Most responsive fuel injection: mechanical or electronic?

I enjoy my Corolla’s electronic fuel injection system, good mpg & power, and it is pretty much bullet-proof. But my prior VW Rabbit’s CIS mechanical fuel injection – definitely not bullet proof – but imo was more responsive to the gas pedal. Engine responded immediately when gas pedal depressed. Corolla, a bit of a delay.

What do you folks think? Anybody else noticed this? Any theories why?

More to do with how the engine is tuned, gearing, etc.

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Electronic is more responsive simply because the system react more quickly than a mechanical system.

But @texases is right. Tuning is key.

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Perhaps the VW rabbit would briefly run the engine too rich during a sudden throttle increase, giving you a bit of a boost. EFI won’t let this happen.

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[quote=“TheWonderful90s, post:4, topic:192277”]
EFI won’t let this happen

EFI can be and is programmed to do this on many cars. There are some 30 year old SAE papers written about this subject.

George, you like older vehicles, get yourself a 57 Belair or Vette with factory fuel injection and compare it side by side with your Corolla.

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There will always be some inherent delay in anything software controlled (latency even in real-time software controls). However, this should be so small as to be almost unnoticeable to humans unless there is some purposeful reason for adding in additional delay. Software makes this easy, not so easy with mechanical means. For example, adding in a longer slew rate from input request to output action would be helpful for emissions reduction. There have been complaints here in the past with throttle by wire systems that had too much delay built into them. There is a fine line where delay becomes excessive and bothersome to the end user…

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I was speculating that perhaps the CIS was more responsive b/c there’s a direct mechanical linkage between the air flow sensor & the fuel flow rate. With CIS, throttle valve opens, air flow into engine increases, air flow sensor mechanically linked to valve which increase fuel injector flow.

The Corolla, by contrast has no airflow sensor. The throttle valve opens, airflow into engine increases, then manifold pressure increases, computer senses increase in manifold pressure via MAP sensor, and then increases fuel flow into engine by increasing injector pulse duration. More steps, more delays, esp the delay between air rushing into manifold and manifold pressure rising enough for the computer to increase fuel flow.

It’s not a delay. I think it’s a deliberate design to keep the fuel mixture at the correct ratio even during quickly changing throttle positions. Cars with faulty throttle positions sensors can hesitate, as the mass air flow sensor can’t respond quickly enough. The TPS is used to create the fuel map for those sudden throttle changes.

I’m guessing the mechanical fuel injection responds too quickly by injecting more fuel even before the air pressure in the manifold has a chance to catch up.

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This is a good point.
It could be the older mechanical injection system provided behavior similar to a carburetor’s accelerator pump.

No one cared back then if the mixture was overly rich while the accelerator was being depressed. The important concern was to not have any lag in performance.

I suspect the follow-on electronic fuel injection systems need to preserve a 14.7:1 stoichiometric air-fuel mixture during times when the accelerator is being depressed.

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There should be ZERO delay unless you’re using a chip designed in the 90s, especially with off the shelf processers that can easily do over 10 BILLION instructions per second.

Good ideas. Trading off throttle responsiveness for a cleaner burn & less air pollution seems a reasonable compromise , esp for an econobox daily driver like a Corolla. I doubt the delay is caused by the computer’s inability to process the data quickly enough; as suggested above, the delay is probably part of the design.

That has to be the most naive statement I’ve seen you make on this site. However, since your background is essentially system level software, it doesn’t surprise me. If you had any background in real time, software based embedded programming you would have understood what I wrote and that ANY processor has latency. If it takes 1ms or 1ns, it doesn’t matter, both are below human detection. But you missed the real point being made…reread it.

Realtime systems is a large portion of the telecom solutions our company provides. I’ve written embedded code for microprocessors (mostly in C). Also, early in my career, I’ve written device drivers. I did understand what you wrote.

Mechanical fuel injection systems have to make adjustments to system load and variables. This isn’t easy and many times NOT EFFICIENT. In many instances EFI can handle these adjustments FASTER…and far more efficiently. Many mechanical FI rely on vacuum for it’s mechanical adjustments. There’s latency in that. EFI can do it almost instantly.

My money is on the fact that the Corolla transmission is not as responsive. The issue isn’t throttle response, it’s driveline response. It’s why I dumped Hondas and Toyotas after many years. The Mazda drivelines are much more responsive to driver input and I think it is almost entirely the use of the Skyactiv Drive technology in their automatics. My last Honda had throttle response that was instantaneous, but the transmission made acceleration feel like the car was being pulled by a rubber band.

One problem with that, OP’s Corolla is a manual transmission, IIRC but could be wrong his VW was a manual also…

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I’ve driven a Rabbit with a manual and I owned a Corolla with a stick as well. The Rabbit had a much snappier clutch engagement while the Corolla was smoother but with a longer throw on the clutch pedal. It’s still hard to tell what the OP is attributing to “faster throttle response”. Is he sitting in the driveway and gunning the engine and timing the response from gas pedal press to revving of the engine? This sounds like one of those subjective measurements that has not been documented with actual controlled testing. Kind of like when people get their oil changed and say their car runs much better. Piffle!!!

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Corolla has 5 speed manual trans. Prior Rabbit had 4 speed manual.

The throttle response effect , Corolla vs CIS Rabbit, is not dramatic, but most noticeable when driving 15 mph in 2nd gear. Noticeable difference in responsiveness, either stepping on the pedal, or removing foot.

No dispute.

Were the rpms the same? My GTI was VERY responsive, partly because of being ‘short’-geared.

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More or less. The 4 speed manual Rabbit transmission did seem to be designed in the low gears for extra-good acceleration, so may be part of the reason. The Rabbit’s engine power was less than the Corolla, 75 vs 100, which is probably why the Rabbit’s transmission was geared that way. . Don’t know about the weight difference. I’d guess the Corolla is somewhat heavier.