mightyscoob

My 96 WRX STI has for awhile has been having several problems

1) On a damp cold morning, it appears to run on 3 cylinders but ok when reached operating temperatures.

2) Carried out all the engine sensor value checks at the ECU from the listing on the "Jollygreenmonster pinout" site. Most are within 0.3v

3) After over running (engine braking) down a hill or slowing from high speed to a roundabout, the engine light comes on. I'm used to this where I know when its going to come on or if it does, I let it idle for a few seconds while still slowing down the light will go out or stay out before engaging a gear to drive on.

4) Cleaned the ICV and MAF both values are OK to ECU.

5) The only possible problem I can find is the Water Coolant Sensor where it appears the voltage stays at 1.9v cold or hot.

When checking any of the error codes at the ECU, it most often points to either ICV or Crank sensor, yet ICV values are correct.

Cannot find any info of what the cold and hot values should be for the Water sensor.

Changed the 02 sensor in the header with no results.

Also cleaned the Crank position sensor, but again cannot find any method of measuring any values for this except I know it gives a waveform so without a oscilloscope type device cant check it..

Anyone got any clues if the above faults are to anyone sensor or anything else.

Thanks

Big 'D'

Do you have an after market ecu fitted? The factory ecu has a built in test function which will allow the ecu to tell you what the fault is without guessing, do a search for reading ecu fault codes you will find a guide for doing this, a failed engine temp sensor will cause the ecu to run the rad fan/s constantly whilst the engine is running.

The built in test function is basically connecting 2 single pin black connectors together under the dash on the drivers side, then switch the ignition to on with dash lights on, engine not running. The check engine light will flash a code or multiple codes at you, slow flash = x10 fast = x1. There will be a slight pause between codes and they repeat in a loop so if you dont get it first time just keep watching, once done switch off ignition and disonnect the black plugs.

Cheers Iain

mightyscoob

It is a Japanese factory fitted ECU with no remaps with the above error codes.

thanks

silver6933

Oops I posted the below without reading the 2nd post fully.

Look under your dash for the two BLACK connectors(male and female) . single pin each

These are the read DTC connectors. Connect them, then turn ignition ON.

The CEL will flash the DTC code out. If the flash is perfectly rhythmic, then there is no error codes

Note some cars have the plug wrapped up in the loom. You may need to pul;l back the insulation to find it.

BUT from your diagnosis, I also lean toward the coolant temp sensor. It is common for these symptoms.


Testing sensor

To be frank, i have not done this below test on your model year car.

Easy test remove unit place tip in pan with water(keep rest of unit in water tight bag and keep separate connectors . Connect VDM to pin in ohm mode.
Crocodile clip convertors work best. Keep it away from edge of pad(wooden spoon over pan works well)

Check if resistance changes as water heats up. Do not let water boil, as steam can cause other issues.

Note some units have one pin and the body of the unit is ground.


DTC


Note the apparent misfire, might be giving the other DTC codes(i know it is redundant, but reads well). Easiest test to see if it really is a crank sensor failure.

Is warm the car up until the miss goes away. reset ecu. Go for a good blast. Check if Crank sensor code comes back.

Also put the crank sensor near a normal spanner. It is sticks weakly = failing (mostly if it does not stick, = failed unit). If it sticks well, it still might be going out.

Remapped

Your unit requires an additional EEPROM on board. Not very likely.

point 3

Also you do not mention where this happens hot or cold or both.

The ICV might be reading correctly electrically. But remember it also is a mechanical side to it. Which might be partially sticking or blocked.

Connect the test mode connectors (green plug under dash) And turn on key. Use a flat screw driver to check if ICV is working. The other thing to do is(when cold)

Start car. At idle does it sound rough. Rev engine to 3000rpm. Does the engine stabilize? ICV also works when in coast down