Mechanics

ISSUE WITH O2 SENSOR HEATER CIRCUIT &

1988 Toyota Pickup

Engine Performance problem
1988 Toyota Pickup 4 cyl Two Wheel Drive Automatic 44000 miles

22REC engine (Calif), 1-ton

I replaced O2 sensor because I was not getting a good reading then I noticed it appears O2 sensor heater is not being activated. HT pin on ECU is used to ground heater circuit, but is staying high. If I manually ground this pin I get about 1amp, which seems right.

Q: Should this heater be turned on as soon as engine starts, or are there other conditions that gate it? Is this a burned out ECU?


When warm idles poorly, almosts stalls when put into gear. Failed smog due to high HC. Power seems low. Smooth acceleration, but not very quick. Revs up high eventually fine. Freeway speed is no problem. Starts fine.

Added an air leak and that made it worse, so it seems like it is running lean. Haven't found air or exhaust leak. Idle speed air bypass screw is turned out almost all the way to get idle when warm.
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Larkimg
August 4, 2010.




Hi larkimg,

Thank you for the donation.

The O2 heater circuit is turned on as soon as the engine is started.

The idle adjust screw being turned out almost fully indicates the passage is clogges and rrequires cleaning. Get the throttle body cleaned and retest if it runs well.

Have you tried to retrieve for troube codes?
Was the Mass Air Flow Sensor tested?

KHLow2008
Aug 6, 2010.
Yes, turns out ECU was bad. New (used) ECU activates heater as soon as engine starts. I also noticed it turns it back off when RPM gets to a certain point (1750?). Seems reasonable as exhaust gas at that higher RPM should keep it heated.

Idle problem was valves were too tight.
Runs better now.
I suspect it should pass smog now.

Thanks,
Larry

Tiny
Larkimg
Aug 6, 2010.
Glad to know you have fixed the problem.

Have a nice day.
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KHLow2008
Aug 7, 2010.

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