Important tech stuff if you own a 240. Or any car really. MAF CTS TPS O2 AFR A/F

[rsmithdrift]

These are the proper diagnostic values and procedures for the important sensors on the 240.

Also about 3/4 of the way down is an excellent discription of a/f ratio's and how they affect horsepower and performance. I highly recommend anybody tuning a sports car read and know this stuff.

I've collected all this info by copy and pasting from various sources such as the FSM and various car websites/forums. So I am not taking credit for the information itself. I just wanted it all to be in one place so it's easily accessible for people in the future.

Mass Airflow Meter:

Probe the signal wire with a voltometer set to DCV 20. It should be 0.25v with ignition on and engine off. With car at idle it should read 1.2v. Signal (max) is 5v which is approx. 290hp worth of airflow. This is the computer's primary means of dictating your car's A/F ratio. Lower reading = less air flow = computer adds less fuel. The inverse is true. If this reading is inaccurate IT IS IMPOSSIBLE FOR THE CAR TO RUN PROPERLY

Coolant Temp Sensor:

to test your cts get an ohm meter and unplug the sensor and check the resitance of the sensor. you will also need a thermometer to check the temp of your coolant. the values are as follows:Resistance 2.1 - 2.9 K ohms at 68 deg F 0.68 - 1.00 K ohms at 122 deg F 0.236 - 0.260 K ohms at 194 deg F

As this value decreases the computer increases fuel load and retards timing to lower cylinder head temps and reduce detonation.

Throttle Position Sensor & Soft/Hard Idle Switch:

The Throttle Sensor responds to the accelerator pedal movement. This sensor is a kind of potentiometer which transforms the Throttle Valve position into output voltage, and emits the voltage signal to the ECU. In addition, the sensor detects the opening and closing speed of the Throttle Valve and feeds the voltage signal to the ECU.

Idle position of the Throttle Valve is determined by the ECU receiving the signal from the Throttle Sensor. This system is called "Soft Idle Switch" and controls engine operation such as fuel cut. On the other hand, "Hard Idle Switch", which is built into the Throttle Sensor unit on the A/T equipped models, is not used for engine control.

Trouble Diagnoses:1. Disconnect Throttle Sensor harness connector.2. Make sure that resistance between terminal #1 and #2 changes when opening the Throttle Valve manually.Looking at the "pins" of the connector w/ the locking tab of the connector pointing up, terminals #1 is the one on the LEFT. #2 is in the MIDDLE and #3 is on the RIGHT.

The results of the test should be:

Accelerator Pedal Condition Resistance in k OhmsCompletely released Approx. 2Partially released 2 -10Completely depressed Approx. 10If test shows "No Good", replace Throttle Sensor.

Adjustment:

If Throttle Sensor is replaced or removed, it is necessary to install in proper position, by following the procedures shown below:

1. Install Throttle Sensor body in the Throttle Chamber. Do not tighten bolts. Leave bolts loose.2. Connect Throttle Sensor harness connector.3. Start engine and warm up sufficiently.4. Measure output voltage of Throttle Sensor using voltmeter.5. Adjust by rotating Throttle Sensor body so that the output voltage is 0.45 - 0.55 volts.6. Tighten mounting bolts.7. Disconnect Throttle Sensor harness for a few seconds and then reconnect it.

With the locking tab of the connector pointing up and looking at the back of the connector as the wires from the wire harness go into it, terminal #1 is the one on the LEFT. #2 is in the MIDDLE and #3 is on the RIGHT.

Output voltage is measured across terminals #2 and #3 from the harness side of the connector.

POWER SUPPLY:

Disconnect the TPS harness and look at the terminal side of the connector. (this is the side with the terminal connectors in it) With the locking tab pointing UP, the terminals are A, B, and C, from left to right. This is measured from the male half of the connection that goes to the engine.

Turn the ignition ON and measure the voltage between terminal C and ground. It should be approx. 5v.

GROUND CIRCUIT:

Ignition OFF. Check for continuity between terminal A and ground. Continuity should exist.

RESISTANCE:

Make sure that resistance between terminal A and B of the connector half (female) that goes to the TPS changes when opening the Throttle Valve manually.

The results of the test should be:

Accelerator Pedal Condition Resistance in k Ohms

Completely released Approx. 2Partially released 2 -10Completely depressed Approx. 10If test shows "No Good", replace Throttle Sensor.

VOLTAGE ADJUSTMENT:

1. Loosen the 2- bolts that hold the TPS.2. Start engine and warm up sufficiently.3. Measure output voltage of Throttle Sensor using voltmeter.4. Adjust by rotating Throttle Sensor body so that the output voltage is 0.45 - 0.55 volts.5. Tighten mounting bolts.6. Disconnect Throttle Sensor harness for a few seconds and then reconnect it.

Note: With the locking tab of the connector pointing up and looking at the back of the female connector as the wires go into it, terminal #1 is the one on the LEFT. #2 is in the MIDDLE and #3 is on the RIGHT.

Output voltage is measured across terminals #2 and #3 from the harness side of the connector.

Adjusting the idle is pretty straight forward:

Disconnect the TPS harness and turn the idle adj. screw on the IAA to get the car to idle at 650 rpm. Reconnect the TPS harness and your beloved should purr at 700 or so rpm. (The Factory manual gives a +/- tolerance of 50 rpm.) The IAA is at the back of the intake manifold. You can see it standing over the right (passenger side for N.A.) fender and looking at the funky device with the dime size recess for the adj. screw.

O2 Sensor:

A bad O2 sensor can have a significant affect on gas mileage. Here's a procedure for checking the O2 sensor. The procedure may be the same for your year.

Checking the O2 sensor

The following procedure applies to all 1991 and up 240-SX models:

1 - Turn on ignition switch (do not start engine).2 - Turn diagnostic mode selector on ECU fully clockwise.3 - Wait a few seconds.4 - Turn diagnostic mode selector fully counterclockwise.5 - You are now in MODE-II.6 - Start engine and let fully warm up (temperature up to normal).7 - Run engine at 2000 RPM or higher for about two minutes under no load8 - Check that the inspection lamp (red LED) on the ECU goes on and off more than 5 times during 10 seconds at 2000 RPM.

A dirty or old sensor will tend to read lean which would result in a rich condition. o2 sensor does not control the mix at idle!

Testing o2 sensor with volt meter:

This is basically duplicating the mode2 self-diagnostic test. This can be easier than reading the codes off of ecm. If you get a reading other than alternating 1 and o , the information is not that useful as you dont know if the o2 sensor reading is accurate. ie if you get .5 volts which is stoichiometric you dont know if that reading is right.

A.O2 sensor disconnected:

Unplug the O2 sensor from harness. Place one probe on sensor wire and one probe on ground. It should alternate between 1 and 0 if mix is optimal.This test makes sense at idle as o2 sensor does not have any say in the mix.

B.o2 sensor connected

The o2 sensor is in the circuit so your test is the same as ecm mode 2 test.Above 1500 rpm, it should altenate between 1 and 0

1 is rich and 0 is lean. a reading from .2 to .85 is optimal. the car has to be heated up by driving. if you sit around idling o2 sensor will get dirty and cool and read lean. if you get a reading above .85 it is safe to say you are rich as the o2 sensor tends to read lean when it is dirty or cool



Edelbrock has compiled a list of A/R ratio descriptions and how they affect engine performance.

5:1: Rich burn limit due to excess fuel. Combustion is weak or erratic

6-9:1: Extremely rich mixture. Engine will produce black smoke and low power.

10-11:1: Very rich. Some supercharged engines run in this range at full power to control detonation.

12-13:1: Rich. This slightly rich mixture produces the best power for unsupercharged engines. When you read engine dyno charts for performance engines particularly, maximum power will usually be found in this A/F range.

14-15:1: A 14.6:1 A/F ratio is considered stoichiometric, which is chemically ideal. Theoretically, there's no excess fuel or oxygen remaining after combustion. This is the A/F ratio that the ECU in an EFI equipped car is trying to maintain. Overall, this range is best for part throttle cruise.

16-17:1: This lean mixture is the best A/F ratio for economy. It can be borderline for part throttle, since this lean mixture is unstable and prone to detonation. THis ratio is worse if EGR is used.

18-19:1: Very lean ratio. It's considered the upper limit of drivelability. If the ratio is any leaner, detonation will occur, if it hasn't already!!

What is the optimum air-fuel ratio to run for best power?

I've heard racers say that we need to run a bit lean for best power - is this true?

Maybe. It's somewhat true that running a tad bit richer will help quench detonation (knock), but only to a certain extent. The stochiometric AF ratio for gasoline is 14.7:1. Stochiometric means that at this point, the fuel is completely burned with no unburned hydrocarbons left, giving you best emissions. This is the AF ratio the PCM is shooting for under idle and cruise.

However, best power is achieved for gasoline at around 12.5:1, leaving excess unburned hydrocarbons, but no unused oxygen molecules! (This is why 12.5:1 is typically the best power point.) So under ideal circumstances, the best power AF ratio to shoot for is around 12:1 to 12.5:1. However, running a tad bit richer will throw excess fuel (gasoline) into the combustion chamber, and the extra unburnt fuel actually acts as a heat sink, absorbing heat and cooling the combustion temperature, hence reducing the tendency for detonation to develop. However, this only helps to a certain extent. If you're knocking severely, you can throw all the raw fuel you want into the mix and it won't quench the detonation.

When you run richer than 12:1 on gasoline, you're losing power. Between 11:1 and 12:1, the power curve is fairly flat and you're not losing very much power, much richer than about 10.5:1 and you're starting to lose power drastically, and probably not helping your detonation problem either.

So the answer is to achieve around 11:1 AF ratio for your best compromise, not going richer than about 10.5:1 at most. You won't be inherently down very much on power due to the AF ratio, but you're probably delaying the onset of detonation enough so that your spark advance isn't being severely retarded, thus helping your power - end result, you get the optimum power / knock control balance.

When racers speak of running on the "rich" side they're really referring to running around 10.5:1 area, whereas when they speak of running on the "lean" side, they're really referring to the 12.5:1 area, whether they know it or not. They're not actually running "lean" (which would be something greater than 14.7:1), they're just running on the "lean" side of best power.

AFR for a NA engine needs to be in the 13-13.5:1 range under WOT, with it ending up around 13:1 towards redline at optimum.

A FI engine should probably have an AFR between 11.5-12.5:1. 12.0:1 is a good compromise in my opinion. Offers a bit of excess cooling, and helps ensure no lean pockets in the combusiton chamber.

A NA engine around 11.5:1 AFR will probably be down quite a bit of HP over one running 13:1 AFR.

"A lack of air-flow during dyno testing will almost always alter the fuel mixture in the rich direction as the radiator cannot exchange enough heat, resulting in the computer compensating by retarding timing and richening the fuel mixture to prevent the engine from overheating and detonating. In addition, the intake air sensor will read substantially higher temperatures than that seen on the road with proper airflow. This issue is particularly important to address when testing high output cars like the M5 or M3, and even more so on forced induction cars with intercoolers as the heat exchanger is not able to cool as efficiently because of the reduced air flow. The engine compartment is normally flushed with air driving down the road, particularly at speed, cooling the manifolds and other associated engine components. Cooler engine components and lower air intake temperatures will result in a leaner air/fuel mixture and ignition timing will be advanced, invariably resulting in greater power on the road than on the dyno. In simpler terms, accurate measurements can only be achieved when the dyno tests are conducted in a manner that simulates the car driving down the road, in as much as is possible. "

Again I am not taking credit for this info. It's not my info. I just compiled it all together and posted it here. It has helped me more than anyone could possibly imagine and I hope it helps someone who's searching for this info in the future. I spent weeks looking for this stuff when I needed it.
Modified by rsmithdrift at 6:11 AM 2/3/2010

[frftw]

this is awsome!bookmarked

[speedeast]

From the 240 gods themselves

[rsmithdrift]

Somebody should sticky this.... Seriously