need help to understand semi-sequential without cam sensor

[zaq123]

I'm setting up the injector harness to run semi-sequential with Haltech.
I'm going through Haltech docs and they recommend to run the following groups: 1-6, 2-5, 3-5 for M20 firing order. I'n running OEM distributor for the ignition and no cam sensor. This pairing makes sense to me for the wasted spark setup but I can't wrap my head around for the injection grouping. Link ECU has semi-sequential recommended as 1-5, 2-4, 3-6 but it also calls for a cam sensor to see through 720 degree cycle.

Below is what Haltech specifies. Basically spraying a fuel into one cylinder on the intake stroke while the paired cylinder is on the exhaust stroke (360 apart) ? Or the only reason they sudjest it because the other arrangement would require a cam sensor (for 120 apart setup).

can anyone explain this and why Haltech specs that?



Semi-Sequential

Each injector output fires twice per engine cycle (once per crank rotation) and is timed with its associated cylinder pair. Half of the calculated fuel amount is delivered per injection event. This setting requires at minimum a Half Sync Trigger Type such as a crank-only trigger (eg. missing tooth triggers with no cam position sensor). Typically used when there are not enough injector outputs for all injectors.

Common injector pairings are as follows:

	Cylinder Pairs
Firing Order	Output 1	Output 2	Output 3	Output 4
1-3-4-2 / 1-2-4-3	1 4	2 3
1-3-2-4 / 1-4-2-3	1 2	3 4
1-4-3-2	1 3	2 4
1-5-3-6-2-4	1 6	2 5	3 4
1-2-3-4-5-6	1 4	2 5	3 6
1-6-5-4-3-2	1 4	3 6	2 5
1-8-4-3-6-5-7-2 / 1-8-7-2-6-5-4-3	1 6	5 8	4 7	2 3
1-3-7-2-6-5-4-8	1 6	3 5	4 7	2 8

Injector wiring can also be confirmed by checking the Fuel System > Wiring node.

[digger]

1&6
2&5
3&4

are 360 degrees apart which is what is needed if firing twice per 720 cycle

[zaq123]

1&6
2&5
3&4

are 360 degrees apart which is what is needed if firing twice per 720 cycle

I get it for the spark. But for the injection? spraying into the paired cylinder on the EX stroke? Why? Why not to pair with to spray 120' apart ? Digger, if I recall you used Wolfv550 with semi-sequential and dizzy (or used to years ago). Did you pair those injectors the same way as Haltech recommends?

[digger]

I get it for the spark. But for the injection? spraying into the paired cylinder on the EX stroke? Why? Why not to pair with to spray 120' apart ? Digger, if I recall you used Wolfv550 with semi-sequential and dizzy (or used to years ago). Did you pair those injectors the same way as Haltech recommends?

i would think you would want each cylinder to have the fuel injected at the same piston position for consistency

i am running older V500 "full" sequential with cam sensor now. It originally had dizzy as it was a plug and play setup but i dont recall whether it was single batch fire or two (2) batches like the motronic. it never had 3 pairs though.

For all the effort you seem to be going through why not do sequential?

[e30davie]

On my mega squirt I only have 2 groups of 3 (i just copied the oem m20b25 injector pairing for this), but there was a setting to do 50% of the fuel every 360 degrees. Cant remember the setting name. but i figure this was better than squirting all the fuel at the "wrong" time.

there is also "timed" and "un-timed" semi sequential, as megasquirt calls it, not sure what haltech calls it. I suspect you are refering to "timed" where the ecu knows which injector is firing at which pair (requires a cam sensor), but "un-timed" I understand it just fires them constantly with no regard for its position in the 720 degree cycle (no cam sensor required). which is why I feel like the 50% even 360 degress is a good compromise. basically a constant flow of fuel. i think ive got that right..

[zaq123]

a) I want to keep dizzy no mater what. Yes weird but It's 80s car and I want to keep something from 80s.
b) I have Nexus S2 so it's only 4 drivers

I didn't want to hack stock harness so here is pnp harness/adapter/brackets I built. Pretty much stock with the exception separating IAT and temp sensor grounds to a dedicated signal ground (all using stock harness) and now rewiring oem injector harness to get these injectors in groups.

[zaq123]

On my mega squirt I only have 2 groups of 3 (i just copied the oem m20b25 injector pairing for this), but there was a setting to do 50% of the fuel every 360 degrees. Cant remember the setting name. but i figure this was better than squirting all the fuel at the "wrong" time.

there is also "timed" and "un-timed" semi sequential, as megasquirt calls it, not sure what haltech calls it. I suspect you are refering to "timed" where the ecu knows which injector is firing at which pair (requires a cam sensor), but "un-timed" I understand it just fires them constantly with no regard for its position in the 720 degree cycle (no cam sensor required). which is why I feel like the 50% even 360 degress is a good compromise. basically a constant flow of fuel. i think ive got that right..

Haltech is doing "untimed??" just from a crank trigger. Here is from Haltech for semi-sequential settings:

"Each injector output fires twice per engine cycle (once per crank rotation) and is timed with its associated cylinder pair. Half of the calculated fuel amount is delivered per injection event. This setting requires at minimum a Half Sync Trigger Type such as a crank-only trigger (eg. missing tooth triggers with no cam position sensor)."

I just don't get their cylinder pairing 360' apart for the injection. So basically the opposite cylinder will have fuel spraying on closed intake valve while the piston is in the combustion stroke?

Like here is what Link ECU suggests and it makes sence but they call for cam sensor to do this:

"injectors are wired in pairs according to the firing order with the pairs wired to the injector driver that corresponds to the lowest numbered cylinder in the pair.
elect Sequential Injection Mode when using this wiring configuration. Note that unused injection drives will not be available for other use and will still be firing according to their position in the firing order.
Examples:

• 6 Cylinder, firing order 1 5 3 6 2 4. Works nicely as per rule. Fuel sits in port for 120 degrees longer on the higher numbered cylinder in the pair than the other.
  • Injector drive 1 is wired to injectors for cylinders 1 and 5.
  • Injector drive 2 is wired to injectors for cylinders 2 and 4.
  • Injector drive 3 is wired to injectors for cylinders 3 and 6.

[e30davie]

hmmm wel its good you're thinking about this. I think ultimately its unlikely to make a huge difference either way. I understand that squirting fuel onto the back of a hot valve is advantageous.

I wonder if there are any OEMs that run 3 pairs of 2 injectors. and see how they are wired up?

[zaq123]

hmmm wel its good you're thinking about this. I think ultimately its unlikely to make a huge difference either way. I understand that squirting fuel onto the back of a hot valve is advantageous.

I wonder if there are any OEMs that run 3 pairs of 2 injectors. and see how they are wired up?

for example here is stock JZX90 in the diagram below ( the same 153624 firing order but has the cam sensor). Pretty much Link ECU suggested pairing only shifted 120 degrees. My tunner insists I split injector from the batch of 2 (e30 stock) to Haltech semi-sequential aka the batch of 3 to dial in engine response and low rpm operation.
not a big deal at all, even using stock e30 harness. Luckily, OEM Motronic 55 connector has plenty of empty slots. All I have to do is to take a useless wire in e30 injector plastic housing harness that is going to c191 (one wire on the fan temp switch is useless because the switch is grounded through the body hence the switch has only one pin but its brown plug has two wires there), cut useless wire from the brown connector and redirect that wire to the 3rd pair of injectors. Now c191 7th pin will drive my 3rd group of injectors. Harness's end of c191 has only 6 pins so I'm adding the 7th 2.5mm pin in the empty 7th slot and running a wire back to Motronic 55 connector into the empty slot. Easy job.

One wire mod. Just want to understand if the Haltech suggested pairing is what I should do and why ....or do something else.

[e30davie]

Thats interesting on the jzx90. paired as you suggest. 5/3,4/1,2/6

I would be inclined to give haltech an email or phone call to get their opinion as to why they have suggested what they have and tell them about your theory and the jzx evidence. Everything i have heard suggests they are responisive and helpful. I emailed them yrs ago about an issue I had on a very old ecu (E8), and they even responded to that very quickly.

[zaq123]

Thats interesting on the jzx90. paired as you suggest. 5/3,4/1,2/6

I would be inclined to give haltech an email or phone call to get their opinion as to why they have suggested what they have and tell them about your theory and the jzx evidence. Everything i have heard suggests they are responisive and helpful. I emailed them yrs ago about an issue I had on a very old ecu (E8), and they even responded to that very quickly.

my only guess is that's for 120 setup on semi-sequential injection, ECU needs to know the whole orientation during the entire 720 degrees aka cam sensor is required. Haltech setup with just a crank sensor (reading 360) is still better than 3 per group in stock e30 setup but not perfect.

from my tunner regarding Haltech setup : "Substantially better control over the injection window / small pulse-widths. This improves economy, drivability, and overall engine response."

Considering I refuse to let go dizzy (no cam sensor), probably the best setup I can get. I just want to understand why

[digger]

Haltech is doing "untimed??" just from a crank trigger. Here is from Haltech for semi-sequential settings:

"Each injector output fires twice per engine cycle (once per crank rotation) and is timed with its associated cylinder pair. Half of the calculated fuel amount is delivered per injection event. This setting requires at minimum a Half Sync Trigger Type such as a crank-only trigger (eg. missing tooth triggers with no cam position sensor)."

I just don't get their cylinder pairing 360' apart for the injection. So basically the opposite cylinder will have fuel spraying on closed intake valve while the piston is in the combustion stroke?

Like here is what Link ECU suggests and it makes sence but they call for cam sensor to do this:

"injectors are wired in pairs according to the firing order with the pairs wired to the injector driver that corresponds to the lowest numbered cylinder in the pair.
elect Sequential Injection Mode when using this wiring configuration. Note that unused injection drives will not be available for other use and will still be firing according to their position in the firing order.
Examples:

• 6 Cylinder, firing order 1 5 3 6 2 4. Works nicely as per rule. Fuel sits in port for 120 degrees longer on the higher numbered cylinder in the pair than the other.
  • Injector drive 1 is wired to injectors for cylinders 1 and 5.
  • Injector drive 2 is wired to injectors for cylinders 2 and 4.
  • Injector drive 3 is wired to injectors for cylinders 3 and 6.

to me the haltech makes sense. if you are doing semi sequential then you need injectors to fire the same piston phase position for each cylinder.

[digger]

with waste spark coil 1&6 are shared, 3&4 shared and 2&5 shared

[zaq123]

with waste spark coil 1&6 are shared, 3&4 shared and 2&5 shared

Everything is wired and ready to go. Actually was pretty straightforward job. One wire back to the ECU and one new pin in the empty slot of the stock harness connector C191. Injector harness plastic rail just needs wires separated and unused wire crimped to 3rd injector group hence no changes to its c191 plug.
ECU is installed and fits nicely under the glovebox upper trim just like stock. I went with Nexus s2 because for the price, it is actually not a bad buy considering all it features (built in LSU 4.9 wideband controller, knock, wifi, app connection, throttle by wire if one what's to go that route plus newer processor etc etc). Nexus S3 would make more sense for 6 cyl but I never getting rid of the dizzy on this m20, otherwise I would have just swapped it instead of building the stroker.
Now to the fun part. Hopefully it will run haha.

[TobyB]

My guess is that they are doing it that way (360) to keep the on and off windows for the injectors as separate as possible.

When the 'off' time for the injector gets too short (injector dependent) then metering becomes unpredictable as the window varies-
will the injector close, part- close, hang open?

This was a problem with 'first generation' injectors that took significant time to open and close...

t