VX injector cutoff?

[guest001]

and this is on a standard transmission or automatic? Do all civic's do this or just the vx?

[R.I.D.E.]

Most fuel injected engines utilize DFCO. One easy way to check is to use a screwdriver as a stethoscope. Place the tip on one injector and the handle on your ear. You should be able to hear the injectors ticking when you have it right.

Rev the engine and let off the throttle. If you have DFCO you will hear the ticking stop while it is in DFCO.

All Civic VXs were manuals.

regards
gary

[guest001]

ok, I'll have to try that then. I didn't know all vx's where manual. good to know.

but I have a question for you. How does the computer know when to cut off the injectors?? how does it work technically?

[R.I.D.E.]

Ill give it a guess.

When the throttle position sensor is at idle position, and the engine RPM is above the DFCO threshold, the CPU eliminates the ground connection to the injectors.

That was the way it worked on the older Nissans I worked on. I know they started using it in 1981, but I would not be suprizied if it was not incorporated into their first fuel injected Z engine in 1975. The earliest of the FI Z cars were not sequential injection, they were simultaneous.

Basically they found that with FI you could use DFCO to eliminate the air injection system, that was used on carbureted engines.

They also used a BCDD valve that kept engine peak vacuum lower in the same conditions where DFCO would occur.

In the carbureted days when you let off the throttle the engine vacuum would go sky high, which meant that any fuel that entered the engine would not have enough air to ignite. The result was a huge spike in unburned fuel going into the exhaust. Air injection came on the scene in 1968 (old memories).

By 1975 Nissan had gone to FI on all of its 6 cylinder engines. The 1975 and 76 Federal emission Z cars had no EGR either. Without the EGR the inside of the intake manifolds stayed clean, because there was no exhaust gas to mix with oil vapor to produce the tar like desposit.

The first year of the Nissan FI Z car the ECU was actually a Bosch unit.

regards
gary

[guest001]

great info. I need to check on mitchell and ondemand if I can find any info for how and when DFCO occurs on my 89 civic. which technically has a 90-91 computer. I have few random harness's from mpfi models but everything lines up. and all connects except a/c are connected.

[nowhhs]

The best way is to tap one of the injector leads at the ecu and monitor it with a dmm that has a duty cycle feature. When DFCO occurs, the duty cycle goes to zero.

[guest001]

well, I have a wbo2 and I can see it immediately go to the leanest it can read which it just displays air. I think the highest it'll show is around 19.1-20.1. I was kinda freaking out that it did this, but if its normal. I'm trying to find the exact parameters when it engages on older, 88-91, honda civics.

[1993CivicVX]

Originally Posted by nowhhs

According to the factory service manual, page 11-29: "During deceleration with the throttle valve closed, current to the injectors is cut off to improve fuel economy at speeds over following rpm:... D15Z1 engine 850 rpm". Although this is out of a 1992 manual, I have a P07 from a later (94 I think) VX and have observed that behavior once the engine is warm. It doesn't cut off when the engine is cold. Is that definitive enough for ya?

I concur. It will cut off when the engine is warming up, but it seems to do it at a higher RPM. (You can subtly detect when it cuts off.) See if you can detect it at 850rpm!