The Problem:
I have a 1986 f150 4.9 i6 300 with a 4 speed. I did something similar to the duraspark conversion, but I am having trouble. I installed a Davis Unified Ignition HEI distributer with the coil and all included in the unit. It is supposed to be calibrated and fine tuned to the 4.9 I6. I also bought a reman carter single barrel non-feedback carb. I installed the distributor first, and it ran smoother than ever, but after a few minutes the engine started knocking/clicking (spark knock??? Detonation??). I could not adjust this noise out with the timing. I got scared and put the old distributor back on (this is my daily driver).


The Question:
Could my problem be that I did not go ahead and install the non-feedback carb? Could the eledtronic feedback carb be causing this knock? If not, What else am I missing?


Thanks so much in advance for your help.

 

My guess is yes...the feedback carb. wont work once the computer is disconnected/you start unhooking stuff.You need to swap the carb/distributor and unhook the computer stuff "BEFORE" you fire it up. Good Luck!!

 

I've done that exact conversion. The Non-Feedback carb is what you want with the DUI ignition. The Old Feedback carb helped adjust timing with the OLD distributor.

By moving to a DUI Ignition and standard feedback carb, you are actually simplifying things.

A couple of things;

The DUI ignition needs DIRECT BATTERY POWER. The FULL voltage. Without that, spark plugs will foul, and you'll get the symptoms you described.

Connect the DUI ignition to full battery power via a relay that will trigger with Key-On power. I have a sticky write up on this conversion.

Check you plugs - they might be pretty fouled..

My write up gives full details including how to get rid of the computer and convert the EVAP and EGR from computer to vacuum control.

I'll help where I can. PM if you need anything..

 

Thanks a ton to both of you. Ill let you know how it goes.


Thanks!

 

KScop
Excuse my ignorance. I am new to this site. How do I find your sticky on this conversion?


Thanks

 

Here you go... https://www.ford-trucks.com/forums/1...emissions.html

 

I cant see the pictures whats up

 

Unfortunately, the original poster has since removed the pictures, so they're missing.
I wish I would have kept them so I could post them back up.

 

These are what I point people at these days:

https://www.ford-trucks.com/forums/11...swap-help.html
https://www.ford-trucks.com/forums/96...-86-i-6-a.html
https://www.ford-trucks.com/forums/10...g-harness.html

 

Today i finally got around to putting the DSII system in my Bronco but i can't get it to fire. Everything seems to be wired correctly. I had to splice in the coil power wire because the '78 harness I got had the wrong connectors but I now have 12v to the plug going to the coil. Then when I plug in the coil i only get around 7v at the connector coming from the truck harness.

I have tried two different coils (round canister & original TFI) and wired the positive side of each directly to the battery to give it full 12v.

The only thing i can think now is that something on the switching side is wrong. What's the possibility that a Motorcraft module would be bad out of the box?

 

Not likely the module is bad out of the box, but you can test it. Put your volt meter on the ground/module side of the coil and crank it. You should see the voltage go all over the map as the module grounds and the releases the coil. If not, either the module is bad or something else isn't right. It could be the module doesn't have 12 volts. Or it could be the pickup in the dizzy is bad.

 

I don't think the 78' harness will work.

 

The negative side of the coil switches during cranking but the positive side only has 7.5 volts with the coil plugged in and jumps to 12 as soon as it's unplugged.

 

You should be using a DSII Harness.

 

I just pulled a spark plug & cranked it and the plug is getting spark.