Son of Idle Switch

[Telkwa]

I didn't want to hijack the "idle switch?" thread.  Our 720 quit idling months ago.  It's definitely carbureted, not fuel injection.  It's always had lousy mileage, but I attributed that to the dually rear axle and low final gearing.  I'm hoping for some help from datzenmike or anyone else. 

If I do have broken wires, as suggested in the previous thread, how can I test?  I've got a multimeter.  Where do the wires usually break?  Also, the solenoid that datzen referred to - where do I find that solenoid?

[datzenmike]

The idle cut is a hexagonal shape with a red wire going to it. If you turn the ignition on off on off you should hear a clicking sound from it. No idle cut = no idle.

 

Dirt can block the idle circuit. Carefully remove the idle cut, watch out there is a spring, washer and a small needle in there. Get it out and spray carb cleaner in the hole. Use the kind with the plastic straw.

 

Unfortunately the idle jet itself, is plugged at the factory and not easliy removed for cleaning.

[JWJohnson]

You have any photos of this? I understand the description, but am curious as a location on a carb in case I run into this issue?

[datzenmike]

 

Hexagonal thing on the end of the red wire.

[Telkwa]

OK, thanks for the pic.  That helps.  In the "idle switch?" thread you mentioned the round plug at the back of the carb.  Do you have any directions for checking those wires?  It might take a few days but I'll be back with results.

[datzenmike]

That's this type?

 

.

 

 

I guess a multi meter set on resistance and check for continuity.

[Telkwa]

Thanks very much!  I'll be under the hood again this weekend.  Then ibuprophen.  This isn't as much fun as it was 30 years ago

[datzenmike]

Nothing is.

[Telkwa]

You've got a point there. 

 

So, there's this pair of wires that just disappear into the "front" of the carburetor body.  I have no idea what they do.

 

 

Then there's this plug-like contraption on the passenger side of the carb.  Anybody know what this does?

 

 

Then there's the gaggle of wires that datzenmike described.  The idle cut doesn't look exactly like mike's but I assume this is it.

 

 

This carb is so filthy I'm thinking about pulling it out, attempting to rebuild it, and replacing several feet of vacuum tubing.  I found some pretty good pictorials on NICO forums.  I'd appreciate any input, especially from people who've had carb headaches and gotten them resolved. 

Oh, hey, one thing I forgot to mention - this truck has always had a weird rhythmic surge at idle.  It used to settle down, then rev up a little, then settle back down, every couple of seconds.  I squirted some carb cleaner or something similar around the base of the carb hoping for a reaction but never got one.

[datzenmike]

You've got a point there. 

 

So, there's this pair of wires that just diappear into the "front" of the carburetor body.  I have no idea what they do.

 

That's the wires to the air/fuel mixture solenoid. It opens and closes many times a second constantly adjusting the mixture. The ECU is under the driver's seat and this is as close to EFI as a carb can get. The throttle position, coolant temp, RPM, air temp, and oxygen sensor all feed indo to the ECU and it sets the pulse rate for the solenoid.

 

Then there's this plug-like contraption on the passenger side of the carb.  Anybody know what this does?

 

Yes that's the plug for the electrically heated element under the carb. It warms and helps evaporate the fuel so the motor runs smoother (and with lower emissions) when starting up in the cold.

 

Then there's the gaggle of wires that datzenmike described.  The idle cut doesn't look exactly like mike's but I assume this is it.

 

Yup red (and black) wires to the idle cut solenoid. That round connector is a source of loose or broken wires. When idling try moving the plug and it's wires. If there is a bad connection the idle may change (for good or bad) If so this would indicate a possible broken wire. As you can see one bad or intermittent connection can tell the ECU all kinds or wrong things. Because the oxygen sensor is used as a feedback to keep the mixture as close to stoichiometric as possible, and to prevent damage from an over lean mixture there is a 'limp home' default mode that forces an over rich condition.

[Telkwa]

That round connector is a source of loose or broken wires. When idling try moving the plug and it's wires. If there is a bad connection the idle may change (for good or bad) If so this would indicate a possible broken wire.

 

Thanks very much for the help! 

 

It won't idle.  Someone's gotta keep their foot on the throttle.  If I get my wife to sit in the seat and hold the rpm just above stall, is there any point in messing with the wires?  Or would the truck be off whatever circuit that might tell us something by wiggling wires?  I think for now I'll just disconnect the plug and check it out visually as best I can.

 

The secondary is actuated by vacuum, right?  Would a person see the secondary move if the truck's parked and in neutral?  I twisted on the linkage the other day and never saw the secondary do anything.

 

The choke comes off as the little heater warms up the spring, right?  Or something like that?  I should be able to just turn the key on, and the choke should open up after 5 minutes or so? 

 

I'm just trying to figure out where to start.  This truck is a mess, and I've neglected it for too long.  It leaks oil, the paint is ruined, I've got slow voltage leaks on two circuits ('horn' and 'tail lights/cabin light', according to the fuse block cover), won't idle, the mice have moved in again, etc.

 

What's the best way to figure out what carb kit I need?  Is there a place on the carb to look for a Hitachi part #?  It's not the original carb.  I bought this one from a remanufacturing outfit years ago.  If I recall the original's linkage bushings were bad.  Maybe I shoulda gotten the original one fixed instead of buying this replacement, because the replacement caused that rhythmic surge at idle right from the get-go...

[datzenmike]

 

It won't idle.  Someone's gotta keep their foot on the throttle.  If I get my wife to sit in the seat and hold the rpm just above stall, is there any point in messing with the wires?  Or would the truck be off whatever circuit that might tell us something by wiggling wires?  I think for now I'll just disconnect the plug and check it out visually as best I can.

Try that, if the idle comes back it may be a bad connection. Also have someone turn the ignition on/off/on/off/on/off (don't start) see of you hear a faint click sound at the idle cut solenoid.

 

The secondary is actuated by vacuum, right?  Would a person see the secondary move if the truck's parked and in neutral?  I twisted on the linkage the other day and never saw the secondary do anything.

Yes operated by vacuum. You would have to rev pretty high at full throttle to see it just for a split second. I just hold throttle open, (with motor off) and lift up on the vacuum canister arm and the secondary throttle plate should open freely. As long as it moves the vacuum should open it.

 

The choke comes off as the little heater warms up the spring, right?  Or something like that?  I should be able to just turn the key on, and the choke should open up after 5 minutes or so?

Actually no. For the choke heater to be working the engine must be running. It was designed that way. 

 

I'm just trying to figure out where to start.  This truck is a mess, and I've neglected it for too long.  It leaks oil, the paint is ruined, I've got slow voltage leaks on two circuits ('horn' and 'tail lights/cabin light', according to the fuse block cover), won't idle, the mice have moved in again, etc.

Does the horn work?

 

What's the best way to figure out what carb kit I need?  Is there a place on the carb to look for a Hitachi part #?  It's not the original carb.  I bought this one from a remanufacturing outfit years ago.  If I recall the original's linkage bushings were bad.  Maybe I shoulda gotten the original one fixed instead of buying this replacement, because the replacement caused that rhythmic surge at idle right from the get-go...

Are there wires going to the other side of the large plug that match the wires in the front that go to the carb????

[Telkwa]

Yes, the horn works. I had a multimeter inline between the positive side of the battery and that secondary plug on the battery terminal that feeds the fuse block.  With all fuses pulled the multimeter finally dropped off to "almost" zero voltage.  When I plugged the "HORN" fuse back in it jumped to battery voltage.  I went around to the front of the truck and unplugged the single connection going to the horn. (EDIT: There are 2 horns.  Didn't realize that until I took the valance off)  The voltage leak remained.  Maybe I should sell the horn since that's about the only 'known good' part.

 

The wires coming off either side of that round plug at the back of the carb don't match up.  Most of them don't anyway.

 

Here's the "truck" side of the plug...

 

 

And here's the carburetor side...

 

 

I'll start with the carb side of the plug.

 

The green/white wire goes to this gizmo perched underneath the carb on the valve cover side.  Something I hadn't spotted yesterday.

 

 

If we continue clockwise from the green/white wire, the black wire and the red wire go to the idle cut thingie you described a couple of days ago.

The dark blue wire goes to the choke.

 

The last two wires are the yellow/black wire and the white wire.  These go around to the front of the carb.  The two wires that you described as the air/fuel solenoid wires.  Is this solenoid inside the carb??  Or under the seat?  Or somewhere in between?

 

I double-checked this next part to make sure I didn't screw up.  "Carb side" means I'm starting with the wire at the carb, and following it across the round plug to the loom. 

The carb side green wire connects to a white/black wire on the other side of the plug.

The carb side black wire (idle cut) goes to a yellow wire.

The carb side red wire (idle cut) goes to a red/yellow wire.

The carb side choke wire, which is dark blue, connects to a lighter blue wire.

The carb side yellow/black wire connects to a yellow/green wire.

The carb side white wire connects to a red/yellow wire.

 

I don't remember for sure because it was a long time ago, but I don't think I did any research when I replaced the original carb with this rebuilt one.  The plug fit together, and that was good enough for who it was for.  The truck ran OK but not great for several years.  It had the wobbly idle right off the bat, but the 'no idle' problem is fairly recent.

[datzenmike]

I was afraid that it was , you know, regular carb swapped on. This one should work but there are adjustments to be made like the throttle position switch. Won't idle sounds like the idle cut. Did you turn the ignition on off on off on off? and listen for the click it makes???

[Telkwa]

I had my wife click the key over several times.  I put a fingernail directly on the idle cut solenoid, and leaned over as close as I could to listen.  I did not hear or feel anything from the idle cut solenoid.   To be absolutely sure I could open the round plug and borrow some voltage from the battery.  Tap some voltage across the leads and see if I can hear anything.

 

If I can find a replacement I should be able to get the leads out of the round plug or splice the wires if I have to.  Are replacements available? 

 

Something right up by the carb goes ticketyticketytickety when the key's on, but it's always done that.  I've always thought it had something to do with the electric fuel pump?

 

That gizmo with the green wire behind the carb on the valve cover side... do you know what that is?  Never mind - I googled "720 idle cut solenoid" and found several Ratsun forum threads which discuss the throttle switch.  So, you already answered this, I just had to find the earlier posts...

 

Also, I don't know what you mean by a 'regular carb'.  Do you mean an earlier model that wouldn't be able to talk to the computer under the seat?

 

I forgot to mention that I kept it running long enough this afternoon to see the choke opening up.  So that appears to be working.  I won't say it's perfectly adjusted or anything, but the choke was pulling open.

[datzenmike]

I had my wife click the key over several times.  I put a fingernail directly on the idle cut solenoid, and leaned over as close as I could to listen.  I did not hear or feel anything from the idle cut solenoid.   To be absolutely sure I could open the round plug and borrow some voltage from the battery.  Tap some voltage across the leads and see if I can hear anything.

Try wiggling the plug and wires with the key on. If a loose wire it may make contact and the solenoid will click. Power to the solenoid is likely on the red wire and goes to ground on the black. I guess you could connect a 12 source to the red wire to power the idle cut solenoid. This would give you your idle back. Better to fins a source that is on with the engine so it does not drain the battery. Best to find out why it's not getting power fom the ECU

 

If I can find a replacement I should be able to get the leads out of the round plug or splice the wires if I have to.  Are replacements available?

No sense changing stuff until proven it's not working. It may just not be getting voltage from the ECU under the driver's seat. 

 

 

That gizmo with the green wire behind the carb on the valve cover side... do you know what that is?

 

Maybe the throttle position switch ground. It should be closed above 1,300 RPM to let the ECU know you are stepping on the gas, and open below and at idle.

 

 

 

 

Also, I don't know what you mean by a 'regular carb'.  Do you mean an earlier model that wouldn't be able to talk to the computer under the seat?

Yes

 

 

 

Can you unplug the two plugs on the ECU and check that none of the pins are bent and they are making good contact?

[Telkwa]

Yes, I'll check the ECU plugs right now. 

 

I didn't explain myself very well re: the idle cut solenoid.  When I mentioned 'borrowing some power', I just meant for testing.  I don't need this thing running by Monday morning no matter what it takes.  I'd like to take a stab at fixing this old rig, not start hacking away at it.

 

Any links to trouble-shooting the ECU would be much appreciated.  It sounds like there are some lights that might help if a person knows what they mean?

 

So the idle-cut gets its signal from the ECU?  Wow, OK, maybe I'm starting to understand a little bit of this.

 

The throttle position switch must be tricky to adjust.  I'm guessing I'd need an engine tach and a multi-meter?  Move the rpm around until I see the throttle position switch close (or open), then adjust, then try it again, adjust, repeat...  The switch doesn't actually see rpm, all it sees is the mechanical arm that it leans on, right?  I'm gonna go look at that too. 

 

I pulled the hood off yesterday, and the cowling underneath the wiper arms.  Removed several cubic feet of mouse nest.  Industrious little ba$!@rds...

 

Removed the driver's seat and the ECU.  The pins all look really good.  Notice there are two wires coming from the black plug that look like they've been re-taped with some brown electrical tape.  I thought, uh-oh, better take a look at that.  The odd thing is, the black outer tape that bundles this entire gaggle of wires doesn't end at this end.  Whoever taped this loom together started at this end and taped back in the other direction.  I couldn't find an obvious seam where someone had cut the original outer tape, then re-taped.  That makes me think maybe the wires were messed with at the factory, before the entire loom was taped up.

 

 

The parts inside the ECU look OK to me.  The half dozen times I've found something obviously bad on a circuit board like this it's usually a capacitor that's blown up.  In this case, that would be those brown wafers standing up on two wires.  The outer epoxy coat ruptures and bits of molten material will spray the immediate area.

 

 

Here's a shot of the ECU part #

 

 

It's raining so I'm takin' a break.  Gonna pull the idle-cut solenoid off next.  The idle-cut wires will be severely twisted while removing unless I can pop those two wires out of the round plug, or disconnect everything else that feeds thru the round plug.

[Telkwa]

So, I should be able to test whether the ECU is sending a signal to the idle-cut solenoid easily enough.  Open the round plug, turn the key on, check the red/yellow wire coming from the loom side of the plug for 12V.  Right?  The red/yellow wire goes thru the round plug to the red wire that goes to the solenoid.

 

UPDATE - After cleaning up the ECU, I put it back in place.  Opened the round plug behind the carb.  Turned the key on.  The little green LED inside the ECU turned on.  Turned key off.  Hooked a multimeter inline between the red/yellow wire on the truck side and ground.  There are 2 red/yellow wires, which is lame, so I made sure to grab the one that goes to the idle cut solenoid.  Turned key on.  Got voltage at the wire.  So that tells me the ECU is trying to energize the idle-cut when I turn the ignition switch to "run".

 

Unscrewed idle-cut solenoid.  Had to twist the wires a bit to get it out but not too bad.  As others have warned, be careful with the tiny plunger and spring.  Using a couple of alligator-clipped test wires, I rigged things up so that I could hold the solenoid in my hand with a finger on top of the plunger, then swipe a battery post with my other hand to put voltage across the device.  I didn't know if the plunger would suck in or push out, but one thing I did know is I didn't want to lose the internal pieces so I kept that finger on top.  Tried putting 12V across the solenoid several different ways.  Never got any response. 

 

ANSWER: The spring pushes the pin into the idle circuit when the key is turned off, 12V pulls the pin back into the solenoid.  So 12V pulls it inward. 

 

Here's what mine looks like

 

 

With the correct tool you can poke into the round plug and free the wires.  Once you've pushed the tiny barbs back the wires will slip right out of the round plug.  If you look at the ends of the wires you can see the tiny barbs that need to be pried back out a little bit before reinsertion.  Since this one appears to be dead I won't be reinstalling.  Just wanted to pass that on to someone who wants to get the idle-cut solenoid out and bench-test it.

 

So I put the idle-cut housing back in, without the plunger or spring.  The truck is idling again.  Thanks very much datzenmike!

 

Anyone got one of these for sale?  

[slemers]

So without the plunger and spring does it diesel when you shut it off? I bought a parts carb for 30 bucks in Vancouver. The guy had another carb if I recall. I can dig up his number if you like. Maybe he has a idle solenoid that will work for you. I'll take a look tomorrow at mine and see if it has the same solenoid you need.

[Telkwa]

Yeah, it does run on.  I turned it on & off several times yesterday afternoon after a full day of tinkering.  That would be awesome if you have a working spare piece!  They're not readily available.

 

Synopsis of yesterday's events for anyone who's got the time, and/or owns one of these trucks but hasn't spent a lot of time under the hood.

 

I bought 20' each of the two vacuum hose diameters commonly used under the hood, and replaced 95% of the hoses.  Replacing the hoses that connect to the metal tubing that runs across the front of the engine required getting the power steering pump out of the way.  That was kind of a hassle.  I almost ran out of smaller hose, but still have most of the larger hose.  It woulda been fun to use that brightly colored silicone hose, but I couldn't find any in town.

 

I lucked out and got the O2 sensor off without having to buy or rent a special tool.  It wasn't welded onto the manifold like I was expecting.  Used a

to see if there was any voltage left in it.  Nothing.  Bought a new sensor.  NAPA had a Bosch.  Had to splice the wire, but that was no big deal.  The Bosch came with a terminal end for crimping, and a little piece of heat shrink tubing.  The O2 sensors on these trucks are very simple - no shielded wire (I don't think so anyway) and no extra wires for heaters like modern O2 sensors.

 

The oil pressure sending unit has been leaking badly for years.  All this time I'd thought that the rear engine seal was leaking.  Maybe it was just that rotten sending unit!!  The sender is hidden under the intake manifold.  It took over an hour to get it off the car.  If I'd had the proper deep socket it woulda been relatively simple.  I ended up using a plumber's basin wrench.  Couldn't get enough oomph using the little piece of round stock included with the basin wrench, so I used a small pipe wrench.  Got the sender out, but of course the pipe wrench chewed on the basin wrench shaft.  Oh well...  Our local NAPA store had a sending unit with a spade type terminal and a square plastic housing for some kind of connector that our 720 doesn't have.  O'Reilly's had the right unit, which looks like this.

 

New oil filter and oil.  Finally it was time to start it up.  It seems to be idling a little more smoothly, which may be due to the new vacuum hose? 

 

I worked on the time bomb problem, then called it a day. 

[slemers]

When i bought my 720 a couple a months ago, My engine ran on and I just slipped the clutch to kill it. I sent you a pm with a guy that has some 720 carbs for parts or rebuild. I don't think he has the feedback carb you need but maybe he has the idle solenoid you need. He told me that he was looking for a feedback carb himself.

 

Slemers