ODB2 question

[pete c]

I have a '97 Ranger with the 3.slow V-6 and 5 speed.

If I am not mistaken, that means it is ODB2. i seem to recall reading somewhere that all ODB2 engines use FI cutout when coasting in gear.

Am I correct?

I ask because my Ranger sure as hell does not implement it.

I can be coasting down a hill, in gear, with the engine well above idle speed and shut down the ignition with a very definite difference in engine drag.

If the engine was using FICO, this would not be the case.

I have read other threads here about wiring in a manual FICO switch.

Is this a good idea? Will I open other cans of worms in doing so?

[SentraSE-R]

Hi Pete,

Yes, your '97 Ranger is ODB2, but no, not all ODB2 engines use FI cutout when coasting in gear.

My '06 Scion xB has deceleration fuel cutoff. My wife's '06 Hyundai Elantra doesn't have DFCO.

I have wired in a manual FICO "kill" switch. It works well, as long as you're aware of and willing to take the risks of driving with a dead engine.

[Ryland]

My parents have a 1998 ford ranger, but it has the smaller inline 4 engine and it does cut fuel while going down hills, but it's rare, has to be fully warmed up, engine going fast enough and then I'll see the scan gauge hit 9999mpg.

[SentraSE-R]

My xB enters DFCO with the engine warmed up and in gear with rpms >1500 rpm (>35 mph in 5th gear). My '02 Nissan Sentra had to have rpms >2500 rpm (>65 mph in 6th gear) to enter DFCO. Basically, my Scion uses DFCO all the time, and the Sentra hardly ever does.

[diesel_john]

Rigged up a heavy duty switch on the fuel injectors power wire. Also have a heavy duty rheostat in that circuit to vary the voltage to all the injectors.
The resistor value is about 0 to 50 ohms. Have to turn it to 0 ohms to start it cold then can turn it up towards 50 ohms after its warmed up to lean it out. I know it's brute force but i've gotten 19 MPG on the highway by doing this, and putting a check valve in the vacuum line to the fuel pressure regulator. This is OBD-I stuff. OBD-II might be too smart for this to work.

I keep engine braking to a minimum because it's still braking.

[deathtrain]

do you have an AFR guage to watch? and what ratio do you stop at?

[diesel_john]

Sometimes I watch the voltage from the O2 sensor to see if its staying below the crossover. (not going into close loop). Also optimize vacuum. But mostly I lean it out until it loses power. I have not been able to melt anything, it just loses more and more power as I lean it out. The pipes are burning gray to white. Scan gage type testers wouldn't work because pulse width actually increases as the injector can't open fast enough to satisfy the fuel tables.

[some_other_dave]

OBD2 really only means that it has the plug under the dash that communicates via a very specific protocol. It doesn't necessarily say anything about how the engine management works under any particular circumstances--it really only means that you can plug in a single type of tool to find out what is going on.

-soD