Small LH Fan always on

Someone correct me if I'm wrong, but I believe that the same thermostatic switch controls all three fans, even though each has its own relay. My guess is somebody hotwired this fan. You might experiment by pulling the relay entirely and turning on the ignition switch and see if the fan runs.

 

+1 (or, at least, I'd bet on that too)

They completely mixed-up the relay descriptions, the item names, and/or the wiring itself on your OM schematic, but the way the wiring is drawn (which I judge as the most reliable ):

if water temp hot (coolant thermoswitch closed) = all three fans run (AC "on" or "off")

if water temp cold (coolant thermoswitch open) and AC "on" = one front fan and the rear fan run.

if water temp cold (coolant thermoswitch open) and AC "off" = no fan runs

Each motor does have a separate relay, but the way that two of the relays have their outputs connected together, one front fan and the rear fan are wired together (so since you report the rear fan is running independently = must be some sort of modification). Any obvious "improvements" to the plumbing? If the rear fans is always running, when the coolant temp is cold and you turn on the AC, does one of the front fans start running?

 

Steve
I do not believe the pull fan on the left side runs with the AC, instead the two push fans on the right side run with the AC. The AC condenser does not extend to left side of radiator and would make no sense to run. I spent a lot of time checking when I re-wired my fans which still use the standard control logic just no power thru the relay panel (documented elsewhere in this forum).
Ken

 

Ken - I was only reporting what is shown, and described, in the 176/79 OM (for a 1980 400iA) -- your 1984 would use the 250/82 OM so may be completely different (it definitely has a more user-unfriendly schematic that is also a poor scan quality in the online copy so I'm not checking ).

 

Quick rundown on the K-Jet: mixture control is handled by a plunger moving up and down in a bore in the center of the fuel distributor. Moving up in the bore increases the flow of fuel to the injectors, moving down decreases it. Airflow in the induction path causes the plunger to rise in the bore. How high it can rise in response to a given level of airflow is controlled with hydraulic pressure applied to the top of the plunger. It is gasoline itself that the system uses for a hydraulic fluid. Fuel pressure at the top of the plunger is bled off to the warmup regulator ("WUR"). The WUR has a bimetal strip that closes a valve in the WUR when an electric current is applied to the strip and it warms up. This increases the pressure on the top of the plunger, which reduces the amount of upward movement as the bimetal strip warms up. This leans out the mixture. This has the same effect as an electric pull-off of the choke plate on a carburetor.

One possible cause of rough running 30 seconds after starting, in cold-ish weather, is that the mixture is leaning out too quickly. The way to check if it's the WUR doing this is a fuel pressure test. I have posted up a thread with photos from when I did this. I monitored fuel pressure in the line to the WUR as the bimetal strip warmed up. If you find this thread, be sure to read it all the way through, because most of my "how-to" threads have mistakes in them that other members then correct. Reading all the way through, you will get the corrections too.

 

How typical! Don't mean to be Debbie-downer, but, if the coolant thermoswitch is closed (warm) = all three fans should be running. Since you didn't report that F, you must have some other faults/modifications somewhere too...