-----Original Message----- To paraphrase Columbo, there's just one more thing,
Dick. The reason I got on the computer kick was in one of the few times I got
this thing up to running temperature, I tried the trick of biasing the
oxygen sensor lead by touching the battery posts with my left hand while
holding the terminal. There was no change in the idle. Does
this indicate the CCC is still in open loop? Sounds like it. Have you checked the resistance of the EFI
coolant temp sensor? They do fail, it's rare but I've seen a bad one. If
it fails shorted, the CCC stays in the cold engine mode. If it fails
open, (which is much more likely), the CCC goes to the hot engine mode, so you
can check by unplugging the connector when the engine is cold and when it is warmed
up – it should make little difference when the engine is warm. You
can also check the resistance between the two prongs – it should be
somewhere around 900 ohms at room temp, and much higher (1500 ohms or so) at
180F. Don’t remove the sensor unless you are certain it is bad AND
you have a replacement handy, they often crumble when you try to take them out!
This is the two prong sensor mounted at the top front of the engine at
the upper radiator hose connection, not the switch type mounted under the AC
compressor. Be gentle with this critter, it is brittle and it is very
hard to find a replacement. Another thought is that it takes a Looooong time to get everything into
normal operation, especially if you have been disconnecting the battery each
time you park it. The memory gets wiped, and it has to go through the
whole "calibration" routine each time you do that. I assume you are familiar with the calibration routine – if not
study this in your FSM. If you just put the car in normal service, it
will calibrate itself, but you need to drive it for a while to do this. Otherwise,
you can do it in your driveway by following the procedure given in the FSM. And, there's just one more thing (right back at you, Detective):
The keep alive wire to the memory is the most vulnerable wire in the harness -
it's the lonesome red #18 wire that dangles out from the 3 wire connector under
the CCC. If this becomes damaged (and it is easy to stress this guy when you
remove the air cleaner assembly to work on those nozzles!), the CCC loses it’s
memory ability, so the car becomes like the Alzheimer’s patient who can
hide his own Easter Eggs – every day is a new day! (This is the
same as disconnecting the battery every time you turn off the engine). For a cold EFI car, provision has
been made for the "warm-up" transition phase - it is the CCC Memory Module.
Therein lies a fixed program that provides Idle Speed and Fuel/Air Mix
Ratio and Ignition Timing to maintain the engine until it can be more
efficiently controlled by the output of the Oxygen Sensor. Also, during this
time, no vacuum is allowed to either purge the Vapor Canister nor have fresh
air blown into the rear-most Cat Converter; the EGR valve, also with
a temp sensor, will not operate. You will notice a beautifully smooth
drop in "Fast Idle Speed" as the engine warms. The Coolant Temp Sensor will
warm-up and send a signal to the computer which will send a signal to
the 70 second Timer which will proceed to "Time Out." After that
time, the Air/Fuel control, via the CCC, is handed over to the Oxygen Sensor and
we have Closed "Bracketing" may begin,
the Vapor Canister purging begins, the Diverter Valve now sends air to the rear Cat Converter
instead of the back of the engine heads, and the EGR Valve
begins to operate, the Air Flow Sensor comes to life and contributes to the plan
and ignition timing becomes a function of what is necessary for optimum
operation. We now have ideal conditions of Fuel Management and emission
requirements. My comment on the above: I think Bob may have made a small
error: It seems that the air flow sensor comes into operation as soon as the
key is released from the “start” position – that is why the
car will start by stall with the lid off the air cleaner, even when it is ice
cold. I got so many pleas to keep this discussion on the main IML that I’ll
go ahead and post it to the list – when people complain maybe we’ll
have to start a sub group for these cars. Dick Benjamin |