I recently purchased a 84 F150 that had a 351w in it. The body wasn't much more than a pile of rust held together with a little paint. I put a battery in it and noticed when I hooked it up the motor Jerked, i didnt think much of it at the time. poured some gas down the carb and after a few minutes had the fuel pump primed and DROVE the truck back to my house. During the trip home, it simply cut off(10 min or so) as if I had turned the key off no warning no sputtering or anything. I pulled over, checked/wiggled wiring around under the dash and hood to the important as far and the engine running goes tried to crank it a few (8-10) times and finaly it started running again and drove it the rest of the way home with no problems(30 min). Once I got home I took off what parts I could reuse on my other trucks, and pulled the engine and transmission. Now I have put the motor in a newer EFI vehicle converted back to Carb with a New Duraspark II Ignition box. I'm a DC electrician by profession and I'm 99% sure that I have the Ignition box wired correctly

White = Start
Red = Ignition

Green = Ground/Tach signal from Coil
Purple and Orange = Distributor Stator
Black = Distributor Ground

I have a toggle switch and push button to crank this engine, I'm not using anything off the Key/Steering Column.


When I Turn my switch ON and PUSH to CRANK the motor hits as soon as I let off of the push button when I turn my switch OFF the motor JERKS like it did when I went to get it. I can flip the switch on and off a few times and it jerks 2 or 3 times even if I do NOT try to CRANK it.......... I have the same Duraspark IGN in my 78 150 i took the coil and ignition out if it and tried it and it does the same thing. I spliced in to the BLACK wire and added a 12ga ground to the battery just in case it didnt have a good ground and the motor still jerks. Since the motor swap I have yet to hear this same motor run more than 2-3 seconds. the only thing I haven't checked/changed is the Distributor but I wouldn't think it was bad.... I mean, I drove it for about 35 miles around 40 minutes. I popped the cap off and checked if it was WAY out of timing and it passed my TDC eyeball test so its ~close to being in time. I don't think I bumped or hit it hard enough to cause any damage while I pulled the motor





I've done and tried about all I can think of doing to it to get it to crank and run the past 2 evenings. Anyone got any ideas why the motor jerks when the starters not being engaged? The only thing I can think of is its the stored power in the coil exiting the Dis Cap to the closest Plug wire.

Thanks Aaron

 

Aaron,
Classic symptoms of a failing module on your trip home with the truck.
What year is the EFI truck you are trying to get going with the carbureted engine?
Most bullnose trucks will already have the proper DSII wiring in the cab harness. You just have to find it where it comes through the firewall.

Try swapping the red & white wires at the plug of the DSII module.
Looking at wiring diagrams and many threads on the forum you'll see this is the case. https://www.ford-trucks.com/forums/1...ctors-diy.html

You are correct in that the white wire is the ignition retard and has power only when cranking.
The Red wire is 12V power in 'run' to the module.
But! many (most, all?) modules have their wire colors reversed.
The plugs are keyed, so there is no way to do it wrong UNLESS you are making your own connections/harness.

The reason it jerks when power is removed is because cutting power to the coil causes the primary field to collapse, and this creates a spark.

If this is swapped into a EFI vehicle be sure you're using the Duraspark canister coil and + has full 12V while cranking and a 1.3 ballast Ohm resistor while in 'run' or the coil will overheat and fail.

Welcome to the forum!
Hope this helps.

 

I tried switching the red and white around when I did the DSII fed power back to my starter solenoid as soon as I turned my ignition switch on. I have a new ds2 box installed. And I'm using the factory green orange purple black harness from the ignition box to the motor. The motor and wiring are the same as when I got it, the only thing I've changed is the ds2 box and put a toggle switch and push button in

 

White should be connected to the 'I' terminal of the solenoid.
It can't feed back if configured this way.

Once again, I don't know what truck you are trying to put this in...

If it is a Bullnose truck all the connections are there in the cab harness and you don't need to go back to the solenoid.

If later, and your solenoid doesn't have an 'I' terminal you could add a diode to the white wire.
(or switch to an old style solenoid)

 

I'm actually putting the motor in a 89 mustang but I'm going to use a toggle switch and push button to operate the engine with the truck ignition system. I have some 1.2k ohm, resisters would that work in place of the 1.3 ohm resistor you mentioned To keep the coil from over heating?

 

If it is a ballast resistor that can handle the current then yes it's fine.
In the trucks Ford used a piece of wire, but the common Mopar ceramic resistors are cheap and work just as well.

 

This pic from JBG shows a solenoid with both 'S' and 'I' terminals.

 

One other thing I can say is that if you are using a SPST momentary on push button to start the truck you will want to run a wire from the button to the coil side of the resistor in order to provide a full 12V to the coil while cranking.

You can see how the 'bypass' works in this simple diagram.

 

I have a single pole solenoid I'll install a relay for the 12v "I" feature and try it again this evening I probably need a new coil I may have messed mine up last night by over heating it

 

Thanks! I've looked at that same diagram while I wired my ds2 up. I'm going to take the"new" ds2 back and get another one and also get a new coil. If they can't handle constant 12v over a long period of time I'm sure mine's toast. I know I've had 12v on mine for over 4 hrs. I'll hook a relay up for my "I" feature to supply momentary 12v to the coil when cranking

 

4 hours, the coil may be okay.
Check the resistance of the primary windings.
1.7 ohms IIRC.

The DSII module is meant to receive full voltage (as you can see in the diagram)
If yours was flaking out on the way home it is likely done for.

 

Thanks! I've looked at that same diagram while I wired my ds2 up. I'm going to take the"new" ds2 back and get another one and also get a new coil. If they can't handle constant 12v over a long period of time I'm sure mine's toast. I know I've had 12v on mine for over 4 hrs. I'll hook a relay up for my "I" feature to supply momentary 12v to the coil when cranking

 

Sorry about the double post I'm using my phone.

Yes, I am supplying 12v to the DSII. I was going to use a relay for the resistor bypass to the coil while in the start position. I also need to splice a write from the same relay to the white wire on the DSII. Correct?

 

You're using an additional relay to isolate the bypass and retard function from the 'S' trigger wire?

Why not just hook them to the starter terminal of your solenoid?
It's effectively the same as the diagram if you have to use a pushbutton to start the car.

 

I went to the parts store this evening and had my DSII checked, and It was fine. I got a new coil, resistor, ignition coil pick up, and came home and started installing the listed items. Everything was going fine until I got to the distributor pickup. Every screw I turned broke off. When I went to remove the distributor from the engine it wouldn't budge. I had to use my cherry picker to pull it out. It destroyed the distributor. I went back to the parts store and got a new one came back installed it, the motor runs great. Must have been the pickup in the distributor. The only thing I did different with my wiring was install the resistor between the DSII and coil. I wouldn't think that was the prob. But she's counting then off now. Thanks for your help Ard