Well to make this short.
I put the Scangauge on both trucks.
1 is a 1999 3500
and the other is a 2002 3500
The 99 Map starts reading at 14.8+
The 02 Map starts reading at 29.5+

Same city and altitude. Is one of the Map sensors bad?

This has me confused and I would like to change the correct one.

One has a flat 3 prong plug and the other has a round 3 prong plug.

THks in advnace! T

 

my 98.5 shows 14.x at idle. I think that is correct. you need to subtract the 14.7 to get the boost pressure i believe. Ed

 

just jumping on this thread

 

OK so why different readings in the 1999 and 2002 CTD engines?
Is one bad?
Some one with scangauge or knowledge should know this!
T

 

That confuses me also.My 01 shows 14.9 at idle and I was told that that was atmospheric pressure. Should it not start reading at zero? If not why does the oil pressure gauge start at zero?

 

m.A.p.---manifold ABSOLUTE pressure. atmospheric pressure at sea level is 14.7 absolute or 0 P.S.I.G.

 

OK again why 14.+ on 99 and 29.+ on a 2002 Same truck and house location or seal level? ??!!!!?

 

Both trucks run fine with no cel? 14.7 or so at idle is normal. 29 + sounds like its already seeing boost? I do remember some early trucks that started reading at 0 , but none should start at 29 !

 

Both run fine and idle fine and have plenty of power. Some others with a 99 or and 2002 should chime in!

 

What does each truck read driving down the road at WOT? Are the numbers comparable? Each should gain 30 or so psi due to boost. While I still can't imagine why it would start at 29, if it goes up to 59 at WOT, then it is reading boost correctly at least. Like i said before, I remember going thru that same scenario with a Chrysler engineer one time. Just can't remember for sure the years of the trucks. I thought one was 0 and the other was 14.7, but it could just as easily have been 14.7 and 29 ! I guess my old timers is kicking in!

 

Well no one else knows?

 

I seem to remember the calibration of the MAP sensor changed when the HO Cummins engine was introduced (2000?). There was also a change in the electrical connector so the wrong MAP sensor could not be substituted between engines. This caused all kinds of problems for companies like Edge when people bought used boxes and could not connect them.

My 98.5 SO engine MAP puts out a signal that is proportional to gauge pressure (0.5 volts at 0 psi gauge or 14.7 psi absolute) and The HO engine MAP puts out a signal proportional to absolute pressure (0.5 volts at 0 psi absolute). This might explain the 14.7 psi difference between the two readings on your Scangauge but it does not explain why it reads the wrong absolute pressure for ‘02 unless the Scangauge was calibrated to read absolute pressure with the old MAP. So the real problem is in your obsolete equipment and now Cummins can sell more MAP sensors for dealers to put on their shelves.

 

My truck, an 02, reads around 25 at idle or shut off. I am guessing that is 25 inHg, which is darn close to atmospheric pressure at 4000 feet.

Possibly, the older truck reads out in psia and on the newer truck reads out in inHg? I think inHg is a more common pressure unit for MAP, especially for aircraft.

FWIW 14.7 psia is roughly 30 InHg.

Jim

 

While that all makes sense, most scanners do not change the units they are reading from one vehicle to another. PSI=PSI, and "HG = "HG. While I am not 100% familiar with the scanguage, I can't see why it would be any different.

 

checked my 02 with my scanguage this morning. 29.5 at idle.