No Start Issue

[Bullitt-]

I'm reminded of something that comes up from time to time involving the tachometer.
If you have a tach disconnect it from the coils negative terminal (gray wire) & see if the issue goes away... apparently a bad tach will kill the ignition   

[DeathProofCuda]

I'm reminded of something that comes up from time to time involving the tachometer.
If you have a tach disconnect it from the coils negative terminal (gray wire) & see if the issue goes away... apparently a bad tach will kill the ignition   

That's a good point to consider.  I hadn't heard of it, but I guess it makes sense that the tach could create a short to ground in the primary system.

In addition to some of the ECUs being junk, it sounds like grounding of the ECUs is also a common problem.

[dodj]

Can't say that I agree with that philosophy.

That's ok. There's lots of ways to skin a cat.
In my experience the connections and grounds on ebodies account for lots of issues so I like to ensure I'm working with a cct that is not compromised before I start swapping out parts

[DeathProofCuda]

Can't say that I agree with that philosophy.

That's ok. There's lots of ways to skin a cat.
In my experience the connections and grounds on ebodies account for lots of issues so I like to ensure I'm working with a cct that is not compromised before I start swapping out parts

Agreed! 

[DeathProofCuda]

@bluemp301 did you and your dad make any progress on this issue over the weekend?  What did you figure out?

[bluemp301]

@deathproofcuda mostly progressing with my dad wanting to sell it/set it on fire haha.

I did play with the voltmeter and seen with the key ON, the coil was getting 11.5 volts on both the + and - side of the coil.
While cranking it dropped to 10 volts on both sides.

Dad figured he'd changed out almost everything else so he figured it might be the distributor. We swapped it out with a new one and still got the same results.

With that being said I've been doing a lot of reading on the dart/slantsix forums who've had similar issues. I'm going to print out some wiring diagrams and have my brother who's more savvy with electric stuff take a look. The weird thing is everything seems to be getting power where it needs to but still no spark.

The only other logical thing I can think of is the coil. My dad said he swapped it out and it didn't change anything so he put his back in. I might either try to swap mine in off my mustang or "hot wire" the coil from the battery to see if anything changes.

[DeathProofCuda]

You have sufficient power to the coil, so hot wiring it to the battery shouldn't change a thing.

Based on your cranking voltage test at the coil, you have determined that the problem lies between the battery side of the coil and your spark plugs.  To test the coil, see the tip above provided by Chryco Psycho.  You can "trick" the coil into firing by disconnecting its connection to ground on the negative side.  Let me know if you need more details on how to do this.

My money is still on your ECU, either the unit itself or its ground connection.  Remember that the ECU isn't screwed into the firewall just to hold it in place, it also makes its connection to ground through this connection.  Lots of folks have firewall ground connection issues after a shiny new paint job.  Best bet is to sand a small spot down to shiny metal on the firewall and ECU body to get a good connection (unless you are running a rev n nator ECU, which apparently has a separate wire for the ground connection).  Also check your ground connection for resistance using your volt meter set for ohms or continuity to confirm it's a good connection.

Did you try it without the tach hooked up, as suggested by Bullit?

Good luck 

[DeathProofCuda]

Here's a pic I pulled from an A body forum that shows what pin on the ECU that you should be checking for continuity with ground.

[bluemp301]

I really appreciate the advice!

Just one of those frustrating deals where it's probably something really simple that's being overlooked.
It's almost laughable with as simple as these cars are.

We have not done anything as far as testing anything with the tach disconnected but I think we'll check the ECU mounting points to verify it's getting a good ground before messing with anything else.

[bluemp301]

Alright I'm back with an update.

The good part is that my dad replaced his new ECM with another one and his car fired right up! He let it idle for a while and took it around his neighborhood and felt good about it so he took it for a little cruise

The bad is it left him stranded again (fortunately only a few miles from home). With that being said I've heard these ECM's can be hit or miss as I've read and now seen (1st one being defective and now a 2nd evidently failing) is there an ECM of quality or are they all like that? I believe he just purchased something from a local auto parts store. It's not OEM Mopar or anything.

[Chryco Psycho]

I figured that , Mancini had Blue ECUs for about $15 but I don't see them listed on the site right now but worth checking , they work well , the next option I would look at is Rev-N-ator for a high quality ECU

[Brads70]

Maybe consider an MSD box? I know Neil doesn't like them but I've never had one go bad in over 30 years of owning them. 

[dodj]

Maybe consider an MSD box? I know Neil doesn't like them but I've never had one go bad in over 30 years of owning them. 

I'm a fan of MSD as well, been bullet proof for me.
I believe all of them are better than the original Mopar design. Not knocking Ma Mopar, it's just that it is over 40 years old. Functional but not optimal.

[Chryco Psycho]

I have had numerous MSD fail , not cheap & 4 x the size of an ECU

[Jay Bee]

I replaced a failing orange ECM with a black one in my car sometime in the mid 1980's (I'm guessing) and it hasn't let me down yet. It was probably made before the Chinese junk era began.