospheric pressure at sea level
2.6 60 Normal atmospheric pressure at 10,000 feet

DIAGNOSTIC TROUBLE CODE DESCRIPTIONS
DTC Description
0108 Signal voltage was greater than 4.9 volts for more than .2 seconds
0107 Signal voltage was less than .04 volts for more than .2 seconds

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post #5 of 11 Old 12-27-2018, 04:17 PM
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Don't care what it say's. As a mechanic that has worked on these engines for many years I have never seen the baro sensor adversely effect how the 94-97 run's whether it was good, bad, or unplugged. the 99-04 7.3 will set a code for a bad baro sensor.

Jack

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post #6 of 11 Old 12-27-2018, 05:11 PM
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I get it @1Dieselman . I think that I read a bit too much into the "if anything" comment.

Thinking more about what you said in reply and my post from the TSB...

If the BARO sensor is out of range, there shouldn't be any difference in operation at all - because the MAP sensor at low idle is used. If both the BARO and MAP are dead, then sea level gets used. It seems that the only difference that would ever be seen is when/if someone had both sensors fail/disconnected and were at high altitude - which isn't likely.

So, the only difference in operation that might occur is when the sensor isn't out-of-range. ...and - if it isnt out-of-range - the difference wouldn't matter much anyway.

I also thought about the 5V thing. If the BARO output were really 5V, that would be seen by the PCM as an altitude of about 1000ft below sea level. That would be out-of-range and the BARO would be ignored for the MAP. So, again - as you said - no difference.

Thanks.

2004 F550 CC Lariat
BPD oil cooler relocation and upgraded EGR cooler (spooled), BPD oil bypass filtration, aFe Magnum Force CAI, Mishi radiator, 7.3L fan clutch, EC1 ELC, XDP coolant bypass filtration, '08 trans pan/filter, PTP direct clutch solenoid, blue spring, 6.4 starter, MBRP y-pipe, BD boots/clamps, '05 intake elbow, ccv reroute, Torque Pro + OBDLink™ LX, Autometer EGT
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post #7 of 11 Old 12-27-2018, 05:41 PM
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Chased that one down the rabbit hole, ...I was waiting with my shotgun, ...rabbit stew for supper. But srsly, the exchange of information is how we learn more about these trucks, it was a good exchange.

"Also the truck runs great builds 16 PSI boost and my problem is the fuel mileage used to be around 16 MPG now its around 13.5 MPG no smoke"

The OP still needs to replace the BARO sensor to get some of that fuel mileage back

In my defense, I was unsupervised
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post #8 of 11 Old 12-27-2018, 09:29 PM
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Have a bad BPS with an automatic truck and you will see it does effect how these things act.

Replace it either way.
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post #9 of 11 Old 12-28-2018, 04:06 AM Thread Starter
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Quote:
Originally Posted by 1Dieselman View Post
The barometric pressure sensor has little if anything to do with how the obs 7.3 runs. It became a little more involved with the 99 models. What you are reading is more likely voltage than pressure (analog 5 volts). Diesel engines do not run rich or lean, it's more about how much air is being pushed through them. As for less mpg, winter blend diesel fuel always nets less than summer blend. You can run power service diesel kleen in the white bottle (winter) silver bottle (summer) and get a little mileage back. You should always be using a fuel additive in these older engines anyways because they where not designed to work with today's low sulfur fuel. I'm guessing that with 16psi boost your engine is 100% stock.

Found out the sensor does matter. If the barometric pressure sensor is un hooked, the automatic transmission shifts harsh. As soon as I hooked it back in it shifted fine. Also by unhooking the BARO sensor the truck responsiveness increased.

So from my experience it does make a difference if its working or not working or unhooked.

1995 F250 Ext Cab 2WD E40D, FludDmpr, Rebuilt Injectors, 6337 Intake, CCV Re Route, Cat Delete, E Fuel.
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post #10 of 11 Old 01-02-2019, 07:16 AM Thread Starter
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Quote:
Originally Posted by 1Dieselman View Post
Don't care what it say's. As a mechanic that has worked on these engines for many years I have never seen the baro sensor adversely effect how the 94-97 run's whether it was good, bad, or unplugged. the 99-04 7.3 will set a code for a bad baro sensor.

So I have found that unplugging the sensor does cause shift issues in an automatic. I replaced it with an OEM ford product it is even stamped ford on top.

Further information I did all of the above tests on all of the electrical wires. Ive pinned it out on the PCM and verified only continuity to the appropriate pins on the PCM also I have ohm tested all lines and they all check out within the specs listed in the above tests. Also checked voltage KOEO and it all checks out.

So the old sensor reads 8.2 PSI and the New OEM Sensor reads 8.2 PSI when it should in fact be reading 14.7 PSI which is what the EBP and the MAP read +/-.3 KOEO.

Does anyone else have any ideas here?

Also when I checked continuity I checked between ALL pins on the PCM just in case it was shorted to another PIN seemed unlikely but I checked anyway. There was not continuity except on the pins they should be on.

thanks in advance.

1995 F250 Ext Cab 2WD E40D, FludDmpr, Rebuilt Injectors, 6337 Intake, CCV Re Route, Cat Delete, E Fuel.
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