Mopar Electronic Pickup Polarity and Rotor Phase

[67Dart273]

If only this was corrected in dumbed down English.

Let's try this. Think of a points dist.

Unless the dist is improperly manufactured, or modified, or wrong parts, a breaker points dist, the mechanical advance and rotor phasing will always be correct because as the trigger device (points) are moved mechanically by the advance, the rotor is always still kept in the same relationship to the points cam. The cam/ rotor cannot move in relation to each other.

HOWEVER the vacuum advance is a different story. The vacuum advance moves the trigger point by moving the points on the breaker plate, BUT THE ROTOR has not been moved accordingly. So vacuum advance depends on the width of the rotor to stay properly aligned. This explains why, if you find certain 4 whanger and 6, mostly V6 rotors, they sometimes have odd, wide shaped rotors

So when you swap polarity on a magnetic pickup, the trigger wave is moved, just like when the vacuum advance moves the points, only in the case of breakerless, it moves far enough that the rotor can now be clear out of alignment with the plug tower contact when the trigger fires the spark

On a side note, some of these foreign rigs with the black stuff there is a radio suppression resistor, and I was tricked once on a dead Toyota where that burned up. After finally figuring it out, and no spare, we jerry rigged a piece of wire to jump across to get home.

 

[RustyRatRod]

Let's try this. Think of a points dist.

Unless the dist is improperly manufactured, or modified, or wrong parts, a breaker points dist, the mechanical advance and rotor phasing will always be correct because as the trigger device (points) are moved mechanically by the advance, the rotor is always still kept in the same relationship to the points cam. The cam/ rotor cannot move in relation to each other.

HOWEVER the vacuum advance is a different story. The vacuum advance moves the trigger point by moving the points on the breaker plate, BUT THE ROTOR has not been moved accordingly. So vacuum advance depends on the width of the rotor to stay properly aligned. This explains why, if you find certain 4 whanger and 6, mostly V6 rotors, they sometimes have odd, wide shaped rotors

So when you swap polarity on a magnetic pickup, the trigger wave is moved, just like when the vacuum advance moves the points, only in the case of breakerless, it moves far enough that the rotor can now be clear out of alignment with the plug tower contact when the trigger fires the spark

On a side note, some of these foreign rigs with the black stuff there is a radio suppression resistor, and I was tricked once on a dead Toyota where that burned up. After finally figuring it out, and no spare, we jerry rigged a piece of wire to jump across to get home.

View attachment 1716338022

Thanks, Del. That helped a lot.

 

[Mike69cuda]

Should you be able to see the difference in timing with a timing light? Seems like you could take a reading, swap the wires & try again. This may tell you how much of a change is really happening & maybe you could see some instability in one setup. Just a thought…

 

[67Dart273]

Should you be able to see the difference in timing with a timing light? Seems like you could take a reading, swap the wires & try again. This may tell you how much of a change is really happening & maybe you could see some instability in one setup. Just a thought…

Yeh but the timing does not tell you which way is correct, in other words I don't know whether wrong is retarded or advanced from correct

 

[Mike69cuda]

Yep, but thought he might get lucky if the timing was erratic one way due rotor phasing. Just a blind chicken pecking for feed solution…..

 

[RustyRatRod]

Yep, but thought he might get lucky if the timing was erratic one way due rotor phasing. Just a blind chicken pecking for feed solution…..

You ain't alone.

 

[BillGrissom]

The Summit Billet distributor uses the same trigger setup as factory Mopar electronic distributors; it looks exactly the same under the cap. Where it differs is in the mechanical advance, it uses weights and springs supposedly adapted from the old Mallory units; much easier to adjust than the Chrysler stuff although according to @Mattax doesn't provide as linear/consistent advance with RPM. From what I've seen online it's also the same as the Firecore distributors.

I drove the truck to work today and it seems better but still not as good as it should be. Idk if I'm expecting too much but I feel like at idle with a stock cam it should be smooth enough to 'balance a quarter on the air cleaner'. I also filled it up with gas and this past tank only got 8.5 MPG, the horrible gas mileage is another reason I've been making myself crazy trying to get the tune just right. I've already gone through the carb and know that's good (tuned Edelbrock AVS2). I suppose at some point I'll try switching the pickup wires around and go from there. I do know I need to slow down the mech advance, it's all in by about 2000-2200 RPM which is way too quick, should be more like 3000-3200 RPM.

8.5 mpg is horrid, but insure you are measuring it accurately. Use gas station fuel pump readings (fill-up to fill-up) and mileage markers (or GPS), not the tics on the dash fuel gage and odometer. I carefully recorded mileage in my 1969 Dart w/ slant-six in the 1980-90's and consistently got 22 mpg highway, back when the national speed limit was 55 mph and before 10% ethanol. At 75 mph, expect 30% poorer. If truly that bad, it may be running rich to put raw gas on the cylinder walls, which is why engines used to wear out faster in the day.

 

[MopaR&D]

8.5 mpg is horrid, but insure you are measuring it accurately. Use gas station fuel pump readings (fill-up to fill-up) and mileage markers (or GPS), not the tics on the dash fuel gage and odometer. I carefully recorded mileage in my 1969 Dart w/ slant-six in the 1980-90's and consistently got 22 mpg highway, back when the national speed limit was 55 mph and before 10% ethanol. At 75 mph, expect 30% poorer. If truly that bad, it may be running rich to put raw gas on the cylinder walls, which is why engines used to wear out faster in the day.

Understood, I do try to keep measurement methods accurate. I guess "horrible" is a relative term, it is after all a 3/4-ton truck and has 33" tires with fairly aggressive all-terrain tread pattern. Based on what most people over at Ramchargercentral tend to get on their old Dodge trucks though I think it should be more like 12-14 MPG. I know it also doesn't help I have a hard time keeping it below 70 mph on the freeway, need to work on being patient lol...

 

[BillGrissom]

Understood, I do try to keep measurement methods accurate. I guess "horrible" is a relative term, it is after all a 3/4-ton truck and has 33" tires with fairly aggressive all-terrain tread pattern. Based on what most people over at Ramchargercentral tend to get on their old Dodge trucks though I think it should be more like 12-14 MPG. I know it also doesn't help I have a hard time keeping it below 70 mph on the freeway, need to work on being patient lol...

Makes sense. I assumed an A-body. That loud noise you hear from knobby tires is energy being wasted. Shift to "N" and see how fast it slows from 65 mph. If it keeps decelerating the same after 40 mph, the drag is more from the tires than aero.

 

[MopaR&D]

Makes sense. I assumed an A-body. That loud noise you hear from knobby tires is energy being wasted. Shift to "N" and see how fast it slows from 65 mph. If it keeps decelerating the same after 40 mph, the drag is more from the tires than aero.

The tires definitely have drag. Back when I had an XJ Cherokee I put these same tires on it and it went from averaging 20 mpg down to 17-18.

I will say I drove the truck yesterday and I'm not convinced the ported vacuum advance is the way to go. Performance was fine but when idling in traffic (evening rush hour) the coolant temp would climb where before with MVA it didn't do that. I am for sure going to redo the mech advance curve and try swapping the pickup leads.

 

[Mattax]

I wouldn't switch the leads at the same time you are reworking the curve unless you know its backwords.

Yes, switch to manifold source if the current setup is causing the coolant temps to rise and not stabilize at idle. Not toalking about the usually rise that accompanies the reduction in airflow when coming to a stop.

Idk if I'm expecting too much but I feel like at idle with a stock cam it should be smooth enough to 'balance a quarter on the air cleaner'.

I agree.

I also filled it up with gas and this past tank only got 8.5 MPG, the horrible gas mileage is another reason I've been making myself crazy trying to get the tune just right. I've already gone through the carb and know that's good (tuned Edelbrock AVS2).

Fuel mixtures and timing work together. Can only do so much with the fuel mix if the timing isn't where it ought to be.

I guess "horrible" is a relative term, it is after all a 3/4-ton truck and has 33" tires with fairly aggressive all-terrain tread pattern. Based on what most people over at Ramchargercentral tend to get on their old Dodge trucks though I think it should be more like 12-14 MPG. I know it also doesn't help I have a hard time keeping it below 70 mph on the freeway,

Well there's part of your answer! And unlike your car, 70 mph probbaly hurts milage vs. 60 mph.
Also any time spent idling, tuning, etc is a gas milage killer. The mpg of both my vehicles plummets when driving in the city. Literally more time spent idling than moving.
All these things add up.

 

[MopaR&D]

I wouldn't switch the leads at the same time you are reworking the curve unless you know its backwords.

Yes, switch to manifold source if the current setup is causing the coolant temps to rise and not stabilize at idle. Not toalking about the usually rise that accompanies the reduction in airflow when coming to a stop.


I agree.

Fuel mixtures and timing work together. Can only do so much with the fuel mix if the timing isn't where it ought to be.

Well there's part of your answer! And unlike your car, 70 mph probbaly hurts milage vs. 60 mph.
Also any time spent idling, tuning, etc is a gas milage killer. The mpg of both my vehicles plummets when driving in the city. Literally more time spent idling than moving.
All these things add up.

Well I don't really know a way to tell for sure if they're backwards but based on the fact that it runs better now with the ign box set to rising edge and that I had to change the phasing of the reluctor wheel (swap roll pin location) when I first got the distributor so it wouldn't misfire like crazy leads me to believe that's the case. I'll try swapping the pickup leads first, check how it runs then go from there.

I know for sure there's a lot more wind resistance above 60 mph, the truck is shaped like a brick with big flat frontal area and fairly high ground clearance. It cruises really nice at 70-80 mph with the 2wd fully independent front suspension and has plenty of power, I just need more self-discipline to keep cruising speeds lower.

 

[halifaxhops]

OK my 2C I have never ever seen a OEM Mopar distributor with phase issues unless one of these happen.

Reluctor set in wrong rotation, one is CW the other is CCW that is to get the rising edge signal to the trigger the ecu using the same pickup for both, cost saving for Mopar
Dual point MP pickup used in a aluminum housing
slant six pick up used in 8 or vice verses.

Those reluctors out there slotted for the phasing fix compensates for the wrong combinations only, Seriously. Seen the mis match a few dozen times at least,

 

[MopaR&D]

OK my 2C I have never ever seen a OEM Mopar distributor with phase issues unless one of these happen.

Reluctor set in wrong rotation, one is CW the other is CCW that is to get the rising edge signal to the trigger the ecu using the same pickup for both, cost saving for Mopar
Dual point MP pickup used in a aluminum housing
slant six pick up used in 8 or vice verses.

Those reluctors out there slotted for the phasing fix compensates for the wrong combinations only, Seriously. Seen the mis match a few dozen times at least,

That's where I messed up, if I had known then what I know now I would have tried swapping the pickup leads first. Or... are you saying the rotor-to-cap phasing shouldn't have been off even with the leads reversed?

 

[92b]

That's where I messed up, if I had known then what I know now I would have tried swapping the pickup leads first. Or... are you saying the rotor-to-cap phasing shouldn't have been off even with the leads reversed?

Are you thinking of trying this combination?
1. original reluctor position
2. original phasing
3. set box to back to falling edge
4. reverse the polarity that is currently at the pickup coil
5. set timing

Another way to check rotor phasing is to sacrifice a distributor cap by cutting, drilling and or die grinding a wndow in the cap. This will tell you if the phasing between the rotor and cap is correct. I prefer to use #1 cylinder (because I won't have to change the timing light pickup to set engine timing) but if that doesn't give you a clear line of site any cylinder will do. Also some times a bright mark placed below the rotor tip will make it easier to see.
I have a few windowed caps on hand at the dyno for when a quick check is needed. Just clip the timing light to the plug wire that is windowed and shoot it at the rotor through the window while the motor is running. You can observe the rotor position at different rpms. With the vac advance unpluged, the rotor should stay steady and lined up with the contact on the cap. It might be slightly to one side but when the advance is plugged in and activated it should pull it closer to the center of the contact and maybe even sweep to the opposite side of the contact when full vac advance is applied. Good luck! I hope you find your problem.

Ps: Pay no attention to the epoxy holding the cap together in the picture. It was new cap damaged in shipping and me being cheap (to the point of impractical) spent enough time and money on epoxy mending it back together that I should have just bought a new cap. Here's what happened. When I told my buddy I was thinking of trying to epoxy this cap back together to make a cap for testing phasing, he said " that will never work" . So....

 

[Hysteric]

Are you thinking of trying this combination?
1. original reluctor position
2. original phasing
3. set box to back to falling edge
4. reverse the polarity that is currently at the pickup coil
5. set timing

Another way to check rotor phasing is to sacrifice a distributor cap by cutting, drilling and or die grinding a wndow in the cap. This will tell you if the phasing between the rotor and cap is correct. I prefer to use #1 cylinder (because I won't have to change the timing light pickup to set engine timing) but if that doesn't give you a clear line of site any cylinder will do. Also some times a bright mark placed below the rotor tip will make it easier to see.
I have a few windowed caps on hand at the dyno for when a quick check is needed. Just clip the timing light to the plug wire that is windowed and shoot it at the rotor through the window while the motor is running. You can observe the rotor position at different rpms. With the vac advance unpluged, the rotor should stay steady and lined up with the contact on the cap. It might be slightly to one side but when the advance is plugged in and activated it should pull it closer to the center of the contact and maybe even sweep to the opposite side of the contact when full vac advance is applied. Good luck! I hope you find your problem.

Ps: Pay no attention to the epoxy holding the cap together in the picture. It was new cap damaged in shipping and me being cheap (to the point of impractical) spent enough time and money on epoxy mending it back together that I should have just bought a new cap. Here's what happened. When I told my buddy I was thinking of trying to epoxy this cap back together to make a cap for testing phasing, he said " that will never work" . So....

View attachment 1716341461

View attachment 1716341472

I keep an old dizzy cap with a big hole drilled in the top to see if the phasing is correct

 

[halifaxhops]

That's where I messed up, if I had known then what I know now I would have tried swapping the pickup leads first. Or... are you saying the rotor-to-cap phasing shouldn't have been off even with the leads reversed?

Leads reverses will set the low sig in the high position if that makes sense. Got a pic of the dist with the cap and rotor off from the top?

 

[MopaR&D]

Are you thinking of trying this combination?
1. original reluctor position
2. original phasing
3. set box to back to falling edge
4. reverse the polarity that is currently at the pickup coil
5. set timing

Another way to check rotor phasing is to sacrifice a distributor cap by cutting, drilling and or die grinding a wndow in the cap. This will tell you if the phasing between the rotor and cap is correct. I prefer to use #1 cylinder (because I won't have to change the timing light pickup to set engine timing) but if that doesn't give you a clear line of site any cylinder will do. Also some times a bright mark placed below the rotor tip will make it easier to see.
I have a few windowed caps on hand at the dyno for when a quick check is needed. Just clip the timing light to the plug wire that is windowed and shoot it at the rotor through the window while the motor is running. You can observe the rotor position at different rpms. With the vac advance unpluged, the rotor should stay steady and lined up with the contact on the cap. It might be slightly to one side but when the advance is plugged in and activated it should pull it closer to the center of the contact and maybe even sweep to the opposite side of the contact when full vac advance is applied. Good luck! I hope you find your problem.

Ps: Pay no attention to the epoxy holding the cap together in the picture. It was new cap damaged in shipping and me being cheap (to the point of impractical) spent enough time and money on epoxy mending it back together that I should have just bought a new cap. Here's what happened. When I told my buddy I was thinking of trying to epoxy this cap back together to make a cap for testing phasing, he said " that will never work" . So....

View attachment 1716341461

View attachment 1716341472

Thanks for the details on how to check rotor phasing, I'll confirm the cap from one of my spare distributors will fit this one and try it out.

I got a chance to work on it today, I swapped the pickup leads and had to retard the timing a bunch just to get it to start. Seemed to run a little better than before but not much. I then switched the ignition box to falling edge trigger and had to advance the timing this time to get it to run. I set initial to where it should be. From the test drive, runs a bit smoother now and the timing seems more steady when using the timing light. I didn't swap the reluctor wheel pin but no signs of rotor phasing issues, I couldn't hear any buzzing/arcing from the distributor like it did before but it wasn't very loud to begin with so can't say for sure.

I think that aspect is fixed but I still need to adjust the mech advance curve for sure and maybe play with the vacuum advance canister. I switched back to MVA and readjusted the idle speed back down, the light chugging/shakiness when free-revving came back so I think AJ was on to something. It runs noticeably better with manifold than ported vacuum though, I barely need to touch the throttle to get the truck moving so idk what exactly is the best move. I want it to have more idle timing than what the current initial is but not the full 24° or so it gets with MVA. I might reduce the amount of mech advance so I can run more initial and then put the vacuum advance back to ported.