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Discussion Starter · #1 ·
Got an 85 interstate. Just changed the engine control module because the fuel pump had no voltage when the bike was running. Now I do, but the pump refuses to run. I jumpered the pump, it does work. With the motor running, the fuel pump line voltage goes to about 14.2 volts, but still doesn't work. Testing the line amperage with a light, it doesn't come on, yet it still reads good voltage.

My guess is the line amperage isn't there to operate the pump. What would cause that?

Just to add insult to injury, the dammed bike fired up after sitting idle for 9 months. Without me trying to really start it. I thought the carbs were dry!

(I have another 1200 I ride. but I want this one going too!)
 

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Discussion Starter · #3 ·
No I haven't. But I also don't have the Honda service manuel. I've got the Haynes manuel, and I haven't found a pump relay test in that.
 

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No I haven't. But I also don't have the Honda service manuel. I've got the Haynes manuel, and I haven't found a pump relay test in that.
I don't have a Haynes manual for anything but I was underwhelmed by the few I've seen for various vehicles.:sadguy:
 

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Haynes manuals are very generic for all types of vehicles. To me, they make bathroom literture to use when you are done sitting there.
 

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Junior Grue
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Got an 85 interstate. Just changed the engine control module because the fuel pump had no voltage when the bike was running. Now I do, but the pump refuses to run. I jumpered the pump, it does work. With the motor running, the fuel pump line voltage goes to about 14.2 volts, but still doesn't work.
You do know that it is a demand pump and will do nothing if the float bowls are full?
 

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Discussion Starter · #8 ·
Yes, I knew that, but currently I've got it at gravity feed, enough fuel in the tank to feed the carbs. The fuel pump is out of the system, no pressure on it to tell it to stop running. I'm thinking it may be the fuel cutoff switch that's taking all the amperage.

I'm about to the point of just hardwiring it into a lead that comes on when the ignision is switched on, and just forget the fuel pump relay. Or power up the relay. If the pump shuts off at a certain fuel pressure, then it's the simplist way to fix it. I've grown weary at throwing money at it.
 

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Junior Grue
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How did you jumper the pump to get it working?

If you jumped both wires then it's likely you have a ground issue.
 

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This is a 12v circuit and very easy to diagnose.
Using a test light, NOT a DVOM, test the power supplied to the pump at the connector on the right side of the seat. White wire. Connector disconnected.
It is important you use a cheap, ordinary, garden variety, seen one seen 'em all, everyday test light. You can get them at the dollar store for....well....a dollar. All it is, is a light bulb in a housing. It measures amperage very well. No numbers, it just lights up.
While cranking the engine, see if the test light "lights".
If it lights bright, you know there is most likely enough amperage to drive the pump, and you have a ground issue. If it doesn't, you'll need to backtrack to the relay. You can use the same test. 12v in on the black/white.
You can also use your DVOM to check for voltage drop. Back probe the white wire at the fuel pump connector (connected) and see if the voltage falls away when trying to energize the pump. This will verify substantial line loss on the feed wire or the relay.
 

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Junior Grue
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From your first post
With the motor running, the fuel pump line voltage goes to about 14.2 volts, but still doesn't work. Testing the line amperage with a light, it doesn't come on, yet it still reads good voltage.
As I said before that would indicate a bad ground or that the fuel pressure was up to where the pump had nothing to do.
 

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Discussion Starter · #13 ·
Oh could be the ever notorious bad ground. I should know better.

Jumpering the pump, at least the way I did it was, to remove the pump totally out of the bike. Then, one wire to positive (black) Green, which is grounded to the pump case, laid on negative post of the battery. Pump has no fuel lines on it. It runs.

It just occured to me to try to ground the pump to the battery negative, to see if the pump will run plugged in.
 

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Discussion Starter · #14 ·
Took the power leads and just ran them to accessory pickups, bike runs fine that way. Found out the fuel pump is no good, won't hold steady pressure, very noisy. The heck with it- got a Carter boat fuel pump to use instead. It'll get changed out when I rebuild dirty carbs.

Never a dull moment!
 
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