TC35A Won't Start

Chender · Jul 1, 2014

This one has me baffled.

Two days ago, changed from hay spear to bush hog, and mowed a bit. Later, the engine would crank, but not start. Noticed a bit of water in fuel filter bowl, and cleaned that out and replaced the fuel filter. Bled line of air. Still no start.

Eventually, traced problem back to no power to injector pump solenoid. Checked solenoid with jumper from battery, and it actuated. That left the fuel shutoff relay as potential problem. Jumped pins 3-5, after which shutoff solenoid actuated and engine would run. Deduced relay was defective. As cross-check, tried the flasher relay (they're all the same model) in place of the fuel shutoff relay. No start. Checked voltage to relay coil (pins 1-2), and that's present when key is turned on, although the relay did not actuate.

So, in summary, there appears to be voltage to relay coil (pins 1-2); certainly voltage between pins 3-5 (verified with voltmeter and jumper), but, unless I jump pins 3-5 of fuel shutoff relay socket, the injector pump solenoid will not actuate and engine will not run.

The one improbable conclusion is that there is not sufficient current to actuate the relay. As said before, baffling.

I'm hoping someone can spot something I've missed.

Thanks in advance for your suggestions!

tcreeley · Jul 1, 2014

Wish I could, but can't!
Good luck!

dave1949 · Jul 1, 2014

If there is voltage between pins 3-5, then that is an open. The jumper would be closing that. What else is in the circuit/harness between pins 3 & 5 that is not completing the circuit? I'm not looking at a diagram, so hopefully that isn't a stupid question.

It sounds like you have eliminated the relay itself.

Chender · Jul 1, 2014

Normally, when the relay closes, pins 3 & 5 contact (short), delivering the voltage to the injector solenoid. Unfortunately, the relay won't close (nor does any replacement relay). Hence the quandary! It's puzzling that there is some 12 v. present (with the key on) between pins 1&2 - the relay coil pins. But the relay doesn't actuate (although, when checked with the battery + ground to pins 1 & 2, the relay DID close. that's what made me think there is sufficient resistance somewhere in the relay actuation voltage that prevents current flow sufficient to activate the relay....

dave1949 · Jul 1, 2014

I see.

Can you test your resistance idea by running a jumper in parallel to just a portion of the existing circuit feeding the relay coil?

You said going from the battery worked. Working forward from the battery in circuit segments might find a high resistance section. Sort of divide and conquer.

The test would be something like jumping from the battery to the next connection point: doesn't work (that section isn't the problem). Jumping from that connection to the next one: does work (something between those points is the problem).