Fuel Pump Power Supply

I've been troubleshooting an intermittent fuel supply problem to the carbs. Currently, the pump is set to pump into a gas can so all testing has been done without the engine running. So far, I have determined the problem is not the fuel supply, the pump, the relay or the fuel pump power wire, L/B, going from the relay to the pump.

When I power the pump through the relay connection, with the relay removed, directly from the battery, it will pump until I remove the power. However, when I apply a jumper from the R/W wire at the relay connection to the pump wire, L/B, it will pump briefly and then stop and the voltage drops to below 10.

So, what could cause a 2 volt power drop? I believe it could be the kill switch and I think there is a way to test resistance across it but I'm not sure how or where to do it. Anything else?

Any advice is appreciated.

OK first thing to try. When you jumper the R/W to the L/B wire and the volts drops to 10 volts, measure the voltage on EACH side of the Ignition fuse to ground and get back to me...

OK first thing to try. When you jumper the R/W to the L/B wire and the volts drops to 10 volts, measure the voltage on EACH side of the Ignition fuse to ground and get back to me...

11.3 left and 11.28 right, at battery terminals voltage is 12.3.

OK then rule out corroded/bad fuse holder!! Now you will find two R/W wires at the kill switch. Do the same and I almost bet you will find 11.8v on one and 10v on the other, indicating the kill switch needs cleaning...

I was looking for one of Dingy's cleaning pictures for the kill switch in the read only tech section but didn't see one, may have missed it.

11.3 left and 11.28 right, at battery terminals voltage is 12.3.

You may have a combination of issues.

If the battery is at 12.3 and the fuse is only getting 11.3 that is a full 1 volt drop, that is bad. Look for the bad connection between the battery and the fuse block first. Once you have that one found and fixed, then continue to chase the fuel pump power issue. There is no sense chasing the original issue when you have already found one problem.

It wont pump into a can continuously. It needs to have back pressure and when the presure drops it pumps until it gets it back within range. So as if to say you crash it won't pump enough to drain the tank, just hose you down enough to need a Burn unit to recover.

I know, I tried to make a transfer pump out of one. No workie. And when I inquired they said it works like that.

You may have a combination of issues.

If the battery is at 12.3 and the fuse is only getting 11.3 that is a full 1 volt drop, that is bad. Look for the bad connection between the battery and the fuse block first. Once you have that one found and fixed, then continue to chase the fuel pump power issue. There is no sense chasing the original issue when you have already found one problem.

He has almost 12 volts coming off the fuse and only 10 volts downstream at the relay, and the only thing in between is the kill switch. He already stated if he runs a jumper to the fuel pump it does not die. I'm having him confirm this by testing the voltage on both sides of the kill switch...

That is why I said he may have multiple issues going on.

The ignition switch should not drop a full volt from 12.3 down to 11.3.

IF he had 11.8 or more at the fuse I would agree to go on to the next step, the kill switch.

OK then rule out corroded/bad fuse holder!! Now you will find two R/W wires at the kill switch. Do the same and I almost bet you will find 11.8v on one and 10v on the other, indicating the kill switch needs cleaning...

 

I was looking for one of Dingy's cleaning pictures for the kill switch in the read only tech section but didn't see one, may have missed it.

Here is link to thread for cleaning throttle side switch on 86-93 bikes.

http://www.venturerider.org/forum/showthread.php?t=42433

Gary

If you suspect the kill switch is an issue, there is a fairly easy way to bypass it. Pull the side stand relay out of its socket, it is the only relay in the head light bucket with a blue base on it. With the relay pulled, the bike will not shut off when side stand is put down with bike in gear.

Take a 12V jumper from the positive battery post on the battery and connect it to the R/W wire is the side stand relay plug. This will bypass the kill switch and the fuse panel. See if that makes a difference.

Gary

That is why I said he may have multiple issues going on.

The ignition switch should not drop a full volt from 12.3 down to 11.3.

IF he had 11.8 or more at the fuse I would agree to go on to the next step, the kill switch.

Just for giggles and a comparison I just checked my bike.

The kill switch was replaced mid last summer.

Across the battery - 11.94V (It has not been ridden or on a charger since October.)

At fuse - 11.87V

other side of fuse - 11.87V.

That is only a 0.07 volt drop across the ignition and main fuse.

I also checked the voltage on the R/W wire at the fuel pump relay. I got 11.65V. So that is a 0.29V drop from the battery to the relay.

This gives you something to shoot for.

Thanks to all for the advice. I am going to start at the beginning and try to find the reason for the voltage drop at the fuse box. I still have the original one.

I will also test across the kill switch but I am going to remove the switch and do the maintenance on the switches and cables. Have never done it to the right side so not looking forward to it but the step by step instructions are helpful and I can lubricate the cables while I'm in there. Thanks.

There are two things that may cause the loss at the ignition fuse, the ignition switch, and the main 40 amp fuse. Not sure about the MK2, but the MK1 is a metal link affair that is mounted with screws. You need to have some kind of a load on the circuit to develop a voltage drop to be detected. From the battery you will see two lines, one going to the starter solenoid, and the other going to a plastic box with a clear cover on it. This is the main fuse. With a load, such as your fuel pump setup on read the voltage on the wires if possible on both sides. There is a good possibility that the fuse link has corrosion or the screws are loose, dirty, or corroded.

If you are only seeing a tenth of a volt or two across the main fuse then you issue is most likely the contacts on your ignition switch...

There are two things that may cause the loss at the ignition fuse, the ignition switch, and the main 40 amp fuse. Not sure about the MK2, but the MK1 is a metal link affair that is mounted with screws. You need to have some kind of a load on the circuit to develop a voltage drop to be detected. From the battery you will see two lines, one going to the starter solenoid, and the other going to a plastic box with a clear cover on it. This is the main fuse. With a load, such as your fuel pump setup on read the voltage on the wires if possible on both sides. There is a good possibility that the fuse link has corrosion or the screws are loose, dirty, or corroded.

 

If you are only seeing a tenth of a volt or two across the main fuse then you issue is most likely the contacts on your ignition switch...

Thanks. Just took some readings to test all the fuses and this is what I found. Battery is 12.13, All fuses are between 11.1 and 11.2. The pump relay was at 9.8 while I tested.

So, then what you said seems likely being the drop is consistent across all the circuits. How does the ignition switch operate and should I clean it somehow? I will check the main fuse now.

Also, I just ordered a new fuse box from skydoc to upgrade the fuses.

The ignition switch is like any rotary contact switch, it has fixed and moving contacts. You disassemble and polish similar to the other switches. Check the 1st gen Read Only tech library and see of Gary (Dingy) did a write up on the ignition switch.

If you are getting only a tenth or two volt drop across the fuses then they are OK but yes it is a good idea to switch over to modern plug in fuses, the glass ones are getting harder and harder to find!

I am hoping the problem exists on the main fuse which will be a quicker fix than removing your ignition switch and rebuilding that! The fact that you are getting 11 volts out of the fuse and only 10 volts at the fuel pump with the relay jumpered most likely means you are loosing voltage across the kill switch. The reason it works for a few seconds is because the kill switch contacts are offering circuit resistance, they heat up, and heat makes the resistance go higher lowering the voltage on the pump side to the threshold of the pump operation...

It wont pump into a can continuously. It needs to have back pressure and when the presure drops it pumps until it gets it back within range. So as if to say you crash it won't pump enough to drain the tank, just hose you down enough to need a Burn unit to recover.

 

I know, I tried to make a transfer pump out of one. No workie. And when I inquired they said it works like that.

Mine has been pumping into a can a ground level but just to simulate resistance I elevated the can about 4.5 feet above the pump which is about 2 psi and it still pumped into it with no problem. But, thanks for the thought.

The ignition switch is like any rotary contact switch, it has fixed and moving contacts. You disassemble and polish similar to the other switches. Check the 1st gen Read Only tech library and see of Gary (Dingy) did a write up on the ignition switch.

 

If you are getting only a tenth or two volt drop across the fuses then they are OK but yes it is a good idea to switch over to modern plug in fuses, the glass ones are getting harder and harder to find!

 

I am hoping the problem exists on the main fuse which will be a quicker fix than removing your ignition switch and rebuilding that! The fact that you are getting 11 volts out of the fuse and only 10 volts at the fuel pump with the relay jumpered most likely means you are loosing voltage across the kill switch. The reason it works for a few seconds is because the kill switch contacts are offering circuit resistance, they heat up, and heat makes the resistance go higher lowering the voltage on the pump side to the threshold of the pump operation...

Unfortunately, it isn't the main fuse. Same voltage as the battery while the voltage was 10 at the pump relay connection. So I guess I'll check the ignition next and the kill switch. Thanks.

Check the connector to the ignition switch, they have been known to cause problems but that is more of a second gen problem...

Check the connector to the ignition switch, they have been known to cause problems but that is more of a second gen problem...

Unfortunately, it isn't the main fuse. Same voltage as the battery while the voltage was 10 at the pump relay connection. So I guess I'll check the ignition next and the kill switch. Thanks.

The main fuse is connected directly to the battery. Does not go through ignition switch.

Problem is either at battery terminals, connection to main fuse, or where ground side of meter is at.

Other than that it is ground side connection.

Edit: Are you saying you got 10V at fuse, I may have misunderstood what you mean., If you got Battery voltage on both sides of fuse, then do what Bob said and go to ignition switch.

I have a spare ignition switch I would part with. Tumblers can be changed in it to keep keying the same.

Gary

Here is a screen capture of main fuse area of schematic.

Gary

http://i1007.photobucket.com/albums/af193/gdingy101/Mainfuseon86-87venture_zpsc15fbf95.jpg

Attached are some pictures of a main 1st gen switch dis-assembled.

1st picture shows difference between smaller connectors, one with 3 wires is for a bike with a CLASS system (connector on right in both pictures).

Gary

Yah Gary, I had him check the voltages on each side of the main fuse at the wires for a possible voltage drop across the fuse link. The link can develop corrosion where it screws into the block. Hopefully he did the checking on the wires to ground and not on the screws on the link as if the corrosion was on the screw and the bottom of the link the IR drop would not show up on the screw head possibly. At this point he is dealing with two separate issues, a voltage (IR) drop before the 10A ignition fuse and another IR drop somewhere between the fuse and the relay socket, the latter being most likely the Kill Switch. Before the fuse block there is the main fuse and the ignition switch...

Vito, pictures 2 and 6 show the contacts that need polishing. If they are really badly pitted and corroded you may want to consider replacing them...

Thanks for the info. I removed and cleaned the stop switch (not impressed with the construction) and the problem is currently not happening. I installed the relay and reassembled the bike. I have a new fuse box arriving this week so will install that asap. So, for now, I am OK. And the knowledge I've gained about the pump system will enable me to make repairs on the road if needed. Thanks for the ignition switch offer but I will hold off for now. Thanks again, you guys are great.