MSefi.com read only forum (Jan.15,2018)

hi,

i am just confused with the way my engine is set up from stock. its a mitsubishi 4g15 dohc 16valve. the stock ecu is 76 pin. the ignition system is distributor based, which is driven by the exhaust cam. I've verified the pinouts of the distributor and its a camshaft position sensor. there is no signal on the distributor that says its a crank sensor nor a tdc sensor. i've looked into the crank sprocket, and there is no sensor there as well.

the list of sensors that i have for this engine are:
- camshaft position sensor (inside distributor)
- o2 sensor
- manifold absolute pressure sensor
- coolant temperature sensor
- intake air temperature sensor
- throttle position sensor

can anyone shed some light on my confusion?

i need to verify this info before jumping in to switching to a standalone. i'm targetting ms2 btw.

The MS can run a distributor using most Mitsubishi crank sensors. They usually have four equally spaced teeth, which is pretty easy to use.

With that setup (no crank sensor, one signal per piston on the cam) the ECU does not need to know when the engine is at TDC of piston #1, it just needs to know when it is getting to TDC of any power stroke. It uses that to determine RPM and when to fire the coil. Where the rotor is pointed mechanically determines which spark plug fires. The injectors are fired in batches per each power stroke so fuel is in the intake ready for when the valve opens.

In order to fire the injectors in sequential order and/or to fire a coil for each plug in the right order, you would need the crank angle as well as when you are at TDC of the #1 piston.

Hope that helps explain it. Brian.

bleoh wrote:With that setup (no crank sensor, one signal per piston on the cam) the ECU does not need to know when the engine is at TDC of piston #1, it just needs to know when it is getting to TDC of any power stroke. It uses that to determine RPM and when to fire the coil. Where the rotor is pointed mechanically determines which spark plug fires. The injectors are fired in batches per each power stroke so fuel is in the intake ready for when the valve opens.

In order to fire the injectors in sequential order and/or to fire a coil for each plug in the right order, you would need the crank angle as well as when you are at TDC of the #1 piston.

Hope that helps explain it. Brian.

so what you're trying to say is, the crank angle sensor's purpose is to support sequential injector squirts and/or coils. and without the crank angle sensor, the injectors fire in batches?

lnbn wrote:so what you're trying to say is, the crank angle sensor's purpose is to support sequential injector squirts and/or coils. and without the crank angle sensor, the injectors fire in batches?

Actually, it's usually the other way around - crank sensor (missing tooth wheel or some other pattern) for batch firing, add a cam sensor for sequential. Because your cam sensor wheel is symmetrical, it doesn't indicate which piston is coming to TDC, so you're limited to batch injection; spark is of course driven by the distributor. If you were to remove one of the teeth, MS2/Extra code 3.0.3 could then be used for sequential fuel.

Hi,

I've uploaded the circuit of my distributor.

Notes:
- Engine DOES NOT have a crank angle sensor
- Engine uses a distributor for spark plug firing
- From the excerpt in the service manual, this engine IS fuel injected sequentially

The oddity here is that, how does the ECU determine the "sequential injection" without a crank angle sensor? It only has a distributor that fires the plugs.

What the ECU does to the distributor is, it gives the signal to turn ON the power transistor when the right to to fire the plug occurs. On the other hand, what the distributor does is it gives the engine speed and the camshaft position signal to the ecu.

Any ideas how sequential injection works here?

Well, the camshaft and distributor are fairly well tied to the crank, just turning half as fast - two crank revs per cam rev. If the cam is say 30 deg BTDC for a particular piston, then the crank is 60deg BTDC for that piston. Since the cam turns once per engine cycle, you know which piston is coming to TDC on its power stroke.

DonTZ125 wrote:Well, the camshaft and distributor are fairly well tied to the crank, just turning half as fast - two crank revs per cam rev. If the cam is say 30 deg BTDC for a particular piston, then the crank is 60deg BTDC for that piston. Since the cam turns once per engine cycle, you know which piston is coming to TDC on its power stroke.

well, that's gonna be one h*ll of an algorithm and math for the ecu. is the ms2 capable of such functionality, or will there be a source code change?

That diagram implies the engine isn't running sequential injection. The ECU just needs to tell how long the injector pulse width will be and when to fire the coil in such a situation; the distributor takes care of which cylinder to fire.

lnbn,

The engine doesn't need a crank sensor for sequential injection, it needs a cam sensor. The cam sensor can tell the engine which cylinder is firing. This cam sensor is sometimes installed into the distributor (such as on the Mazda KL engines, as well as yours apparently).

The crank sensor is useful for mis-fire detection, and is sometimes used for 'wasted spark' ignition systems, but is never sufficient for sequential injection.

Lance.

I just thought of something... Just take note, all we have is a camshaft position sensor and a distributor.

Mechanically, a straight 4 cylinder fires in a 1 3 4 2 manner. For every 180 degree turn, 2 piston pairs are in TDC - one just came from intake going to combustion, and the other just came from exhaust, going to intake.

Assuming piston 1 is going to combustion - this requires spark plug to fire. If #1 is on this cycle, and the next cylinder going to combustion is #3, it means that #3 needs fuel injected.

In essence, w/o a crank angle sensor, the sequence would be as follows:
1 - spark; 3 - injection
3 - spark; 4 - injection
4 - spark; 2 - injection
2 - spark; 1 - injection

Now, in terms of algorithm,
- how will the ECU/MS2 know when exactly to "inject" fuel relative to the overall positions of the piston? CMIIW, injection should take place "as soon as" the intake valve opens.
- how will the ECU/MS2 know when exactly to "fire" the spark plug relative to the overall position of the piston? IIRC, spark plug fires at varying times depending on the engine rpm (spark advance).

I think I'm getting closer, just need some confirmation.

lnbn wrote: Now, in terms of algorithm,
- how will the ECU/MS2 know when exactly to "inject" fuel relative to the overall positions of the piston? CMIIW, injection should take place "as soon as" the intake valve opens.

Standard MS2 code does not attempt to time the pulses - it batch fires the injectors.

- how will the ECU/MS2 know when exactly to "fire" the spark plug relative to the overall position of the piston? IIRC, spark plug fires at varying times depending on the engine rpm (spark advance).

I think I'm getting closer, just need some confirmation.

It starts a countdown after it gets the appropriate signal from the crankshaft position sensor. The amount of spark advance is determined by a spreadsheet-like table based on manifold pressure and engine RPM.

here is what the inside of my distributor looks like.



i only have 4 vanes inside, which i think corresponds to a cylinder for each. on the pic the "cylinder 1" vane just passed the sensor.

This is the oldest sort of tooth pattern I've seen for computer controlled distributors - one pulse per cylinder, ECU calculates a time delay after the pulse and uses that to fire the coil, no sequential injection possible.

is it possible to splice into the wire going to the ignition coil for the ecm and use that as an rpm signal for ms ?

Not the wire going to the ignition coil, but theoretically you could use a pick-up on the #1 cylinder wire. You would need code that can will fire the spark plugs before it gets sync from the second trigger.