How do I cure a lean condition?

[whooppee777]

update please

[whooppee777]

my stock afr sensor is moved away from my nitto midpipe to prevent it from reading crazy readings because of not having a cat. and i monitor the readings through my blitz r-vit and i took a look at it last night. it was reading 14 all the time and i my eyes immediately exploded but then i remembered i moved my sensor away from the pipe with a spacer.

anyways the point is i have been getting readings of 14.such and such for months and the ecu has never set a code saying its running lean

[LtNoogie]

If it isn't raining too hard tomorrow, I'll see about routing the wideband harness through the firewall. I was going to clamp it to the end of my tailpipe to take a reading but remembered that on the automatic, the S/C does not engage in Park or Neutral so I'd only be reading NA operation.

[LtNoogie]

I finally got my vacuum/boost gauge and wideband a/f gauges installed and working. I really don't see a lean condition according to the wideband until I go into DFCO. According to the Autometer paperwork, I'm spending most of my time in a stoichiometric range.

Sometimes after WOT and releasing the throttle, the a/f mixture will briefly go rich. Perhaps there has never been a problem.

This video has been cross-posted in another thread. You won't want to watch it again.

http://www.youtube.com/watch?v=05RZSyraA5Y

[LtNoogie]

Originally Posted by camelll

How far back from the manifold is your a/f sensor or do you have egt?

It's still in the same spot between the two cats. It was a real PITA to arrange for the car to be lifted and the stereo guy drill a hole in the floorboard. It was too hard to get the muffler shop to put in another bung closer to the header while the stereo guy was standing around. Luckily the two shops are next to each other.

There's been all kinds of debate on this thread about whether the further back you have the wideband sensor affects the reading or whether it affects the lag time between throttle and the reading. Seeing as how the dyno guy read from my tailpipe, where I have the sensor now is fine by me.

What I don't get is that from the a/f readings I got before the S/C, I was actually running a little rich during WOT. The S/C puts me right in the middle now.

[largeorangefont]

Originally Posted by LtNoogie

What I don't get is that from the a/f readings I got before the S/C, I was actually running a little rich during WOT. The S/C puts me right in the middle now.

That is typical. All cars come from the factory tuned on the rich side.

[AlexNet0]

correctumundo^

[PHXDEMON]

Originally Posted by Tamago

fuel pump is fine

bigger injectors would definitely help. source a set from a celica gts or a scion tC (i run tC injectors) you can find them both for cheap (i got mine for free, make friends with a service tech at toyota)


until then, STAY OUT OF BOOST, you're gonna blow your engine running lean like that on boost.

I just assumed something the size of a D cell battery would be stressing

[largeorangefont]

I just watched the Youtube video. It looks too lean under boost, unless the timing has been retarded by the SC adjustment box (which could be the case). The first cat is not falsifying your AFR readings much. Clearly your wideband is very close to accurate because you are seeing 14.6 AFR during cruise.

Only way to tell for sure would be to datalog the timing, or get an EGT gauge, or both. Either way, the car would benefit from a tune, probably in the neighborhood of 15-20 HP.

[LtNoogie]

Really? So the dyno guy was correct? Where would one find the optimum a/f readings for engines under boost?

[largeorangefont]

Originally Posted by LtNoogie

Really? So the dyno guy was correct? Where would one find the optimum a/f readings for engines under boost?

There is a balance, and the key is really exhaust gas temperature, or EGT.

You can run a lean AFR, with retarted timing, and get acceptable EGT values.

You can run a richer AFR, with advanced timing and get the same acceptable EGT values.

The proper AFR for a forced induction car is debateable, but generally in the 11:1 -12:1 range is acceptable depending on type of forced induction and boost level.

I don't think blitz would send you out into the world with a tune that will pop the motor, but just be aware, the tune is far from its full potential.

[largeorangefont]

Originally Posted by camelll

In between the cats or after the cats is not the optimal spot for the sensor, the instructions say: "If cast iron manifold(s) or shorty headers are used, install the sensor in the pipe just below the manifold."

We have been over what the instructions say. His setup is not optimal, but in this case it is fine. As you can see in the video, his wideband shows 14.6-14.8 AFR in closed loop conditions which we know is accurate.

It is showing high 13s low 14s under boost. While this may not be exactly accurate, the cat will not change the readings by a 2 full points.

[largeorangefont]

Originally Posted by camelll

My sensor is right after the manifold pre cats and under wot I get between 11 and 12. I would think after the cat or cats his readings are okay.

Well that is interesting...

[LtNoogie]

I found this to be an interesting read on the topic.

http://automotiveu.com/BlowerTuning.htm

[LtNoogie]

Originally Posted by camelll

My sensor is right after the manifold pre cats and under wot I get between 11 and 12. I would think after the cat or cats his readings are okay.

Does that mean that the first cat is oxidizing, or whatever a cat does, the exhaust mixture to lower the amount of unburnt fuel thereby raising the a/f mixture?

[largeorangefont]

Originally Posted by LtNoogie

Does that mean that the first cat is oxidizing, or whatever a cat does, the exhaust mixture to lower the amount of unburnt fuel thereby raising the a/f mixture?

Yes, but the cat does the same thing all the time. Your AFR is accurate while cruising. We have to assume it is close to accurate under boost conditions.

[LtNoogie]

Ok. I was planning to run the SpeedVentures Streets of Willow on April 10 where I expect prolonged WOT operation and lots of boosting. Based on what you're telling me, that may not be a good idea until I get the AFR under control, right?

[largeorangefont]

Originally Posted by LtNoogie

Ok. I was planning to run the SpeedVentures Streets of Willow on April 10 where I expect prolonged WOT operation and lots of boosting. Based on what you're telling me, that may not be a good idea until I get the AFR under control, right?

No, I believe you will be ok. What I would do is get or borrow a fancy scangauge and monitor your timing. Compare it with a stock car and see if there is a difference. Then you will know what the black box is doing. If your timing is lower, you should be just fine.

I may be going to the April 10th day as well.