Engine miss under load - ignition concerns

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VTICH

VTICH

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Hello all, hope you can help (I know you can).
I've read up on a couple dozen posts through the search function with people having various ignition troubles and I've learned allot thanks to all that have contributed.

My car and a bit of what I have checked so far:
1973 Duster
Stroked 360 Magnum based engine
MP electronic distributor and orange box with new harness between box and distributor.
Fresh rebuild but was miss firing before hand.
New Champion RC12YC plugs.
Firecore wires. (unknown age and I haven't measured resistance)
I do have a copy of the wire harness schematics and I believe everything is back as it should be. Was hacked up quite a bit and I removed all unused wires from other projects PO must have skillfully (sarcasm here) installed. I did leave the original ignition system wires in place though they are all dead ended - it used to be connected to a MP connection MSD like box at one time from the old photos I have of the car.

New ballast resistor
Battery holds good charge and car starts easily and idles OK after it warms up a bit (No choke on dual 4BBL setup with cam duration 236o @ 0.050)
Alternator main wire puts out 15V
Alternator field wire puts out 13.75V.
About 13.65V on feed side of ballast (all voltages with car idling @ 950RPM)
6.75V on ballast out to + side of coil and at + side of coil.
3.62V on negative side of coil. Was over 4.2 but tried grounding ECU better and it helped lower - side of coil voltage.

What I haven't checked:
Timing (I have to borrow a light but I have moved it about a bit. Pulled back from hard start a bit and it starts well, tried retarding more but ran worse, advanced timing to a hard start position and no change to miss under load)
Plug wire resistance
Reluctor clearance.

From what I have read my negative side of coil voltage may be too high which could be a bad ECU? (Orange box).

Have I given enough information to lead to a diagnosis or do I need to do the remaining tests and adjustments before pointing to the ECU?

I do have a complete MSD HVC 6601 ECU, Coil and Soft Touch system I could install but I'd rather save for another project but if the Duster needs it it needs it, LOL! Currently mocked up on a 340 engine......
 
Over 3V at coil NEG sounds high to me

Coil+ voltage is going to vary

13.65 to ballast should be fine.

I would REALLY check ECU grounding, and body to engine ground

Don't discount "simple stuff" like cap, rotor and coil wire

I'm not a chemist. Don't discount plugs. They seem to get the ceramic "cooked" under certain engine conditions. Years ago I fought a problem I "outthunk" had CD ignition, and a high speed miss. Plugs "looked" fine. FINALLY changed the plugs, and WHAM Ran great
 
Wow, quick reply and thanks 67DART273.
It was your reply in a previous post the noted the voltage on the negative side should be down around 2V or so that lead me to try better grounding first.

I will not give up on the grounds just yet. I did not check the body ground. I do have a good ground from engine to frame. Continue the testing tomorrow I guess.

Thanks again for the body ground check idea, Paul.
 
I'm fighting the same issue on a stock 5.9 from a 2000 dakota transplanted into a 65 dart. I've changed everything I can think of. Nothing helps. Does this voltage at the coil hold true on these EFI engines? I've checked the grounds over and over. I'm at a loss.
 
VTICH said:
Wow, quick reply and thanks 67DART273.
It was your reply in a previous post the noted the voltage on the negative side should be down around 2V or so that lead me to try better grounding first.

I will not give up on the grounds just yet. I did not check the body ground. I do have a good ground from engine to frame. Continue the testing tomorrow I guess.

Thanks again for the body ground check idea, Paul.
Click to expand...

I may have lead you astray. Did you take the NEG coil reading running or with key on and engine stopped?

RUNNING would be higher, STOPPED should be very very low

Here's the thing about that coil NEG reading. The Mopar ECU takes the place of the old breaker points, switching the coil on / off by grounding the NEG coil terminal. Points have "a little" resistance, and worn / bad points have "more" resistance

An ECU has the same equivalent resistance......it's going through a big switching transistor (the one you see on the case) and you are dealing with the "resistance" of that device plus possibly other components.

So ANY resistance between the ECU case and the battery NEG terminal is going to reduce the current through the coil
 
easyrider said:
I'm fighting the same issue on a stock 5.9 from a 2000 dakota transplanted into a 65 dart. I've changed everything I can think of. Nothing helps. Does this voltage at the coil hold true on these EFI engines? I've checked the grounds over and over. I'm at a loss.
Click to expand...

I'm just not that familiar, but I would guess "yes." Again, RUNNING voltage will be higher. This is because the coil is turning on and off, generating a pulsing which gives an "average" reading on your meter.
 
I'll 2nd the "yes" for the 5.9L. It still has a single coil and a distributor. The spark driver is built into the engine controller and with more modern electronics (similar to GM HEI), so doesn't need a ballast. But, the basics are the same. The main upgrade is that the distributor doesn't apply any spark advance. That is all done electronically by the computer, which gets rpm & Pman signals. But, that hasn't changed from the 1980's where Chrysler's "spark computer" did the advancing (my 1982 Aries). The Magnum engines use a crankshaft pickup instead of in-distributor as in 70's A's. There is a pickup in the distributor, but that is a "cam pickup" for "sequential" fuel injection timing.
 
Well I think I have tracked down the engine miss. Installed new braided ground strap to chassis. No change to engine miss. Installed a buddies spare ECU (Chrome box) and running fantastic. I'll run it this way for a bit to make sure it is / has been resolve.

Do you think it wise to upgrade ignition system to something else? I have the MSD. Could convert to HEI? Thoughts?
 
A PROPERLY working Mopar box should be fine. One problem is, I no longer "know" of anyplace reliable to buy good quality replacements

I'm big on HEI. Even with a stock coil, an HEI allows you to do away with the ballast, giving you more coil "juice."

There's lots and lots of threads on this, some guys have even put a 4 pin HEI module inside a scraped-out Mopar box for "originality"
 
I have an HEI 4-pin mounted under my distributor. Made a WORLD of difference vs my old Orange box.
 
Thanks for the feedback with your experience on the HEI set ups. I have read the (very simple) conversions others have done on this site. I too would likely bury an HEI Module inside the factory box if I did this to at least make it look OEM. Maybe I'm too nostalgic, this being my first Mopar and all LOL!
 
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