Hello, I have a problem

[Dakotasmoll]

Hey all. I’ve recently picked up an 85 720 base 4x4, California emissions 🙄. Already had quite an adventure getting it running smoothly but I’ve run into a problem recently. I do not understand how this anti diesel solenoid is supposed to work with two wires that are apparently live?
 

According to the manual if you turn ignition on, you should get battery voltage on pin G, which eventually connects to the black solenoid wire. But at the same time you got power on Red/yellow which is connected to the red solenoid wire. Is my solenoid not working correctly and should be grounding through its chassis? I have confirmed the solenoid works when red wire is +12 and black wire is (-). 
 

I also have a newer solenoid with only one wire that works normally and grounds through chassis but then it leaves my yellow wire (G) to the ECC empty, and I’m wondering if it needs some sort of feedback that the solenoid is open.

 

 

[Stoffregen Motorsports]

I can't give 720 specific info, but two positive wires sounds wrong. Is it possible that the other wire goes to another device?

 

I would say, most smog techs won't notice, or won't care if the wiring is not original. Make the solenoid work, by what ever means possible.

[Dakotasmoll]

I think either my ECC is not working correctly, or my yellow wire is crossed with something, giving it +12 all the time. The oem solenoid only works with red on postive and black on negative, and no variation. It’s just confusing to me that somehow, when troubleshooting, you’re supposed to be able to measure battery voltage on the “ground” with ignition on. Maybe the ECC is supposed to flip that circuit to ground or something?

 

my mixture solenoid apparently needs voltage on both wires in order to run…

 

 

what I’m experiencing in totality is that when starting the truck cold it runs like crap and I need to keep my foot on the gas to keep it from dying. If I unplug the mixture solenoid the idle comes up and no more problems, runs really well. Plug it back in and it will cough and try to die. (So I have a toggle switch wired to the mixture solenoid to turn it off when I start up). I’m wondering, though, if the ECC isn’t getting the right signal from the anti diesel solenoid and is therefore causing the truck to run badly (must be lean) on startup. Once the truck is hot it seems to run fine. My other guess is it’s just a bad mixture solenoid…it’s just buried in the carb and I don’t feel like digging it out. Especially because I have a New Weber sitting on the shelf. 

[Dakotasmoll]

So, in short, yes my new anti diesel solenoid works correctly, but the signal wire is no longer connected to the ECC.

[datzenmike]

There are certain conditions when the idle cut solenoid is turned off by the ECC's ECU. This would be under deceleration (over a preset vacuum limit) while in gear and clutch engaged. The throttle is at idle but the fuel usually mixed with the air for idle is not being used and just gets wasted out the exhaust so it is shut off till the vacuum lowers, clutch is disengaged or transmission is placed in neutral. 

 

 

 

There is no power on both wires, only the Red. Red has 12v from the ignition. THE OTHER YOU ARE READING VOLTAGE THROUGH THE SOLENOID. Disconnect the 6 pin connector to the carburetor. Check Red is 12v with ignition on. Black is ground.

 

 

The ECU should not need to be connected to the idle cut solenoid other than to provide cut off on deceleration.  If you have the two wire solenoid, ground the Black wire and connect the Red to the Blue auto choke heater. If you have the one wire solenoid just connect the Red wire to the Blue auto choke heater wire. The solenoid grounds through the carburetor to the engine.

 

[Dakotasmoll]

Ahhh very informative. Thank you. If I disconnect the yellow wire I can read 12v on one end and 3v on the computer end, with the ignition on. Im going to go ahead and use the new single wire solenoid and forget about that yellow wire. 
 

I’ve checked all of my senders connected to the ECC and still have this rough start, however with the mixture solenoid turned off it starts normally, I just get terrible MPG. So, I start with the mixture solenoid off and toggle the solenoid back on after the truck has warmed up 🤷‍♂️ Haha

[datzenmike]

One of the inputs to the ECU is the engine water temperature sensor. (not sender, that's for the temperature gauge) This tells the ECU if the engine is cold and would result in a richer mixture. If the sensoer were bad the ECU may think the engine is warmed up.

 

On the ECU place the resistance meter positive probe on the 8 pin and the negative probe on the 16 pin with ignition on. If above 68F you should get a resistance reading of 2.9 k ohms or less.

 

The temperature sensor is on the intake near the thermostat. Don't mistake for the temperature sender for the gauge.

 

 

[Dakotasmoll]

I seem to get a normal resistance on the sender as the truck warms up, at the ECC. I checked my spark plugs today and they were grey…I think I’ve been cooking them. I have a feeling this mixture solenoid is clogged and running very lean at all speeds. If this were not a California emissions truck, I would consider digging into the carb and cleaning that solenoid, but I think the easier path is to slap something else on it. With that many sensors on a car, I think having a code light/obdii is pretty essential. My 2c.
 

Would one of these 2 wire carbs for like $100 work pretty well? Everyone seems to swear by the Weber 32/36… “the best thing I ever did”. We do not have emissions here on the olympic peninsula, in fact the previous owner had the cat removed at some point. 

[Dakotasmoll]

I also looked for a replacement mixture solenoid…they are pricey! $100 could be a whole new carb or a nice portion of a Weber kit…IF you can get the solenoid. I didn’t inquire about availability.