4.0L J10 Swap Wiring Issue - JeepForum.com
 
LinkBack Thread Tools
post #1 of 6 Old 08-13-2019, 11:24 AM Thread Starter
designdca
Registered User
 
Join Date: Aug 2019
Posts: 3
4.0L J10 Swap Wiring Issue

New member, first post. I should probably start by explaining I've never actually worked on a vehicle of my own unless it had a carburetor - so no good experience with electronics. I recently bought a '77 J10 that a previous owner had swapped in a '93 4.0L drivetrain and electronics. Here's what was explained to me by the previous owner as best I can recall from the conversation a few weeks ago:
It was all running fine and then one day he went to start it and....nothing. Like a dead battery, but battery was fine. He search and found a bad relay(?) near the firewall on the driver's side. He removed the relay and ran a jumper wire (photo attached). After doing this it started and was sitting idling fine when he noticed he had used too small of a jumper wire and it was overheating and melting the insulation. He turned it off and ran a larger wire - same configuration. After running the new wire, the engine turns over, but never fires.
From what I've been able to investigate, I don't think the fuel pump is getting power. Other than this rigged up alligator clip situation that he did as a temporary fix, all other wiring seems pretty good and intact. Does anyone have any good, hopefully easy to understand suggestions of what I should check?
Thanks!
David

Attached Thumbnails
jeep wiring.jpg  
designdca is offline  
Sponsored Links
Advertisement
 
post #2 of 6 Old 08-27-2019, 08:36 PM
rjbruzan
Moderator
2004 TJ Wrangler 
 
Join Date: May 2008
Location: Lake in the Hills
Posts: 3,087
Any luck?

Of all the things Ive lost
The one I miss most is my mind

Its like a fart in a windstorm
It smells good but thats about it

Registered Six Offender
Home of the Buzzin Half Dozen
rjbruzan is offline  
post #3 of 6 Old 08-28-2019, 02:03 PM Thread Starter
designdca
Registered User
 
Join Date: Aug 2019
Posts: 3
Nothing yet.
designdca is offline  
 
post #4 of 6 Old 08-28-2019, 10:23 PM
mukluk
Web Wheeler
 
mukluk's Avatar
2000 TJ Wrangler 
 
Join Date: Oct 2010
Location: Clyde
Posts: 5,218
I'm betting that if you would determine which model of '93 Jeep the donor was then pose your question in that applicable subforum, you'll have better luck getting help.

For right now I'd advise to check all the fuses to make sure none blew, then use a meter or trouble light to see if you're getting power and ground where you should at the fuel pump and automatic shutdown (ASD) relay sockets. Ignition off you should see battery voltage present at terminal 30, and ignition on you should also now have battery voltage present at terminal 86. For roughly two seconds after switching the ignition on, you should have a good ground at terminal 85.

Some pertinent information that may help in troubleshooting is the computer will kick the ASD and fuel pump relays on for roughly two seconds when you first switch the ignition on. The fuel pump relay obviously sends power to the pump module so that it can pressurise/prime the fuel rail, while the ASD relay is what provides power to the coil and to the fuel injectors. If the computer doesn't see an alternating high/low signal from the crankshaft position sensor, normally indicating the engine isn't rotating, it kicks those two relays back off after two seconds. Once the computer sees an alternating high/low signal from the crank sensor, it will kick the ASD and fuel pump relays back on until either the crank sensor signal drops off again or you switch the ignition off. This method of controlling those two relays is a safety measure to automatically shut off fuel and ignition in the event of the engine stopping, such as in a crash. What it also means is unless the engine is running, checking for power to the coil, injectors, and fuel pump can only be done by forcing the relays to stay energised, or by removing the relays and installing a jumper wire between the 30 and 87 terminals of the relay sockets. One more implication of this setup is if the crankshaft position sensor is bad or has a fault with its wiring harness, the computer will not send power to the fuel pump or ignition/injectors except for that very brief initial two second period. The computer controls the ASD and fuel pump relays via the ground leg at terminal 85, the coil and injectors likewise are controlled via their ground wires through the computer.

2000 TJ SE
2005 LJ Rubicon
mukluk is offline  
post #5 of 6 Old 09-01-2019, 01:31 PM Thread Starter
designdca
Registered User
 
Join Date: Aug 2019
Posts: 3
I finally had some time to really look things over today. I unbolted the ECU and someone wrote 93 YJ on the bottom in paint pen, so at least I know now what the donor vehicle is. I did confirm that the fuel pump is getting no power. Unless I am COMPLETELY blind, there is no relay center box. How or why would that have been removed in the swap?
designdca is offline  
post #6 of 6 Old 09-01-2019, 02:23 PM
mukluk
Web Wheeler
 
mukluk's Avatar
2000 TJ Wrangler 
 
Join Date: Oct 2010
Location: Clyde
Posts: 5,218
That's very good question as to what the PO did to make things work without using relays. It sounds like at the very least you're going to have to trace the wiring for the fuel pump to determine where it's supposed to be getting power from and how it's controlled; my guess is they either tapped power directly from the ignition switch output, or used switched power leads in the fuse block.

2000 TJ SE
2005 LJ Rubicon
mukluk is offline  
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.



Email Address:
OR

Log-in











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



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