I have worked on a few vehicles before and I had a mil light come on on my truck. I hooked my code reader up to my truck, only to find out that it was a bad purge flow problem.

While i had the comp hooked up I also ran the data stream on the truck. When I looked at the MAP readout, I was kinda confused.
It read: IDLE: 6-9 (Bounced around) at SIXTY mph under load : 28

I thought that the in per mercurey is higher at idle than at 60 under speed.

Did Dodge do something different or has the MAP sensor gone nuts?
Also if any of you know what the readings should be, Id like to know that to.
Thanks

 

i can't remember right off the top of my head what the readings are i'd get the purge solenoid fixed first and if there is nocode for map sensor its fine

 

Im not worried about the purge flow, I have just never seen the readout for the map act that way. Every other vehicle I have worked on the numbers are higher at idle, and the numbers are lower when the engine is under load
Am I incorrect or did Dodge try something different?

 

MAP is lowest at idle (same as 'high vacuum')

MAP is highest at wide open throttle (low vaccum)

28 inches of Mercury is nearly full air pressure
so that sounds a bit too high for highway cruise at 60 mph.

On a stock 1995 Magnum 5.9V8 at wide open throttle and 4000 rpm
the MAP sensor reads about 1.5 to 1.8 inches of Mercury lower
than the air pressure that day from a weatherman's barometer.

This is the 'restriction' of the combination of
throttle body, air filter, air box, plastic tube over to the fender, minus any 'ram air effect from how fast the vehicle is going.

do a search on my name and 'KN Drop In Filter'
to find an old post with info on the inches mercury drop at WOT.

Here's an old post with more MAP sensor info:
=======
On a trip from Durham NC to Knoxville TN on Saturday 5-13-00
I decided to take a side trip up Mount Mitchell,
the highest mountain east of the Mississippi (6824 ft).

My truck is a 1995 club cab 2wd with the 5.9V8.

Here's what I found on the MAP sensor readings:

The Ram was cold and had sat overnight in Durham when I hooked up the ScanTool
and did a key-on but engine off MAP reading: 29.4 inches Hg/ 4.53 volts. My
cheap pocket hiker's altimeter also said that the reading should be 29.4.
Battery temp sensor read 73F.

With engine on, at idle the MAP read 11.7 inches Hg/1.55 volts.

I drove 10 miles to a gas station and filled up with Amoco 87 octane.
The coolant temp had come up to the 195 degree level.
With the key-on but engine-off at the gas station the MAP was still 29.4/4.53
volts. I was glad to see this as I was concerned that maybe underhood
temperature affects the MAP reading. Apparently it does not much.

I did a full throttle entry onto I40 East.
The initial MAP reading was 28.1 inches Hg but began to drop to about 27.9 as
the rpms got close to 4500 rpm.

I guess this means that the combination of the Dodge-Dealer-sold KN air
cleaner element in the stock air cleaner hose system, and the fully opened
butterflys of the stock throttle body restricts the airflow at full throttle
by about 1.5 inches of Hg, or about 0.8 psi.

At Morganton NC I stopped again for 87 octane Amoco gas. The pocket altimeter
showed an altitude of 975 feet. The key-on engine-off MAP reading was 28.8/
4.41volts. I checked my mpg and had gone 174.5 miles on 8.08 gallons for 21.6
at a mostly cruise controled 70 mph. That is one of the best mpg I have ever
gotten at 70.

I took the turn-off at Marion NC and drove up the mountain. Ram seemed to
handle the climb fine. Overlook views and the look of the spring trees made me
glad i took this side trip.

At the Mt Mitchell parking lot the sign says 6578 feet. My pocket altimeter
read 6625 feet. The official looking big brass barometer at the ranger
station next to the parking lot read 23.41 inches Hg. The key-on engine off
reading of my Ram's MAP read 23.8/3.57 volts.

On top of the mountain the temperature was now about 50 degrees and the wind
was gusting to 30-40 mph. Clouds would blow in and fog the place in for 3-4
minutes then turn to a slightly hazy clear view.

I reset my pocket altimeter to read 23.41 at 6575 feet and headed down the
mountain.

At an overlook the sign read 5200 elevation and the key-on engine-off MAP
reading was 24.9/3.76 volts. Altimeter read 24.5.

3926 feet overlook sign. MAP 26.2/3.96volts. Altimeter 25.65

3107 feet MAP 26.9/4.08volts Altimeter 26.3

2000 feet/27.5 inches Hg on Pocket Altimeter at road junction at Asheville:
Ram's MAP 27.7/4.24 volts.

What I got out of this side trip was that my MAP sensor seems to read slightly
high: approximately 23.8 divided by 23.41 times 100% = 1.7%
I would guess that this means that the computer sets the mixture 1.7% rich at
full throttle.

For what it is worth, with this MAP sensor my Ram will ping slightly (sounds
like one cylinder) from 3800-4200 rpm at full throttle on 87 octane gas. To
hear the ping I need to roll the windows up and turn off the radio. On 89
octane gas the ping almost completely goes away, and with 93 octane there is
no hearable ping. I presently have a 205 Stant 'standard grade' thermostat
installed but the coolant temp on the ScanTool almost always reads 195F, so I
guess the thermostat wasn't made right. I also have Bosch Platinum+4
sparkplugs and they do seem to ping a bit more than old style single Bosch
Platinum sparkplugs FR7DPX.

I hope these reading may help someone else investigating their Ram's MAP
sensor.

-HankL

 

dang hankl your fingers tired (lol)

 

hmm it sounds like i need to get a new sensor. mine reads completly oppisite of it, but it might be the scanner im using, it might be readding something else.
at idle it reads around 6-9 and that should be what it reads under a load. I got a print out of how to check the sensor to see if its bad or not. Havent got around to checking it yet, but I will