Cherokee is Misfiring and "hiccuping" - 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 Cherokee & Comanche Forums > XJ Cherokee Technical Forum > Cherokee is Misfiring and "hiccuping"

Savvy Billet LED Tail LightsLight up the holidays with LED lights from JeepHutIntroducing MONSTALINER™ UV Permanent DIY Roll On Bed Line

Reply
Unread 05-03-2013, 05:52 PM   #1
cavalier
Registered User
 
Join Date: Jun 2010
Location: Va
Posts: 160
Cherokee is Misfiring and "hiccuping"

It runs fine until it gets a little warm, then it starts misfiring. I can still drive it, it just "hiccups" every once in a while, especially while going up hills.

I recently changed the plugs, wires, cap, and rotor. I'm not sure what's going on. When I rev my engine and let off the gas, the revs drop too low and it almost starts to choke, but then it bumps back up.

Would a ****ty (airtex) fuel pump cause a misfire? Maybe a clogged injector? Maybe a sensor? HELP!

There's no check engine light. 1992 XJ with 228,000 on the 4.0.

cavalier is offline   Reply With Quote Quick reply to this message
Unread 05-03-2013, 06:03 PM   #2
tjwalker
It's the crank sensor!
 
tjwalker's Avatar
1999 XJ Cherokee 
 
Join Date: Nov 2007
Location: Central Minnesota, MN
Posts: 8,516
Checking fuel pressure is easy. Fuel pressure gauges can be rented inexpensively from many parts stores. Testing is the only way to confirm a fuel delivery issue.
__________________
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
tjwalker is offline   Reply With Quote Quick reply to this message
Unread 05-03-2013, 07:01 PM   #3
cavalier
Registered User
 
Join Date: Jun 2010
Location: Va
Posts: 160
Hmm. Would a bad ignition coil cause a misfire?
cavalier is offline   Reply With Quote Quick reply to this message
Unread 05-03-2013, 07:54 PM   #4
79chiefs
Registered User
1988 XJ Cherokee 
 
Join Date: Dec 2012
Location: Lillington, NC
Posts: 988
Quote:
Originally Posted by cavalier View Post
Hmm. Would a bad ignition coil cause a misfire?
Yes, test the spark.
It should be blue, and snapping spark.
__________________
99WJ Laredo I6-A 2wd
88XJ-Building on a budget.
95 E34 540i-DD
79chiefs is offline   Reply With Quote Quick reply to this message
Unread 05-04-2013, 10:17 AM   #5
cavalier
Registered User
 
Join Date: Jun 2010
Location: Va
Posts: 160
So I just did a fuel pressure test. Here's what I got:

Key in "start" position: 36 psi but gradually goes down as I let it sit
Vehicle idling: 32 psi
Giving it gas: goes up for a second, then stays around 32 psi
Disconnect vacuum line to pressure regulator: goes up to about 42

Thoughts?

Now, I do notice that my exhaust is leaking at the manifold gasket. Bubbles of oil are popping in that area (spilled oil, that is). I'm wondering if an exhaust problem would cause a misfire (like a clogged cat). I haven't noticed any loss in power, just a misfire.
cavalier is offline   Reply With Quote Quick reply to this message
Unread 05-04-2013, 10:47 AM   #6
cavalier
Registered User
 
Join Date: Jun 2010
Location: Va
Posts: 160
OH MAN! I just pulled my plugs. THEY ARE FRIED! Check out this pic:

They are only 1 month old!

What's going on?
jeepplug.jpg  
cavalier is offline   Reply With Quote Quick reply to this message
Unread 05-04-2013, 11:54 AM   #7
tjwalker
It's the crank sensor!
 
tjwalker's Avatar
1999 XJ Cherokee 
 
Join Date: Nov 2007
Location: Central Minnesota, MN
Posts: 8,516
Do all of your plugs look like that?

That looks like ash deposits. Excessive amounts can cause misfires.

*Have you been using any gas or oil additives? Additives can sometimes cause ash deposits.
*What type of oil are you using and how often are you changing it?
*Otherwise, it's an internal problem, possibly head related.
__________________
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
tjwalker is offline   Reply With Quote Quick reply to this message
Unread 05-04-2013, 11:56 AM   #8
cavalier
Registered User
 
Join Date: Jun 2010
Location: Va
Posts: 160
Quote:
Originally Posted by tjwalker View Post
Do all of your plugs look like that? How many miles on them?
At least two of them look like this. I'll pull the rest, but I think they do all look like that. About 800 miles on them.
cavalier is offline   Reply With Quote Quick reply to this message
Unread 05-04-2013, 12:37 PM   #9
cavalier
Registered User
 
Join Date: Jun 2010
Location: Va
Posts: 160
So I thought: maybe it's running rich? I pulled the coil and got 1.3 ohms for primary circuit and 12.47 Kohms for secondary. Seems fine to me...
cavalier is offline   Reply With Quote Quick reply to this message
Unread 05-04-2013, 12:57 PM   #10
79chiefs
Registered User
1988 XJ Cherokee 
 
Join Date: Dec 2012
Location: Lillington, NC
Posts: 988
Your fuel pressure is low, and how fast does it drop?
Sounds like bad regulator.
__________________
99WJ Laredo I6-A 2wd
88XJ-Building on a budget.
95 E34 540i-DD
79chiefs is offline   Reply With Quote Quick reply to this message
Unread 05-04-2013, 01:01 PM   #11
cavalier
Registered User
 
Join Date: Jun 2010
Location: Va
Posts: 160
Quote:
Originally Posted by 79chiefs View Post
Your fuel pressure is low, and how fast does it drop?
Sounds like bad regulator.
It won't drop while I'm running it. At idle, it stays at 32 psi no matter how much gas I give it. Just when I first put the key to "start" and wait a while. It drops about a psi every 20 seconds.
cavalier is offline   Reply With Quote Quick reply to this message
Unread 05-04-2013, 01:17 PM   #12
cavalier
Registered User
 
Join Date: Jun 2010
Location: Va
Posts: 160
Quote:
Originally Posted by tjwalker View Post
Do all of your plugs look like that?

That looks like ash deposits. Excessive amounts can cause misfires.

*Have you been using any gas or oil additives? Additives can sometimes cause ash deposits.
*What type of oil are you using and how often are you changing it?
*Otherwise, it's an internal problem, possibly head related.
No additives. Cheapest 10w 30 I can find. Napa or Supertech. Change it about every 3k.
cavalier is offline   Reply With Quote Quick reply to this message
Unread 05-04-2013, 03:14 PM   #13
cavalier
Registered User
 
Join Date: Jun 2010
Location: Va
Posts: 160
Oh man. I'm starting to think maybe I need a head rebuild. NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!!!! !!!!!!!!!!!!!!!!!!
cavalier is offline   Reply With Quote Quick reply to this message
Unread 05-04-2013, 04:15 PM   #14
79chiefs
Registered User
1988 XJ Cherokee 
 
Join Date: Dec 2012
Location: Lillington, NC
Posts: 988
You also need a pressure regulator, it should be 49psi +/- 5psi all the time. But should NOT drop that quickly. 1psi/30min i believe is how it should drop when not running.
It does not drop while running because the fuel pump is always running, when it is not running and the key is on it only primes till your start it.
__________________
99WJ Laredo I6-A 2wd
88XJ-Building on a budget.
95 E34 540i-DD

Last edited by 79chiefs; 05-04-2013 at 04:17 PM.. Reason: More info
79chiefs is offline   Reply With Quote Quick reply to this message
Unread 05-04-2013, 04:43 PM   #15
cavalier
Registered User
 
Join Date: Jun 2010
Location: Va
Posts: 160
Quote:
Originally Posted by 79chiefs View Post
You also need a pressure regulator, it should be 49psi +/- 5psi all the time. But should NOT drop that quickly. 1psi/30min i believe is how it should drop when not running.
It does not drop while running because the fuel pump is always running, when it is not running and the key is on it only primes till your start it.
I'm not sure it needs to be that high. I think 31 psi is the spec.
cavalier 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






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.