Adjusting the ECU
 

I have been wondering what would happen if I messed with the inputs from some of the temp sensors to the ECU.

Here's the idea, The cylinder head temp sensor (CHT) and the air temp sensor work off a resistance value. If you put a variable resistance pot in the circuit you could change the reading the ECU gets.

I've always notice my 87 NA runs stronger when it's not up to temp yet. I figure the ECU is adjusting the mixture as it sees the temp/resistance change. You could put the adjustment right on the dash so you could make changes as you drive.

Just a crazy idea???

I found this info in the FSM. If you want to read it all it somewhat confirms what I thought. The ECU does change what it doing when the engine is cold. The last line says under 140 deg.


Fuel Injection Control
The E.C.U. calculates the basic injection pulse width by processing
signals from crank angle sensor and air flow meter. Receiving
signals from each sensor which detects various engine conditions,
the E.C.U. adds various enrichments, which are pre-programmed
in the control unit, to the basic injection amount. Thus, the
optimum amount of fuel is injected through the injectors.
1) Fuel enrichment
During warm-up
When starting
After idle
With heavy load
The enrichment rate for "when accelerating" and "with heavy
load" are pre-programmed for engine speed and basic injection
pulse width.
In each of the following conditions, fuel is enriched.
When cylinder head temperature is high.
2) Mixture ratio feedback control
The mixture ratio feedback system is designed to control
the mixture ratio precisely to the stoichiometric point so
that the three-way catalyst can minimize CO, HC and NOx
emissions simultaneously. This system uses an exhaust gas
sensor located in the exhaust manifold to give an indication
of whether the air-fuel ratio is richer or leaner than the
stoichiometric point. The control unit adjusts the injection
pulse width according to the sensor voltage so the mixture
ratio will be within the narrow window around thestoichiometric
air fuel ratio.
However, this system will open under the following conditions:
When starting.
When engine and exhaust gas sensor is cold.
When driving at high speeds or under heavy load.
At idle
When exhaust gas sensor monitors a too lean condition for
more than 10 seconds.
When fuel shut-off is in operation.
When exhaust gas sensor is malfunctioning.
When pressure regulator control system is in operation.

3) Injection timing
Two types of fuel injection systems are used - simultaneous
injection and group injection. In the former, fuel is injected
into all six cylinders simultaneously twice each engine cycle.
In other words, pulse signals of the same width are simultaneously
transmitted from the E.C.U. to the six injectors
two times for each engine cycle.
In the group injection system, six injectors are divided into
two groups - No. 1, No. 2, No. 3 and No. 4, No. 5, No. 6.
And fuel is injected into each group separately once each
engine cycle.
When any of the following conditions are met, fuel injection
shifts to simultaneous injection from group injection.
* When starting.
Engine speed is more than 3,000 rpm.
Cylinder head temperature is below 60°C (140°F).

The only thing that will happen if the computer senses the car is overheating is it will pull timing and increase injector duty cycle.

as long as you keep the adjustments in the right range the ECU would never read that the engine was overheating. in fact I think the best results would be to make it think the engine was cold.

probbaly better off to put in a new chts and let the car operate as designed. If you want to diddle electronics go megasquirt.

Screw megasquirt, go nistune. :icon_pidu: