1JZ running WAY lean

BlackMKIII

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Jan 6, 2007
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The car: 1JZ, manual, stock ecu/injectors, APEX-i AFC NEO, AEM Wideband gauge/controller.

Symptoms: Idles poorly, A/F ratio off the lean scale at idle and cruising, richens normally under boost. No ECU codes, vacuum reading normal, no leaks detected.

When it started: After cruising on the freeway a bit, took my kitten into the vet. Dropped her off, came back out, and the strange idle started. When I went to pick her up 2 hours later, noticed a/f ratio issue.

Possible causes: My theory is MAP sensor or the wideband sensor is bad.

The pressure reading (on the AFC) has never really quite matched the display that my boost controller says. They've always been off between 6-12 kPA depending on random chance it seems. If this is normal I'll say the MAP is good.

When I blew up the engine in July a lot of oil went into the exhaust, enough for it to drip from the connection to the downpipe. It's possible that the oil has contaminated the sensor with enough carbon deposits to shorten its lifespan considerably.

Everything was fine as long as I was driving the car on the freeway regularly, but after sitting in the garage for almost a week, it's worse. I actually had to program the AFC to richen the mixture at idle just to keep it running today when I had to run an errand.

As long as I can get the car into boost, the mixture goes all the way rich and everything is fine. Just can't seem to figure why it's so lean under vacuum. Any ideas?
 

BlackMKIII

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Jan 6, 2007
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suprahero;1187706 said:
Have you tried increasing your fuel pressure?

Oh, I guess I didn't mention that I had the fuel pressure set at 43 with the line off. It's an Aeromotive, for reference.

Um, I honestly hadn't thought about it since it seemed like an electrical problem to me. I did check it however. Hmmmmmmnnnnnnnn. It's an interesting thought to see how much I'd have to crank it up to get the AFR to normal.

Although, if the o2 sensor IS bad, than shouldn't I be getting faulty readings to begin with, since the sensor is working the ECU? Maybe it only richens up because it goes into open loop? Hmmmmmmmm..............

I'm confused.
 

suprastanger507mgte

2x88+2x89+1x91+2x92=ME
Apr 5, 2005
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Hayward , Ca
make sure none of the piping is popped off and none of the vacum lines are venting. I know a map based car will run with the piping off, but it iwll run poorly at lower idle...been there...its always wse to check.
 

BlackMKIII

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Jan 6, 2007
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WELL

I finally tested the theories I had. I checked the wiring to the ecu, no resistance there. So I wired the factory o2 back in, turned the correction off, and went for a test drive. Drives flawlessly, runs damn good again. The only thing I can't figure out is this:

If, with the factory o2 hooked up, it runs perfect, then the o2 sensor must have been the problem, right? Except now the a/f ratios I'm seeing on the gauge are perfectly normal. If the wideband sensor is the one transmitting to the gauge, then the gauge translates that signal to one the ECU can interpret, than maybe it wasn't the sensor after all? Maybe I have a bad gauge that isn't converting it properly?

Or maybe I'm just confusing myself again. :-\