injector service off car. worth it ?

I met a Toyota owner recently who told me he changed the

---------------------------------------------------------------------------------------------------------------------- Food for thought,

Ohh this is just too good to let alone. I've been really busy in the shop lately and even today had to fly through most of the responses gaining just enough information to attempt to catch the highlights and make some comments.

Remember this, "I'm not an engineer, just a technician that fixes the things automotive engineers create"

A DIRTY AIR FILTER WILL NOT AFFECT NORMAL DRIVING FUEL ECONOMY ON TODAY'S MAF (Mass Air Flow) sensored vehicles. There was a lot of disscussion, but little spelled out for Jsteve to go and test to prove the result. One of the tests that techs like myself use regularly when in the process of diagnosing a vehicle performance issue is to calculate the "reported VE" (Volumetric Efficiency) of the engine at several WOT engine speeds. We use this calculation combined with fuel trim data, (long and short term) to help analyze MAF sensor performance, which is easily confirmed to be accurate or not based on VE variance, combined with an associated fuel trim correction. In short, if VE is low say 60-70%, and fuel trim is making a correction to add fuel, that indicates unmeasured air is entering the engine. The air could be pirate air getting in through a torn air inlet tube after the MAF, or could be a faulty MAF. If VE calculates low, and there is NO fuel trim correction, now we look for a mechanical reason that the engine isn't breathing correctly. That could be a restricted exhaust, engine mechanical issue, or in fact an air filter issue!

In all of my years as a technician (30+) the number of times that I diagnosed a bad air filter as a performance problem accounts for only a handful. Most of them were related to rodents storing food in what appeared (to them) to be prime real estate. VBG. Almost every one of the rest were related to an exhaust manifold or gasket failure, where the thermostatic air cleaner system was picking up the leaking exhaust gasses and coated the air filter with them.

The fact that an air filter that is truly dirty is a diagnoseable condition without lifting the air filter lid and looking is important. That also means that no matter how dirty an air filter looks when inspected, proper testing can prove beyond any doubt as to whether it actually needs replacement.

From this point here is your test Jsteve. If you don't have access to this formula e-mail me and I can send you a version of it. You will need a good scan tool that will give you data as fast as possible. The faster that the data scrolls, the more accurate that the RPM, VS the Airflow reading in grams per second will be.

Go ahead and take your first VE measurement with whatever air filter you have in the car. Take note of long term and short term fuel trims under normal driving conditions at varying vehicle speeds, and throttle openings. Also take note of the calculated spark timing, and if there is spark retard occuring from a knock sensor input. (MAF vehicles use the MAF to assist in not only fuel mapping but spark timing mapping as well) Then take the air filter out for testing purposes and repeat the test! Make sure that your air inlet assembly is clean of any deris etc.

Now the fun starts. Take a can of spray paint and a cheap replacement air filter. Paint 1/4 of the filter to completely block it of airflow. Install the filter after it dries and re-test. Use an enamel paint to make sure it seals the filter. If you have access to an O.E. level scan tool such as an IDS on a ford you could go ahead and drive some type of a course and measure actual fuel economy. In fact backing up you could have started out this test that way!

Now paint another 25% of the filter. You now know without question that you have a filter that is 50% restricted, right? See how this measures out now.

Now go another 25%, so your filter is definately 75% restricted. Do you think you have ever driven a car with a filter that was THAT dirty?

You now have a filter that only 25% of it has airflow. Paint half of what is left and repeat the test, with only 12.5% of the filter allowing airflow. Depending on circumstances I'll wager this to be the first time you see a significant difference in MAX VE. However, I'll also wager you will not yet see a loss of fuel economy, and you could in fact lend this car to another person and they could drive it and not notice anything wrong!

The reason for all of this is gasoline engines are of course an air pump. The speed of the engine is set by the airflow that it recieves, and it does NOT matter where the restriction to that airflow is. The greatest restriction will always be the limiting factor. If you would take my Ford Explorer and restrict the filter to about 12.5% area, you would still have 80% of the cross-sectional area of the throttle body and therefore almost no noted restriction.

Now one of the other responses was asking about variable cam timing. We should start a thread specifically about that, instead of doing it here. Suffice it to say at the moment that scavenging of the cylinder gasses is only the tip of the iceberg. The engines actually effectively control displacement, eliminate the need for EGR, since the cam can do that job, and much more!

----------------------------------------------------------------------- Excellent thread. Here's my low-tech anecdote that supports the conclusion reached by the group. I've a Toyota Landcruiser that I use to haul the family to our summer house on a lake over 200 miles away. It's stored over the winter. I always fill up at the same two gas stations at either end. I'm particular with logging MPG, which has averaged 13.4 MPG over a couple of years. Before putting it away two winters ago, I changed oil & all filters (including air) Last summer, brought it out, and it seemed a bit sluggish on it's first trip of the summer. Checked MPG; showed 13.6 on the way down, 13.5 on the way back. Same thing on the next trip. Finally got around to sniffing out the source of the sluggish operation. Opened up air filter box, and found it virtually plugged with a huge rodent nest. From the density of the nest, I struggled to understand how the engine produced as much power as it did. However, I rechecked my fuel log, and could not discern any noticeable change in fuel economy, with an almost totally plugged filter. Luckily, the mice did not chew through the filter, so nothing nasty made it's way into the engine.

Yes and no. If the MAF were the ONLY sensor that affected mixture, then the above would be true. But the actual fact is that mixture is set by a combination of throttle position, MAF, O2 sensor, and other parameters. When the air filter gets extremely dirty, the throttle will have to be cracked open more than "normal" to get a particular power from the engine, so the MAF and throttle position sensors will "disagree" slightly, meaning that the calculations the computer does to determine the fuel injector duty cycle may be slightly skewed.

So there IS an effect, but its probably too small to measure in real-world conditions where changing temperature and humidity (among other things) would easily mask the fuel penalty.

Of course the dirty air filter will reduce peak power available, and it will still cause the mixture to be significantly rich during open-loop operation where the MAF sensor is ignored.

And speed-density systems (MAP sensor instead of MAF) will be affected differently than MAF systems.

You are ignoring the fact that the throttle position sensor is a very gross indicator. It doesn't supply the fine sort of data that would be needed to cause the effects you are suggesting. Take a look at a shop manual for a Toyota and you'll see that the acceptable range of response for a particualr throttle opening is more than +/- 5%. This is a far greater effect than any slight change in air flow at part throttle attributable to "normal" air filter restriction. Furthermore the PCM learns paramters to compenstate for gradual/minor changes such as air filters loading up. If a filter is so bad that it affect fuel economy significantly, you will get a mil indication.

It will be so small that you won't be able to measure it with instruments either. It will be well below the noise level in most cases. I won't say a dirty air filter will never effect fuel economy, but it will be an unusal case if it does.

The MAF sensor is not ignored during open loop mode. The O2 sensor is. And fuel trim learned during closed loop mode will modify the open loop mode parameters so that even during open loop mode, the effect on fuel economy will be trivial. I do agree a dirty air filter will affect maximum power.

True, but again, the PCM modifies the operating parameters based on closed loop operation. A "normally" dirty air filter won't have asignificant effect on the fuel economy of speed density systems either, at least after they have operated long enough to learn the proper fuel trims. Speed density systems primarily calculate air intake using rpm and manifold pressure, not the throttle position sensor. If you look at performance curves for throttle position sensors, you'll see that they simply not capable of providing the sort of detailed precise data needed to determine the amount of fuel to be injected. TPS are used to indicate gross changes in the position of the throttle so the fuel inection can reacted to changes. Think of them acting in place of an accelerator pump or a dashpot, not a metering device. The most import positions are closed (for idle control) and wide open. There are some throttle position sensors that only indicate idle and full throttle, with no indications in between. Most provide a signal that varies with throttle angle, but it is usually a linear relation ship, while the air flow through the throttle bore does not vary in a linear measure with throttle angle.

Ed

Built_Well wrote in news:130be0b0-57bb- snipped-for-privacy@w7g2000hsa.googlegroups.com:

He may know oil, but he has very little idea of what happens inside a gasoline engine that puts in the oil what he finds there.

Basically, he can tell you what's in the oil, but he can't tell you why it's there. He may think he can, but he can't.

I'm not ignoring it, I'm just pointing it out as a potential source of skew- which it is in some cases. And I said it isn't large.

No thanks. I don't do Toyota.

Yep, my bad. Speed-density systems do have a limp mode in case the MAP sensor fails, in which case the whole system is run on nothing but the TPS and a look-up table and that's what I was thinking of- although that's an aberrent case and not really relevant to the discussion. Gotta say, though, it works surprisingly well in that the engine will run and get you home. I assume decent MAF-driven systems have a similar fail-safe mode.

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Now that I can believe :-)

Dude, like I said, I keep a little black book in every car, with oil changes, repairs, maintenance, and fill ups.

If I change something I can see the effects, if any of the change.

For some reason, it doesn't work with the Supra...

Open loop is usually VERY short. On my car it's about 20 seconds. (80F)

WHere is that located on the 4afe engine ?

And yeah, I have used techron on it and seafoam another time. no change

Oops, my bad, I think your car may have a MAP sensor instead of a MAF sensor. The MAP sensor is on the firewall on the passenger (right) side of the car. Go to

and look up the repair guide for a 1997 Corolla, then look under "component" locations for the location of the MAP sensor and under "drivability and emission controls" for the procedure for testing it.

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AutoZone is a great store. They even have a *free* loan-a-tool program of seldom-used, expensive tools, like a CV clamp tool, serpentine belt tool, etc., etc.

They require a deposit, but refund it when you return the tool.

Here's just some of the great tools they loan out for free:

A list of more tool categories is in the right margin of that page.

Why borrow a tool when you can buy it and own it and justify the need for a larger tool box as you accumulate even more tools?

Seriously, a tool loaner program is a great idea to get people to come to the store to buy parts.

I will buy a cheap tool from someplace like Harbor Freight if I think that I'll only use it once or twice. If I'm going to use it regularly, I'll get better quality like Snap-On or Craftsman.

ah, that explains why I could not find it in the haynes manual. thanks Ray! .

You're welcome, good luck!