Problem with MAP on Gen 7 DFI

[John Morgan]

Hi Everyone,

I am new to this board but have been looking at it for a while and the TurboBuick web site come very highly recommended. I have a Mustang but have seen that everyone here gives good advice no mater what kind of car you are drivng.

My problem is that I have just finished installing a Gen 7 system ( with the WBO2 and currently running it in bank to bank mode) and the MAP sensor is giving me trouble. I am using the 1-bar MAP with my supercharger not hooked up for now while I break the car in and learn the Gen 7. At idle my MAP sensor is reading 3" of vacuum while my boost gauge is showing 10" of vacuum. I checked for vacuum leaks and found none.

I have tried replacing the MAP with another new 1-bar MAP and the same 3" numbers came up while the boost gauge still showed 10" so I dont think the problem is a bad MAP sensor. I tried using a different vacuum source, and the line to the MAP is a dedicated line off of the intake with nothing else teed into it, but that made no difference either. I get no error codes from the Gen 7 so everything appears to be working ok with the ECM.

Does anyone think I could be getting feedback from another system on the car that may be interfering with my MAP readings? The car is running ok but I cant really start trying to tune it until I get an accurate MAP reading. Any help or suggestions would be very much appreciated.

Thanks, John

 

[Trbobuick]

first, how much boost is this engine going to see?
if its over 12 psi i would consider a 2 bar map.

second, more importantly, when the car is on boost is your gage and map sensor reading the same or still 3 pounds diff?

third, is it rubber hose to the map sensor?

if all else fails, call my buddy mike at DFI 248-380-2780

 

[Craig Smith]

Look in the software. Do you have it set for a 1-bar sensor? It sounds like it's set for a 2 or 3 bar sensor.

Even while you are learning I would get the right MAP sensor. That way you can have a good tuneup when you are done. I personally don't think you are at any "beginners" advantage by using the wrong sensor for the application.

Good luck. Hope this helps.

 

[John Morgan]

I dont have the blower hooked up yet but when I do I will be running 20lbs of boost. I do have a 3-bar MAP sensor as well that will be going on the car when the rings have seated and the motor is broken in.

The MAP and boost gauge ( vacuum gauge ) read different amounts of vacuum. I havent had it in the boost range yet. They are about 7 inches off from one another ( gauge reads 10" while the MAP reads 3").

I do have the settings in the DFI setup set to 1-bar KPA. I could put the 3-bar on it but the 1-bar gives me so much more adjustability for now that i wanted to learn with it.

Any other suggestions?

Thanks again I do appreciate all help, John

 

[Craig Smith]

OK, I understand now why you don't have the 3 bar MAP in. I assumed (always a bad idea ) that the blower was hooked up.

If you have already tried a different MAP sensor, I would next try a different gauge. Connect the MAP sensor where the gauge is and vice versa. See if that makes any difference, many times it will. Also make sure that the connection to the MAP sensor isn't restricted somehow.

Does the TPS seem to work properly? I will once again ASSume that the DFI works like the FAST in that the 5V signal for the MAP and TPS is shared. A MAP sensor related problem sometimes triggers a problem with the TPS.

Through a simple process of elimination you should soon know what's ailing you. I would have to add that a problem with a MAP sensor input on a computer is rare at best.

Good luck and enjoy the weekend!

 

[ChrisCairns]

Originally posted by John Morgan
Hi Everyone,

At idle my MAP sensor is reading 3" of vacuum while my boost gauge is showing 10" of vacuum.
Thanks, John

Mine is similar. It was explained to me that the gauge is measuring psig (not inches of vacuum)....and the MAP sensor is psia...(absolute).

I believe there is a conversion formula....but ya need someone smarter than me to recite it.

 

[Taffy]

After thinking about it a little, Chris has the right line of thinking, but not quite correct. 30" HG is 0 PSIA, so 10" HG is 10 PSIA (2" HG is 1 PSIA). Something is wrong (obviously). ERIC.

 

[John Morgan]

I never noticed that the boost gauge and the Gen 7's monitoring tables looked at the vacuum numbers in different ways. Now that that was pointed out it makes total sense.

My Gen 7 does messure the MAP in PSIa while my boost gauge is a Auto Meter and messures in In.Hg. I guess that both the gauges are correct then and I am worrying about demons that dont exist.

Thanks to everyone who helped me with this. I really appreciate it and im sure I will need your help again. This is a fun but steep learning curve...................John


P.S. If anyone has a DFI setup that is close to my car I would really love to get a look at your program.

My cars basic stats are...
340ci SB Ford ( 331 .080 overbore )
9:1 compression
TEA Twisted Wedge heads 2.04/1.60 valves 327 intake 229 exhaust at .550 lift
Cam is a Crane Hydro Roller .574/.595 236*/244* 114*
TFS R-Series manifold 80mm TB
83lb injectors

Thanks again everyone.

 

[ijames]

Originally posted by Taffy
After thinking about it a little, Chris has the right line of thinking, but not quite correct. 30" HG is 0 PSIA, so 10" HG is 10 PSIA (2" HG is 1 PSIA). Something is wrong (obviously). ERIC.

30" Hg is 0 psia is -15 psig, 20" Hg is 5 psia is -10 psig, 10" Hg is 10 psia is -5 psig, and 0" Hg is 15 psia is 0 psig (approximately; don't quibble about the last 5% ). Think of inches of Hg as a vacuum scale while psia and psig are pressure scales so they go up as the pressure rises while inches Hg goes down as the pressure rises.