It controls the voltage by controlling the pressure which in turn controls the voltage, and my point is that a mechanical pressure regulator can't control the pressure precisely enough to control the voltage to a 0.8% accuracy! If the regulator limits the voltage to 4.93 volts to avoid an over boost light at 22 psi, then it will also cause the voltage to be considerably less than the correct value of 4.89 volts at 21 psi! This means that with your OBA installed you're getting a little LESS fuel at 21 psi than you'd be getting without the OBA installed!

Click this link....
https://www.ford-trucks.com/forums/638960-bye-overboost-annihilator-hello-diode-wire.html?highlight=zener+diode

and read my discussion on how all types of limiters work, or in this case don't work very well! An ideal limiter would let the exact input pressure through for all input pressures less than 22 psi, and then limit the output to 22 psi for all inputs above this level.

Real world limiters, like your OBA, start limiting the output some before the input reaches 22 psi. For example, for a 21 psi input your OBA might only give a 20.5 psi output! Therefore when you've got 21 psi BP in your manifold, the PCM is only seeing 20.5 psi, and its putting out a little less fuel because of that!

Consider that 0.5 psi out of 22 psi is only 2%, and I doubt the OBA can set a spring loaded regulator valve that accurately, so the effect is probably much worse than in this example. To be fully closed at 22 psi, the spring loaded valve has to start closing well before the input gets to 22 psi, and it's this partially closing that starts reducing the output pressure to a value below the input.

Since you don't want the extra fuel above 22 psi anyway, you're better off ditching the OBA and putting up with an occasional momentary SES light, and not having whatever fueling compromises are caused by the OBA in the say 18 to 22 psi range.

 

Uhmmmm, you assume that the stock MAP sensor is spot on too. How do you suppose it reads boost? Mechanically converted to electronics perhaps? This can account for a lot of the discrepencies we see. I may need to remove my OBA and datalog to see what is going on in different settings. BTW, how do you account for my readings in the stock tune which is still a chip tune with the OBA connected? I think we may be falling victim to sampling rates on the AE but I will have to confirm that.

As for the "fueling compromises between 18-22", if I feel that is an issue, then I will crank up the OBA beyond the SES threshold to keep the fueling going rather than start defueling too early. I didn't buy all this crap to run around in a stock fueling situation.

I guess what I am saying is that I may need to crank up my OBA to the point I get an SES and then check the readings and performance. With a chip, does the SES for boost mean defueling? Do we know?

....and finally, I have not noticed performance fall off when I go beyond 24psi, well beyond. How do you account for that?

 

As far as I know there is no difference in fueling if the PCM sees 18 psi of boost or 22 psi of boost. From what I've been told, the PCM see's "max boost" somewhere in the range of 14-16 psi (never got confirmation on exactly what psi is considered the max boost level, but it's in that 14-16 psi range). Once you reach that threshold, you will max out your fueling at that boost level. Anything higher makes no difference. Of course there are other fueling tables that all play a part in this, so the MAP readings are only one of many factors contributing to your ability to deliver all your fuel.

I only know this because I had posted a while back about fueling and the MAP sensor readings back when I found that my OBA was mis-adjusted and causing the MAP to read only 13 psi of boost.

So out of all this from a fueling standpoint, there are only two thresholds to be concerned with. The first is the boost level that allows max fuel, the second is the boost level that causes an overboost condition and results in a defuel.

 

I'm assuming you've already checked for the usual boost and exhaust leaks.

What are your EGT's like when you are at WOT? EGT's play a big factor as to whether or not you are actually getting fuel, air, or neither.

 

Good info there Curtis. Thanks.
Mike

 

To avoid whatever negative effects the OBA might have in the 18 to 22 psi range, hook the OBA input to a fitting on the turbo outlet. Now in the BP range of 18 to 22 psi, the OBA input see's a pressure that's about 2 psi higher than the BP in the intake manifold due to the drop in the IC. Now the MAP sensor output to the PCM will be 22 psi for BP's down to about 20 psi, and the PCM should then command a little more fuel in this range of BP.

 

What negative effects? I haven't seen any yet? I am talking about giddyup and go not some stupid reading.

 

Go to the 99-03 psd forum and click on start a new topic. Post it there. Won't find it within a thread but it is there in the threads list. Lots of things it can be. Post year of truck along with tranny etc. Probably need to scan for codes.

 

The MAP sensor isn't intended to be a limiter, only a gauge which has a maximum upper range. It doesn't have a spring loaded shut off valve like an OBA, that's trying to control an output vs an input. I don't think the differences between the AE and boost gauge has anything to do with the OBA, because your data shows differences in the 14 to 21 BP range. Then follow the advice I gave above, which is what I posted over 6 months ago after Smokin when I noticed several trucks including Jody's plumbed that way.

 

How can I make this any simpler? I have a gauge/map sensor/AE reading discrepancy. No performance issues. Any questions? Why would I move anything? Because you theorize I should?

PS. Don't get ill with me Gene, I have to fill in untll Izzy gets back. Nevertheless, you have provided nothing to compell me to change anything. You have however, provided me the motivation to look at that again though, 4 days from now as the grind begins in the AM. Remember that? I know, spare me, but I've been doing it 26 years and counting.

 

But why won't a 3rd party programmer edit these lines in the Ford code so that, for example, instead of saying "when the BP reaches 22 psi, set the SES light and defuel" to read "when the BP reaches 30 psi, set the SES light and defuel" ? That's the question I asked to several chip programmers, and I reported those answers in my quote in post #7 on this thread.

 

I honestly believe it is because they can't for whatever reason Gene. Probably the same reason we cannot reverse engineer windows version whatever without bigtime problems. Proprietary stuff maybe. I bet if they could they would, I would.

 

BTW, I finally replaced my dvd drive with an old unit IOT look this up. At 10 psi the reading should be 2.8 volts ± 0.3 volts. FYI. I see he posted 3.38. I doubt this is enough to write home about.

 

Ditto. There are a lot of limitations when it comes to tuning and the PCM. But on the bright side, Jody is still learning new ways to crack that nut.....

 

Well this isn't my theory, I saw several trucks at Smokin plumbed that way, and when I was in Asheville I noticed Jody had his OBA connected to a fitting on his turbo. As I reported over 6 months ago, Jody said that when he moved the input to his OBA from the intake manifold to the turbo outlet, that he could feel a "definite SOP increase in throttle response and off the line acceleration".