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Do all 4 fuel injectors inject fuel simultaneously?

I was looking at the fuel injection schematics of my early 90’s Toyota Corolla with electronic fuel injection, and it appears all 4 of the injectors are controlled by the same electrical signal. I would have guessed the injectors would time their injection with the valves, but it appears they simply all inject at the same time, independent whether the intake valve is open or closed.

Am I correct? Is this the way Toyota fuel injection worked in the early 90’s? Does Toyota do it the same way same now? Or are there fuel injection systems that time the injection – on an injector by injector basis, so each injector has its own control signal – to the respective intake valve now? It seems like this later method might produce better combustion and therefore less pollution and better fuel mileage.

If this is a multi port system, they should fire independently. Not all at once, unless it’s a throttle body set up (but usually they only have two injectors). You must be reading it wrong??

There’s definitely four separate injectors, an injector situated in the head near each intake valve.

Well, Bosch had CIS (continuous injection system) that injected a modulated stream of gas continuously, maybe this is something like that. The amount of fuel injected was proportional to the total air flow, with no on/off.

Each injector has a common power supply like a string of Christmas tree lights. The computer has what are drivers for each injector. The drivers in the computer grounds each injector at the appropriate time to fire them individually.


I had a 1994 Saturn SL-2 that had multi-port fuel injection, and the injectors all fired simultaneously. The next year they went to a sequential fuel injection as part of an engine quieting revamp. I suspect port fuel injection without the sequential firing may have been somewhat common in 1990 when computer power was much more expensive than it is now.

During this period, car makers were doing everything they could to avoid paying Bosch licensing fees. Bosch held the patents on most of the injection designs…GM was pretty proud of their TBI system which did not infringe on Bosch patents and worked well from a cost and emissions standpoint…Honda got involved in a nasty court battle with Bosch, lost, and they stayed with carburetors longer than they should have…The other companies worked out deals with Bosch they could live with and moved on. Today, all those old Bosch patents have expired and the injection systems have become pretty much standardized with the latest advancement being “Direct Injection” like Diesels have. High-pressure fuel being injected directly into the combustion chamber at the right moment…This allows much higher compression ratios to be used with regular grade gasoline, improving mileage, power and performance…The difficulty here is dealing with the high-pressure gasoline.

A quick look at some schematics (keeping in mind I’m no Toyota wiring expert and there may be something missing in the diagrams) shows several different methods of injector wiring up through '95. They all have a common power source and ground is made through the ECM either with one lead or a pair of leads, all depending. This would point to injectors being fired simultaneously or in pairs.

In '95 the 4A-FE engine shows 2 grounding leads and the 7A-FE engine (both 4 cylinders) shows to have 4 leads; one for each injector. The latter continues on from 1996 and up.

Multiport fuel injection isn’t necessarily the same a sequential fuel injection. It’s entirely possible to have an engine with individual fuel injectors that fire one entire bank at a time; it’s called batch fire IIRC. I know some Fords had it in the late mid-late 80’s. As for your specific car, I couldn’t tell you.

Here’s the schematic. What do you think? Do all 4 injectors fire simultaneously?

Yes. That’s not unusual for a car of that era. Most V6 engines of that time fired all the left injectors simultaneously and all the right injectors simultaneously. The old Ford 4.9 inline 6 fired the front 3 and the back three. Some Ford V8s fired 2 left and 2 right simultaneously. Technology for practical, reliable, and economical sequential injection just wasn’t around back then.