MSefi.com read only forum (Jan.15,2018)

Does anyone know where to get a gas engine back pressure sensor for a turbo car?

any reason why a sensor off of a diesel won't work?

i would use one off of a ford diesel, new ones are available on ebay for about $40

I've seen the use of a MAP sensor, suitably plumbed. This was: manifold->foot of stainless tubing->rubber tube->sensor. The user said it reliably worked for some time. There is no flow of hot gas in the line so I suppose it's at least possible.

-Mike

Hey Mike

Thanks for the reply

Was it immune from the gases because of the 12" of stainless and the air inside of it? Or was there some sort of inline isolator that made this work well?

I wonder how well this would hold up to it?

We haven't tested it with exhaust, but if you have a long enough metal tube to cool the exhaust I suspect you won't have a problem.

The problem is that with exhaust cooling, there will be pressure loss because it will contract.

What I don't know is how significant or insignificant this pressure loss due to contraction will be?

Is there an isolator that would work well for this? Kind of like the idea where you have a fuel pressure isolator in the cabin for a fuel pressure gauge?

Matt Cramer wrote:We haven't tested it with exhaust, but if you have a long enough metal tube to cool the exhaust I suspect you won't have a problem.

gte, I don't think there would be pressure loss from cooling since it's not an enclosed or flowing column of gas - the pressure will communicate just fine through the column of gas at the local speed of sound. If a volume of warm gas is allowed to cool in an enclosed volume it will gradually reach ambient temp and lose pressure while it's cooling. Conversely that volume of gas will want that heat back when it's released and be cold when released to ambient. It's not enclosed or trapped at all in the case we're discussing. Also, yes, there are isolators available but they are expensive and most require a fluid filled line instead of a gas filled line to the transducer/gauge/whatever precisely due to the adiabtic problem you asked about - this would exist in a gas volume between the isolator and the sensor as temps changed. I do like the diesel sensor idea - emissions related products engineered from scratch for a particular purpose are generally very robust and perform well. Anybody have a lead on cost/availability? Are they to be found in the boneyards?

-Mike

Edit: Duh, checked on ebay, $37.00 NOS, http://cgi.ebay.com/ebaymotors/ford-6-0 ... enameZWDVW

Could be an excellent alternative depending on the electrical interface and temp rating - gasoline engine exhaust is quite a bit hotter than diesel exhaust. Matt Cramer would probably know!

Mike,

That makes sense, it probably would be negligible.

My only concern with the diesel sensors is how I can calibrate them and what their range is, as well as how large they are and how I could adapt their thread pitch to a 1/8" npt hole (one ebayer said he thinks it's -6?). I agree that diesel temps are about 500F lower then turbocharged gas engine temps, but I think with the sensors being as far away as they are from the actual manifold, it shouldn't be an issue.

Yes, I hear you on those concerns. I'm currently fabbing a Mazda 12A turbo project and plan on using the steel->rubber->sensor to sense preturbo temps. You don't want to be sensing pressures down the system, the whole point is to measure the pressure at the exhaust port. Future EFI software will use this as an input to help accurately determine real VE on the fly, from what I hear. That's why I was concerned about temps on the diesel sensor - my rotary app can easily hit EGT==1600-1700F transiently in a well tuned state, higher if I'm on the lean side of optimum AF/R or the timing is a bit retarded.

-Mike

Well, I did find this, it at least reads up to 43.5 psi? I guess I'll put a manual gauge on my car and see if that's enough


http://www.thedieselstop.com/faq/9497fa ... d/ebp.php3.



SIGNAL FUNCTIONS
The EBP (Exhaust Back 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 exhaust back pressure.

The EBP sensor's primary function is to measure exhaust back pressure so that the PCM can control the exhaust back pressure regulator when needed.

FAULT DETECTION MANAGEMENT
An EBP signal that is detected out of range high or low by the PCM will cause the engine to ignore the EBP signal and disable exhaust back pressure operation.

The NGS tool will display a fixed PID value of 43.5 PSI (300 kPa) for EBP when exhaust back pressure is in default.



After removing connector 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
A to Grd. < 5 ohms Resistance to chassis grd. check w/key off, if > than 5 ohms harness is open -Signal Grd.
B to Grd. > 1000 ohms Resistance less than 1000 ohms indicates a short to ground. - VRef
C to Grd. > 1000 ohms Resistance less than 1000 ohms indicates a short to ground. - EBP signal

Connector Voltage Checks
(Check with sensor Connector Disconnected and Ignition Key On)
Test Points Spec. Comments
A to Grd. 0 - .25 volts If greater than .25 v signal ground is open or shorted to VRef or battery.
B to Grd. 5 ± .5 volts VRef check with key "ON," if voltage not in spec., see VRef circuit
C to Grd. 0 - .25 volts If greater than 0.25 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 A < 5 ohms Resistance from sensor connector to 104 pin connector - Signal ground
#90 to B < 5 ohms Resistance from sensor connector to 104 pin connector - VRef
#30 to C < 5 ohms Resistance from sensor connector to 104 pin connector - EBP signal

Test Points Operational Voltage Checks
(+) #30 to (-) #91 (Check with breakout box installed in line with the PCM)
Voltage PSI KPAG Comments
.8-1.0 v 0 o Signal with key "ON" and engine OFF (Value dependent upon atmospheric pressure and altitude.)
.8-1.0 v 0 0 Normal warm idle signal.
1.19 v 14.8 10.0 Minimum signal expected at 2300 RPM with warm engine. (See EPR diagnostics)

Circuit Faults: Diagnostic Trouble Code Description
0472 = Signal voltage was less than .039 volts for more than 0.2 seconds.
0473 = Signal voltage was greater than 4.90 volts for more than 0.2 seconds.

Excellent find! That should be way more than enough - EBP for a gas engine should be WAY less than that. Thanks for the research - your Google-fu is better than mine....

-Mike

Haha

Mike, I'll be getting manual measurements of what the pressure is soon enough, and I'll be posting those results. The car has a 3L motor and a small turbo on it, so I think it will give a great indication of maximum (worst case scenario) exhaust back pressure.

As an update, 43 psi is not enough

I talked to my buddy that has measured back pressure on a turbo 2jzge with a gte short block

He said with a restrictive exhaust housing (.70) he measured a peak of 89 psi in the exhaust manifold with 30 psi at the intake manifold

He increased the housing size to a .96 and it dropped down to 56 psi.

That tells me what type of sensor I need, one that reads at least to 100 psi

I'll be getting a sensor from this site

http://www.mouser.com/Search/ProductDet ... faFw%3d%3d

Holy backpressure Batman! That's quite interesting. Keep the info coming....

-Mike

I've been interested in incorporating this for the sake of research. Has anyone measured the the EBP on a NA or supercharged car? The cheapest sensor on ebay right now is $50 + $30 for a connector. I'd like to see the combo below $40. Any resellers listening?

The cheapest place to get MAP sensors is a U-Pull-It junkyard. Huge selection and you can use a vacuum pump and voltmeter to map the curve if you can't find any info online.

C|