MAP sensor voltage

[rubberneck]

ok got a question for all the cummins techs out there, or anyone in general who has played around with a scanner on our trucks. Put the Snap On scanner on my truck this evening to clear some codes and what not. i noticed that at idle. the voltage is 1. 1. Here is the wierd thing, according to the scanner, that is 15 psi of boost. when driving, i saw as high as 2. 4 volts, and 34 psi, but why in the heck is the thing not setting overboost codes, and defueling?? It was strange, because the boost reading on the scanner and on my boost gauge were proportionally 15 psi off (ie my boost gauge said 0, scanner 15, my gauge 5 scanner 20 etc etc. ) all the way up to my gauge showing 19 psi, scanner showing 34, then the scanner quit increasing, even though i ran the boost all the way up to 39 psi on my spa. i assume this is due to the boost module in the ez doing its job. so is it just the values are off on my scanner or what??, i am assuming this is the case, as i even unhooked the ez thinking this may have something to do with it, results same. (didn't drive it to see if values kept going above max) Hoping to hear from some of the guys with a snap on scanner to see if you have had similar results. thanks

 

[Snow man]

Remember the Edge EZ is fooling the computer into think you have some boost already,when you dont,to give you the low speed fuel quicker,if you move the jumper in the EZ,I bet you could watch the boost at idle change to a lower number. I wonder if the boost is read in other measurements,other than PSI,or the reading is double the actual boost,making 39 on the scanner,actually 19. 5 lbs of boost,as read by the scanner,after the ez has intercepted the true reading,and dropped it (clipped it)to one that wont exceed stock specs. I wish my scanner was updated to read my 2000,I cant affor the upgrade now.

 

[rubberneck]

nope, i completely took off the ez box, and the reading is the same. i actually thought the same thing. was thinking that perhaps that is the way they get the earlier fueling is to make the truck "think" there is boost present. but, with the map plug and the data link of the ez unhooked, still same

 

[KLockliear]

The scanners read the sensor in absolute values. 14. 7psi would equate to standard air pressure at or around sea level. 15psi would be about right for ambient. We typically see 13-14 in Vegas at 2100' elevation.

 

[rubberneck]

duh

keith thanks, after thinking about it, that makes total sense. by the way, have you guys had any experience with trucks having a shudder between 16-1900 rpm at moderate throttle?? not there at light or full throttle, and mostly when towing. that is why i was scanning truck to begin with, hoping to see some parameters out of wack to give me an idea of what is going on. have fuel press gauge, and that is good, problem is less pronounced with ez unplugged, but not gone

 

[Brandon]

duh on me too phil... ... .....

 

[Diese1nut]

Bucking

Rubberneck

You are not alone. There is a lot of us with this same problem, and so far no solution.

This is very frustrating.

Look at the Hesitation thread.

 

[GDouglas]

There could be a couple of posibilities for the shudder that you describe, especially when using above stock HP and/or towing a load.



1. It may be the torque converter clutch slipping under increased strain.



2. It could also be the driveshaft center bearing isolation rubber with some free play in it.



Both of the above possibilities may not be present when at the stock power levels or no load and show their ugly faces with more power/load.



Hope this helps.