What should MAP sensor read with scanner? - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep Grand Cherokee & Commander Forums > ZJ Grand Cherokee Forum > What should MAP sensor read with scanner?

Rampage Bowless Soft Top Oconee offroadAlloy USA Still AvailableAdvance Adapters SYE Kits

Reply
Unread 06-04-2010, 11:35 AM   #1
toyotapilot
Registered User
1997 ZJ 
 
Join Date: Oct 2009
Location: houston
Posts: 12
What should MAP sensor read with scanner?

I have been attempting to diagnose my '97 Jeep Grand Cherokee and find out why I am getting the random misfires and sometimes cyl 1, 4 or 6 misfire. The Jeep doesn't seem to be running bad, just the codes. And according to my scanner they always occur at 1,856 RPM, usually at 63 mph.

What should the range on the MAP sensor be with the scanner? For the last four codes the reading has been 44, 35, 46 and 47 kph. With the ignition on but the engine not running with the scanner connected the reading is 99 kph. With the engine running in park the number sits in the high 30's and drops when I increase the RPM's. Elsewhere on the web I have seen that the number should increase as the RPM increases.

What should the numbers be for the MAP with the scanner? Just trying to do some diagnostics before I take it to a shop. It just seems a little strange that the code always appears at the same RPM (1,856 rpm).

So far I have replaced plugs, wires, cap, rotor, then an OEM distributor assembly (distributor, cap, rotor, cam sensor) due to a worn bushing. The injectors are new, and the coil has been checked. The engine was a new engine installed about 10,000 miles ago.

toyotapilot is offline   Reply With Quote Quick reply to this message
Unread 06-04-2010, 01:49 PM   #2
rm2001wj
Web Wheeler
 
rm2001wj's Avatar
2001 WJ 
 
Join Date: Aug 2005
Location: Memphis, TN
Posts: 3,104
Sea level air pressure is close to 100 kPa and that's what your 99 (kph?) with engine off is indicating. That is also equivalent to 29.9 in Hg and 14.7 psi. Anything less than that is usually referred to as a vacuum. To calculate manifold vacuum, subtract MAP sensor reading (in kPa) from 100. With a MAP of high 30s, the vacuum is in low 60s at idle. That vacuum would be about 18.5 inches which is about what it should be at idle.

When driving, the MAP reading will correspond fairly closely to the load being placed on the engine. When accelerating hard, accelerator pedal on the floor, the MAP sensor reading will go up close to 100, corresponding to a manifold vacuum close to zero. If you are moving at a moderate speed and get off the accelerator pedal (load on the engine gets smaller than when idling), and the MAP reading goes down to the low 30s and even the 20s). As the vehicle speed increases, there will generally be a greater engine load, and that will produce higher MAP readings.

But, you can't really predict exactly what the MAP readings should be in various phases of driving of a particular vehicle; you have to measure it. However, using your readings, I would say that the MAP sensor is not the cause of your misfires.
__________________
2001 WJ Limited with Quadra-Drive, Kenne Bell Supercharger, 3-inch Kolak exhaust, Stillen rotors (F/R) and MM pads, Addco sway bars (F/R).
rm2001wj is offline   Reply With Quote Quick reply to this message
Unread 06-04-2010, 01:52 PM   #3
toyotapilot
Registered User
1997 ZJ 
 
Join Date: Oct 2009
Location: houston
Posts: 12
Thanks for the information! I understand a little bit better now....
toyotapilot is offline   Reply With Quote Quick reply to this message
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.
Note: All free e-mails have been banned due to mis-use. (Yahoo, Gmail, Hotmail, etc.)
Don't have a non-free e-mail address? Click here for a solution: Manual Account Creation
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.


Thread Tools


Suggested Threads





Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.