I'm still using the standard wiring loom in my car and l'm once again trying a different ecu.
From the Toyota workshop manual wiring diagram it looks as if all 4 injectors are wired to fire together even though there are two injector outputs labelled for different cylinders.
Can anyone confirm this?

There is plenty of evidence that MAP-sensored 16V 4AGE engines are batch fired
with half the required fuel being delivered every revolution. This is despite the Official
Toyota manual not including the 4AGE in the list of engines using this option. Outputs
#10 and #20 are strapped together inside the ECU and fired by a single transistor. If
you check you should find that there is continuity between the outputs.

In the official manual the 4AGE is listed as having grouped injection if used with the
Bosch L-Type system. Indications are that these will be MAF-sensored engines as shipped
to the US (and possibly a few other countries) where the MAF system was used to meet
more stringent emissions standards.

Cheers... jondee86

Might be a relavent to mention the MAP injectors are rated at a lower flow rate than the MAF.

That's quite interesting about the outputs being linked in the ecu, l have just checked a Freedom ecu (l don't have a standard ecu) and the outputs are not linked internally.
If the linking is done in the loom as the diagram suggests, would it just be case of doing a continuity test between the injector pins and the two output pins?

The Freedom ECU should be able to drive the injectors separately. A little wire work and a few keystrokes and you're in business. That is assuming you're using the programmable ECU.

sirdeuce wrote:The Freedom ECU should be able to drive the injectors separately. A little wire work and a few keystrokes and you're in business. That is assuming you're using the programmable ECU.

Group firing with the Freedom should be relatively easy then
What l'm trying to ascertain is if the injector outputs are wired together in the loom.
I'll check tomorrow and post here.

On the factory AE86 loom that I dismantled, the injectors were definitely wired
in pairs and each pair was connected to one of the ECU outputs. That is also the
arrangement shown on virtually every reliable Toyota 16V 4AGE wiring diagram
I have ever seen. If the pairs are shown as being linked externally I think that is
just another way of saying that they are driven from the same transistor.

Here is an example...


If in doubt as to what you have in your loom, providing you have two separate wires
leading to the ECU, you can test for continuity from the ECU end to the injectors.
You should only get continuity to two injectors on each ECU pin.

Cheers... jondee86

Super interesting, thanks Jondee86,
Reading more about batch vs sequential injector firing since I never have seen a wiring harness like this... just sharing info:
20v BT&ST 4A-GE has individual wiring for each fuel injector to the ECU. (Interestingly wire gauge is different per injector if I recall correctly.. maybe just to fit into the connector)
Nissan 240sx S13 and S14, Nissan 300zx z32 all have individual injector grounds to ECU. (I'm familiar with these)
but...
Megasquirt-1 and Megasquirt-2 are both setup for batch firing!
It sounds like batch is used way more frequently than I thought, and might be used for everything past low RPM regardless of wiring setup until way later ECUs. In case of 16v 4A-GE, it just is wired together.

Yeah... I never bothered to look into it but I guess that when EFI was in its infancy
the designers just tried to emulate what was being done with a carb and a single coil.
The first 16V 4AGE ECU's basically just had one ignition output and one injection
output. Then Toyota kept improving things it until we ended up with full
sequential injection and ignition.

Batch injection may be simple but its works just fine. It only falls down due to the
fact that only one cylinder gets a squirt of fuel at the optimum time (open inlet valve).
The other three are getting fuel delivered onto a closed valve. Sequential injection
means each cylinder get fuel at the optimum time which has some benefits for idle
quality and emissions.

Being able to coordinate the actual start or end of the injection cycle with the valve
timing, also means that it is possible to avoid injecting while both the intake and
exhaust valves are open. So no raw fuel gets lost out the exhaust during valve overlap.
The injection timing can also be optimised at low to medium rpm to improve emissions,
economy or power.

However, at high rpm as injection duration increases and valve open time decreases,
fuel starts to get delivered onto closed intake valves and the result is pretty much the
same as batch injection. Some engines revert to batch injection and fire the injectors
twice as often to reduce the injector open time at high rpm.

Cheers... jondee86

A simple continuity test reveals that on a U.K (map) car #10 and #20 injection outputs are linked in the loom, one trigger from either output fires all four injectors at the same time.

Another downside to firing all the injectors at the same time is the fuel has more time per cylinder to condense on the port walls. I do believe the MAP ECUs fire once per revelution, twice per full cylinder cycle. Would be interesting to see if the transistors, #10 and #20 fire separately, one per engine rev or simutaneously. Would it even be worth the effort to investigate? That would give the capability to go with two groups of injectors.

Too bad my motivation has died.

I would guess they would fire in sequence, two outputs to halve the load on them?
My motivation comes and goes these days too, when l need some... l try a different ecu!

If #10 and #20 are linked in the loom then there is no possibility that the
loom could be used with grouped injection. Out of interest I went and looked
thru a few wiring diagrams and to my surprise several of the MAP diagrams
do show an external link between #10 and #20. However, the USDM AFM AE86
wiring diagram does not, leaving the door open to group injection if there
is indeed a second transistor inside the ECU.

Have to admit that it is now 15 plus years since I opened up my factory AE86
loom, and I do remember having to cut a few wires to be able to separate all
the individual circuits. I'm pretty sure that the wires I cut were ground wires but
who knows, one of them may have been an external link between #10 and #20

In reality, from a performance point of view there is very little difference
between batch, group and sequential injection. Once the revs are up all the
fuel that you can squirt into the ports will end up in the cylinders no matter
what injection mode is in use. Hilborn worked that out a long time ago !!!

Cheers... jondee86

I agree about the different fuelling strategies. l just needed to know about the wiring so that l could allow for it in my calibration.
Hasn't helped much though, just added to the confusion!
AEM tooth control tables are a law unto themselves.

disconnect the plug at the ECU and disconnect the plugs at the injectors
turn the meter on tone
connect one side to wire harness 10 and then prob the injector plugs one at the time

see when you have tone
if they are connected in the harness you will get tone 4 times (one on each plug)

good luck

Davegt27 wrote:disconnect the plug at the ECU and disconnect the plugs at the injectors
turn the meter on tone
connect one side to wire harness 10 and then prob the injector plugs one at the time

see when you have tone
if they are connected in the harness you will get tone 4 times (one on each plug)

good luck

Sorted now thanks.
My car definitely uses batch injection.

Hi all
try to look for the article of Jeremy Ross, regarding the 4AGE ECU "lifting the lid"' it has a lot of information.
USDM ecu are wired in batch, European and the rest of the world, must of them are wiring in the loom together.
kind regards

kakico wrote:Hi all
try to look for the article of Jeremy Ross, regarding the 4AGE ECU "lifting the lid"' it has a lot of information.
USDM ecu are wired in batch, European and the rest of the world, must of them are wiring in the loom together.
kind regards

http://gallery.ostportworks.com/displayimage.php?pid=3473 - click on pdf icon

hopefully the link will work.

Didn't HKS have a piggy back that was a sequential injection adapter?

sirdeuce wrote:Didn't HKS have a piggy back that was a sequential injection adapter?

Never ran across that one, but thinking about it, maybe it could work. The piggy would
have to intercept the ECU injector ground signal, mimic it and direct it to four separate
injector drive transistors. Then it would need to switch the transistors sequentially in the
correct order. So far so good... easy stuff to this point

Injector duration would need to be doubled as the whole point of sequential injection is to
deliver fuel when the intake valve is open. And end of injection timing would need to be
adjustable to make sure the injection occurs at the optimum time. Reference injection
timing could probably be derived from the crank and and cam position sensors in the
distributor. By this time the electronics have become a bit more complicated !!

Realistically, it would be a lot of effort for for no appreciable gain. Better to spend the
cash on getting a dyno tune... car will run better and you will gain a few hp

Cheers... jondee86

This didn't say which generation 4AGE, but is a diagram how batch injection worked for "a" 4age.
Can't imbed the image.. apologies for the gdrive link
https://drive.google.com/file/d/1dRh1Ud ... share_link

This is the original diagram...



The technical article that contains the diagram does not indicate where the MAP 4AGE
belongs, but there is plenty of evidence that it sits in the Simultaneous category for
ECU's with only one transistor. This omission is most likely due to the fact that the
article was written for USDM Toyotas and the AFM 4AGE with L-Type EFI.

To resolve this question (which comes up from time to time) the simple answer is for
someone to open up an AFM ECU and trace the #10 and #20 pins. It should be easy to see
if the outputs are strapped together or if each output has its own transistor.

Now who is in this for the glory of solving this mystery once and for all !!!!

Cheers... jondee86