Case Colt Ingersoll Tractors banner

Electric Fuel Pump

11K views 32 replies 7 participants last post by  Hydriv 
If you have the original Onan engine in your tractor, then it has an ignition coil that gets fed 12 volts from the key-switch. Run the the power lead for the pump to the + terminal on the coil.
 
Help me out here.


You still have the CCKA engine in this tractor?

Prior to installing this pump, the engine would start with the key-switch and shut off with the key-switch.. no problems.

All you have done is add this 12volt negative to ground fuel pump and you have run one pump lead to a good ground on the engine or tractor frame and the other pump lead to the ignition coil.

And as soon as you do that, the key-switch will no longer make the engine shut off.

Do I have it correct?


And if the engine is running and you disconnect the pump lead from the coil and then turn off the key-switch at that point, then the engine will stop. YES.
 
Ted Miller said:
Hydriv said:
Help me out here.

You still have the CCKA engine in this tractor?

Prior to installing this pump, the engine would start with the key-switch and shut off with the key-switch.. no problems.

All you have done is add this 12volt negative to ground fuel pump and you have run one pump lead to a good ground on the engine or tractor frame and the other pump lead to the ignition coil.

And as soon as you do that, the key-switch will no longer make the engine shut off.

Do I have it correct?

And if the engine is running and you disconnect the pump lead from the coil and then turn off the key-switch at that point, then the engine will stop. YES.
You ae correct
If you have a DC voltmeter set to read low voltage, then connect the meter's negative probe lead to the battery's negative post and the meter's positive lead to the fuel pump supply lead while it is still connected to the ignition switch or ignition coil. Are you seeing 12 volts with the key switch in the ON position, as well as the OFF position?

If so, what happens when you turn the key to OFF and then remove the supply lead to the pump? Do you still see 12 volts at the coil or is it now gone?

If it is gone, then put the meter lead onto the supply lead to the pump that you just disconnected. Do you see 12 volts there?

If so, then where is the ground lead for the pump attached? Something is backfeeding 12 volts to the coil to keep the engine running after the key switch is turned to off.
 
This is a most bizarre problem and it makes no sense to me at all.

You are seeing a voltage drop at the coil once you turn off the key but 10 volts is still enough to provide spark and keep the engine running. The voltage drop implies that there is a resistance in series with the supply voltage. The obvious choice of that resistance is the electric fuel pump but I am stumped how any voltage could be flowing back through the pump when you have it grounded directly to the negative post on the battery. Essentially, if you put a relay in place to switch the current, then all you have done is to replace the pump motor with the coil on the relay. A path for back-fed power would still exist. Only the level of resistance would change.

I've been studying the 646 wiring diagram and I see that the voltage regulator has one wire going to the + terminal of the coil. I also see a wiring harness that has a plug and socket for the voltage regulator. Have you inspected both halves of that connector to make sure they are totally clean and free of any corrosion? Yep... I'm grabbing at straws here but that's about all I've got left. Unfortunately.
 
So... was it my remark about the regulator wiring that sent you for a second look? :sidelaugh:

What matters most is that you finally got to the source of the problem and it's running as it should. :thumbsup: :thumbsup:
 
OK... good. However, I still don't understand why it was that installing this new fuel pump made the engine keep on running when the old pump did not do so. Do you have an explanation for that? Curious minds want to know. :lol: :headscratcher: :headscratcher: :headscratcher: :headscratcher:
 
The only thing i can figure here is that there is a big difference between the two types of pumps. The coil is controlled by an ON/OFF switch known as the points. That might have been enough to fool the regulator into not sending power to the coil but perhaps the new pump provided a continuous current path that the old pump did not.

That's the best I can figure. You would have to dismantle the old pump to see if it has some sort of switching inside that is related to the pressure it was detecting.
 
What happened here also makes for a good argument about the problems that come from re-powering a tractor. While that was not what happened here, the fact remains that it is often hard enough to solve problems with a dead stock tractor...........trying to solve similar problems in a re-powered tractor are a nightmare because members don't have accurate parts and service manuals to fall back on to try and analyze what might be wrong.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top