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Discussion Starter · #1 ·
Hi Everyone. I have a question about boost. I have installed a boost gauge into where the AIH would be. I also have a ScanGauge II reading off of the OBD 2 port. If I set up the ScanGauge and go for a drive the boost numbers are never the same as what the gauge says. For example, If I run the truck hard the numbers are almost 10 psi or better off. The standard gauge tells me Im at 20 psi but the truck is only reading about 8-10. Could the MAP sensor be going bad? or what should I be looking for?
The only reason im asking is because my fuel mileage is way down (like 5mpg). Its been this way since I installed the chip to run the new injectors. I used to get 18-20 and now its 13-16. I would like to get it back to the way it was.

The truck is an 2002 F-350 Auto. 160/30 injectors. Custom intake and exhaust. TS chip by Tony W (daily, econo, towing, 100hp, 120hp). Riffraff boost fooler. Band new HPOP.

Thanks, Steve.
 

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First - how are you measuring boost on the ScanGauge? Are you reading MAP and subtracting atmospheric, or did you XGauge boost for a known atmospheric?

You've got a boost fooler onboard? That may be part of the issue - I would suggest plumbing around that for a test. Why do you have the boost fooler anyway - doesn't Tony's programs eliminate the need for that? DP-Tuner tunes don't need a fooler to perform correctly.
 

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your max is 20 psi? you should be 30 psi atleast. I read 30+ psi on stock injectors

the boost fooler will protect the map from high boost pressures.

what is your Duty cycle and HPOP pressure?

any obvious boost leaks at the up pipes? torn CAC boots?
 

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I would first check to make sure your boost fooler is adjusted properly. If it is only set at 10psi, that is all the MAP sensor will see, regardless of what actual boost is. You ideally want to set it at about 23psi. That should give you full fueling without popping an overboost code.

With those injectors, you want to be able to hit around 35psi during hard throttle. Otherwise you will likely have smoke and EGT issues.
 

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Discussion Starter · #5 · (Edited)
For the scangauge I set up the XGauge function on it. The 20psi and 10 psi were just numbers to show everyone that when the truck is actually at 20 psi the computer is only reading 10. The truck will boost up to 30 where I let off since its a stock turbo (just my preference).

The boost fooler I got for free from riffraff in a give away so I threw it on the truck (shouldn't hurt, right?). I don't know if tony's tunes won't throw the code or not. But I can plumb around it for testing.

Boots are new and there are no obvious leaks anywhere. Rem this all started after installing the 160/30 injectors and the re-tuned chip to run them. before that on bad stock injectors I was still getting 18 mpg and the correct boost on both the scangauge and boost gauge.

Duty cycle seems normal. 38-40 with ICP holding 2800-2900 WOT.

The fooler is non adjustable but the MAP will show more than 10 (this was just a number to show the difference I am seeing in the gauges).

Exhaust temp and smoke seem normal. Maybe 1200 under a long pull. Mostly 1000-1100 normal and turned all the way up on 120 setting. Smoke really doesn't occur unless I bog the truck down and roll into it.

I am just wondering that if the truck isn't seeing the correct boost and not fueling correctly and that's why my mileage is so far down. Or if the MAP sensor is bad.

Thanks for everyones input so far.
 

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Just want to clarify. Did you set up the Boost XGauge and if so what value did you use for atmospheric? That's a calculated value. If you are watching MAP on the scangauge, that will always be about 14 points off what you see on the boost gauge.
 

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Discussion Starter · #7 · (Edited)
No problem.
And yes. On the Scangauge website you can get the XGauge codes for a 7.3. I went to the Boost table they give for the Key on engine off boost value. If I remember correctly I ended up using either 11.1 or 11.2 for my value I needed to enter into the scangauge.
Before the injectors and re-programed chip the scangauge and boost gauge had the same reading for boost. But after the values are different (as in at idle they both read 0 but as I accelerate the boost gauge goes up a lot faster than the scangauge. That's why im asking about the poor fuel mileage im getting and this being the cause.

thanks, steve

Edit: I will double check everything after work and make sure of the numbers I used.
 

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Good idea. I've dropped a zero more than once programming those X gauges. Where are you with an atmospheric pressure in the 11's? Pike's Peak?
 

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Discussion Starter · #9 ·
LOL. No. Im in southern PA. When I went through the directions and when I put the XXXX value in and then turn the key on that what I got. Going with the 11. something as the "offset value". I will double check though.
 

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Well that's your first clue something is wrong with your MAP sensor. Atmospheric at sea level should be 14.7. Your values would be normal for 7-8,000 feet above sea level.
 

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Discussion Starter · #11 ·
The only way I could check for sure is display the Boost and also EBP on the scangauge and watch the values.
If so. I can grab a MAP sensor on my way home (don't thing they are too expensive).
 

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I think that would be worth doing. The only other possible issue is the atmospheric pressure sensor which is integral to the PCM.
 

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In the PCM itself is an integrated atmospheric pressure sensor which the PCM uses to tell itself what altitude it's at.
 

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Discussion Starter · #16 ·
This does make sense though. If the MAP sensor is good and also the scangauge. Which I will check on my drive home.

I did some reading on the sensor and its actually the Barometric Pressure Sensor. Has to do with fueling. It give the computer a baseline to actually know what boost the motor is making.

I have noticed the truck "short shifting" second gear. Basically in any program the truck shifts to second but doesn't hold power, if that makes sense. When it shifts I lose all boost and it bogs down till it powers though and gets the boost up again (now im talking like dropping from 10-12 psi to 2-3 and then having to build it up again after the shift). The more you get on it the more noticeable it becomes. Maybe its the program itself and totally unrelated but hey, that's why im here to ask questions and learn.
 

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Discussion Starter · #17 ·
Ok. Ran the tests. I used boost on both the scangauge and also the boost gauge. And compared the 2 with the EBP readout also on the scangauge. The boost gauge stayed at almost a constant 14.7 difference from the EBP. But the boost on the scangauge was always a lot lower. So where should I go from here? New MAP sensor?
 

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Why are you comparing it to the EBP sensor? You can read MAP directly. That's what you need to read with KOEO to get the atmospheric value to use for determining which boost correction to use. Did you verify your XGauge programming?
 

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Discussion Starter · #19 ·
I did not verify KOEO on the xgauge. I can do that when I get back to the house.

I was comparing the EBP to boost because that is a known 14.7 difference. Just to verify that the EBP and boost gauge were reading the same.
 

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But what you want is for the boost gauge and the MAP sensor to be the same. EBP is usually 2-3 points higher.
 
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