Schematic for delco ignitin module

[davidgoodin]

Greetings,
anyone have a schematic for the delco ignition module?

I purchased aTbi system from affordable fuel injection to replace the carburetor on my boat. I did this the same time I replaced the engine. All is mostly well with the system but I think the wiring for the new distributer is wrong.

David

[Six_Shooter]

What makes you think it's wrong?

Any GM TBI service manual should have the pin out. The Mega Manual also has pinouts for several different GM ignition modules.

[davidgoodin]

What makes you think it's wrong?

The idle is not smooth.

The B+ line for the distributer is connected to the positive line of the coil. However, the positive line for the coil is still connected to +12 through the resistor wire.

I am curious if this is an issue for the "refernce" signal from the distributer to the ECM.


Any GM TBI service manual should have the pin out. The Mega Manual also has pinouts for several different GM ignition modules.

I would like to get a schematic for the internals of the ignition module. That way I can know what to expect signal wise when I look with a scope.

[dave w]

I hope this helps.

dave w

[Six_Shooter]

Oh, I don't know of any public domain schematic of the internals.

If you look in the Mega Manual I believe it has a description of the signals there.
Also some pinouts for the ECM will have what the the signals should be on those wires. So look at TBI pinouts charts, not the schematic. You shoudl be able to find some of those in the '7747, '7427 and other TBI therads found on this site in the GM hardware forum (a sub forum of this very forum).

Basically though, The Black/red is ground so there should be near zero volts on it, the tan/black is the bypass and should have 0 volts when off or cranking and 5V when above 400 (or so) RPM, the white and purple/white are signals too and from the ECM and have TTL level pulses IIRC on these. The signals vary based on RPM and commanded timing. The pink is 12V ignition and the white paired with the pink is the coil trigger that will have an AC signal on it, I just don't recall the magnitudes or exact wave form off hand.

Basically if it's working, then it's wired correctly. Swapping any of the pins on the ICM will cause a no run condition.

Get rid of the resistor wire, and your idle should smooth out then. The GM ICM and coil needs a full 12V to it, not through a resistor wire.

The 12V feed to the distributor being connected to the coil is how GM did it, so that is not of concern.

[davidgoodin]

Thanks,
the boat has a shift interrupter circuit that momentarily grounds the coil to make the engine "stumble". This circuit requires the coil to be fed with a current limited source. This is the resistor wire. But this is an issue for the new coil and distributer that wants the full 12 volts.

More study required.

[billygraves]

.............

[davidgoodin]

If I remember wright. You can use the REFERENCE incoming to the ECM. This will shut off the Injector pulse width. I just hope I remember correctly. I know there are Delco Ignitions that are for this interrupt.

I have an interrupter circuit that is designed to interface with a deco efi distributer. This is NOT meant to be connected to a distributer with an ECM. When used with the EFI distributer, the shift interrupter causes the distributer to intermittently go back to base timing thereby removing the timing advance. It does this by pulsing the input on the distributer.

The input on the deco distributer that comes from the ECM to tell the distributer that the ECM will now control timing is likely the best choose to use in this instance. I just need to create an interface that will allow the interrupter to intermittently cause the timing to go to base timing resulting in the engine "stumbling" during the shift.

[1project2many]

Thanks,
the boat has a shift interrupter circuit that momentarily grounds the coil to make the engine "stumble". This circuit requires the coil to be fed with a current limited source. This is the resistor wire. But this is an issue for the new coil and distributer that wants the full 12 volts.

More study required.

That circuit will be incompatible with stock type HEI installations. billygraves provides a working suggestion: Ground the REF signal. Although removing power to the injectors might be preferred to ensure the ecm doesn't accidentally utilize anti-stall logic. However, if the interrupter uses a relay I'd switch to a solid state circuit. Relay contacts can bounce which can cause problems.

[davidgoodin]

You are correct on the "incompatibility". The company that makes the shift interrupter have another model that is compatible with the delco "EST" troupe distributer. The company I purchased the EFI kit from claims it is good for "marine" applications, but they are a little fuzzy on the details when it comes to shift interrupters.
So, I am left in limbo doing more R&D.
My current plan is to use the "EST" type interrupter and build a circuit that will give the correct voltage to the ignition bypass input to the distributer. The circuit will essentially AND the input from the ecm and the input from the shift interrupter.

Whe the ecm wants to take over timing from the distributer, the new circuit will pass that signal as long as the interrupter is not sensing that the boat is shifting. If the boat is shifting, then the new circuit will pass the pulses from the interrupter circuit making the timing go from what the ecu wants to base timing. This will make the engine "stumble" momentarily uploading the dogs on the transmission and allow the boat to shift.

This is essentially what that circuit does to the EST type distributer.

A few resistors, a couple voltage comparators and a transistor should take care of it.

[Six_Shooter]

The circuit could possibly be more simple than that, I would have to see the schematics for the interrupter to know for sure.

[davidgoodin]

The circuit could possibly be more simple than that, I would have to see the schematics for the interrupter to know for sure.

Yes, a, it could be as simple as a couple of transistors as well.

basically, the ECM sends out a 5 volt signal to the distributer when it wants control of the timing. The shift interrupter sends out 4 volt pulses when it wants to make the timing go back to base timing. The output is low when the circuit is inactive.

So, a logic inversion, level shift plus an ANDi g function.

any ideas on the simplest circuit possible are welcome.

[sturgillbd]

What I did was use a relay on the power to the coil on my boat. When the shift interrupter gets tripped, the power to the relay coil is dropped momentarily during the shift. It works well on mine.

HTH
Brian
I don't know if this will set a trouble code on the ecm. My old boat is has a carb and I changed over to an HEI distributor.

[davidgoodin]

Thanks Brian,
the current interrupter hold the negative lead of the coil to ground preventing the coil from firing. I am getting error codes on the ECM complaining that the ignition circuit has a problem. Possibly a short. Go figure.

That is one reason I am trying to move away from that system. Would really be cool if the ECM had an input that would stumble the motor during a shift. But, alas, this is an old '299' from a truck that the guy says is optimized for a boat.

[sturgillbd]

If it is a Mercruiser I/O drive, I have a service manual for them. Does the engine run with it shift interrupter switch disconnected? If is is grounded all of the time, the interrupter may be out of adjustment or stuck. I'll try to find my service manual this eve.

Brian

[davidgoodin]

I guess I forgot a detail in my description. It should say " when the drive is shifting, the interrupter pulses the negative lead of the coil.
The engine runs now, I just need to get the shifter working so it will not short the coil (as the carbureted systems do) and cause the ecm to put out errors.

[1project2many]

any ideas on the simplest circuit possible are welcome.

You could actually accomplish a similar function within the ecm. The ignition cut is to reduce the sudden application of torque to the drive. If the 4V signal is timed correctly you could tune the ecm to retard timing during the shift. If the 4V signal only occurs between shifter positions it would work well. The ecm can reduce timing based on p/n input. The timing would change during the transition and return to original once the shifter is placed fully in gear. The only question is what is the minimum voltage change needed for the ecm to detect the change in state. The sensor is originally 12V so the closest to stock design would also supply 12V.

[davidgoodin]

That would be great. I have a 16146299. I have not found a complete pinout for that ecm yet. The shift interrupter put out 4 volt pulses during the shifts there is a switch on a mechanical linkage with a bunch of monkey motion that can " sense" that the outdrive is in the midst of shifting.

[Six_Shooter]

The pinout of the '299 is identical to the '7747.

[davidgoodin]

That's great! Now, if I had the pinout for the 7747, I would be set.

[Six_Shooter]

Both pinouts will be in the subforum that has bin files as well.

[davidgoodin]

Hmm...knock sensor input looks interesting. The boat has no knock sensor, but if that input causes the timing to retard, that could be a great way to do the shift...

Anyone know the required voltage to that pin to get the timing to retard? Is it a simple digital input or is it an analogue input that retards the timing based on the magnitude of the input?

[1project2many]

Not the best way. ECM runs through sensor test sequence before utilizing sensor input. Test sequence won't initialize if engine is idling.

[davidgoodin]

Not the best way. ECM runs through sensor test sequence before utilizing sensor input. Test sequence won't initialize if engine is idling.

Well, it was a great idea while it lasted...

I guess it would make sense that the ECM would figure that an idling engine is not knocking...

Any other ideas on how to use a direct 4 volt input to the ECM to tell it to retard the timing?

[Fast355]

Well, it was a great idea while it lasted...

I guess it would make sense that the ECM would figure that an idling engine is not knocking...

Any other ideas on how to use a direct 4 volt input to the ECM to tell it to retard the timing?

I used an interupter to operate a normally closed relay to break the signal between the ignition control module and the coil on the ground side. Doing this droppd the spark for a few tenths of a seconds, but allowed the ECM to still read the RPM signal. As soon as the dog clutch engaged the rpm would drop and the stall saver would keep the engine idling. I had to do some tweaking with the stall saver enter/exit rpm to keep the rpm more or less stable while shifting.

[davidgoodin]

Thanks for the idea on the relay. Is the "stall saver" a property of the ecm?

[Six_Shooter]

It was a relay that I was getting at earlier, but with only 4V a standard Bosch type relay wouldn't work. You'd still need a small amplifier circuit to drive the relay (Only about a dozen ways to do that haha).

I was going to suggest interrupting the tan/black bypass instead of the coil drive circuit directly, but then remembered that this would cause a check engine light if a simple interrupt circuit is used. I have half a thought on how I would do this without a CEL appearing, but this would only be useful if returning base timing is the desired result AND it would limit torque enough.

[Fast355]

It was a relay that I was getting at earlier, but with only 4V a standard Bosch type relay wouldn't work. You'd still need a small amplifier circuit to drive the relay (Only about a dozen ways to do that haha).

I was going to suggest interrupting the tan/black bypass instead of the coil drive circuit directly, but then remembered that this would cause a check engine light if a simple interrupt circuit is used. I have half a thought on how I would do this without a CEL appearing, but this would only be useful if returning base timing is the desired result AND it would limit torque enough.

You do realize that you can buy 6V automotive type relays and that the 6v relay would likely trigger just fine on 4 volts.

[davidgoodin]

I have some 5 volt relays in stock. I was trying to stay away from relays. It, it would be simpler than the other circuit. You know what happens when you turn loose an E.E. On an electrical issue...

[davidgoodin]

Darn, it was the bypass wire I was considering. But you are right about the check engine light. Didn't even think of that but now recall the light being on when I was setting the base timing.

[davidgoodin]

Also, one of the interrupter / shift assist modules I have works with a delco electronic ignition distributer and makes the distributer go to base timing. It does this in a pulsating pattern that reduces the torque on the dogs so they can shift.

[Six_Shooter]

You do realize that you can buy 6V automotive type relays and that the 6v relay would likely trigger just fine on 4 volts.

Yes, along with a multitude of other relays. Automotive grade relays that are less than 12V are not very common, I also specifically mentioned the Bosch style relay because of it's commonality. This being in a boat I would not want to use anything else, or at least anything less sealed than a Bosch style. There are other relays that use weatherpack type connectors as well, but have only come across those in 12V applications.

I would create a small amplifier circuit that uses the 4V signal to trigger a 12V sealed relay given the application.