Test port usable for air fuel ratio duty cycle monitoring

[bry]

I'm curious to find out if anyone knows about that connector that's near the overflow bottle.  The connector has seven pins and four are populated with wires. As I'm looking at the wiring diagram it looks like one of the wires is the air fuel ratio solenoid control. Does anyone know where I can get that mating connector? Would it be possible to hook up a Bluetooth oscilloscope to that test port?( labnation ) I imagine monitoring the air fuel ratio solenoid operation real time while driving. Does anyone know where I can find what the different color wires do on that test port?

[DwayneOxford]

Someone here did that awhile back.

[datzenmike]

The mixture solenoid works somewhat like a fuel injector in that the primary jet opens and closes rapidly with a signal from the ECU, adjusting the fuel mixture with feedback from the O² sensor. Pretty sure the O² sensor is not a wide band so only tells the ECU if above or below stochiometric. Using a clock analogy that's like it's saying it's fast or slow and not much else. 

[Sephakrid]

You might be able to find the right connector on AliExpress. That's where I found some replacement 4 pin connectors for the turn signals.

 

Personally, I used a portable scope and probed the connector at the ECU under the driver's seat.

[Sephakrid]

I'm going off of memory, but does the connector look like this?

 

 

[datzenmike]

On 11/27/2024 at 10:59 AM, bry said:

I'm curious to find out if anyone knows about that connector that's near the overflow bottle.  The connector has seven pins and four are populated with wires. As I'm looking at the wiring diagram it looks like one of the wires is the air fuel ratio solenoid control. Does anyone know where I can get that mating connector? Would it be possible to hook up a Bluetooth oscilloscope to that test port?( labnation ) I imagine monitoring the air fuel ratio solenoid operation real time while driving. Does anyone know where I can find what the different color wires do on that test port?

 

What is this going to tell you? It's a signal varying in pulse length that rapidly opens and closes the primary jet to let fuel pass into the primary barrel. The on and off frequency keeps the air/fuel mixture precisely within stochiometric with feedback from the 0² sensor.

 

In the off position or if there is a failure, the mixture fallback position is an over rich condition so the engine is not damaged by an over lean mixture. 

[DwayneOxford]

Again, someone did that fairly recently, posted up oscilloscope pictures, etc.

[bry]

I've done search words searching for the words oscilloscope and solenoid and I don't see any mention of this.  Does anyone have any suggestions on how to find the previous post about this ? The reason I want to be watching the voltage to the solenoid is and of course correct me if I'm wrong it looks like there is a lot of different stages of this air fuel ratio control it looks like there's open loop control when driving at high speeds when the engine is cold or under heavy load and then there's closed loop control. If there's another way to verify all of this is operating properly I would be interested in hearing about it. I looked at the shop manual 1986 edition and after about an hour I found that the test fitting near the overflow bottle only hooks to anti-diesling solenoid and auto choke heater. (Ef & ec-6) After looking around the engine bay I noticed that there's a green and yellow wire back on the right side of the firewall I think that goes to the air fuel ratio solenoid. 

[Sephakrid]

Here it is!

 

 

[datzenmike]

On 12/5/2024 at 10:10 AM, bry said:

I've done search words searching for the words oscilloscope and solenoid and I don't see any mention of this.  Does anyone have any suggestions on how to find the previous post about this ? The reason I want to be watching the voltage to the solenoid is and of course correct me if I'm wrong it looks like there is a lot of different stages of this air fuel ratio control it looks like there's open loop control when driving at high speeds when the engine is cold or under heavy load and then there's closed loop control. If there's another way to verify all of this is operating properly I would be interested in hearing about it. I looked at the shop manual 1986 edition and after about an hour I found that the test fitting near the overflow bottle only hooks to anti-diesling solenoid and auto choke heater. (Ef & ec-6) After looking around the engine bay I noticed that there's a green and yellow wire back on the right side of the firewall I think that goes to the air fuel ratio solenoid. 

 

 

1/  There is an 0² sensor in the exhaust to let the ECU know when the air/fuel mixture is above or below stochiometric.

 

2a/  There is a throttle closed switch to let the ECU know you are at idle and goes into open loop mode.

2b/  There is a transmission switch to let the ECU know you are in any gear

2c/  There is a clutch switch to let the ECU know that the clutch is engaged

 

If 2abc are closed then the ECU knows that the engine is in gear and decelerating so it shuts off fuel to the idle circuit via the idle cut solenoid.

 

3/  a 12v battery supply so the ECU can compensate for the 12.6 to 14.5v range.

 

4/ Tach signal from negative coil terminal to let the ECU know the engine speed. If below 400 RPM (starting) the ECU goes into open loop..

 

5/ A water temperature sensor (not sender) so the ECU knows when engine is warmed up and can switch from open to closed loop mode.

 

6/ Mixture ratio solenoid in the primary barrel. Variable pulse control of the open/close of the solenoid to keep the air fuel ratio optimum with feedback from the 0²sensor. 

 

 

Any fault, and the system reverts to a 'limp home mode' where the mixture is overly rich. This avoids a dangerous over lean condition which can damage the engine. It's assumed that the owner will at least notice the terrible gas mileage and investigate and fix the problem.