Jump to content

Key on, engine off, something near the carb is ticking like a time bomb


Recommended Posts

Anyone know what makes that ticking noise?  Our '86 720's done it since I can remember.  This is with the key in the "run" position, but the engine off.


The ticking is fairly quiet.  When I try to google it I keep getting Ratsun and other hits but they're always about engine noise when running or testing the idle-cut solenoid.


I always thought it had something to do with the electric fuel pump.  Maybe some sort of relief valve.  Now I'm wonderin' if it's something else.

Link to comment
  • Replies 10
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Well, thanks to you guys I've been learning about our old '86 720 with its feedback carb. 


The time bomb ticking is definitely the air/fuel ratio solenoid.  I removed the the white wire from the round plug (post #13 of this thread).  Put the round plug back together.  Turned the key to "run".  No tickeytickeytickey.  Went ahead and started the truck.  It seemed to run OK, didn't seem worse than before anyway.  I peeked into the ECU's peephole.  The green LED was not on. 


Turned the truck back off.  Reinserted the white wire back into the round plug.  Turned the key to "run".  Tickeytickeytickey.  Started the truck.  It idled OK, about the same as with the fuel/air ratio solenoid de-energized.  The ECU's green LED was blinking.  The blinking wasn't rhythmic.  It was kind of random.  It was on roughly as much as it was off, but sometimes it was on longer, sometimes off longer.


So I'm left with questions: is the ticking normal?  Is the air/fuel solenoid supposed to tick tick tick with the key turned to "run" but the engine not running?  If not, does that mean that the air/fuel solenoid in the Hitachi carb is broken?  If so, can the solenoid be replaced?

Link to comment
  • 2 weeks later...

Mine ticks without the key turned on.  Continuous ticking coming from the carb.  Does sound like a fuel pump but I know otherwise.  When I have the ticking, I have idle problems.  See my post, idle cut solenoid thread. 

Link to comment

I didn't realize you meant that the carb was ticking with the key off.  That's different!


During my troubleshooting, I'd already disabled our idle cut solenoid, and still had the ticking.  I verified by pulling wires that in our case the ticking was coming from the fuel/air solenoid. 


As far as I know the idle cut solenoid could make a similar sound if it was receiving a continuous on/off signal.  I think the simplest thing for you to do at this point would be to open the round plug and carefully pry back the barbs on either the red wire going to the idle cut, or the white wire going to the fuel/air solenoid, then slip the wire out of the plug.  Put it back together and verify which solenoid is ticking.


Do you know how to use a piece of metal as a listening device?  You might be able to verify which is ticking by listening, but I doubt it.  Both are attached to the carb, and they're only a few inches from each other.  The idle cut is on the outside of the carb.  The fuel/air is inside the float bowl area somewhere, so maybe it could be done. 


At this point in time I know enough to be dangerous, so please take my advice with a grain of salt.  But from what I've gathered so far the air/fuel solenoid won't stop the truck from running, although it may not run as economically as it should.  A malfunctioning idle cut will definitely ruin your idle.  But once you're off the idle circuit the truck should run OK even with a malfunctioning idle cut solenoid.


Solenoids ticking with the key off, choke plate doing crazy things - I wonder if the ECU is going gunny sack. 

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.