1990 renix 4.0 runs like crap - 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 > 1990 renix 4.0 runs like crap

ECGS Black Friday Sale!!6th Annual, Beat Your Wife to the Credit Card Sale!50 in light bar /A pillar mount less than 500 at JeepHut.c

Reply
Unread 01-09-2011, 03:40 PM   #1
underpowered
Bouncin' on a Budget
 
underpowered's Avatar
1998 ZJ 
 
Join Date: Nov 2005
Location: northern kentucky
Posts: 2,742
1990 renix 4.0 runs like crap

no better way to describe it. all started new years day. was out wheeling, after a long steep climb turning high RPM's the whole way up it began to run terribly. the fan contacted the radiator and put a hole in it, so my initial thought was wet electrical system, no biggy.


Today i repaired teh radiator, rolled a core or two on it to stop the leak, good as new. fired it up and still ran horribly. checked the oil, not milky so a head gasket is not looking like the culprit. pulled plugs to see what they looked like.

first one i pulled is not a good sign, the electrode has had physical contact of some sort and has 0 gap. pulled the other 5, all look like it is running a bit rich, but not bad at all. for all i know, the first plug may have been that way from when the PO gave it a tune up. new cap, rotor, and plugs later, it seemed to run great for 20 seconds or so, then back to its old ways of missing, coughing, nearly dying at idle, along with some valve noise as well.

gonna replace wires tomorrow, but after that i am stumped. fuel pressure looks good as well, not sure what it is supposed to be, but i figure 50lbs at idle should get the job done.

__________________
1998 ZJ 2" bb and 31's. street queen but sees the woods once in a while.

2000 powerjoke tow pig

Anti-jeep--1989 K5 blazer. the new off road ride
underpowered is offline   Reply With Quote Quick reply to this message
Unread 01-09-2011, 03:43 PM   #2
1990JEEPXJ
Registered User
1990 XJ Cherokee 
 
Join Date: Aug 2006
Location: San Diego, CA
Posts: 7,059
check the vacuum line to the MAP sensor. that one little line will make the jeep run rich if it is leaking or not connected. if the line is fine, then maybe that sensor is bad. also, has the o2 sensor been replaced lately?
__________________
Completely stock, and keeping it that way...

My POS
Quote:
Originally Posted by Joe Dillard View Post
Yea, and I thought it was one of the 11 Commandments:
11) Thou shalt love, cherish, and honor till death, thine square headlights above all other earthy things sayith the Lord.
1990JEEPXJ is offline   Reply With Quote Quick reply to this message
Unread 01-10-2011, 06:54 PM   #3
underpowered
Bouncin' on a Budget
 
underpowered's Avatar
1998 ZJ 
 
Join Date: Nov 2005
Location: northern kentucky
Posts: 2,742
o2 has never been replaced. but it is not excessivly rich. richer than ideal for sure, but not near bad enough to make it run like it is. only light hints of black smoke when revved. rich enough to make it run like it is, this thing would look like a diesel.
__________________
1998 ZJ 2" bb and 31's. street queen but sees the woods once in a while.

2000 powerjoke tow pig

Anti-jeep--1989 K5 blazer. the new off road ride
underpowered is offline   Reply With Quote Quick reply to this message
Unread 01-10-2011, 06:57 PM   #4
tjwalker
It's the crank sensor!
 
tjwalker's Avatar
1999 XJ Cherokee 
 
Join Date: Nov 2007
Location: Central Minnesota, MN
Posts: 8,497
1. Finish the tuneup by replacing the wires, cap, rotor.

2. 50 pounds of fuel pressure? Measured with a fuel pressure gauge? Not good! For a renix, you should have "31" psi at idle. Then disconnect the vacuum line to the fuel pressure regulator and the pressure should jump to approx. 39 psi. Be sure that the vacuum line leading to the regulator is pulling good vacuum and is not WET with fuel. If it is, you have a ruptured diaphragm in the regulator and you must replace it.

3. Here is a link to an article that can help you with testing many things on your RENIX.

http://www.lunghd.com/Tech_Articles/...iagnostics.htm

Good luck and check back in and let us know how it goes...........
__________________
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 01-10-2011, 07:03 PM   #5
underpowered
Bouncin' on a Budget
 
underpowered's Avatar
1998 ZJ 
 
Join Date: Nov 2005
Location: northern kentucky
Posts: 2,742
yupp 50 psi. and it has a new cap/rotor just not wires. worth a shot to replace them i guess, but all tested fine. insulation is good on all, 15kv is when they blew at on the electrical insulation tester at work, which is more than a new one blew for my truck

then on to the fuel system. might check pressure with another gauge to confirm though.
__________________
1998 ZJ 2" bb and 31's. street queen but sees the woods once in a while.

2000 powerjoke tow pig

Anti-jeep--1989 K5 blazer. the new off road ride
underpowered is offline   Reply With Quote Quick reply to this message
Unread 01-10-2011, 07:27 PM   #6
tjwalker
It's the crank sensor!
 
tjwalker's Avatar
1999 XJ Cherokee 
 
Join Date: Nov 2007
Location: Central Minnesota, MN
Posts: 8,497
Definitely confirm. 50 psi is out of spec. More is NOT better with fuel pressure.

You could easily have a fuel pressure regulator problem here.
__________________
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 01-10-2011, 07:36 PM   #7
underpowered
Bouncin' on a Budget
 
underpowered's Avatar
1998 ZJ 
 
Join Date: Nov 2005
Location: northern kentucky
Posts: 2,742
definitly worth a shot.
__________________
1998 ZJ 2" bb and 31's. street queen but sees the woods once in a while.

2000 powerjoke tow pig

Anti-jeep--1989 K5 blazer. the new off road ride
underpowered is offline   Reply With Quote Quick reply to this message
Unread 01-10-2011, 07:50 PM   #8
toates89
Registered User
1989 XJ Cherokee 
 
Join Date: Jan 2006
Location: long island, new york
Posts: 2,189
check the vacuum line to the FPR
toates89 is offline   Reply With Quote Quick reply to this message
Unread 01-10-2011, 08:53 PM   #9
underpowered
Bouncin' on a Budget
 
underpowered's Avatar
1998 ZJ 
 
Join Date: Nov 2005
Location: northern kentucky
Posts: 2,742
gonna check FPR tomorrow for sure.
__________________
1998 ZJ 2" bb and 31's. street queen but sees the woods once in a while.

2000 powerjoke tow pig

Anti-jeep--1989 K5 blazer. the new off road ride
underpowered is offline   Reply With Quote Quick reply to this message
Unread 01-11-2011, 04:11 PM   #10
underpowered
Bouncin' on a Budget
 
underpowered's Avatar
1998 ZJ 
 
Join Date: Nov 2005
Location: northern kentucky
Posts: 2,742
checked pressure again today. 41 whiel running, pull the vacuum hose and it jumps to 49. TJwalker, i think you maybe 10PSI off on your specs, cause i looked up a new FPR and it says it regulates to 41, in that case i am spot on.

but meanwhile it seemed to run better today, took it out for half an hour or so in the snow, and other than an excessively high idle it ran great. and i believe the idle to be a bad TPS.

however, my Rad fix did not work, still has a slow leak so time for a new one.
__________________
1998 ZJ 2" bb and 31's. street queen but sees the woods once in a while.

2000 powerjoke tow pig

Anti-jeep--1989 K5 blazer. the new off road ride
underpowered is offline   Reply With Quote Quick reply to this message
Unread 01-11-2011, 05:53 PM   #11
tjwalker
It's the crank sensor!
 
tjwalker's Avatar
1999 XJ Cherokee 
 
Join Date: Nov 2007
Location: Central Minnesota, MN
Posts: 8,497
Pretty sure the spec for the RENIX (87-90) is 31 psi at idle. 39 psi with vacuum line disconnected. If it is incorrect, I've been giving the wrong advice for years!

The spec needs to come from the manual, as what the FPR can regulate to is not the actual factory spec.

Someone else please chime in if I'm wrong.............
__________________
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 01-11-2011, 07:08 PM   #12
underpowered
Bouncin' on a Budget
 
underpowered's Avatar
1998 ZJ 
 
Join Date: Nov 2005
Location: northern kentucky
Posts: 2,742
hmm, found conflicting answers online.

on site claims exactly what you are 31 connected, 39 disconnected.

while another site claims 45 and 54. but as i said, the regulator i found says it regulates to 41 as a set output pressure.
__________________
1998 ZJ 2" bb and 31's. street queen but sees the woods once in a while.

2000 powerjoke tow pig

Anti-jeep--1989 K5 blazer. the new off road ride
underpowered is offline   Reply With Quote Quick reply to this message
Unread 01-12-2011, 05:04 AM   #13
tjwalker
It's the crank sensor!
 
tjwalker's Avatar
1999 XJ Cherokee 
 
Join Date: Nov 2007
Location: Central Minnesota, MN
Posts: 8,497
The spec for 45 psi and 54 psi is for the 97 and newer.

Your spec is 31 and 39 with FPR disconnected................

There is a big difference in the design of the older and newer fuel pressure systems; therefore the difference in high / low specs.

Are you sure that your FPR SETS the pressure to 41 or does it "cap" the high pressure at 41. Big difference. May want to double check the part number for correct application.
__________________
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 01-12-2011, 03:19 PM   #14
underpowered
Bouncin' on a Budget
 
underpowered's Avatar
1998 ZJ 
 
Join Date: Nov 2005
Location: northern kentucky
Posts: 2,742
might try a new FPR just in case, but hate to throw money at it without knowing it is gonna fix it.
__________________
1998 ZJ 2" bb and 31's. street queen but sees the woods once in a while.

2000 powerjoke tow pig

Anti-jeep--1989 K5 blazer. the new off road ride
underpowered 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.