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Old 12-03-2009, 07:14 PM   #1 (permalink)
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DFCO question

Does anyone know if my '96 ford contour, 2.0 5sp m/t have the DFCO feature? My manual doesn't say anything about it...

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Old 12-03-2009, 07:28 PM   #2 (permalink)
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Rainh2o -

I am guessing yes, but you need to know when it happens. I thought I *didn't* have it, but I was wrong :

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SentraSE-R -

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Deceleration fuel cutoff in my '02 Nissan Sentra and '06 Scion xB differs considerably. My wife's '06 Hyundai Elantra doesn't have it. So you can't tell from the age of the car whether it has DFCO.

Both the Nissan and Scion have to have the throttle position sensor at idle, open loop, transmission in gear, and rpms above a certain level. The Nissan's rpms have to be >2500. The Scion only >1500. So in sixth gear, the Nissan doesn't go into DFCO unless the car is rolling >65 mph. The Scion goes into DFCO at any speed above 35 mph. Both will stay in DFCO below the initial rpm, but they have to be above that limit to enter DFCO. In practice, I can let the Scion coast down any hill and be sure it's not using fuel. The Nissan, OTOH, has to be in a lower gear to get fuel cutoff.
Thanks for posting this. You made me look. I *do* have DFCO after all, just like the Nissan. Today I tested this going downhill in 3rd gear. It went lean until I went below 2500 RPM. I didn't see this before because I am below 2500 RPM most of the time. Because of the way I drive, I never saw it, .

This implies to me that I have a DFCO operating window. On steep (down)hills I can put the engine in a gear that keeps the engine above 2500 RPM.

...

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Old 12-03-2009, 09:21 PM   #3 (permalink)
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Anyway I can find out without a scanguage or mpguino? Someplace on the web or Library? Or is there a definite sound or "feel" I would be looking for when it happens?
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Old 12-03-2009, 09:24 PM   #4 (permalink)
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DFCO is easy to determine, by two methods.

Use a mechanics stethoscope to "listen" to the injectors ticking. Rev the engine and let off the throttle. If you have DFCO the injectors will quit "ticking" until the engine speed drops down close to idle.

Second method, accelerate in 3rd gear to a decent speed, then let off the gas, let the engine slow the car down until you feel the engine start to actually come back to life and start to add some power to the car. It won't be much but is noticeable.

In most cases DFCO has been around for a long time. I know it was in 1981 Nissan Z cars, and possible in the earlier ones dating back to the first fuel injected Z cars in 1975.

With fuel injection DFCO eliminates the need for air injection that was used in carburetors to burn the excess fuel during deceleration.

If you dont have a mechanics stethoscope you can improvise by using a phillips head screwdriver. Place the tip on the injector body and the handle on you ear.

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Old 12-03-2009, 09:28 PM   #5 (permalink)
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That sounds better then this method I just found on another forum...

<b>How can I tell if a vehicle other than the Yaris has DFCO?

Be careful with this test as you may lose Power Steering and Power Brakes during it! Choose the right time and location to perform the test.

On any level or slightly downhill road get up to at least 40 MPH, then start engine braking by keeping the vehicle in gear and letting all the way off the throttle while keeping the clutch disengaged (MT) or keeping the transmission in a gear lower than D (AT). Notice the deceleration force and the sound of the engine.

Now tun off your ignition (This is where you may lose your PS/PB, so be wary!) and watch for any harsher deceleration or change in the pitch of the engine for a few seconds.

If nothing was any different with the ignition turned off then your vehicle uses DFCO. If it decelerated at a different rate or pitch with the ignition off then it does not use DFCO.</b>

ALSO..someone on another forum said to hang an LED off the injectors...then you could tell...might try that if I cant tell anything from old mechanics suggestion...

Last edited by Rainh2o; 12-03-2009 at 09:30 PM.. Reason: spelling
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Old 12-03-2009, 10:12 PM   #6 (permalink)
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I know some people have provided evidence of their cars not having DFCO, and they are probably right.

When you let off the gas pedal, the engine vacuum skyrockets to almost a perfect vacuum. In my Echo it comes close to 26 inches of vacuum. At 30 inches (depending on atmospheric pressure) you have a perfect vacuum. Think outer space.

With virtually no air getting into the cylinders (very close to none) you do not have enough air to compress and create enough pressure for decent combustion.

If there is any fuel available under those circumstances, that fuel will end up in the exhaust and the catalytic converter. It could create a nice kaboom in the exhaust, as well as very high unburned hydrocarbons which fails emissions tests and requirements.

DFCO is an easy way to eliminate the nasty consequences of fuel that has passed through the engine without combustion. Just eliminate the fuel.

Now all that being said, I believe there may be some emissions systems that do allow some fuel to be introduced (a very small amount). If so there has to be some air bypass to allow the fuel to burn in the converter, but it makes much more sense to me that the best solution is to just shut off the fuel altogether.

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Old 12-04-2009, 03:34 AM   #7 (permalink)
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Rainh2o -

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Anyway I can find out without a scanguage or mpguino? Someplace on the web or Library? Or is there a definite sound or "feel" I would be looking for when it happens?
I am lucky because I have a digital AFR (Air/Fuel Ratio) gauge that monitors my pre-cat oxygen sensor. When DFCO happens, I *see* the AFR go lean.

Here's a site with a bunch of them (I got my digital AFR from here) :

In-Car Air-Fuel Ratio Gauge Buyers' Guide - Part One

You can also do it extra cheap. Tap into the 02 sensor wire and use a voltmeter to monitor the voltage. As you can see from the article, when the voltage gets closer to "0.0", the AFR is going lean.

Here is an example of someone installing a fancy AFR gauge :

Installing an Air Fuel Ratio Gauge

CarloSW2

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