PappyFeb 20

Cross-posting this here in case there are any Car-stodon folks who have a thought as to what could be wrong.

'96 Toyota 4Runner with the v6, crank no start. When the key is in the ACC position the engine makes a constant clicking sound (in the video you can hear it.)

https://www.reddit.com/r/3rdGen4Runner/s/jy2djjXYne

#CrankNoStart #Toyota #5vzfe #CarRepair #mechanicadvice

Show threadPappyFeb 23

Updates:

Noticed no RPMs on gauge when cranking. Pulled the crank position sensor. Sensor tested good. Wiring and connection was oily but nothing chaffed or broken. OBD scan tool would not connect to the ECU, gives ‘Linking Error.’

Pulled ECU and inspected. Looks fine, no loose pins, the inside looks clean and new, no corrosion or burn spots, no loose parts or debris.

Show threadPappyFeb 23
The OBD port has 4 wires. Two grounds (pins 4 & 5 - tested good,) power (pin 16 - tested good, batt voltage) and a signal wire (pin 2.) I measured 0.44v at pin 2 with the key on (ACC position.) The voltage never changed and the scanner would not link with the ECU. I am assuming this means the scanner and ECU are not talking to each other. Chat says the signal should vary as the two communicate. I did not observe that.
Show threadPappyFeb 23
I tried to ascertain where the comm line is at the ECU but could not find good information about the position and color of the wire. According to Chat It is either a Violet or White - Red Stripe wire on connector E10 (there are 4 connecting plugs: E9-E10-E11-E12.) I measured no signal on either wire. In case there was a wire break I jumped pin 2 on the OBD plug and the violet wire on E10. Still no communication. I'm now thinking I may be measuring the wrong wire per my Haynes manual.
Show threadPappyFeb 23
The IAC valve was the source of the clicking. I unplugged it and the clicking stopped. I was able to start the engine with it unplugged by holding the throttle body open a bit. It would only run for a moment before dying. Later I plugged the IAC valve back in and got it to run for a bit longer but it was definitely running rich (a bit of white smoke out the exhaust) and it smelled like fuel, would pop and sputter a bit. It did not run well.
Show threadPappyFeb 24

IAC Valve clicking,

https://youtube.com/shorts/znLBagVW56U?si=KU0VKWkpNz0bd5Iw

Opened up the ECU, looks fine,

https://youtube.com/shorts/sxfvrvgdFIQ?si=piMmTYS9VYha2j-4

February 23, 2026

YouTube
Show threadPappyFeb 24
I've finally found a '96 wiring diagram. The OBD comms line is a white wire on a different plug. I was measuring the wrong wire, lol.
Show threadPappy

For anyone curious, it was the ECU. I put in a used one I got from a parts dealer on eBay and the engine runs like nothing was ever wrong with it.

On Friday I verified mechanical timing and that the engine had compression. I tested the wiring again, verified grounds and powers, tested fuses and relays. Since I had a wiring diagram that matched my ECU I was able to verify that the communication line between the OBD reader and the ECU was good.

Mar 1 at 12:49pmWeb
Show threadPappyMar 1

It only ever showed 0.44V, no variation, even with the OBD reader plugged in and attempting to communicate. I had no idea if that was normal or even if my multimeter would show any variation while communicating normally.

Once the ECU came it was a simple swap. I did test the communication with the OBD reader and it was good. You CAN observe the variation in voltage. Resting is about 0.45V and it will vary up 0.85-1V. I was using the 2V DC scale. I forgot to try the AC volts scale.