Mopar Orange box conversion problem.....

[Michael Harmon]

Please help!

I'm simply trying to convert to EI using the Mopar orange box and distributor Kit for my '66 Charger with 318 poly. Everyone knows how important it is to make sure that the box is grounded! Right? Ok so, here's my problem. When I mount the box to the firewall (ground), I get NO signal out of it. But when I detach the box (not grounded), I get signal! WTF? This is backwards! But I can't figure out why. I've been working on old Mopars for almost 30 years. Never seen or heard of this problem. The wiring is connected correctly (not rocket science). I've tried 3 different boxes. Same results. I've tried new coil, new voltage regulator, ignition switch and starter relay. No luck. Ive talked to many guys and nobody has been able to figure out this problem. Its completely holding up my restoration because I can't start my engine! I'm completely baffled and need help. If I've left out any other important information, please let me know. Thanks!

 

[JimCoronette]

My first checks would be:

continuity from firewall mounting point to battery negative cable.

no continuity from any pin in the ECU harness connector to ground.

 

[Don Frelier]

perhaps the pickup coil in the distributor is has a wire thats grounded.
They shouldn't be.

 

[BeepBeepRR]

Make sure you have the K-frame to engine ground strap, body to engine rear passenger side firewall to head, and a ground from battery negative to body near the battery.

 

[The Shoe]

perhaps the pickup coil in the distributor is has a wire thats grounded.
They shouldn't be.

Yes I like your idea, I’d swap the distributor with another good unit and see what’s up. That’s simple and quick.

 

[Don Frelier]

You can just plug in a loose distributor and spin the shaft. You can easily check for a grounded pickup with a meter

 

[Nacho-RT74]

As mentioned, you can check for pickup coil conditions and isolation from chassis. It should get you on 150-900 ohms rate between leads and totally isolated from chassis, but tipically it gets into 250-350 ohms rate.

You can just plug in a loose distributor and spin the shaft. You can easily check for a grounded pickup with a meter

Dist housing would need to be chassis grounded as far I recall... right?

 

[Don Frelier]

No the housing does not need to be grounded.
(Distributor that is, I was using Nacho's reference)

 

[Nacho-RT74]

Weird! I think I had to ground my dist with a wire to make it work in the air spinning the shaft with my hand! But it was loooong time ago. I can be wrong.

However, grounding the dist housing would replicate the setup in the air to check for the issue I think. If pickup coil is not isolated ( shorted to ground ) and you spin the shaft being dist not grounded could maybe make it work still correctly and no replicate the fail?

Just thinking out loud!

 

[RJRENTON]

Weird! I think I had to ground my dist with a wire to make it work in the air spinning the shaft with my hand! But it was loooong time ago. I can be wrong.

However, grounding the dist housing would replicate the setup in the air to check for the issue I think. If pickup coil is not isolated ( shorted to ground ) and you spin the shaft being dist not grounded could maybe make it work still correctly and no replicate the fail?

Just thinking out loud!

Once again, your thinking/suppositions are incorrect. There is nothing in the MOPAR distributor that needs grounded. IF the pick up coil is open, there will be no spark produced; IF the pickup coil is grounded, there will be no spark produced. IF the resistance of the pickup coil is within published values, the system will produce a spark providing all other system components are OK.
BOB RENTON

 

[Don Frelier]

It may still work with one of the pickup coils grounded. I'd have to see the schematic to be sure, obviously if they are both grounded you would get nothing.
Edit: one wire on the pickup coil is grounded sorry.

 

[451Mopar]

The pickup create a small voltage signal to the ECU, but that voltage need to have a good ground reference for comparison inside the ECU.
If the dist signal has a different ground reference than the ECU (ground loop problem) the ECU may not sense the signal.
The ECU also needs to be grounded to control the coils ground (-) terminal between open and grouns through the power transistor.
A ground strap between block (Distributor) and Firewall (ECU) helps maintain both have the same ground reference.
I would check the distributor pickup too.
I personally have moved away from the original style ignitions, and just use CD Ignition boxes (MDS, and Crane).
If you watch the new Engine Masters, they just did a test of ignition system(s), and even they had issues with the old MP ECU.

 

[HALIFAXHOPS]

OK this is weird. Make sure the pick up wires in the distributor are oriented properly to the wiring harness., then mount the box and go from the silver transitory to ground in volts. You have anything re ground it. Your body is prob the ground it is "looking" for. Also new ECU'S suck look for 80's and back.

 

[RJRENTON]

The pickup create a small voltage signal to the ECU, but that voltage need to have a good ground reference for comparison inside the ECU.
If the dist signal has a different ground reference than the ECU (ground loop problem) the ECU may not sense the signal.
The ECU also needs to be grounded to control the coils ground (-) terminal between open and grouns through the power transistor.
A ground strap between block (Distributor) and Firewall (ECU) helps maintain both have the same ground reference.
Totally disagree with your premise. The "pickup coil" in the distributor is nothing more than a pulse generator that furnishes a negative going pulse, when amplified and applied to the power Darlington switching transistor turns OFF the coil's primary winding current creating the spark. The distributor is bolted to the block via the hold down clamp and does not need or require a superfluous ground connection to function. IF the MOPAR engineers thought that it was required, they would have furnished it. There is a flexible ground strap connection between the block and the fire wall to insure that the alternator and subsequently the ECU will have an appropriate connection because of the the paint and primer applied to metal. Just my opinion of course.
BOB RENTON

 

[RJRENTON]

The pickup create a small voltage signal to the ECU, but that voltage need to have a good ground reference for comparison inside the ECU.
If the dist signal has a different ground reference than the ECU (ground loop problem) the ECU may not sense the signal.
The ECU also needs to be grounded to control the coils ground (-) terminal between open and grouns through the power transistor.
A ground strap between block (Distributor) and Firewall (ECU) helps maintain both have the same ground reference.
Totally disagree with your premise. The "pickup coil" in the distributor is nothing more than a pulse generator that furnishes a negative going pulse, when amplified and applied to the power Darlington switching transistor turns OFF the coil's primary winding current creating the spark. The distributor is bolted to the block via the hold down clamp and does not need or require a superfluous ground connection to function. IF the MOPAR engineers thought that it was required, they would have furnished it. There is a flexible ground strap connection between the block and the fire wall to insure that the alternator and subsequently the ECU will have an appropriate connection because of the the paint and primer applied to metal. Just my opinion of course.
BOB RENTON

 

[451Mopar]

The pickup create a small voltage signal to the ECU, but that voltage need to have a good ground reference for comparison inside the ECU.
If the dist signal has a different ground reference than the ECU (ground loop problem) the ECU may not sense the signal.
The ECU also needs to be grounded to control the coils ground (-) terminal between open and grouns through the power transistor.
A ground strap between block (Distributor) and Firewall (ECU) helps maintain both have the same ground reference.
I would check the distributor pickup too.
I personally have moved away from the original style ignitions, and just use CD Ignition boxes (MDS, and Crane).
If you watch the new Engine Masters, they just did a test of ignition system(s), and even they had issues with the old MP ECU.

Totally disagree with your premise. The "pickup coil" in the distributor is nothing more than a pulse generator that furnishes a negative going pulse, when amplified and applied to the power Darlington switching transistor turns OFF the coil's primary winding current creating the spark. The distributor is bolted to the block via the hold down clamp and does not need or require a superfluous ground connection to function. IF the MOPAR engineers thought that it was required, they would have furnished it. There is a flexible ground strap connection between the block and the fire wall to insure that the alternator and subsequently the ECU will have an appropriate connection because of the the paint and primer applied to metal. Just my opinion of course.
BOB RENTON

Not everyone has the flexible ground strap connection between the block (where the dist housing is grounded) and the fire wall (ECU Ground.)
There is no ground wire into the ECU so it has to ground through the firewall. The starter (and alternator) ground through the engine block.
If the vehicle is wired where the batteries large cable is connected to the block, and the body is just connected with the negative battery cable pigtail at the battery/fender, any resistance in the large battery cable, and/or engine connection, will create a ground voltage differential when under the load of the starter current (Voltage = Current x Resistance). That is where the flexible ground strap helps equalize the ground levels of the block and firewall
I don't recall the exact ECU box input conditioning circuit, but I think it went through some shottkey diodes before triggering the dwell timing circuit that turns the transistor off.

 

[RJRENTON]

Not everyone has the flexible ground strap connection between the block (where the dist housing is grounded) and the fire wall (ECU Ground.)
There is no ground wire into the ECU so it has to ground through the firewall. The starter (and alternator) ground through the engine block.
If the vehicle is wired where the batteries large cable is connected to the block, and the body is just connected with the negative battery cable pigtail at the battery/fender, any resistance in the large battery cable, and/or engine connection, will create a ground voltage differential when under the load of the starter current (Voltage = Current x Resistance). That is where the flexible ground strap helps equalize the ground levels of the block and firewall
I don't recall the exact ECU box input conditioning circuit, but I think it went through some shottkey diodes before triggering the dwell timing circuit that turns the transistor off.

I'm well aware of Ohm's Law and the fundamentals involving the vehicle's circuit dedign, being a degreed Electrical Engineer eith the a PE credential. Re the ECU's design parameters, there is an amplifier that triggers a programmable Unijunction Transistor (PUT), which in turn switches the power Darlington transistor. To control the transients developed by the coil's collapsing primary winding, there are several Dv/Dt snubber circuits, as well as Shottkey avalanche diodes in the Darlington control circuit. Redundant grounds insure minimal voltage drops under high current draw loads, as you noted, in the starter motor supply loop, which can exceed 400-500 amps with a cold engine and high compression ratios. But to run a separate gtound wire to the distributor to the ECU seems totally useless and serves no real purpose.
BOB RENTON

 

[451Mopar]

I'm saying the flexible ground strap is the redundant ground connection, but is often missing.

Are you saying you designed the ECU? Can you tell us how to make it reliable too?

Sorry, I re-read what I posted and it sounds like a dig. I don't mean it that way.
From what you have posted, you either designed the ECU, or have reverse engineered it like I did. I am truly interested to learn what the parameters for the ECU are, to help trouble shoot ignition issues. I reverse engineered the box a long time ago, and don't recall how the distributor pickup signal is detected? I just suspected that the ground loop might explain some of the un-explained no-start conditions? I thought the pick signal was floated with a ground level trigger? if the signal is not susceptible to ground loop than I apologize. What other modes of intermittent failure should we look for and how to test those?

 

[Nacho-RT74]

Once again, your thinking/suppositions are incorrect. There is nothing in the MOPAR distributor that needs grounded. IF the pick up coil is open, there will be no spark produced; IF the pickup coil is grounded, there will be no spark produced. IF the resistance of the pickup coil is within published values, the system will produce a spark providing all other system components are OK.
BOB RENTON

1st... I’m asking, not assuming
2nd... I’m saying just to replicate the same installed status IF that changes anything ( once again, not assuming )

 

[RJRENTON]

I'm saying the flexible ground strap is the redundant ground connection, but is often missing.

Are you saying you designed the ECU? Can you tell us how to make it reliable too?

Sorry, I re-read what I posted and it sounds like a dig. I don't mean it that way.
From what you have posted, you either designed the ECU, or have reverse engineered it like I did. I am truly interested to learn what the parameters for the ECU are, to help trouble shoot ignition issues. I reverse engineered the box a long time ago, and don't recall how the distributor pickup signal is detected? I just suspected that the ground loop might explain some of the un-explained no-start conditions? I thought the pick signal was floated with a ground level trigger? if the signal is not susceptible to ground loop than I apologize. What other modes of intermittent failure should we look for and how to test those?

YES....you are correct regarding the flexible ground connection, usually atrached to the back of the block to the fire wall, as it is often eliminated or damaged when removing the engjne. The other redundant ground is at the negative battery cable to the core support, it least on B bodies with the R/RB engines.

I'm presently trying to determine the failure mode of a P4120505 "Orange Box." And in addition, making an Auto Cad drawing of the circuit. Because of the different potting compounds used, this has become a formidable task. After removing the switching transistor, preliminary analysis of the Darlington transistor, looks as if it has failed, with no continuity between all combination of the Base Emitter Collector junctions. Usually, a failure is based on exceeding a design parameter, like too much emitter collector current, such as using a coil with low primary winding resistance and a coil with low primary reactance causing a higher than normal impressed voltage, possibly exceeding the emitter collector breakdown voltage.
NO....I'm not the designer of the unit. My background (maintenance manager of a 75 man maintenance department in a chemical plant, where equipment on time is of the essence and failure is not an option) drives me to determine what caused the failure of the unit, AND by possibly reverse engineering out the short commings.
I believe the reluctor generates a pulse train and a corresponding PWM averaging voltage, when amplified and inverted is applied to the switching transistor for on/off switching. Perhaps, not to duplicate your effort, we could collaborate, outside of this venue, as to not to overwhelm most of the subscribers.... your thoughts.....drop ne a PM at your convenience.
BOB RENTON