ford-swap

Hey all,

I am just curious to know how the stock gm ecm controls the spark timing on tpi/tbi engines? All I have been able to find is that the 'four wire' connector is the computer controlled distributor. I was just wondering what these four wires do

My ultimate goal is to use a gm tpi or tbi (haven't decided yet) system on my 351C engine.

Thanks for the help

RBob

iTrader: (1)

Easiest method is to use the GM ignition module and trigger it with the stock pickup coil. Will need to lock the distributor so that the vacuum & centrifical advances are not active.

RBob.

jiffydos

Hey Rob,

Could you clarify this to me?

I'm looking to do something similar, adapting GM TBI to my 351M. I'd like to use the '747 to control advance however. It appears in the above post your refering to simply getting a tach signal to the ECM, but can the '747 actually control advance?

(without buying an electronic advance HEI distributor for the ford).

Dave

jwscab

To expand on what Rbob stated, you would basically NOT use the factory distributor module. The distributor would be used for it's pickup assembly only. You would lock out the mechanical and vacuum advance, and use a GM ignition module, and your ignition coil of choice, wired properly of course.

This works in alot of cases, actually. Any distributor that can generate the signal from a reluctance coil is a direct plug and play. With some other external circuitry, you could also run it from points, or hall effect as well, but that is another topic.

jiffydos

So, to re-hash, I can use the original 351M distributor. I would take the position signal from the distributor to the ECM. Then, the timing would be controlled through ECM, to the GM ignition module, wired back into my stock dissy?

If I have this right, any specs on how this is wired?

Thanks,

Dave

anesthes

iTrader: (12)

Hows he gonna get the the ECM to advance the distributor?

-- Joe

Toehead

AFAIK The ecm advances the coil triggering, not the distributor physically.

anesthes

iTrader: (12)

Well the rotor is going to fire the terminal closest, regardless of when the ECM tells the coil to fire.

If I recall, the electronic advance dizzy's all have a electronic controlled mechanical advance. Or am I mistaken?

-- Joe

RBob

iTrader: (1)

The position signal goes to the GM ignition module. This is from the pickup coil. There is 4 wire connector on the module that goes to the ECM. This is the timing siginal to the ECM and the timing control signals from the ECM back to the ignition module.

The ignition module also has a 2 wire connector. This is IGN+ in (power), and the coil - out to the coil. A real GM module has the signal references molded into it at the connectors. Brief, but there.

Note that the module needs heat sinking and the mounting screws need to go to the engine block as a ground. Doesn't need to be mounted to the engine, just needs to be grounded to the engine.

RBob.

s24a

This is the correct assumption.
Attached is a PDF of the GM ignition module by itself, and another one showing how it interfaces into the GM ECMs. Schematic shown is for a C3 or early MAF (165 type) P4 ECM. For the later P4 ECMs (like the 1227730) the Knock Module is a thick film in the MEMCAL, so that is not used.

But basically, the pickup reluctor goes to the two leads on the upper right, and the lowerright side of the module are the bypass for timing setting, and the control of the coil firing, either by the ECM or as a default through the module. Coil output is the left side of the schematic.

This action is similar to that used in the Ford TFI units, but they use a Hall input (square wave) rather than the reluctor (sine wave) input. The reluctor triggers on the FALLING edge of the signal.

anesthes

iTrader: (12)

Soo. What your saying is the position of the rotor has no bearing on the advance.

So electronic advance could have spark scatter and light off another cyl if the commanded advance is too high...

Why isn't the rotor on an electronic HEI stationary with the shaft? it moves about 40 degrees.

-- Joe

s24a

OK...Try to answer this a best possible.
The rotor on an electronic distributor does NOT move with respect to the stator poles on a GM (or Ford TFI) distributor.
The spark does move in point at which the coil is fired to acheive the desired advance.

I need to elaborate on a concept called "rotor registry".
Basically, the distributor is set up (timed) with a default advance value (say 10 degrees BTC for a Ford, or 6 degrees BTC for a GM engine).
This is the locked-down position of the distributor, and the ECM makes an adjustment in its calculations to resolve this offest into the absolute timing.

BUT, the rotor is NOT centered to the spark termainal post at this point. It is "lagging" the post slightly. But the correct plug fires because it is much closer to that terminal than the next in rotation.

As you "advance" the timing, the rotor moves through absolute alignment with the terminal post, and then at high advance is "leading" the post by some degrees. But still it is closer to that one than the last post in rotation, so the spark jumps to the correct post and fires the correct plug. The co-alignment of rotor and terminal centerlines occurs most likely around 25 degrees of advance or so, giving the the distributor a bias to have over twice as much advance as retard capability.

This is the "rotor registry", and determines maximum advance and retard on a cylinder.

Hope this explanation helps.

anesthes

iTrader: (12)

Ok. So the spark timing is controled, but rotor position is not.

I'm still not understanding why the rotor moves on the electronic dizzys though. I know I can take mine for example, and with the dizzy in place in the car move the rotor back and forth. You would think it would be stationary with the shaft...

-- Joe

s24a

I think the "movement" you are speaking of is the geartrain "slop" onbetween the cam drive gear and the distributor driven gear. Since they are helical cut gears, there will be some translation (and also some vertical movement as the gear teeth slide against each other).
This is done to allow for oil to get into the spaces for lube, and also to adjust for vertical stackup tolerences beteeen the distributor, the engine block assy, and the oil pump in the base of the engine.

What you will see is that when the rotation is kept in a contant direction, the "slop" is taken up and the distributor then has no "wobble" back and forth. When you decelerate, the engine is still running in the same direction, so speed of the cam/distributor drive interface may change, but direction is still in one direction, so all is still well.......

anesthes

iTrader: (12)

I don't think it's that. Like on the small cap dizzys, I can hold the gear in my hand and grab the rotor, twist it and it springs back. Almost like a mechanical advance. Same with the large cap. It's like a spring loaded retard. If I recall, I think it turns counterclockwise.

-- Joe

s24a

Will have to try this on a large and small cap dizzy when I get home (at work right now). Could be a coupling between top and bottom sections of the distributor. As long as the rotation takes it up when the dizzy is installed and running, there still should be no backa and forth relative motion beteen rotor and stator in the dizzy.

BTW, the Ford dizzy's do NOT have this, and neither do the Chrysler V8s as well, and they function just fine.

Will look at this and see if I see a manufacturing reason for it on GM dizzys.

anesthes

iTrader: (12)

I actually stopped by the junkyard and tried it on a small cap dizzy, and now I'm second guessing myself. I'm tempted to take the cap off my vette and check it.

Perhaps, memory from inspecting mechanical advance dizzy's is getting the best of me.

Anyhow, Dave and I are putting TBI with a '746 ECM on his '78 bronco which is 351M powered. We need to figure a way to wire up his dizzy, so thats the point to this. So I guess as long as the hall effect pickup can be used with the GM module, we can get the '747 to control timing.

-- Joe

Guest

The movement you may notice changes not only the horizontal position of the rotor, but vertical as well. Its riding up the gear on the cam. The rotor, once mounted to the bar on the distributor, is fixed with the shaft as the bar is permanently mounted to it.

Since you wont be using a TFI distributor (I assume, being either 351C or 351M, neither OE a TFI but rather the wonderful unDuraspark if they were even electronic to begin with) you'll need to disable the mechanical advance and use the signal off the Ford pickup to your module of choice. GM would likely be easiest. Aside of the difference in Hall effect mentioned above, shouldnt be any issues as long as you wire it up correctly. I think posted here somewhere is a link to a site converting a IH distributor that you may find of interest.

Here:
http://www.justih.org/Binder-Bench/s...ead.php?t=1182
From here:
https://www.thirdgen.org/forums/diy-...02-gm-efi.html
And this is going to be useful
http://www.justih.org/Binder-Bench/a...tachmentid=137

s24a

OK...

I just tried this on TWO small cap TPI distributors, and one large cap TPI distributor that I had in my stash at home.
All OUT of vehicles, so I am grabbing the distributor gear and trying to translate the rotor while holding the dizzy gear stationary.
I get NO movement from this!
Additionally, I pulled one apart. Solid shaft up through rotor (small cap dizzy).

So your movement, if checked on a vehicle, HAS to be the sliding gear translation, and you must be getting some vertical movement.

My original hypothesis holds true....

scuzz

This is really interesting stuff! Thanks guys.

s24a

Joe...

A 78 Bronco (used to own one!) will have a Ford distributor with vacuum and mechanical (governor) advance that features a Reluctance sensor!
So you are really set up for this....

I would do the following:

Remove the distributor (mark timing first) and take it down to guts.
Remove the advance weights and springs, and double safety-wire the mech advance mechanism. This will make it a "solid" distributor for that part.
Now, remove the vacuum advance can and make a plate to seal the hole.
Into that, drill a hole (1/8" dia) and slip a piece of welding rod or 1/8" tubing into it, and flatten the end and drill a hole for the pickup point of the vacuum advance arm.
Pull it into position where the "resting" position was for the old advance unit, and braze it in place, and finish off the surface.
Paint it with some good (Duplcolor) engine paint to match, and voila, an electronic Ford distributor.
The two leads on the reluctor will go to a remote mounted GM electronic module, and the ground wire can be hooked onto the same ground the module uses.
Time it, and you are ready to tune!

jiffydos

Well, you certainly appear to be correct. Joe and I went to the junk yard today and tried to find a dizzy with the "slop" we were both thinking we recalled. And... what did we find... we found we broke the rotor of the distributor... ROFL. So, clearly the movement of the rotor he and I recall was the result of either mechanical, vacuum, or mechanical/vacuum advance.

Also, for my own learning experience, I pulled apart the dizzy in the junk yard and found that it truly is simply the GM module reading the the dizzy shaft and nothing else. That is VERY interesting. You guys are helping out a lot!

--Dave

jiffydos

Joe has talked about how helpful you guys here on the thirdgen forum are for years. I have to say, he was very right. In just a few short days I feel quite confident in the swap Joe and I are going to perform on my 78 Bronco.

We pulled the complete TBI system (Throttle Body, MAP, Coil, GM Ignition Module and ESC) and I think we are ready to go. (Note, Joe already has the ECM and harness ready for hacking.) I think all I need now is a fuel pump/lines and the carb intake adapter.

The only other thing I might do is find a late mode (EFI) 460 in the junk yard and grab that distributor. It might require less hacking. I think they are just like GMs.

Any other advice anyone?

--Dave

jiffydos

OH... one last thing Joe and I were discussing... Knock Sensor. What one should I run and where should I install it? I presume the one for the 5.7 GM that I pulled the above TBI system out of is probably not quite right.

Suggestions?

--Dave

s24a

Dave...

Late model 460 (EFI) dizzy is a remote TFI distributor. Still uses the Ford Hall effect vane syste,. so square wave out (0 to 5V switch). No zero (go below 0V) crossing, which is what the GM EFI module wants to see.
Also, that distributor will NOT fit a 351/400 engine.
Trust me. I used to work for Ford in Powertrain (EEC-IV System area).
What you CAN do is scavange a crank trigger wheel off a 302/351 with CFI (find a Lincoln Versaille or Crown Vic, early 80s), and you can machine the back side of the harmonic balancer on the 351M to fit it. Then you need to install the VR sensor onto a bracket FIRMLY onto the front of the engine timing cover that picks up the 4 toothed wheel pulses. Set it up to either the Ford 10 degrees BTC or the GM 6 degress BTC between centerline of sensor and REAR edge of the tooth. You will make the offeset adjustment in SW in the ECM calibration. Dizzy then is a "dumb" locked down spark dizzy only, no pickup.

This "crank trigger" is best possible solutiion for accuracy, if you have good machine shop access.

Second solution is to remove the guts out of a 351W EEC-III distributor and put it into a 351M housing. The shafts are very close in length, but make sure you measure and adjust if necessary. I know you have to transfer the distributor drive gear (different). That will give you a "Large Cap" (with spacer adaptor) dual plane EEC-III distributor for your engine. This has an advantage of increased rotor registry as well over a GM dizzy.

s24a

Use a Knock sensor off a GM for a 4.00" bore application (matching the impedence for either a C3 w/EST module or a P4 with internal Knock Thick Film MEMCAL).
Frequency generally goes with the bore diameter, and a 351M has a 4.00" bore.

jiffydos

Wowa... that's a lot of info.

What about my stock 351M dizzy? Just do what you said above by locking the mechanical and vacuum advance? and just sending the position signal to the ecm? Is that a bad route?

Interesting that you say the 460 dizzy won't fit the 351M. I know summit isn't perfect, but their 351M distributors all say they also fit 90s 460 motors.

--Dave
----------
Interesting... what GM motors had a stock 4.00 inch bore?

--Dave

Guest

The 350 is a 4" bore motor. On the 350 its screwed into one side of the block in place of one of the two coolant drain plugs near the oil pan rail. I cant remember if a 351M has those or not, probably does. Put it there.

anesthes

iTrader: (12)

So it sounds like if we wire the dizzy to use the GM module, mount the GM module to a bracket thats engine grounded, and use an L05 knock sensor (87-95 GMC truck, 5.7l Dave) it 'should' work.

The only thing we'll lose is probably DFCO, and throttle follower stuff at low speed due to the lack of VSS.. But that might be ok I think.

Thanks guys!

-- Joe

s24a

My last qoute:

"Late model 460 (EFI) dizzy is a remote TFI distributor. Still uses the Ford Hall effect vane syste,. so square wave out (0 to 5V switch). No zero (go below 0V) crossing, which is what the GM EFI module wants to see.
Also, that distributor will NOT fit a 351/400 engine."

OK, they physically fit. However, the distributor is not a VR type pickup. so no go.
Last comment has to do with the distributor gear. By the time the 460s got EFI a lot of stuff had changed. Distributor gear is my concern. Attached is the Comp Cams page on 351C/351M/400 and 429/460 gears.
Notice the multiple drillings to accomodate both shafts.

The 351C could be considered a "low-deck" 351M (although RFB is different)
This can be confusing, and since the sensor pickup is incorrect, it really is irrelevent.

But JEGS or SUMMITT are correct that if you specify the engine correctly, they can sell a distributor that could be assembled to fit either a 351C, a351M/400, or the 429/460 engine (the 370 S.D. is also a "385" engine in the H.D. trucks)

s24a

The easiest way is to lock down the stock dizzy from e 351M....I have done this before on other apps, it it works well.

Most 350s have 4.00" bores, so I would start with a 350 setup.
If C3, you need a 350 Knock sensor and equivalent EST module.

If you are using a P4 (like a 1227730), you need a 350 MEMCAL for it Knock thick film and NetRez IC pack, and the 350 Knock sensor for the 90-92 TPI.
----------
Actually, some Fords have inline VSS setups (I think for cruise).
I may have one. If so, I will post the part number here.....

And the part number is:
Engineering number on Sensor: D4AF-9E731-B
Service Number: D4AZ-9E731-B
Motorcraft PN: DY-145

This is an inline sensor, and will need a stub cable from the transmission speedo gear.
Since it says"D4" as a prefix, I would reference full size Ford and Lincoln vehicles of around 1974 and up......

jiffydos

Joe and I were talking about this part today... nice to have a part number to go along with it. I never imagined getting this much info this fast.

Dave