1983 280zx turbo ECU Pin 22 FICD input

[Dave WM]

been working away on the test stand. other than an intermittent spark (think its a wire harness issue with the CAS but still need to confrim that with some more testing) all going well.

I tested the idle up servo for the AC control. Works by applying a vacuum to a small hose, this allows bypass air to increase thus upping the idle speed. Works great.

Question, the FSM calls 12v to be applied when the FICD is active. This goes to Pin 22. I cant for the life of me figure out what its supposed to do. If the idle up servo is work to increase the bypass air, what could the ECU add? If the ECU is only responsible for fuel mix and ignition fire and time, I would assume it has to be adjusting one of those. Seems to me bypass aire by default would take care of fuel mix do to the AFM. So that leaves timing. Perhaps it adjust timing, but seems to me added RPM would automatically deal with timing. 

Anyway hope someone has found out what this is for. Driving me nutz...

[cgsheen1]

In stock form, the FICD is controlled by a solenoid valve - Nissan calls it a "Magnet Valve". The solenoid is mounted near the vacuum bottle (one of two) and serves to control the vacuum applied to the FICD. I think nearly every ECU has a pin tied to the A/C clutch. In the swap into my 260Z I didn't use any of that (vacuum bottles, magnet valves, FICD) and:

A. The ECCS ECU didn't seem to care

2. My A/C worked fine and the turbo engine has enough torque that it doesn't seem to mind the extra load of the A/C compressor at idle.

c. The stock ECCS kinda sucks and I moved to a different ECU (not nearly as soon as I should have) cuz the stock harness REALLY sucks after all these years.

I my opinion the 1983 FSM is MUCH more difficult to navigate than the 1982 FSM and there are only minor changes between the years. I normally refer to the '82 manual much more often.

[Dave WM]

I have it working pretty well now. the idle up just uses the vacuum from the stock FICD solinoid (rather than operating a pull up servo, is directly access charge air and adds that to the intake manifold). I may end up scoping the duty cycle of the injectors just to see if there is any change with 12v on the pin 22. 

My next goal is to adapt the wire harness to the 6 pin connector of the stock 75 harness. My goal is to be able to wheel the run stand next to the car, plug in the harness from the run stand to the under dash harness, start the engine on the run stand from the key in the car. Then test to make sure all the normal indicators work (tach, oil, temp) I just want to make sure the rest of the body harness is not effected. The igntion will still use the + coil connection from the body harness, but the blue neg wire from the ign module inside the car will be disconnected, the ECU drivin transistor driver will take over that duty. I presume the tach is in the wire engine harness, hence the reason for leaving that installed and just disconnecting at the stock ign module.  I had quite a journey getting the crank angle sensor issue worked out (intermittent cut off after running for a few minutes). I did check for exhaust gases in the rad again, all good. cooling seems to be fine as well, revs out nicely. Not sure how to check the ecu for closed loop operation. I did not notice the typical oscillation of voltage at the O2 sensor, but it did hover right around .5v the whole time. 

 

[Zed Head]

1 hour ago, Dave WM said:

Not sure how to check the ecu for closed loop operation.

I thought that there was a flashing light involved on the ECU somewhere.  Vague memory.  Might be mentioned in the FSM troubleshooting section.

[Dave WM]

there is a green led, I see it come one with KO and goes out after start. I will need to get a turbo FSM and study it. All I have done so far is consult the wiring diagrams. Some where I recall reading that it will not go into CL until completely warmed up (both the engine and the O2 sensor which does NOT have a heater built it). Also IIRC something about the led comes on when the mix is rich, dont recall where I read it. Clearly FSM is next.

[Zed Head]

Found it.  This is from the 1982 FSM.

[Dave WM]

roger that thanks, will do some testing, pretty sure I never looked at it unless it was idling. I suppose my warm up period where it gets to about 165f will be ok, If it does not work I will try a 185f T stat. I also have a new bosch O2 sensor I can try.

[Dave WM]

ok so the green light comes and goes when doing the described test. It also runs like poo when just held there at a very high idle (and the green led is flashing on and off. I seemed to be lean as I could depress the flap on the afm and it would clean up, as if the CL was causing a lean run. The O2 sensor was showing over .5v when this was going on as well, as if the O2  sensor was telling it your rich when it was not. So my only guess is this is:

this rough running at 2k plus no load is normal

the O2 sensor is not correctly reporting the oxygen levels

I have missed some thing in the wiring of the sensors.

I checked the throttle position sensor (on at idle off above idle), the head temp sensor (340 ohm at about 170f right on the chart line). Forgot to check the air temp sensor, will do that (located in the AFM). Timing set at 20 BTDC (per FSM for turbo). 

The only other thing I can think of is maybe getting some new plugs in there just to make sure that is not an issue, its been idling a LOT on those plugs, maybe they are a bit fouled and not happy with a lean run. 

 

[Dave WM]

oh and it will run fine if I just goose it when the poo begins. Revs up fine.

[cgsheen1]

The L28ET ECCS uses the O2 sensor rarely (unless you're doing a lot of freeway cruising at a constant speed). It's effectively used only to trim fuel economy during cruise. At idle, under load, at low RPM or high RPM the ECU is just reading its maps and ignores the O2 sensor. Don't make the assumption that the ECCS is smarter than it actually is. There is no Throttle Position Sensor - It's just a switch that "senses" idle. And there's no brilliant use of the O2 sensor in controlling fueling or any other engine function. It's only a small step smarter than the EFI of the N/A engine. The CHTS is just the EFI engine temp sensor mounted in a smarter place.

The ECU only polls the sensor under very specific conditions - fairly narrow RPM and Load values. When the ECU IS in closed loop mode it varies fueling until a RICH condition is reported, then it cuts fueling slightly to get a lean signal, rinse and repeat in a fairly continuous pattern as long as the "cruise" conditions exist. It tries to keep the exhaust output just on the edge of the lean/rich flip of the sensor (so, close to stoich). That's what the Green LED is telling you when you have the engine in a cruise configuration and the ECU is attempting closed loop.

Edited March 2, 2023 by cgsheen1

[Yarb]

Impressive information

[Dave WM]

cgs, I will post up some video of the actual test run later. Any idea on why the running poorly takes place as soon as the green led becomes active? Perhaps as you say I should look elsewhere for the reason I have the poor running condition at 2k rpm constant speed after warm up (other that closed loop O2 that is). 

I will conduct some more test after I get some new plugs. That way I can read them as well to if indeed the mix is rich or lean. Suppose I could install my color tune plug as well to see what is going on. 

I suppose since it takes place after warm up the CHTS should be the 1st suspect, it seemed to have the correct value for the heat range, but I did not test it at the ECU pins so will do that also. 

Edited March 2, 2023 by Dave WM