What should MAP sensor read with scanner? - JeepForum.com
LinkBack Thread Tools
post #1 of 3 Old 06-04-2010, 12:35 PM Thread Starter
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  
Sponsored Links
post #2 of 3 Old 06-04-2010, 02:49 PM
Registered User
rm2001wj's Avatar
2001 WJ 
Join Date: Aug 2005
Location: Memphis, TN
Posts: 3,252
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.
rm2001wj is offline  
post #3 of 3 Old 06-04-2010, 02:52 PM Thread Starter
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  

Quick Reply

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:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.

Email Address:


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.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Similar Threads
Thread Thread Starter Jeep Forums Replies Last Post
Do you have this ABS scanner ? SIU ZJ Grand Cherokee Forum 0 08-16-2009 12:49 PM
How can I read codes without using a scanner. Bekim ZJ Grand Cherokee Forum 3 07-15-2009 07:01 PM
What scanner sys can be used in 93 ZJ. Hamid ZJ Grand Cherokee Forum 3 07-04-2009 06:04 PM
DRB scanner neilo123 ZJ Grand Cherokee Forum 2 06-06-2009 06:49 PM
Code read: PO720, Low Output Spd Sensor RPM Above 15 MPH ats1968 ZJ Grand Cherokee Forum 0 08-30-2005 09:33 AM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome