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Working on my 87 TRX350, and having an issue with the voltage at the fuel pump.

Backstory, have been having issues with intermittent issues with the fuel pump, right up to a no run situation, which I had no spark, as well as no fuel pump. Atv sat for a year or so as life got on the way.

Found threw this site the pump was controlled via the fuel relay under the pass side fender, as well as the spark. Ended up changing to a new OEM relay and coil, as the coil had been patched togeather before we got it.

Fresh charge to the battery, and it fired right up, but noticed the fuel pump wasn't ticking like it used to and not filling the fuel filter. Checked the voltage, and only was reading 6.5 volts at the fuel pump connection. This was with the engine running at an idle, on neutral. Did seem when I revved it up, it would go up to 7.5-8, and the pump tick more often. Ran it in the garage for 20-30 min to get some fresh gas threw it and warm it up to change the oil.

Shortly there after, it quit pumping and popped the fuse, as the pump failed internally, ohm'd it out and seems to have grounded out somehow. Pump was a cheap amazon unt, I have a OEM one on order.

I understand the pump doesn't run all the time, but seems like there should be 12v at the pump. Quad does charge 13.4 at the battery, which seems low, but im used to automotive systems.

Any ideas why it's only getting 6.5v at the pump?
 

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Working on my 87 TRX350, and having an issue with the voltage at the fuel pump.

Backstory, have been having issues with intermittent issues with the fuel pump, right up to a no run situation, which I had no spark, as well as no fuel pump. Atv sat for a year or so as life got on the way.

Found threw this site the pump was controlled via the fuel relay under the pass side fender, as well as the spark. Ended up changing to a new OEM relay and coil, as the coil had been patched togeather before we got it.

Fresh charge to the battery, and it fired right up, but noticed the fuel pump wasn't ticking like it used to and not filling the fuel filter. Checked the voltage, and only was reading 6.5 volts at the fuel pump connection. This was with the engine running at an idle, on neutral. Did seem when I revved it up, it would go up to 7.5-8, and the pump tick more often. Ran it in the garage for 20-30 min to get some fresh gas threw it and warm it up to change the oil.

Shortly there after, it quit pumping and popped the fuse, as the pump failed internally, ohm'd it out and seems to have grounded out somehow. Pump was a cheap amazon unt, I have a OEM one on order.

I understand the pump doesn't run all the time, but seems like there should be 12v at the pump. Quad does charge 13.4 at the battery, which seems low, but im used to automotive systems.

Any ideas why it's only getting 6.5v at the pump?
Great questions and thanks for the backstory. Do you have a service manual? Click links in my sig block to get it. Look at the flow test–volume not a pressure test. If it fails could be bad pump, clogged fuel lines or low voltage as you pointed out

Excellent going with OEM parts. I will check voltage on my pump today and give you a reading. Should be constant 12vdc when relay energized but I’ll let you know for sure.i can also do an ohms check.

Follow the wire diagram from fuze to pump–any bare wire (insulation chewed off by mice?) the pump internal could be corroded and shorting. I replaced my pump with OEM do you have the OEM Band A Band B and cushion? Be very careful removing the cushion it tears easily especially when fuel wetted!!! Use plenty of warm soapy water.

How clean is your tank? Have you drained the tank of old fuel? There is a drain bolt on the bottom so you can remove water and solids. Want to make sure your fuel suction lines are clear too. I cleared my tank suction lines with a cut off piece of brake cable–careful there are filter baskets welded to each end dont want to pierce them
 

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Evil Matt, yes, you should have 12v at the fuel pump. Can you check the voltage at the blue/black wire at the fuel pump relay? Take two readings, one with the blue/black wire connected as normal at the fuel pump, and one with that wire disconnected at the fuel pump.
 

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Discussion Starter #5
Evil Matt, yes, you should have 12v at the fuel pump. Can you check the voltage at the blue/black wire at the fuel pump relay? Take two readings, one with the blue/black wire connected as normal at the fuel pump, and one with that wire disconnected at the fuel pump.
Ok, I back probed the relay connection, at the black/blue stripe, I got 4.6v while cranking, and 4.4v at the pump wiring.
Unable to test with the pump due to it shorting out internally, and blowing the fuse. I replaced the fuse for this test.

The fuel tank is clean, I drained the old fuel out of it the other day when I began to play with it, and wiped it out with at rag as well. New rec fuel added with sta-bil.

Battery was tested at 12.3 volts before taking the readings.

The pump that died was a cheap amazon unit, but I do still have the rubber isolated and the clamp that I will transfer to the new pump when it gets here.

I haven't downloaded the manuals yet, going to do that tomorrow. I have looked over the wires along the frame, as I had the front plastic's off to get access to the coil, and haven't found any chaffed,/bare wires. The connections are alittle rough, as the rubber has started to break down and crack,but I've isolated those as I found them and taped them up.
 

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I understand that you measured about 4.5 volts at the relay on the black/blue wire with that wire disconnected from the pump, while the engine was cranking. That was helpful because I believe you should see pulses on that wire that alternate from zero volts to 12 volts. It would probably be easiest to see the pulses when using an old analog-style volt meter with a needle. A digital meter would probably just show a mess of changing numbers while cranking. Were you using a digital volt meter? Can you back probe the relay again with an analog meter?

Honda does not give explanations as to how their systems work in the service manual. All they do is give troubleshooting procedures and show how to replace parts. This is bad news, because I find that understanding how systems work is very important when troubleshooting. I have looked over your wiring diagram and used my own knowledge and experience to give an explanation of how your fuel pump system works. I cannot guarantee that it is 100% accurate, but I bet I am pretty close. Here goes:

The black/yellow wire coming out of the CDI unit goes to the ignition coil and then goes on to the fuel pump relay. This wire carries the ignition pulse to the coil. Since it also goes to the fuel pump relay, it carries that same pulsing signal to the relay. These electrical pulses are what make your fuel pump oscillate so the diaphragm inside of the pump will actually pump fuel. Anyway, that oscillating signal on the black/yellow wire causes the relay to turn on and off with each ignition cycle. When the relay is on, 12v at the black/brown wire at the relay is sent to the black/blue wire at the relay. The other end of that black/blue wire connects to the fuel pump, and will cause it to stroke one way when 12v is present. When there is no voltage on the black/yellow wire, the relay turns off, and disconnects the link between the black/brown wire and the black/blue wire. When that happens, the fuel pump strokes in the opposite direction due to no voltage present. With the engine cranking, here is what I would expect to see on a machine that is in good running condition:
1. Steady 12v on the black/brown wire at the relay.
2. Voltage on the black/blue wire at the relay that oscillates between zero volts and 12 volts with each ignition cycle.
If these two conditions are present on your machine, then the fuel pump signal is working as intended. If your tests show this to be the case, then I think that when you replace that shorted fuel pump, it will work just fine.
 

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Discussion Starter #7
The pulsing theory would make sense, as I did notice when it was running before the pump died, that as I revved it up, the voltage would go up to 7.5-8v, and the pump did tick faster.

I did measure with a digital meter, as I don't have an analog meter. I do have a meter for setting points/dwell, I'll see if I can use it to detect the pulses.

I'll get the new pump installed when it gets here and report back.
 

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So finally got some time today to install the new fuel pump. Got it wired up and works now.

Initial observation, at first crank, it pumps like crazy, but the lines were empty. Once the lines were filled, it just pumps occasionally. I do notice the filter draws down alot, and doesn't really fill back up, however that's while idling or free revving in my garage, hard to tell while riding it.

I am having trouble with the carb now, but that's was to be expected, being it sat for over a year with gas in it. I seem to have gotten most of the crap threw it, as it was having a hard time running once warmed up, and I had to hold the choke closed and then it would run. I tried the old trick of revving it up and holding my hand over the intake, and after a couple times it cleared up. Now the idle is high, but runs great, so gonna run with it for the next couple starts and see if it just needs an idle adjustment, or if I'm gonna have to tear the carb apart and clean it.
 

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I was getting similar readings once (only 6.5v) at the fuel cutoff relay and to pump. Turned out to be that my CDI was intermittent. If you see that again, check for spark while it's happening.

Let's see some pictures of that sweet '87!
 

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So finally got some time today to install the new fuel pump. Got it wired up and works now.

Initial observation, at first crank, it pumps like crazy, but the lines were empty. Once the lines were filled, it just pumps occasionally. I do notice the filter draws down alot, and doesn't really fill back up, however that's while idling or free revving in my garage, hard to tell while riding it.

I am having trouble with the carb now, but that's was to be expected, being it sat for over a year with gas in it. I seem to have gotten most of the crap threw it, as it was having a hard time running once warmed up, and I had to hold the choke closed and then it would run. I tried the old trick of revving it up and holding my hand over the intake, and after a couple times it cleared up. Now the idle is high, but runs great, so gonna run with it for the next couple starts and see if it just needs an idle adjustment, or if I'm gonna have to tear the carb apart and clean it.
save yourself the trouble, buy a shindy carb rebuild kit, and just rebuild the carb. don't bother buying an after market china carb !!. be warned !!!!..these carbs are not your average carb ?..they got lots of tricky moving parts, and odd settings that must be right ?..or it won't run right !.
 

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Sorry to revive an old post, but as this thread seems to have a number of people who actually understand the system I'm hoping you could give me a hint please?

I've a trx350d foreman that we've had for probably 10 years and has simply needed an aftermarket fuel pump along with starter motor brushes in its limited service life with us. Last week the pump stopped working (it lasted 4 years) and the top plastic cap was visibly melted. I purchased a new one but was surprised that it didn't then run even though the wires showed a permanent 12v feed when tested. The pump however worked fine when directly tested with 12v. I then opened the fuel cut off relay box to find the relay too had fried itself. From what I can guess the pump short circuited and this lead to the relay being fried from the direct short. The 12v being fed to the pump were from the shorted pins which couldn't supply the current needed to run the pump.

I did spot when originally looking on the net what appeared to be a circuit diagram of the internal workings of that relay and it seems to be considerably more than a simple switching relay, but as the plug that is part of the loom has been damaged along with the connectors I'm considering wiring in a standard relay if I'm able to. Does anybody have any advice before I do so or any information about why the existing relay that appears to simply have a permanent live and negative along with a switching positive from the CDI and an output live to the pump like any normal switching relay would require, needs to be as I believe it to be a complicated electronic device that's completed potted?

Is there any chance it's a solid state relay or could it be simply potted to protect it against the dirt and mud on a quad bike? I can replace it with a sealed unit or a solid state if needed as the only thing I can currently think of is that either the CDI unit puts out such a small signal that a normal relay wouldn't react well to it as a switching current or potentially damage the CDI, or that the significantly high switching rate would burn out a standard relay excessively quickly.

Many thanks in advance!
 

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copperman , seems the people you speak of are gone ----I really don't think there is even any moderators left ------- the foreman club on face book has a bunch of 350D guys
 

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Sorry to revive an old post, but as this thread seems to have a number of people who actually understand the system I'm hoping you could give me a hint please?

I've a trx350d foreman that we've had for probably 10 years and has simply needed an aftermarket fuel pump along with starter motor brushes in its limited service life with us. Last week the pump stopped working (it lasted 4 years) and the top plastic cap was visibly melted. I purchased a new one but was surprised that it didn't then run even though the wires showed a permanent 12v feed when tested. The pump however worked fine when directly tested with 12v. I then opened the fuel cut off relay box to find the relay too had fried itself. From what I can guess the pump short circuited and this lead to the relay being fried from the direct short. The 12v being fed to the pump were from the shorted pins which couldn't supply the current needed to run the pump.

I did spot when originally looking on the net what appeared to be a circuit diagram of the internal workings of that relay and it seems to be considerably more than a simple switching relay, but as the plug that is part of the loom has been damaged along with the connectors I'm considering wiring in a standard relay if I'm able to. Does anybody have any advice before I do so or any information about why the existing relay that appears to simply have a permanent live and negative along with a switching positive from the CDI and an output live to the pump like any normal switching relay would require, needs to be as I believe it to be a complicated electronic device that's completed potted?

Is there any chance it's a solid state relay or could it be simply potted to protect it against the dirt and mud on a quad bike? I can replace it with a sealed unit or a solid state if needed as the only thing I can currently think of is that either the CDI unit puts out such a small signal that a normal relay wouldn't react well to it as a switching current or potentially damage the CDI, or that the significantly high switching rate would burn out a standard relay excessively quickly.

Many thanks in advance!
I would look for a used main harness for your exact model —can find them on fleabay for ~$65. or if you get a damaged harness, scavenge the piece you need with those connectors.

Best to replace with OEM these models run best with OEM

No don’t try to build your own — honestly it’s beyond 99% of us to actually understand how the module works and build a repro.
 
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