ok so im going for my carb setup shortly - parts on way. the only thing im wondering is if i go from the mpfi to carb can i still get the ecu to sort my timing out ? untill i get a vac advance diz, or will i ever need the vac advance diz ?
please no coments on why im swapping ;-)
thanks anthony

 

I dont know of any way to make it work.

IIRC timing is based off RPM and kpa. So if you were to attempt to make it work, you would still need the map or maf, along with the ICM. Then custom program the ecm to ignore all the other crap. IMO, it would be cheaper and easier just to go get your vac dizzy.

 

there are also standalone timing controllers.

The megasquirt guys make one, if you want the ultimate in timing control.

 

he has a maf system.in order for the stock ecm to control ignition timing properly u would have to run the maf and air temp sensor,im not positive but u may also need the tps

but i know for a fact without the air temp and maf the timing will be all screwed up

 

zs&tas, disconnecting either the MAF sensor, and/or O2 sensor will force Open Loop, and in this state, the ECM doesn't control spark advance, the distributor does directly. It is preset to do this in something known as Bypass Mode. I did this very thing on my old LB9, and just did this to my new LG4, and it worked fine (once you adjust the air/fuel ratio on the carb). Some will argue that the stock parameters aren't too great in Bypass Mode, and I agree, but it will work, you just need the carb, set the ECM to Open Loop, and get a lockup kit for the tranny.

 

umm rob remeber what happned to me when i first installed the ms unit and we towed the car to the track,i had full advance under load and the car pinged to high holy hell

 

^ Umm, Dave, the MEGASQUIRT is a completely different animal. The stock ECM does not control timing/advance with an open circuit prevalent, the HEI module in the distributor does, which is the reasoning for the Bypass Lead wire. Under 2-volts, and/or Open Loop, the ECM does not control timing whatsoever....

 

might as well not install the ECM then.


The HEI module is completely capable of sparking on its own.

 

the megasquirt wa sdoing fuel control only remeber, i had it piggy backed

 

Putting your sarcasm aside, the ECM is primarily used to control everything collectively, not just spark. The ECM would still be needed to be used as a power source, as well as controlling other things as well, and it wouldn't be in his best interest to simply toss it. Let us also remember that the original poster is looking for a TEMPORAL fix, and this would easily provide this for him. In Open Loop, all of our factory ECM's do not control spark advance anyway, just air and fuel until it reaches Closed Loop in which the ECM then takes over full timing control....

Yeah, but you disconnected the stock ECM entirely, although the ECM doesn't control spark in Open Loop, the system (Electronic Spark Control) itself is GROUNDED through the stock ECM. Pulling the ECM would be like disconnecting the ESC entirely, because the ESC feeds through the ECM, as does everything else wired into the Engine Control Module, example; the fuel pump....

 

no when i ran piggy backed i still used the stock ecm,the mega squirt had its own o2 tps and ait cts sensors,nothinhg was disconected fromt he stock ecm

 

ok thanks.

 

Yeah, but not only do we not know that it was the spark advance causing the spark knock, were you running Open Loop constant? The whole point is that it needs to remain in Open Loop, because the ECM SETS your timing fixed to a Zero Degrees Base, with the distributor itself advancing for spark according to RPM being realized. The ECM does not control spark advance in Open Loop, it only sets base, which is why it isn't to be removed....

 

true but my point is if he keeps all the sensors,including the maf the stock dizzy will work fine,though im not sure if he needs the tps or not

 

I've never tried that myself, but I do know that that would be considered breaking the feedback loop, and it might just effect spark advance since it's running in a Closed Loop state. I'm sure it would run, but maybe too erratic though....

 

now im curious,but i cant test it out with the megasquirt hooked up lol

 

What do you mean the ECM sets base timing?


Base timing is set by the user, by phisically moving the distributor?

 

^ In Open Loop the ECM ignores most of the sensors and sets the timing fixed to base, which normally occurs during cranking/cold start, and/or Limp mode (bypass mode)....

 

To the original poster, a good example of what I'm trying to explain is when we set and/or check for base timing. The first thing you'll want to do is disconnect the EST wire when doing that. Now, what happens when you disconnect the EST connector terminal is what will further prove my point. With it connected, my ECM (in Closed Loop) ran at a six degree base, and with it disconnected (forcing Open Loop), it immediately reverts back to a zero degree base, w/the distributor being untouched, nor turned by hand....

 

I still don't understand what you are saying.

My base timing is set BY ME at 6 degrees BTDC. The ecm modifies the timing signal to change the timing, but remove the 5 volt signal and it is instantly back at 6 degrees (until a certain RPM, when the module has a built in advance curve. )

 

Followed by...;

Your confusing yourself, and I don't know how much more clearer I can get....

The ECM, in Closed Loop mode, alter's (as you just pointed out) Open Loop mode's base timing. With a 5-volt signal prevalent (Closed Loop), in my LG4's case, it has a 6 degree base timing. With a 5-volt signal NOT prevalent (Open Loop) it reverts back to a 0 degree base timing. I'm referring to "reverts back" because Open Loop occurs FIRST, not Closed Loop....

You still don't understand yet?

As for Spark Advance, as I mentioned a few posts up, this occurs when a reference pulse, determining engine RPM, is fed back and forth (in either Closed or Open Loop mode). Spark advance occurs either with the ECM's help, or without (Closed or Open circuit)....

 

Ok, I understand what you are saying.

Building a megasquirt for a car with no harness really gets you familiar with EFI, so I know how and why the HEI system works, I was just trying to figure out what you were saying

Sorry for the confusion.

 

I'm not talking about fine tuning and/or dialing in base timing, I'm talking about factory settings. Regardless though, whether your base is set by YOU, or you keep the factory settings in Closed Loop applications, base timing is always changed, altered, reverted, switched or whatever other word we can use, back to the Open Loop base. When it is set back to Open Loop base (and the bases vary, depending on the engine), the ECM does not advance the spark....

Not at all....

 

i'm going to have to read that all over again several times. lol

 

It's easier to understand when you look at the schematic view of the EST circuitry. I've tried my best to explain it, but I'm going to try to get a scan of the schematic's up very soon....

The HEI ignition module has seven terminals (eight, if you include the ground);

* Battery Terminal
* Ignition Coil Trigger Signal Terminal
* Pickup Coil Signal Converter
* Pickup Coil Signal Converter
* Compensated Ignition Spark/Timing Signal (to ECM)
* Crankshaft Position RPM (to ECM)
* Bypass 5-Volt Disable (to ECM)
* Ground (to ECM)

The Bypass is literally a coil inside of the ignition module, and when it is in Closed Loop (at the proper voltage), it's leads are directed from the Ignition Coil Trigger Signal to the ECM directly. When the coil switches to Bypass (Open Loop), it's leads are directed from the Ignition Coil Trigger Signal, through the Signal Converter and to the pickup coil only....

 

In other words,

When the module sees five volts at the Bypass pin, it takes the ignition signal from the ECM and uses it to control timing.

If there is not five volts, such as when you are cranking, or have the ESC disconnected, the module ignores the signal from the ECM and does internal timing control.


The 7 pin module has no internal spark advance, and the timing will remain at base in such a condition.

The 8 pin module has some internal advance that kicks in over a certain rpm.

 

Yes, when the Bypass sees 5-volts, there are two lines that immediately reference data to the ECM in the Bypass coil; the Compensated Ignition Spark Timing Signal, and the Bypass Disable...

Yes, when the Bypass does not see 5-volts, data is only communicated between the Ignition Coil, Signal Converter(s) and the pickup coil alone. What's important to point out though, is that the ECM still needs to be connected, as the igniton module itself is grounded through the ECM....

There's really no eight pin module, per se, I just wanted to make note that the seven terminal module has an extra ground wire coming from it to the ECM (this wire is seperate, and is not in the connector terminals), I wanted to cover each and every single line coming to and fro the module and the ECM. The seven terminal module has an internal spark advance built in....

 

* 4 pin module - electronic ignition, but doesn't do computer timing control, top left
* 7 pin module (large) - electronic module that does timing control, used with coil-in-cap distributors, top right
* 7 pin module (small) - electronic module that does timing control, used with some external coil distributors, bottom right
* 8 pin module - electronic module that does timing control, used with most V8 external coil distributors, bottom left
* 5 pin module - rare and not discussed here. not shown



Might be a matter of naming, but neither of the 7 pin modules on this diagram have internal advance built in. That is only present in the 8 pin module.

 

just curious but whats the built in curve look like ?

 

What makes you say this? I have a seven terminal ignition module right here (see pic), in which I'm just about ready to ruin by breaking it open, although I really do need it intact lol. With the ECM in Open Circuit, please explain how the spark advance is being controlled by the ECM? The only thing that the module uses the ECM for during Open Loop, is to get a reading on the Crankshaft Position RPM, but that doesn't mean the ECM is controlling advance, the module is simply using the ECM for a reference pulse. Please explain otherwise, because if I'm wrong, I need to know why....

 

I am basing my statements off of the experiments of another fello on the board who was running without an ECM and using the HEI moduel. His intent was to run static timing, but he found that the 8 pin module advances on its own after a certain rpm, whereas the older 7 pin doesnt.


If you want I can try to find the thread, it's an oldie.

 

Please do so, as normally when a code 42 is triggered, this tells us that either Bypass Mode is on, but the module is still controlling the advance, or that engine speed over 600 RPM with no reference pulse going to the ignition module for 200 msec. Either way, timing is still being advanced, just not by the ECM. Some people are unaware that code 42 might already be stored in the ECM, w/timing controlled by the module.

 

https://www.thirdgen.org/forums/tech...+static+timing


There one talking about the built in advance.


I'll do more searching later.

 

^ I was just reading that thread you posted, and I agree with RBob that there are many variances with factory settings depending on the distributor, as well as the engine. For instance, w/my current setup (the LG4), when the ECM switches to Open Circuit, base timing is set to zero degrees, w/the carburetor's M/C being set to a 50% duty cycle. In L69 applications though, I believe the simplified settings are a little different, well, base timing would be, actually....