What does the exhaust backpressure sensor do? - Diesel Forum - TheDieselStop.com
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99 & up 7.3L Power Stroke Engine and Drivetrain Discussion of the 99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.

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Old 01-26-2007, 05:46 PM   #1 (permalink)
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What does the exhaust backpressure sensor do?

Is it used only to open & close the EBPV, or does the truck computer use it for other things as well?
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Old 01-26-2007, 07:37 PM   #2 (permalink)
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Re: What does the exhaust backpressure sensor do?

If it senses exhaust backpressure that is too high, it will defuel the engine.
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Old 01-26-2007, 07:42 PM   #3 (permalink)
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Re: What does the exhaust backpressure sensor do?

[ QUOTE ]
If it senses exhaust backpressure that is too high, it will defuel the engine.

[/ QUOTE ]I hear the term defuel alot , what is it?...
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Old 01-26-2007, 08:04 PM   #4 (permalink)
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Re: What does the exhaust backpressure sensor do?

it means the computer realizes theres something occouring that may cause engine damage and it levels off your power, slows the rate of fuel to the engine

on a gas engine this is done by opening the EGR or causing missfires to hold the engine back. on a gasser if you hold the fuel back you will cause it to run lean and that may cause damage to the engine
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Old 01-26-2007, 08:07 PM   #5 (permalink)
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Re: What does the exhaust backpressure sensor do?

defueling means that the computer cuts back on how much fuel is injected. The way I understand it, it acts as a sort of safety device to keep from possibly damaging the motor.

At close to WOT, I'm seeing EBP's of around 50psi. The MAP reports about 30 PSI. The CEL light comes on & the code that is there is for overboost (I discovered my pop-off valve was bad, so right now I've got nothing to fool the MAP). I don't see anything related to EBP (using AE). I'm wondering why there is a 20# difference between the two, and why the EBP is so high. I've spent some time doing searches, and I see I can clean the EBP tube & possibly replace the sensor, but would this help (it doesn't seem like the tube is clogged if the sensor is seeing 50 PSI)? I'll check MAP, EBP & Baro tonight with KOEO, but if anyone else could give me ideas on what to look at, I'd appreciate it. BTW, I don't have an EBPV anymore
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Old 01-26-2007, 08:19 PM   #6 (permalink)
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Re: What does the exhaust backpressure sensor do?

[ QUOTE ]
defueling means that the computer cuts back on how much fuel is injected. The way I understand it, it acts as a sort of safety device to keep from possibly damaging the motor.

At close to WOT, I'm seeing EBP's of around 50psi. The MAP reports about 30 PSI. The CEL light comes on & the code that is there is for overboost (I discovered my pop-off valve was bad, so right now I've got nothing to fool the MAP). I don't see anything related to EBP (using AE). I'm wondering why there is a 20# difference between the two, and why the EBP is so high. I've spent some time doing searches, and I see I can clean the EBP tube & possibly replace the sensor, but would this help (it doesn't seem like the tube is clogged if the sensor is seeing 50 PSI)? I'll check MAP, EBP & Baro tonight with KOEO, but if anyone else could give me ideas on what to look at, I'd appreciate it. BTW, I don't have an EBPV anymore

[/ QUOTE ]I thought that was because the HPOP got behind a bit...Intermittent high pressure oil leakage.
This condition usually occurs when the vehicle is cold and the oil is thick. When performing a hard acceleration, the truck suddenly looses power, the check engine light comes on, and once returning to idle the engine runs rough and won't accelerate. Cycling the key may correct the concern, clearing the code from the PCM will correct it temporarily. If you can monitor data stream, at idle the ICP pressure normally is 400-700 PSI and the IPR duty cycle is 9-14%; at cruise, ICP is 700-1200 pSI and IPR is 15-20%; under normal acceleration, ICP is 1200-2000 PSI and IPR is 20-30%; and under WOT accel, the ICP is up to 3600 PSI and the IPR is 35% or higher. When the above symptom occurs, typically the idle ICP reading will be normal, but the IPR duty cycle will be high--over 20% and up to the max 50%. A "blow-by" condition has occured somewhere in the HP oil circuit. If you can get the problem to re-occur with some frequency, the most probable cause is worn or deteriorated injector or IPR o-rings. If the problem is intermittent, it could be a sticking IPR valve. Replace the injector o-rings with the latest-level kits--F8TZ-9229-AA. When replacing the IPR, make sure you get the correct part for the build date/serial number of your engine.

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Old 01-26-2007, 10:21 PM   #7 (permalink)
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Re: What does the exhaust backpressure sensor do?

Our exhaust backpressure sensor eliminator and Overboost eliminator will solve both of these issues, meaning the EBPS code and the Overboost condition.


the EBPS is used for cold weather package operation...as well as an emissions control if my memory serves me right. our sensor dongle takes the sensor out of the loop and renders the PCM happy all the time.
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Old 01-26-2007, 10:53 PM   #8 (permalink)
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Re: What does the exhaust backpressure sensor do?

[ QUOTE ]
At close to WOT, I'm seeing EBP's of around 50psi. The MAP reports about 30 PSI. The CEL light comes on & the code that is there is for overboost (I discovered my pop-off valve was bad, so right now I've got nothing to fool the MAP). I don't see anything related to EBP (using AE). I'm wondering why there is a 20# difference between the two, and why the EBP is so high.

[/ QUOTE ]

The MAP sensor measures pressure between the compressor wheel of the turbo and the intake of the engine, and the EBP measures pressure between the exhaust of the engine and the turbine wheel (exhaust side) of the turbo.

So that means that there really isn't much correlation between the two numbers. They're measuring two different parameters, each loosely related to the fuel delivery and engine load.

The EBP system works like this:

With cold temps, the PCM increases the idle speed, and tells the EBPV to close to put a little load on the engine and increase the exhaust temp. The sensor is there to tell the PCM when the exhaust pressure it asked for has been reached (this is called feedback control), so the PCM can ease the valve open and maintain that pressure. Once the engine oil temp reaches a certain value, indicating that the engine is fully warmed up, the PCM opens the EBPV.

I've never seen anything relating to defueling controlled by the EBP sensor in the Service Manual. It may do that, but the manual doesn't say anything about it that I can find.
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Old 01-26-2007, 11:24 PM   #9 (permalink)
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Re: What does the exhaust backpressure sensor do?

One of our diagnostic CDs clued us into that a few years ago and hence the exhaust backpressure sensor eliminator...we also saw this when testing the old Stage II product with a marginal backpressure sensor on the 99 that was one of the test beds...it's for real
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