OrangeBird

iTrader: (1)

Does it matter which way the low voltage wire harnesses point when installing the dist ?

Specifically , what I want to know is , when GM built the 2.8 , how exactly did they orient the wires ? I dont know if the wires that go to the 12v and computer should face tword the engine or the firewall in their normally installed position ?

Not the sparkplug wires , but the 12v ones , that is the ones I'm asking about . I know that the normal pattern for the sparkplug wires has the #1 at roughly the "7 oclock position" , , or pointing tword the front right fender , but I have no clue as to which way the ign. modules plugs face when the dist is installed ........

Anyone that can help would be greatly appreciated ........

Six_Shooter

iTrader: (2)

Usually any of the connections at the base of the dizzy will be pointed more backwards than forwards, to leave room for plugging in the connections themselves. In the grand scheme of things the dizzy will function just the same with those plugs at any position.

OrangeBird

iTrader: (1)

Hi Six Shooter ,

Thank You for the reply !

I do have a bit of a problem here , and maybe you can help me out further ....

I know that our beloved sixes use what is called a "batch fire" arraingement for pulsing the injectors , and that there are actually only two "channels" of output from the ECM to the injectors . Presumably , it sprays all the odd cyls on one pulse , and the evens on another . Ok , I'm good with that , I guess , but with 3 cyls not being on their intake stroke together at any one time , I don't have the vaugest clue about how they get the fuel to the cyl NOT on intake at the moment the injectors spray ..... BUT ! , leaving all that aside for a moment , doesn't the ECM need to know when , exactly , #1 cyl is at TDC so as to begin the injector spray cycle ? How does the ECM know where the crank is if the distributor doesn't have to index in at one exact spot ? If there is no definitave #1 position for the distributor to be installed in , what tells the ECM exactly when to begin pulsing the injectors so as to have the spray occour at the proper point in the cycle (presumably at or just before the intake stroke ?)

I hope my question makes sense , and the "how does the ECM know where #1 is" question has kinda bothered me since I got this car back in Febuary .

RBob

iTrader: (1)

The ECM doesn't know where #1 is. The distributor has to be timed properly so that the correct spark plug fires. That's about it, ECM doesn't need to know.

The ECM uses batch fire and sprays all six injectors at the same time. With the long runners the fuel isn't going to be borrowed from another cylinder for the current one doing an intake.

Even if it did, then when that cylinder intakes it will borrow fuel from another cylinder that isn't.

In batch fire mode the ECM will fire all injectors on every 3rd cylinder firing, which is once per revolution. This is known as double fire, as the injectors get fired twice for each cylinder cycle (4-stroke engine).

And the ECM doesn't know which cylinder is doing what when it does fire them. It just counts distributor reference pulses and fires.

Single fire mode is when the PW gets short and the ECM doubles it and fires the injectors once every two engine revolutions, or once per cylinder cycle. I don't believe that the 6 cylinders ECMs in the 3rd gens do single fire. I know that in the '90 - 92 ECMs they go into a quasi-async mode, which isn't the best way to go.

Confused yet?

RBob.

OrangeBird

iTrader: (1)

Thank You Rbob for the response !


So , the ECM fires the injectors every three pulses of the distributor , and doesn't fire them in any particular indexing with relation to what stroke any given cylender is on , and those cyls not on intake when the injector sprays will have their fuel "waitin at the door" (behind the intake valve) for them when their intake valve does open .

Sounds logical to me , I guess , but doesn't this arraingement result in somewhat poor mixture density for the cylenders that have their sprayed fuel waiting in the intake port ? It would seem that the fuel , sitting in that port for a second before the valve opens , would be a puddle settled to the floor of the port by the time the intake valve gets around to inducting it into the cylender ?

Anyway , SUPER huge Thank You gents for the responses , I can now Re install my distributor with the confidence of not worrying about timing it to anything other than the spark getting to the correct sparkplug at the appropriate time .

Six_Shooter

iTrader: (2)

The ECM fires all 6 injectors at the same time, no indexing or needing to know what cylinder is doing what, all 6 injectors open and close at the same time.

You have to realize that the intake valve is pretty warm, usually enough so that when the fuel being sprayed at the closed valve hits, the valve, it vapourizes the fuel, which will then remain is suspension, since the time interval is actually very short, even at idle. As the revs increase, the time the intake valve stays closed is so short, that most people can not tell when the valve is staying closed.

RBob

iTrader: (1)

You're welcome. And a little secret, yes the fuel is puddling on the back of the intake valve and the runner walls. However, when the intake valve starts to open there is a back blast from the chamber. It's pressure at this time is higher then the intake manifold pressure.

This little back blast atomizes the mix, which is then rapidly turned around and taken into the chamber as the piston rounds TDC on the exhaust stroke into the intake stroke.

Bada Boom, the induction of air & fuel into the chamber is ready to burn.

RBob.

OrangeBird

iTrader: (1)

So , the "reversionary pulse" as I've seen it called , atomizes the waiting fuel . Brilliant ! ....... I've seen this pulse employed in "walbro" carbs to actuate a fuel pump . It's great to see the engineering that goes into these things !

So anyway , again I say Thank You to both of you guys who helped give me an insight into the workings of this system . You have helped me greatly , and I truly appreciate that