4.0 Conversion wont start - Jeep Wrangler Forum

Go Back   Jeep Wrangler Forum > YJ Jeep Wrangler Forum > YJ Tech Forum

Join Wrangler Forum Today

Thread Tools

Please support our sponsors and let them know you heard about them on WranglerForum.com
Old 07-03-2011, 11:06 AM   #1
Join Date: May 2011
Location: Acworth, GA
Posts: 51
4.0 Conversion wont start


My 1990 YJ with the 4.0 conversion wont start. The new engine and harness are out of a 1992 Cherokee HO. Upon initial crank it fires off once and then just cranks. The fuel pump primes upon first crank and injectors pulse once (checked with noid light) and then nothing. The fuel pump only pumps while cranking (voltage checked at ballast resistor, 12 V while cranking). The only code that comes up is 41, open field circuit (all wiring checks good, and this shouldnt keep me from running.) I assume the 41 pops because I am cranking and cranking without an opportunity for the altenator to send power anywhere.

It seems anytime I read about someone replacing the computer it does not fix anything. However this is all I can think to replace at this point. I have not heard of the auto shutdown relay fixing anything either, will a faulty auto shutdown relay cause this?

I can get the engine to run if I use ether or pour a little fuel into the intake.

I have replaced the Crank Position Sensor, Cam position Sensor, and have installed the proper Fly Wheel for the engine.

Any help is welcomed, I have exhausted myself with this problem.

Please help.

bigskycountry0329 is offline   Quote
Old 07-03-2011, 11:22 AM   #2
RLaFitte's Avatar
Join Date: Mar 2010
Location: Newport, Tennessee
Posts: 169
What engine was previously in there? Everyone says you must change the computer or else it still thinks you are running a 4-cylinder (or other).


Hee Hee, you ass in a heap o trouble, Boy! ...Great big Georgia state cop
RLaFitte is offline   Quote
Old 07-03-2011, 11:26 AM   #3
banks316's Avatar
Join Date: Apr 2011
Location: Longview, WA
Posts: 2,089
Also the 2.5 has a low pressure fuel pump the 4.0 has a high pressure fuel pump.
93 YJ I6 5spd
My YJ Build +1.5 inch SOA ,37 12.50 15R Swamper M16's, 5.22:1/2.97:1 Stak Tcase with 92 Crawl Ratio--------SOLD...
banks316 is offline   Quote
Old 07-03-2011, 11:37 AM   #4
Square_Eyes's Avatar
Join Date: Oct 2010
Location: Hayden, Idaho
Posts: 1,428
Originally Posted by banks316
Also the 2.5 has a low pressure fuel pump the 4.0 has a high pressure fuel pump.
Sounds like you're not getting enough fuel, I would check the fuel pump or just change it out.
Gettin' Stuck Like A BOSS

Darkproximity- Sometimes I wonder if your jeep was assembled by 8 year olds with nail guns and a lot of caffeine
Square_Eyes is offline   Quote
Old 07-03-2011, 01:15 PM   #5
Join Date: May 2011
Location: Acworth, GA
Posts: 51
Thanks for the suggestions.

The previous engine was a carbed 4.2. I am getting 40 PSI to the rail during cranking. If I stop cranking the fuel pump stops pumping.

I also have the 1992 4.0 Cherokee computer installed.
bigskycountry0329 is offline   Quote
Old 07-03-2011, 03:48 PM   #6
Join Date: May 2011
Location: Acworth, GA
Posts: 51
The new installed fuel pump is for the 1992 Cherokee and puts out 40 psi to the rail while cranking.
bigskycountry0329 is offline   Quote
Old 07-06-2011, 07:55 PM   #7
Join Date: May 2011
Location: Acworth, GA
Posts: 51
Well, it is finailly running!!! Hells Yeah!, Finially. Thank you to everyone for your suggestions and pointers. It came down to the the timing. Yes the timing was off. I guess when we installed the distributor after replacing the Cam Sensor we dropped a gear. We corrected the timing per the Haynes manual and "volia."

I am bouncing off the walls. I was just about to roll the thing off a cliff! Almost time to get muddy!
bigskycountry0329 is offline   Quote
Old 07-06-2011, 11:43 PM   #8
Join Date: Jan 2011
Posts: 54
Great. I had the same issue with mine after the swap I did. its tricking when you replace the distro, if you dont get it just right it will throw the timing off. Good stuff.
10huey is offline   Quote
Old 07-07-2011, 02:29 AM   #9
rockcrawln's Avatar
Join Date: Apr 2011
Location: Stockton, CA
Posts: 62
How much was your whole swap? I'm gonna swap mine and I like the fuel injected for smog reasons(ca)!!! Any info would help
ITs a JEEP thang !!!
rockcrawln is offline   Quote
Old 07-08-2011, 09:54 PM   #10
Join Date: May 2011
Location: Acworth, GA
Posts: 51
Where do I start.

I bought a donor 1992 Cherokee 4.0 HO with a new top end for $650.00. My bell housing had the holes to mount the CPS so I lucked out with that and was able to use the donors.

New Fly Wheel...$40.00. The donor had an automatic and my fly wheel on the 1990 YJ is completely different than the donors engine needed.

I had a two pilot bushings milled into one.
big bushing $20.00
small bushing $10.00
labor at the machine shop to machine out the bigger bushing $20.00

K&N Air Intake $206.00 from Amazon

Replaced the faulty Cam Sensor $40.00
Replaced faulty Crank Position Sensor $50.00

Grand Total $1036.

I feel I luck out since I got a great deal on the donor and did not have to get anything from Hesco...ie the CPS relocation kit or wiring harness.

If you have any question at all please feel free to ask. I ran into plenty of problems along the way but I am so close to getting back on the road. Just waiting on the air intake to get here.

bigskycountry0329 is offline   Quote

Thread Tools

Posting Rules
You may not post new threads
You may not 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 Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
1995 Jeep Wrangler YJ will not start after these Symptoms packermanwi YJ Tech Forum 11 09-28-2012 08:52 AM
Will not start ssgggtom YJ Tech Forum 2 05-10-2010 11:10 AM
Jeep wont start.. Kodysteeler43 TJ Tech Forum 0 05-06-2010 12:30 PM
01 won't start Jeepguy TJ Tech Forum 1 03-01-2010 12:15 PM
Help! My YJ won't start 93YJowner YJ General Discussion Forum 5 05-20-2006 11:17 AM

Download our Mobile App

» Featured Product

All times are GMT -5. The time now is 01:26 AM.

User Alert System provided by Advanced User Tagging v3.1.0 (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.

Jeep®, Wrangler, Liberty, Wagoneer, Cherokee, and Grand Cherokee are copyrighted and trademarked to Chrysler Motors LLC.
Wranglerforum.com is not in any way associated with the Chrysler Motors LLC