MAP voltage vs pressure test results
#1
11-11-2007, 12:28 PM
MAP voltage vs pressure test results
I tested the MAP sensor with an oscilliscope today, it is a DC level not a switching frequency as stated in some of the things I have read.
I used the battery (-) terminal as a reference. (5V measure 5.01 and signal return is 24mV). An autometer boost guage was used for pressure readings.
here the data;
psi VDC
0 1.43
3 2.27
5 2.59
8 3.03
10 3.38
14 3.89
16 4.17
18 4.47
19 4.59
20 4.75
21 4.89
22 4.93
23 4.93
27 4.93
So this sensor is saturated above 21psi. I would expect a guard band of 10-20% on the top and bottom of this sensor range so its valid range should be about 1-4.5 volts, but maybe not.
Anyone know at what MAP voltage the truck de-fuel? this condition should also illuminate SES light.
Can someone verify these numbers, please?
thanks
I used the battery (-) terminal as a reference. (5V measure 5.01 and signal return is 24mV). An autometer boost guage was used for pressure readings.
here the data;
psi VDC
0 1.43
3 2.27
5 2.59
8 3.03
10 3.38
14 3.89
16 4.17
18 4.47
19 4.59
20 4.75
21 4.89
22 4.93
23 4.93
27 4.93
So this sensor is saturated above 21psi. I would expect a guard band of 10-20% on the top and bottom of this sensor range so its valid range should be about 1-4.5 volts, but maybe not.
Anyone know at what MAP voltage the truck de-fuel? this condition should also illuminate SES light.
Can someone verify these numbers, please?
thanks
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11-11-2007, 03:35 PM
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11-11-2007, 03:43 PM
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Originally Posted by smoky_diesel
... So this sensor is saturated above 21psi. I would expect a guard band of 10-20% on the top and bottom of this sensor range so its valid range should be about 1-4.5 volts, but maybe not...
So now the $64 question is how does a chip program reliably schedule more fuel as a function of boost for boost's higher than about 18 psi?
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11-11-2007, 03:44 PM
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Originally Posted by ernesteugene
If that measured voltage is correct, the PCM can't tell the difference between 22 psi and 24 psi?
Edit: sorry, slow response. Typing and watching football.
Last edited by Tenn01PSD350; 11-11-2007 at 03:47 PM.
#7
11-11-2007, 06:40 PM
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Originally Posted by Tenn01PSD350
Agreed. Looks like 22 is the defuel point in that map sensor.
Edit: sorry, slow response. Typing and watching football.
Edit: sorry, slow response. Typing and watching football.
https://www.ford-trucks.com/forums/660609-analysis-of-tenns-6637-restriction-data-3.html#post5220683
Originally Posted by ernesteugene
The following is a combination of conjecture on my part along with some things I've been told by various chip tech types I've talked with over the years. BTW the chip guys that are in a position to be the most knowledgeable seem to reveal the least amount on info.
In addition to using various other parameters, I think the PCM uses MAP and TP to control fueling as follows. First, MAP=BARO+BP, and the PCM is measuring the absolute MAP and BARO, it's not directly measuring the differential BP like a boost gauge is. At lower values of MAP the PCM restricts fuel until the MAP is high enough to minimize smoke. At higher values of MAP corresponding to BP above 22 psi, the PCM restricts fuel to limit he max boost. I think that for in-between values of MAP, the PCM increases fuel trying to get the MAP up to the value that it expects to see for a given TP. So if a tune can make the MAP appear lower than actual, the PCM will add more fuel until it see's the MAP it expects to see for a given TP.
I've asked several people why a chip tune can't just change the 22 psi threshold for de-fueling, and I've been told 1) it's in the hardware and can't be changed, and 2) it's in firmware or the Ford instruction code and we won't change it because we don't want to get sued. There has to be some reason why none of the chip tuners can or will change the threshold for de-fueling? Now this is a pure guess, but I think this de-fuel trigger circuit, or whatever it is, might be using an independent processing of the raw signal from the MAP sensor, and the program, data tables, or whatever that is using MAP for the other aspects of fueling is something that chip tunes can mess with. That's why you need an OBA to physically change the raw signal from the MAP sensor before it gets to this de-fuel trigger circuit.
I also think that the PCM might use MAT to limit fuel as a crude way of trying to limit EGT to below 1200F. If that's true, then fooling the PCM to make the MAT appear lower than actual would also allow more fuel to be added before triggering this threshold. I think chip tunes can directly effect fueling by modifying the fueling tables of PW, timing, etc.. but tunes might also have to mess with MAP and MAT to bypass those overriding restrictions on fueling?
If one could find out the volts vs pressure and temp for the MAP and MAT sensors, you could read them directly with a high impedance volt meter, and that's the most foolproof way to see what's going on. I except that AE is reading some version of these sensors that are being reported by the PCM after it processes the raw sensor signal.
In addition to using various other parameters, I think the PCM uses MAP and TP to control fueling as follows. First, MAP=BARO+BP, and the PCM is measuring the absolute MAP and BARO, it's not directly measuring the differential BP like a boost gauge is. At lower values of MAP the PCM restricts fuel until the MAP is high enough to minimize smoke. At higher values of MAP corresponding to BP above 22 psi, the PCM restricts fuel to limit he max boost. I think that for in-between values of MAP, the PCM increases fuel trying to get the MAP up to the value that it expects to see for a given TP. So if a tune can make the MAP appear lower than actual, the PCM will add more fuel until it see's the MAP it expects to see for a given TP.
I've asked several people why a chip tune can't just change the 22 psi threshold for de-fueling, and I've been told 1) it's in the hardware and can't be changed, and 2) it's in firmware or the Ford instruction code and we won't change it because we don't want to get sued. There has to be some reason why none of the chip tuners can or will change the threshold for de-fueling? Now this is a pure guess, but I think this de-fuel trigger circuit, or whatever it is, might be using an independent processing of the raw signal from the MAP sensor, and the program, data tables, or whatever that is using MAP for the other aspects of fueling is something that chip tunes can mess with. That's why you need an OBA to physically change the raw signal from the MAP sensor before it gets to this de-fuel trigger circuit.
I also think that the PCM might use MAT to limit fuel as a crude way of trying to limit EGT to below 1200F. If that's true, then fooling the PCM to make the MAT appear lower than actual would also allow more fuel to be added before triggering this threshold. I think chip tunes can directly effect fueling by modifying the fueling tables of PW, timing, etc.. but tunes might also have to mess with MAP and MAT to bypass those overriding restrictions on fueling?
If one could find out the volts vs pressure and temp for the MAP and MAT sensors, you could read them directly with a high impedance volt meter, and that's the most foolproof way to see what's going on. I except that AE is reading some version of these sensors that are being reported by the PCM after it processes the raw sensor signal.
This leads to my other question. How trustworthy is some of the other AE data like IAT, MAT, ICP, etc... ? Maybe the chip is also distorting these readings to effect the fueling? I've been told by several Ford techs that the Ford scanner can't get good readings unless I pull my chip!
Also, there's only a 0.8% difference between the MAP sensor voltage at 22 vs 21 psi, which supports what I posted here...
https://www.ford-trucks.com/forums/638960-bye-overboost-annihilator-hello-diode-wire.html?highlight=zener+diode
concerning why I think all the devices intended to defeat the over boost defuel at 22 psi do more harm than good, unless you're trying to win a dyno contest. The 99% of the time you're driving at BP less than 22 psi your fueling is compromised just to get a little more fuel the 1% of the time you're at a BP of more than 22 psi. There's just no way that any device can limit the voltage to 4.93 at 22 psi, and still provide the correct 4.89 volts at 21 psi!
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#8
11-11-2007, 07:07 PM
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Originally Posted by ernesteugene
I agree with this assertion, and it tells me that Ford designed the MAP sensor for a usable maximum range of up to 4.5 volts to accommodate the stock maximum boost of 18 psi.
So now the $64 question is how does a chip program reliably schedule more fuel as a function of boost for boost's higher than about 18 psi?
So now the $64 question is how does a chip program reliably schedule more fuel as a function of boost for boost's higher than about 18 psi?
Secondly, and more important, we don't know exactly what chips do to map fuel for sure, so saying that we are floundering around inefficiently is quite a leap based on limited data. Would it not make sense that there is a reason the chip does what it does and fuels accordingly, or do you think Jody just slaps some tunes in and crosses his fingers?
I understand your thinking. I would assume that the program will avoid defuel situations and go off of throttle input and rpms from there. That is why mods need to be advised. At least that is what I think because the stock map will quit at 22. There may not be a way to override that signal in the PCM code by any tuner.
Since I do not know, I will shut up.
#9
11-11-2007, 07:42 PM
On my truck the MAP sensor reads 1 psi lower than my gauge, and I know a few others have posted that their MAP reads 1-3 psi lower or higher than a typical boost gauge. Also on my truck, I can run stock, or any other tune, and the MAP always reads 1 psi lower than my boost gauge, so tuning doesn't change how the MAP is read by the PCM. There are some tuners out there who have in the past fooled the PCM's reading of the MAP sensor, but for sure Jody doesn't do this (I've asked him too).
On my truck, when AE see's 24 psi of boost, my SES light is triggered. Recently I had to re-adjust my overboost annihlator, so I got to play around with the MAP sensor readings quite a bit. Right now the fooler is set so that the MAP is limited to reading 23.7 psi of boost to the PCM, no matter how high my boost actually goes beyond that. At that setting, my SES light is not triggered, and the PCM does not throw an overboost code. But if I adjust it to allow the MAP to read 24 or more, then the SES is triggered when I reach 24 psi.
So on my truck, there is a difference between the MAP reading 23.7 psi and 24 psi. And it's enough of a difference that the PCM does not trigger the SES light or set any kind of code as long as it's under 24 psi.
Like I said before, I think it depends on your truck's PCM, since a while back there were some folks who report having set the SES for and overboost code when the MAP is reading only 22 psi of boost.
And apparently with what Smokey did with his testing, his truck probably sets the overboost code at 22 psi. Or, and here's another way to look at it.... He is comparing MAP sensor voltage to gauge pressure readings. Since the MAP sensor can be off by a few psi compared to a gauge reading, then his results could be off by that same amount. So it's possible that his PCM won't set a code until the MAP reads 24 psi of boost, because MAP pressure reading and gauge pressure can both be different.
On my truck, when AE see's 24 psi of boost, my SES light is triggered. Recently I had to re-adjust my overboost annihlator, so I got to play around with the MAP sensor readings quite a bit. Right now the fooler is set so that the MAP is limited to reading 23.7 psi of boost to the PCM, no matter how high my boost actually goes beyond that. At that setting, my SES light is not triggered, and the PCM does not throw an overboost code. But if I adjust it to allow the MAP to read 24 or more, then the SES is triggered when I reach 24 psi.
So on my truck, there is a difference between the MAP reading 23.7 psi and 24 psi. And it's enough of a difference that the PCM does not trigger the SES light or set any kind of code as long as it's under 24 psi.
Like I said before, I think it depends on your truck's PCM, since a while back there were some folks who report having set the SES for and overboost code when the MAP is reading only 22 psi of boost.
And apparently with what Smokey did with his testing, his truck probably sets the overboost code at 22 psi. Or, and here's another way to look at it.... He is comparing MAP sensor voltage to gauge pressure readings. Since the MAP sensor can be off by a few psi compared to a gauge reading, then his results could be off by that same amount. So it's possible that his PCM won't set a code until the MAP reads 24 psi of boost, because MAP pressure reading and gauge pressure can both be different.
#10
11-12-2007, 12:18 AM
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Originally Posted by Pocket
... On my truck the MAP sensor reads 1 psi lower than my gauge, and I know a few others have posted that their MAP reads 1-3 psi lower or higher than a typical boost gauge. Also on my truck, I can run stock, or any other tune, and the MAP always reads 1 psi lower than my boost gauge, so tuning doesn't change how the MAP is read by the PCM. There are some tuners out there who have in the past fooled the PCM's reading of the MAP sensor, but for sure Jody doesn't do this (I've asked him too)....
https://www.ford-trucks.com/forums/660609-analysis-of-tenns-6637-restriction-data.html
You'll see that Tenn's AE measurements are about 4 to 8 psi less than his gauge in the upper ranges of boost from 14 to 21 psi, when he runs a DP chip.
In post #20, cleatus12r reports a similar effect when running a DP chip... "I noticed that too. Then I switched my chip to "stock" and the gauge and scanner correlated exactly. Once I switched to any tune other than "stock", the actual boost pressure immediately read 1-3 PSI higher than what the PCM saw....at light load. Once the actual boost numbers exceeded 10 PSI, the scanner displayed an even bigger discrepancy. At 25 PSI of boost with a tune other than "stock", the PCM only saw 14 PSI of boost. Switch to "stock" and the PCM sees 17 PSI at an actual 17 PSI. I emailed Jody to ask him why he does this.....I never got a response."
Originally Posted by Pocket
...Like I said before, I think it depends on your truck's PCM, since a while back there were some folks who report having set the SES for and overboost code when the MAP is reading only 22 psi of boost....
Do you have any ideas why chips either can't or don't override the Ford threshold for over boost defueling? Seems to me that's the correct approach, because pressure regulators, relief valves, Zener diodes, etc... don't act as ideal hard limiters very well.
#11
11-12-2007, 02:55 AM
Originally Posted by ernesteugene
///SNIP///
concerning why I think all the devices intended to defeat the over boost defuel at 22 psi do more harm than good, unless you're trying to win a dyno contest. The 99% of the time you're driving at BP less than 22 psi your fueling is compromised just to get a little more fuel the 1% of the time you're at a BP of more than 22 psi. There's just no way that any device can limit the voltage to 4.93 at 22 psi, and still provide the correct 4.89 volts at 21 psi!
concerning why I think all the devices intended to defeat the over boost defuel at 22 psi do more harm than good, unless you're trying to win a dyno contest. The 99% of the time you're driving at BP less than 22 psi your fueling is compromised just to get a little more fuel the 1% of the time you're at a BP of more than 22 psi. There's just no way that any device can limit the voltage to 4.93 at 22 psi, and still provide the correct 4.89 volts at 21 psi!
#12
11-12-2007, 07:44 AM
Originally Posted by Pocket
On my truck the MAP sensor reads 1 psi lower than my gauge, and I know a few others have posted that their MAP reads 1-3 psi lower or higher than a typical boost gauge. Also on my truck, I can run stock, or any other tune, and the MAP always reads 1 psi lower than my boost gauge, so tuning doesn't change how the MAP is read by the PCM. There are some tuners out there who have in the past fooled the PCM's reading of the MAP sensor, but for sure Jody doesn't do this (I've asked him too).
Originally Posted by ernesteugene
Do you have any ideas why chips either can't or don't override the Ford threshold for over boost defueling? Seems to me that's the correct approach, because pressure regulators, relief valves, Zener diodes, etc... don't act as ideal hard limiters very well.
I don't believe that Jody's programming doesn't affect the MAP readings. I personally observe the following when playing with my chip and watching the scanner AND boost gauge:
Stock setting: MAP reading corellates directly with the boost gauge and a maximum reading of 17 PSI is attainable on BOTH readouts simultaneously.
Anything other than "stock": The actual MAP reading does not even hit 1 PSI until my actual MAP (boost gauge) reaches 3.5-4 PSI. This really causes A LOT of lag in the 20T/60T/and especially the 80E because the PCM won't add fuel until it sees MAP pressure (which is REALLY late!!) 120R doesn't seem to care.
Add in the fact that I will NEVER set an overboost code. It's impossible since the pressure readings between the boost gauge and the MAP sensor readings get more "innacurate" the more boost I get. I can hit 25 PSI actual MAP in any tune other than stock. My MAP reading? Well, it's at 13.7-14 PSI.
So I took off the OBA since I'll never need it.
My MAP reading at highway speeds is 0 PSI. I cruise at 70 MPH with 2-4 PSI boost depending on headwind. So I always set an "Underboost" code and subsequent SES light when I go back to the "stock" setting after cruising with any tune for about a minute and then switching back to stock.
I would sure rather have the PCM see actual boost vs. some modified thing.
#13
11-12-2007, 08:20 AM
I don't believe that Jody's programming doesn't affect the MAP readings. I personally observe the following when playing with my chip and watching the scanner AND boost gauge:
All I'm trying to do here is learn how stuff works, and I'm seeing inconsistent reports?
During the 5 years when I had the big head, I triggered an SES light around 22 psi, but the exact value depended on some other factors as well. After 5 years of trying to tow grades and avoid the over boost light, I learned that it comes on at a lower BP in 4th, than in 3rd, so RPM and load seem to have an effect. It might also come on at a little lower BP at higher altitudes, but that difference wasn't as large as which gear I was in. There also appears to be a time constant involved. As I towed long grades I'd vary the BP with a slight increase or decrease in TP, and I could briefly go to 24 psi and return to 21 psi without setting the light. I'd have to stay above 22 psi for about 4 sec before the light would come on. If I was holding a steady 21 psi, and increased TP enough to quickly get above 24 psi, the light would come on immediately.
Do you have any ideas why chips either can't or don't override the Ford threshold for over boost defueling? Seems to me that's the correct approach, because pressure regulators, relief valves, Zener diodes, etc... don't act as ideal hard limiters very well.
That's my theory anyway.
#14
11-12-2007, 12:58 PM
Originally Posted by Pocket
And apparently with what Smokey did with his testing, his truck probably sets the overboost code at 22 psi. Or, and here's another way to look at it.... He is comparing MAP sensor voltage to gauge pressure readings. Since the MAP sensor can be off by a few psi compared to a gauge reading, then his results could be off by that same amount. So it's possible that his PCM won't set a code until the MAP reads 24 psi of boost, because MAP pressure reading and gauge pressure can both be different.
many of you have probaly read some of my other treads in my quest for a properly running truck. Unfortunalty, I am running out of $0 options.
The only thing I can think of left to check is fuel pressure. If the truck really had a fuel shortage problem, then it shouln't run better with a 'hotter tune'?
#15
11-12-2007, 01:11 PM
Originally Posted by Pocket
I don't know why yours is off with Jody's chip, you might want to ask him what would cause that. That was one thing in specific we talked about during one of his live tuning sessions here in Denver. He said that he does not fool the PCM's boost readings from the MAP sensor.
Originally Posted by Pocket
If the PCM controls fueling even in a slight part by the MAP sensor readings, then you can bet that low RPM/low boost fueling will be affected in a negative way if the PCM is seeing lower boost than it should.
Originally Posted by Pocket
That's my theory anyway.