TRX350D fuel pump problem

[semicolon]

Hi, I am having issues with my TRX350D fuel pump.  It suddenly stopped running so I have replaced all the fuses and cleaned all the terminals.  I have fitted a new pump, fuel cut-off relay and rectifier.  Still nothing!!  The pump runs when attached to a battery.  The engine will start on the choke and the filter fills with fuel but it will  not rev and dies when the choke is closed. I have power to the relay but nothing at the pump black/white wire when cranking the engine.  Any ideas where to go from here would be very much appreciated!!

 

[Ajmboy]

Do you have power at the fuel pump relay?...actually I see you posted that. I would start checking the wiring from the relay to the pump.

[Mech]

You have power to the relay, so now you need to check the relay is getting power to activated it, and that it has an earth on it's activation windings. If that side of the relay is operating, you need to check whether the power is getting from the relay to the pump, and that the pump has an earth.

If you tell us what year and model this is I'll try to check in a manual how the pump and relay are actually wired. It's possible that the pump, or the relay, are powered and then get switched by connecting an earth to one or both of them.

[quadmaniac]

I’m with @Mech check power at relay. 

[semicolon]

On 4/14/2024 at 4:42 AM, Ajmboy said:

Do you have power at the fuel pump relay?...actually I see you posted that. I would start checking the wiring from the relay to the pump.

Thanks, I will strip out the loom and check the wiring, it needs checking anyway!!

[semicolon]

11 hours ago, Mech said:

You have power to the relay, so now you need to check the relay is getting power to activated it, and that it has an earth on it's activation windings. If that side of the relay is operating, you need to check whether the power is getting from the relay to the pump, and that the pump has an earth.

If you tell us what year and model this is I'll try to check in a manual how the pump and relay are actually wired. It's possible that the pump, or the relay, are powered and then get switched by connecting an earth to one or both of them.

Thank you, I can't remember which year it is so I will have a look later today and find out.

[semicolon]

7 hours ago, quadmaniac said:

I’m with @Mech check power at relay. 

Thank you!!

[semicolon]

Ok, Finally found out it's a 1986 TRX350 Fourtrax.  I have power from the battery to the relay but nothing at the pump. I have continuity on both pump wires from the relay but the pump is not energising on the starter or when the engine is running so it cant rev.

cheers!!

[Mech]

I think these will be right..  The manual is for 86-89. If it's not right it probably means your bike is the previous model, up to 86.

86wiring.pdf 86 fuelpump.pdf

[Gwbarm]

Sounds like a bad relay did you replace it and still wont work.

[semicolon]

8 hours ago, Mech said:

I think these will be right..  The manual is for 86-89. If it's not right it probably means your bike is the previous model, up to 86.

86wiring.pdf 152.13 kB · 1 download 86 fuelpump.pdf 170.74 kB · 3 downloads

That's brilliant, I will have another go at it this morning!! Thank you!!

[semicolon]

4 hours ago, Gwbarm said:

Sounds like a bad relay did you replace it and still wont work.

Yeh, I have fitted a new relay and rectifier.  If I cant find a wiring fault I can only think either the CDI or the fan actuator may be to blame.

[Gwbarm]

I thought you might have already done that, just thought i would mention it. This is a tough one. You may be right about the fan controller, i would check all the connections very carefully at the controller and CDI for good contact. Is there any other problems going on other than fuel pump? 

[Finnforest]

I had a similar problem on my 350, but if it runs on choke the pump must be working, since the fueltank is lower than the carb. Maybe you have a clogged carburettor? When I crank the 350 for a split second the pump starts and build preassure then it stops. I do this everytime i start it to "prime" the fuel lines so i dont have to crank it so long. Inside the fuelpump is a preassure switch to that cuts the power to the pump when there is enought preassure in the line, The fuel relay somehow works with the rpm of the machine. I hate this setup, almost thought of putting a gastank from a 300 trx on it 😃

[semicolon]

On 4/23/2024 at 2:35 AM, Gwbarm said:

I thought you might have already done that, just thought i would mention it. This is a tough one. You may be right about the fan controller, i would check all the connections very carefully at the controller and CDI for good contact. Is there any other problems going on other than fuel pump? 

Thanks, no, I haven't noticed any other problems.  I have now stripped out the complete wiring loom and will now test each of the wires!! 

[semicolon]

On 4/23/2024 at 9:17 AM, Finnforest said:

I had a similar problem on my 350, but if it runs on choke the pump must be working, since the fueltank is lower than the carb. Maybe you have a clogged carburettor? When I crank the 350 for a split second the pump starts and build preassure then it stops. I do this everytime i start it to "prime" the fuel lines so i dont have to crank it so long. Inside the fuelpump is a preassure switch to that cuts the power to the pump when there is enought preassure in the line, The fuel relay somehow works with the rpm of the machine. I hate this setup, almost thought of putting a gastank from a 300 trx on it 😃

What you say makes perfect sense but I think I must still have enough fuel in the tank to allow it to gravity feed as I tried removing the pressure line and blew into it...still nothing!!  I gave up yesterday after stripping the whole top end and the wiring loom.  Fuel relay working on rpm makes sense but I don't know what activates the fan as I can't find a thermostat!!  Will have another go later today......

[Gwbarm]

As i recall the motor controller, a very expensive part and no aftermarkets available, is activated by the CDI, and it absolutly has to have a good ground to operaate correctly, including the fan, the controller itsself may be grounded through the CDI, not sure, i am having trouble relating what i know to yours because the one im more familar with didnt have a fuel pump. I think what you are doing stripping the wiring loom and checking is the best way to find it, you can throw expensive parts at it all day long and still may not get it. You have worked hard at it i havent been much help, but good luck. 

[semicolon]

On the contrary, you and everyone who have replied have been very helpful, I really appreciate it. That's really good advice, thank you.  I will pay particular attention to the earthing and post any findings.👍

[Mech]

The fan gets switched on when the oil temperature gets high.

The fuel pump gets turned on when you first turn the key but then switches off unless it's getting a pulse from the cdi. The pulse from the cdi is the same pulse that fires the ignition coil, so if you have spark, you have the required pulse to operate the fuel pump relay, you just need to ensure it's getting to the pump control relay.

When wires have no continuity, or have high resistance, it's almost right at the end of the wire where it crimps into the metal terminal, it either corrodes or breaks the wires inside the insulation. Wires do sometimes break if they have been chafing for a long time on something and worn right through the electrical tape, insulation, and then the copper wire, but that's easy to spot by the frayed insulation.

[semicolon]

4 minutes ago, Mech said:

The fan gets switched on when the oil temperature gets high.

The fuel pump gets turned on when you first turn the key but then switches off unless it's getting a pulse from the cdi. The pulse from the cdi is the same pulse that fires the ignition coil, so if you have spark, you have the required pulse to operate the fuel pump relay, you just need to ensure it's getting to the pump control relay.

When wires have no continuity, or have high resistance, it's almost right at the end of the wire where it crimps into the metal terminal, it either corrodes or breaks the wires inside the insulation. Wires do sometimes break if they have been chafing for a long time on something and worn right through the electrical tape, insulation, and then the copper wire, but that's easy to spot by the frayed insulation.

Brilliant, cheers,  there is a good spark so it sounds like I have either a broken/poor live or a dodgy earth so hunting for that will be tomorrow's task 👍

[semicolon]

Well, as an update, and hopefully save others the time and cost of parts, after replacing the fuel cut off, rectifier and kill switch, and stripping and testing every wire and connection, I checked the carb again.  Although I had taken it apart and cleaned, then blown it through with the airline, I had missed a tiny grass seed which was stuck in the main jet!!  After poking it out with a strand from a wire brush, she fired up and revs a treat!! Just shows you that even after 50 years working on motors, even an old fart like me can still make "rookie" mistakes!!🙃DOH!!

Thanks again to everyone for their help👍, ps, all the answers deserve a "tick" as being most helpful.