Renix Distributor Indexing question

[Gojira94]

Is the point of lining up the trailing edge of the rotor tip to the plug wire contact... to give the ECU plenty of rotor tip to work with, for almost any degree of electronic spark advance, not exceeding the rotor tip's radius/ degrees of arc, tangent to the wire contact in the cap? i.e. if that position in tip 13 represents 0* electronic spark advance, what happens if the ECU commands, say, retard -4* due to knock? If we knew the max advance and retard programmed into the ECU's calibration parameters, could the distributor be indexed even more perfectly, like really close to the end of the rotor tip with maybe 6-8* to spare for retard?

[Ωhm]

1 hour ago, Gojira94 said:

Is the point of lining up the trailing edge of the rotor tip to the plug wire contact... to give the ECU plenty of rotor tip to work with,

 

Yes

 

 

1 hour ago, Gojira94 said:

what happens if the ECU commands, say, retard -4* due to knock?

 

I would think/hope the ECU knows enough to never go less than the base timing.

[Gojira94]

6 hours ago, Ωhm said:

 

I would think/hope the ECU knows enough to never go less than the base timing.

GM calibrations in the 727 & 747 ECMs from 87-94 do exactly that, as well as the 16188051 that ran the V8 F-bodies  in 94-95. The GM TBI applications on the 727 and 747 had you disconnect the ESC (electronic spark control) module to prevent the ECM from advancing timing at warm idle so you could set the distributor at exactly 0* with a timing light for the ECM to have a valid starting point with room for retard and advance across the arc of the rotor tip. My 94 Formula has the ability to do an immediate 16* of burst knock retard… and bring it back in over about 4 seconds’ recovery time.

 

I think I’m at the point of reaching out to NickInTime and seeing how far he got, taking a crack at dumping the remaining raw hexadecimal data and seeing what can be teased out into the realm of the known.

[cruiser54]

HERE’S WHY DISTRIBUTOR INDEXING  IS SO IMPORTANT:

Distributor indexing explained:

For clarification though, that’s not a cam sensor inside the Renix dizzy. It’s there to fire the injectors sequentially with the firing order. You’ll never notice if it went bad because the ECU will try to “guess” where it is and does a heck of a job at it.

As for the “timing”, it is controlled by the ECU. Ever notice how wide the tip of the rotor is? Try and wrap your head around this:

When the ECU yells “Fire” to the ignition control module, where is the rotor in relationship to the dizzy terminal? Not to the terminal yet? Past the terminal too far?

What happens to the spark/secondary ignition strength when it has to jump the Grand Canyon in comparison to shooting from a rotor tip? Poor ignition performance, bucking, jerking, longer crank times.

The factory was aware of this and issued a Technical Service Bulletin on it. This Tip, #13, is a condensed version of that factory TSB. You wouldn’t believe how many we found out of whack when I worked at the dealership. Yours is probably messed up also. RARELY did we find one set accurately.

[Gojira94]

47 minutes ago, cruiser54 said:

When the ECU yells “Fire” to the ignition control module, where is the rotor in relationship to the dizzy terminal? Not to the terminal yet? Past the terminal too far?

 

This is the crux of my question. In knock retard conditions it could possibly  be, without a few degrees of rotor tip spared for the programmed limits for that condition.

[cruiser54]

Timing advance/retard is controlled by the ECU. Secondary ignition must have a good path to follow. 

 

Perhaps that is why the factory has the rotor go past the terminal a teeny bit for timing advance? 

[Ωhm]

Isn’t timing retarded ATDC and either ‘more advanced’ or ‘less advanced’ BTDC. Just trying to understand the terminology.

[Gojira94]

4 minutes ago, Ωhm said:

Isn’t timing retarded ATDC and either ‘more advanced’ or ‘less advanced’ BTDC. Just trying to understand the terminology.

Correct. You may not have enough rotor tip available/ within close range of the cap contact at a certain point ATDC, or have a pretty large gap to jump is my point here.

[Gojira94]

With the cap contact at the trailing edge of the rotor tip set as mechanical 0* there's maybe 16-20* arc of rotor tip available for advance in relation to the cap contact. If we knew from the ECU parameters that max advance was, say 12* and max retard was say, 8* you might want to set the rotor/ cap contact relationship for indexing from #1 with the trailing edge of the rotor visible to the right of the cap contact by maybe 4mm or so.

 

Like instead of this:

 

(advance)   |-----------------<+>|   (retard)

 

Do this:

 

(advance)   |--------------<+>---|   (retard)

 

[Ωhm]

As you move the rotor tip more CCW to cover timing for both sides of TDC (0°), you have shifted the gap problem to the MAX advance condition. Moving the rotor tip away from the tower contact at MAX advance. This assumes all things stay the same.

[Gojira94]

One other possibility- the engineers who wrote the TSB must have known enough about the timing advance/ retard parameter min/max values to say what the relative positions of rotor tip and cap contact are optimal. The calibration may have been written to default to max retard at any time, unless advance was commanded, i.e. the position shown in Cruiser54's tip 13 may actually be 4*, 8*, 12* or whatever* retarded, and the ECU always commands some amount of advance. Extra advance is needed during cranking, quite a bit at idle and lean cruise, and a lot when the throttle is snapped closed at higher RPMs. Some, but not as much as you might suppose in power enrichment in the higher RPMs. In essence, some degree of advance is commanded at all times, except in the case of knock retard, where it would be able to fall back to whatever retard limit corresponds to the position shown in tip 13. In which case tip 13 is gospel if this possible supposition holds true.

[Ωhm]

2 minutes ago, Gojira94 said:

One other possibility- the engineers who wrote the TSB

 

Problem was because faulty distributors made their way into production vehicles (I6 only). Fault was tip of rotor and distributor drive gear were misaligned when assembled. Spec'd wrong, causing crossfire at higher RPMs. Solution was replace distributor.

[Gojira94]

36 minutes ago, Ωhm said:

Problem was because faulty distributors made their way into production vehicles (I6 only). Fault was tip of rotor and distributor drive gear were misaligned when assembled. Spec'd wrong, causing crossfire at higher RPMs. Solution was replace distributor.

 

So if the original distributor is long gone this is highly unlikely to be an issue, though still a valid fix in some possible cases where the issue is essentially the same? I'm doing a Renix controlled HO engine from a 93 YJ and am installing a decent quality aftermarket distributor. I'll be interested to see the relative positions of cap contacts and rotor on an unmodified aftermarket dizzy. And tip 13 can always be used to fine tune that relationship.

[Ωhm]

Coil on Plug (COP) is a programmer’s dream come true.

[cruiser54]

4 hours ago, Gojira94 said:

 

So if the original distributor is long gone this is highly unlikely to be an issue, though still a valid fix in some possible cases where the issue is essentially the same? I'm doing a Renix controlled HO engine from a 93 YJ and am installing a decent quality aftermarket distributor. I'll be interested to see the relative positions of cap contacts and rotor on an unmodified aftermarket dizzy. And tip 13 can always be used to fine tune that relationship.

It is still likely to be an issue. The dizzies were made incorrectly. rebuilts are the same way. If they have the complete tab intact, they are suspect.