does engine braking on EFI cars waste fuel?

"aarcuda69062" wrote

It fits perfectly fine. When engine braking, the RPM climbs, but it does increase fuel consumption on a fuel-injected engine if you happen to shift to the second gear to engine brake at 10 - 40-mph and let the rpm climb. Depending on the vehicle computer manufacturer. Honda is known for fuel efficiency, if Honda design their cars like this, others would be even worse.

I don't know where everybody's getting there info from. Reading from the Honda's owners manual, "D2 is used for engine braking... D1 is for traction on snow." If D2 is for engine braking then why didn't the fuel injectors shut-off while at high rpm and throttle closed? I'd theorize that this may be a safety feature in case the throttle position sensor fails.

As the rpm rises, the revolution per minute increases but the injection duration remains about the same, so yes there is increase consumption.

My facts come from reading the schematic diagram and road tests. So, how did everyone get theirs and the methods used to obtain them?

earlier on that was one of the advantages mentioned - that fuel injected cars do not wasted gasoline - while coasting.

mho vfe

What base are you saying the gas consumption increased over. Certainly not increased over the consumption at normal engine and car speeds. Of the cars I've driven with engine performance displays, they all show the following characteristics when a lower gear is used on the downhill:

1. RPM's are increased to somewhere around 1,500 rpm.
2. The instant MPG display shows very high double digit numbers usually close to 99.

It's my understanding that on late-model vehicles the injectors are periodically pulsed during extended closed throttle operation in order to protect the catalytic converter. This is true in any gear.

Oh. I guess I missed the part where the OP mentioned messing with the gear selector.

No such thing when you're in neutral.

Asian EFI systems are at least a decade behind the domestics.

What are you using to measure injector duration?

OEM training.

"John S." wrote

Let's say you're doing 2000 rpm. And one injector spits out 1.2-ms per cylce. That's 1.2 x 2000. Let's see what happens if you're doing 5000 rpm. That's

I'm not sure what this means. But if you mean that normal engine braking is by using the forth or fifth gear, then that's isn't engine braking since this doesn't slow the car down to substantial degree.

I'm not sure what version you're using. One calculates the injector on time versus distance. The other uses two fluid flow meter on the return fuel line and one on the input line. Both I'm unfamiliar with their accuracy in real time since they refresh the math over a certain distance it would unreliable to determine engine braking MPG.

The type I use measures the amount of fluid that goes into the engine at any given time. I can adjust for 0-30 seconds but no more. This is accurate for measuring MPG for a short time frame. This is also good for measuring any selected gas station mileages before I'll go ahead and fill her up.

"aarcuda69062" wrote

Hand-held pulse width DMM.

This sounds more like it's programmed by the EPA. Having the catalytic converter uheated for extended period poses no problem. Having a heated catalytic converter is only good for the enviroment.

Is this a 2 stroke engine?

I wouldn't make that assumption. The injector pulse width would depend not only on RPM but TPS and manifold pressure/mass air flow +or- the trim from the O2 sensor(s).

Does this meter measure strictly off of the on /off signal or can it actually pick out when the injector pintle starts to move?

The electrical signal is meaningless if it doesn't identify the actual mechanical movements of the injector pintle which is the real way to measure injector on time.

And that would be true, except for the fact that the control system doesn't work that way. Instead of opening the injector 1.2 ms at 5000 RPM, it doesn't open the injector AT ALL, except for limited times to keep the catalyst "lit" and the engine warm.

Read the previous posts that explain deceleration fuel cut-off again.

You said there was increased consumption but didn't specify over what.

If there is an increase in fuel usage by using engine braking it is miniscule as others have noted.

I believe that the concern there might be not that the converter cools down, but rather oxygen poisoning of the catalyst.

With a properly functioning injector, current measurement should give an accurate accounting of injector on time. But it's not easy to measure current pulses like these. The DMM guy is probably measuring voltage, which might be close.

"John S." wrote

I don't quite understand your terminology. The increased consumption is over engine braking by shifting to a lower gear. This is comparing low vs high rpm.

"Steve" wrote

This would be true if it were coasting in a high gear down a slope. Except for the fact that the control system allows the injectors to stay on during engine braking when using the low gears, as I've found out thru road testing. You might need to run your road test and report your different findings.

"aarcuda69062" wrote

Wups. It should be 1.2-ms per cylce. That's 1.2 x 2000/2.