While rehabing WRDs, I thought about what happens during engine start and warmup on our FI engines(w/o pollution control).
We need fuel, air, and spark. Fuel comes from the metering FIP and the CSV. The FIP has a range of 50 to 1 or so. At 110 miles/hr the engine burns, say, 1 gallon/10 miles, or 11 gal/hr. This equals about 22 oz/min. Empties the tank in 2 hours at top speed. At idle of 5 mile/hr it burns 1 gal/25 miles or .2 gal/hr. This equals 0.4 oz/min. Empties tank in 4 days. These are rough estimates, but you get the feel for the range of the FIP. Additional gas comes from the CSV. No estimate here, but must be in 2-4 oz/min range.
Air ranges from the whisper thru the idle air valve(to match idle fuel), thru the 10 mm WRD(to support CSV fuel), to wide open butterfly(to match max fuel FIP output). So air has a like turn down ratio of 50 to 1. Take the air filter off the WRD to hear the 'swish' until it closes.
Now the sequence of events when you turn the ignition key on a cold engine. You can take the cap off the rack cover, screw a 5 mm bolt in and watch the rack move thru startup and warm engine.
Key in 'Run'. Electric fuel pump starts running until returned to 'Off' The WRD is cold, Therefore, its pin is retracted and the FIP rack is in an enriched position. Barometric pressure leaning is whatever it is ----.
Key in 'Start' Starter engages turning engine at about 350 rpm and FIP at 1/2 that. 'Start' relay on rear of FIP moves FIP rack to full enrichment and stays there until 'Start' is released on ignition key. The CSV is powered and squirts full blast as controlled by coolant temperature logic system(varies on model) for a few seconds. The WRD is cold, therefore much air is rushing to the vacuum of the intake manifold and its pin is retracted enough to call for fuel enrichment on the FIP rack.
The distributor sparks start the engine and it revs up to 1200 or so rpm in this rich, cold environment.
You release the ignition key to 'Run'. Starter disengages. The 'Start' relay is depowered. This lets the flyweight governor controlled rack return to a WRD coolant temperature position of FIP fuel. Air is coming in thru the WRD and the idle air screw(butterfly closed). The CRV fuel continues spraying per its control logic.
The engine begins to warm up. The coolant temp rises to shut off CSV fuel flow and WRD air(note vacuum loss at WRD air filter). As the coolant temp rises, the WRD pin drives the FIP cold temp lever to less FIP fuel output and the rpm eventually drop to 750 - 800. This takes 60-90 seconds to warm-up the coolant.
At operating temp the CSV is closed, the WRD is closed, and the FIP has no coolant temp adjustment. The FIP is now pumping fuel at a rate determined only by the 'idle fuel' screw. All air is via the 'idle air' screw. The two 'idle' screws are adjusted to a 50 rpm rich setting. Opening the throttle now admits a Bosch factory synchronized mix of fuel and air.
A question is: How is the air/fuel ratio really controlled during the first 90 or so seconds of the warm-up? A plot of the fuel flow vs the air flow is not proportional.......?
Simple isn't it ...? This thousand($) dollar pump has been replaced by a 50 cent chip......
