Dyno'd the Corolla, A/F dangerously Lean!!

[Chris Corolla S]

So this Saturday my club did a dyno day and I decided to throw my 2001 5-speed Corolla on the Dyno Jet for a baseline run. My only mod to the engine is an EL Prototypes Cold air Intake. The car has about 65,000 miles (~104,000 kilometers) on it.
Now most stock 5-speed 1ZZ-FE Corollas put down about 110 WHP and equal Torque. I have seen enough dynos to know this. I expected to see at least that if not a couple more horses from the ELP CAI. A bunch of people went before me and put up the expected numbers for their mods with no surprises.
Well They strap my car on the dyno and when they floor it for the first pull, the A/F ratio shoots up from the 14 or so that it was at during idle to almost 17!! The guy running the machine is like "Whoa, whoa this thing is running really lean!" So the guy in the car backs off. He says sometimes this happens on the first pull and lets try again and see if it richens up. So they rev it up again and again my A/F shoots up with the revs so that it is at 16-17 at redline.
So they decide they don't want to run it hard anymore and take it off the dyno. It put down 98 lb-ft of Torque and 88 HP , obviously because it is not being supplied with enough fuel up top right where the power band is. I have a pretty good idea that either 1, there is a problem with my fuel delivery, like a clogged fuel filter, or 2, my Mass air flow sensor is not reading any additional air past a certain RPM so it stops telling the fuel system to add fuel even though more air is comming through.
I figure I can try switching back to my stock air box, putting some fuel system cleaner in, and changing out the fuel filter, but what is an inexpensive way to see if my A/F is OK?? I would never have known this without the wideband O2 sensor at the performance shop, so how can I check A/F without one?
Thanks

Chris

[Chris Corolla S]

I also have another question which is could their machinery have malfunctioned?? Why isn't my car throwing codes if the A/F is that far off?? Shouldn't it be reading a dangerous lean condition with the O2 sensor or some shit??

[dexter_5000]

one way to check its not as exact but look at your spark plugs, the computer will only throw a code beyond a certain point you may have been just before the point of the code being thrown.

[Tony the Tiger]

Yup, check the plugs... it should tell the story if your car is constantly running lean.

There is a very high chance for the wideband at the dyno to malfunction. These sensors have a service life, and at many occasions, dyno operators are either too cheap to do a routine replacement of the sensors or they haven't had any problems so they don't care much about it.

If you want accurate A/F, best to buy one yourself. Or if you have a friend with a wideband unit, drill a hole into your exhaust before the cat and weld a bung to temporarily install a sensor to monitor the A/F's.

The stock ECU will not know how lean the car is running at WOT... the CEL should trigger only if the stock O2 sensor detects lean conditions during closed loop operation. So if your car runs stoich at closed loop, it would assume the engine is fine. I am not 100% on that for yor particular Corolla, but most of the cars are like that.

For idle, 17:1 is pretty normal... I would tend to believe that cars are now tuned for lean idle, and A/F's frequently rise to 16.5 or higher when the O2 sensor algorithm trims fuel at idle. Even on my Camry (1994), A/F's would rise to 16.0:1 A/F at warm idle from the reading on my AEM UEGO.

[Chris Corolla S]

Hmm so I can pull my plugs and use my color-picture plug diagnosing chart to see if it has been running lean. But then if I do something that I think might fix the problem, I can't pull the plugs the next day to tell if it is fixed or not. They will only tell you the general condition of the combustion over time right?

As for the dyno malfunctioning it worked fine for about 8 cars, then did my car, then worked fine for 3 or 4 morewould it happen like that??

As for the idle being lean, my car and the others there seemed to hover between 14 and 14.5 at idle, but the other cars stayed in that same range throughout the rev range (all 1ZZs and 2ZZs) while mine shot up with the revs. They said I must be getting great gas mileage, but it has been pretty poor latley. I can't belive that my but dyno didn't register a loss of 20 Horse Power .

[dx-r]

I have a wideband on my Tacoma and at idle it registers 14.3-14.6

I would recommend buying a wideband. They cost around $300.

[blownrx7]

if you plan on doing some serious tuning, then invest in a wideband and an EGT gauge, for an NA car running that lean is probably not going to ever give you problems. but you never know, are you using regular unleaded?

[Chris Corolla S]

I have been using 87 octane regualr unleaded fuel since the car was new as suggested by Toyota.
However I ran two tanks of 89 octane in it before I dyno'd the car.

[Peter]

running lean isnt good.......did u have a ratio....????? and also maybe lean ur lines.....fuel ingetor cleaner should clean it up...that could be one possablity...