DFCO in a 1990 Honda Civic STD - Fuelly Forums

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Old 07-29-2008, 01:09 PM   #1
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DFCO in a 1990 Honda Civic STD

I'm looking for confirmation to see if a 1990 Civic STD utilizes DFCO. Searching online for this feature it seems that there are some discrepancies on this.

According to this post Honda introduced this feature in 1990.
http://www.gassavers.org/showpost.ph...6&postcount=73
But because the 4th Gen Civic years range from 88-91 does that mean the 88 & 89 Civics didn't have DFCO? Or was it not included in the 88-91 Civics but it was introduced in the 90-93 Integras & 92-96 Civics?

If anyone can confirm this I'll be eternally grateful!
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Old 07-29-2008, 03:46 PM   #2
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Take it up to 3000 rpm in second when fully warmed up with the A/C off. Take your foot off the gas. It should decel smoothly until the injectors come back on and then it should lurch forward a little. If that is the case you have DFCO. If it decels smoothly until stop you don't.

If it does then experiment around. Try taking it up to 2000 and see if it still does. If it is anything like an 88 CRX HF it cuts off at above 1250 and comes back on below 800
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Old 07-29-2008, 04:31 PM   #3
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If that's the case then I have the DFCO! I wasn't doing it in vain the last few weeks! I felt the "lurch" and assume that it was the injectors coming back on but wanted to confirm it.

I'll test it out tomorrow just to see the specific RPM it engages and disengages. Thanks FritzR!
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Old 07-29-2008, 06:33 PM   #4
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Wow... testing my DFCO I see another plus of having an HF over my STD. My DFCO seems to come on above 1500rpm and disengages at around 1250rpm.

I bow down to the HF's superiority!
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Old 07-30-2008, 04:35 AM   #5
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I found out last night that my wife has DFCO on her element. that is awesome. I have been looking around for a car to replace (actually just to drive) her sort of SUV with. I am also thinking that if I can get 30MPG out of it that I don't really care.

DFCO is awesome.
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Old 10-31-2008, 06:54 PM   #6
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so when it lurches forward is the rpm it which the injectors come back on?

and this is for manual and auto trannys right?
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Old 11-02-2008, 02:33 PM   #7
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With an automatic it might lurch forward like that if it downshifts too. You might want to watch the tach too and make sure that stays constant. On my supermid I can see my injectors shut off and stay completly off for sure with an 88 CRX HF.

I suppose to test you could just put it in L1 take it up to 2 grand or so and then take your foot off the gas to test that.

As for your other post I think that the test you are doing is suggesting DFCO.
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Old 11-02-2008, 03:37 PM   #8
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Remember the DFCO reengagemnt point (when it comes back on) will be higher depending on the number of acessory loads you have running.

More loads higher DFCO shut off point.

I believe there is some form of DFCO on almost every FI vehicle.

If there wasn't when you let off the gas the car wouldn't want so slow down.

Best way to test is to listen to the injectors and blip the throttle.

regards
gary
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Old 11-02-2008, 04:29 PM   #9
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Tap an extension wire from your injector wire and run it into the passenger cabin to your multimeter. It's AC voltage.

I said 1990 as my minimum in that thread because that is the earliest that I personally have confirmed having installed an AFR gauge on a 1990 Si. You let off the the throttle in gear, and the bouncing light goes to full red and stays there until RPM's drop to idle.

Since then I have learned that late model carburetors even had a mechanical DFCO.

It should come as no surprise that every modern vehicle has a DFCO strategy. It's done not only to pass the federal emission standards (different than your periodic smog test) but to prevent a throttle bog after a decel and to save the catalytic converter. I've found that it really doesn't affect your fuel economy much unless you intentionally exploit it.
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Old 11-02-2008, 04:54 PM   #10
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Without it the catalytic converter would never last the 50 k required to be certified. Might be higher now.

In the early days of converters they used many strategies. Air pumps, gulp valves. Then they progressed to methods of eliminating the fuel delivery during deceleration instead of adding air to burn the fuel.

The last of Nissan's NAP-Z 4 cylinders that had a carb, had a heated screen under the base of the carb to better emulsify the fuel air mix. Also fuel shutoff on deceleration, and reed valves in the air cleaner that allowed air in to the exhaust under DFCO type conditions.

When fuel injection came along (actually been there as long as the diesel engine) then it was easy to just shut the fuel delivery off altogether. Other methods were employed to reduct the peak vacuum spike when a throttle plate is closed in a high revving engine, which can approach the atmospheric pressure of outer space (think none).

Use a vacuum guage on an old motor and you can get vacuum readings that approach 30 inches, When this happens, there is no air to burn any residual fuel. It also sucks the oil up past the rings and makes the engine burn more oil that it would normally.

In the mid 60S you could buy a car (made after 63 when required by law) with a plugged PCV valve that burned oil at the rate of 1 quart every 200 miles. Clean the PCV system and watch the oil consumption got to one quart every 2000 miles.

Watch the fames coming out of a NASCAR racer under deceleration.

Every time I follow and old pre emission car on the road I can smell the 60S again.

regards
gary
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