mitcher

Hello my friends, you always have helped me on this forum and this time I need definitively your assistance. I paste below the email that I have wrote to my parts dealer on the USA, my car is an 88 Vette.

Thank you!

Dear friends,

I am Miguel Miranda from Spain (EU). I have purchased to you some times in the past and now I have a doubt about two parts that I bought to you, so I write you hoping to receive a response and fix my problem.

Here in Spain old cars must pass an official check every year. On these checks, always they have told to me that, on the emission test, there was too high the "lambda factor": this means that, after the explosion of fuel/air on the cilinders, there still is too much air on the escape. The check mechanics always have accepted my vehicle but, this time, they say that I definitively must fix this problem.

I think that this too much air on the final escape can be due to one of these parts (or both):

- Throttle Body Flow Booster (Air Foil)

- Power Tower Throttle Body Spacer Plate

Since I have not raised the fuel pressure, but only the air intake, I think that here is the problem. I have seen on your website that te air foil raises the air intake by 30 CFM, but have not seen anything about the spacer plate (it only talks about "better fuel atomization"), so my question is simple: which of this parts you think are raising too much my air intake? Both, or only the air foil? Or do you think that this have nothing to do with my problem? I do not want to remove parts that not affect air intake, in fact I love all my car modifications!!!

Thank you very much for your assistance in advance. Looking forward to hearing from you as soon as you can...

Sincerely, Miguel Miranda

aminnich

I am not sure exactly what they are saying. I am just guessing that by too much air they really mean that it is runnning lean (the air to fuel ratio is off). Give them a call and ask them to clarify exactly what they are meaning. Your mods should not have made any difference, something else is going on. Can you scan the computer for any fault codes?

65Z01

From your description it sounds as though your Air/Fuel ratio is running too lean and I agree that your listed mods should NOT cause such a problem.

More likely is that the O2 sensor is not functioning properly or that you have an air leak in either the intake or the exhaust before the O2 sensor or possibly the coolant temp. sensor in the inake base below the TB is not functioning properly.

In any case you can use the ECM's Field Service mode to see if the system is going into closed loop and if the Air/Fuel ratio is correct; directions are on my site.

mitcher

Here in Spain they do the emission test by measuring the CO and the lambda factor and both must be near 0: too much CO means too much fuel on the mixture and too much lambda factor means too much air in the mixture. I have the second problem, cause my lambda is 1.13

By the other hand, yes, I have an air leak on the exhaust, just before the catalitic converter! I do not know where are the O2 sensors, do you think that this can be the problem of the emission test?

Thank you!

cv67

Exhaust leak needs to get fixed, those "mods" wont affect readings any.

As the others said I bet the A/F ratio may be off a bit.

mitcher

Excuse my ingnorance, but if the problem comes because the A/F ratio is lean and do you say that I must fix my air leak on the exhaust, then I intend that when gas will arrives properly to the O2 sensor, this one will correct the A/F ratio too... is this correct?

So to fix my emission problem, I must simply fix the leak. Are you SURE that the listed parts do not affect in this case? What about the 30 CFM more of air intake due to the air foil?

And a final doubt: if the air do not arrives properly to the O2 sensor, so this one do not detect any problem and do not fix the A/F ratio, why the sensor of the mechanical test do? Search it for a different problem? They introduce it for the escape.

Thank you very much to all the community!

BADDUCK

Those 2 parts don't really do anything. You can take them off and throw them away. They are useless, you have another problem, and your explanation is not clear enough to diagnose it. It could be the O2 sensors and/or a leak.

aminnich

Due to the exhaust leak your 02 sensor is giving the computer bad information. The computer thinks it is running rich and therefore adjusting the fuel/air mix in error. Fix the exhaust leak, the computer will get accurate readings and the mixture will be back to what it should be.

Cyclonite

The oxygen (O2) sensors are located on the exhaust manifold/headers (whichever you may have) and look like a spark plug with a wire coming out of the top.

Fix the exhaust leak, and see if you can get a freebie test to make sure that did the trick. These guys here are smart and given the right info can definitely help you out (they did me!)

65Z01

If you have stock exhaust manifolds the O2 sensor is located in the left side Y pipe just below the header to Y pipe mounting flange.

If your exhaust leak is in front of that point then it can effect the O2 reading, if the leak is between the O2 sensor and the cat then it cannot effect the O2 reading.

Remember that, though the air foil increases the "potential" air flow by 30cfm, it does not in fact cause any more air to flow than the engine is "asking for". That is, it has no effect at low engine speed.

Use a paper clip to put the ECM into Field Service mode and watch the SES flash rate to see if the ECM is going closed loop and if the A/F is OK.

mitcher

Sorry, my english is not perfect. The leak is just before the catalytic converter, do you think it can affect O2 sensor readings?

Thank you!

Vetracr

I agree with others that your problem is probably an air leak causing the O2 sensor to read a lean condition.

There is another possibility. I had this problem on my 86. I believe your model year only has a single O2 sensor. My problem was that I had a leak in a fuel injector on the exhaust side with the O2 sensor in it. The leaking injector caused the O2 sensor to read a rich condition causing the ECM to lean out the mixture on both banks of injectors. The result was that a sniffer test of the exhaust (measuring both banks) showed it to be lean. I know your english is not the best so I hope I haven't confused you. good luck.

Larry

bill mcdonald

yes. I have battled this on a header car with the o2 sensor moved to the headers.
unless this is at the main cat.... then it seems a bit far down stream, and if it leaks I would second guess the whole exhaust

I would look for other leaks, and check the A/f ratio

65Z01

The air foil will NOT cause your problem; that 30cfm increase in only "potential" air flow (maximum air flow capability) not actual air flow.

How is the "lambda factor" measured, by a probe in the tail pipe?? If that is the case, perhaps the leak in the exhaust is the problem cause.

mitcher

Hello everybody! I have passed the check again this year, but there is still the problem with this emission test and I have promised the mechanic that it will be fixed for the next check.

At this, point, I have repaired the leak on the exhaust and I fear the problem is still there: my "lambda factor" was exactly the same after closing this leak.

Do you think my O2 sensor is not working properly? Can i have a leak on other part of the car? Other ideas?

Thank you!

65Z01

As I mentioned, use the ECM's Field Service mode to test that the ECM goes closed loop and manitains proper A/F ratio.
1) jumper ALDL pins A&B (two upper right pins)
2) start the engine and watch the SES flashes
3) after a minute of so the flash rate should slow from 2Hz to 1Hz as the ECM goes into closed loop mode of operation
4) in closed loop mode, the On flash duration should equal the Off duration; this indicates the A/F ratio is stochiometric, i.e. 14.7:1

If the ECM does not go into closed loop mode, suspect either the O2 sensor or the coolant temp sensor is faulty

If the SES On flash duration does not equal the Off duration, suspect the O2 sensor, an air leak, or an exhaust leak.

mitcher

Where exactly are those ALDL A&B pins?

65Z01

The ALDL is the ECM access terminal and is located near the front of the left side hush panel to the right of the steering wheel column.

There are two rows of pins; A & B are the two upper right side pins. Simply bend a paper clip into two prongs and plug it into these two pins to jumper them together.