Stange Electrical Problem, Any Ideas?

[loco340cuda]

Quick backround, I have a 70 340 Cuda that has been converted to an FBO electronic ignition system.

I drove the car last weekend with no issues started right up drove fine, it's been that way for a couple of years with no starting issues.

Today I came out to the garage and did an oil change. I go to start the car and it will not start. After some investigating I found it was not getting spark. I start switching out all the ignition components one by one. After I switched out the ECU, coil, voltage regulator, ballast resistor the car still would not start. At that point I'm scratching my head becase the engine will crank but not fire up (Also I checked and I was getting fuel). Finally I don't know why but I looked at the alternater and said that's the only thing in the system that has not been switched out, so I unplug the blue and green wires from the alternator and crank the engine over and it starts right up.

So I go back and reinstall the ignition components one by one with the alternater unpluged and the car starts right up every time after I put back in each ignition component. When I get to the FBO ECU box and put it back the car will not start. So I put back the MP backup ECU that I have and the car starts again. I then plug in the alternatior green and blue wires and the car starts.

So at this point I have determined the FBO ECU has gone bad but I still not sure why the car would not start will all the parts switched out until I unplugged the blue and green alternator wires. Now the car will start with all the orginal components (execpt the orginal FBO ECU box)even with the alternator blue and green wire plugged in.

At this point I think I am going to buy a new alternator, due to I'm concerned that maybe it is going bad and fried my FBO ECU. Also the alternator is about 8 years old so it is possible it could be going bad.

Anyone ever had a problem like this or have any idea why the car would not start even with all the ignition parts switched out (with backup parts) until the alternator green and blue wires were unplugged? 

[Chryco Psycho]

I have done similar removing FBO parts one by one & the car ran better with every part I removed until I swapped the ECU it actually ran better with the FBO unit , contact Don & ask about warranty , I have no idea why the car wouldn`t start with the Alt plugged in , the it only shares the blue 12v power source

[loco340cuda]

Yeah, the alternator thing did not make any sense to me either but for some reason the car would not start until the alt was unplugged. Now the car starts with it plugged in (with MP ECU) so who knows.  At this point I will call Don to get the FBO ECU replaced. 

My experience with the FBO stuff has been the same as your Chryco, the thing that really seems to make the difference is the FBO ECU.  I currently have the MP orange ECU in the car and it does not seem to be as strong performance wise as when the FBO ECU was in it.  I think I will order an extra FBO ECU so next time the ECU goes bad I don't have to use the MP box as a band aid.

[LAA66]

 Possibly check the ground from the FBO unit (or any other ECU) as they say it is critical. I ran a separate wire to the common negative junction at the radiator support. So far no problems. 

[cudaneil]

 I was told the same thing by FBO...............if the ecu does not have a good earth it will fry the ecu,  no warranty claim.

[loco340cuda]

The ground to the ECU was pretty soild.  The ECU is grounded through the two bolts that holds it to the cowl as well as through a seperate wire (10 guage) from one of the bolts to the engine block.  My guess is that the box just went bad, due to it has been running trouble free for over two years and the bolts were not loose when I switched it out during my trouble shooting session. 

Just for the record, this is the second FBO box that has gone bad over the last 5 years for me.  If the car did not run so much better with the FBO ECU over the MP ECU I would not bother buying another one.  I would prefer to switch over to an MSD or Mallory ignition but money and the trouble to switch the car over is what stops me from doing that. 

[MEK-Dangerfield]

I have an FBO igniton box, and coil in my car. Serveral years with no problems.

I don't for the life of me see where the alternator or voltage regulator would have any affect on you starting the car.   

I'm not bashing you, I just don't see this thru.    Is the area where the ignition box is screwed in clean of paint around the screw holes?

[Chryco Psycho]

Have you tried the mopar chrome box

[loco340cuda]

MEK no worries, I don't think you were bashing me.  The alternator thing did not make any sense to me but I thought I would ask since I have only been messing around with these old mopars for about 5 years and I know there are people on this board with a lot of expeirence that could teach me something that I may not have known.  It appears it was just coincidence.  I switched out the voltage regulator mostly out of fustration/despairation when I could not get the car to start after switching out all the other ignition parts.

As far as the ECU ground goes the ECU is grounded by two bolts that go thru the cowl.  Those bolts have nuts on them that make contact to the cowl metal on the back side of the cowl.  I also have a ground wire that connects to the back part of the ECU which contacts the unpainted back side of the ECU and that is contected to the engine block through a 10 gauge wire.  I know that this ground system is very solid.

As I mentioned before I have had one of these go a bad before and I have talked to other people who have as well.  I just wanted to verify that is was not something else that would of caused the ECU to get fried.

Chryco, I do not have a chrome MP ECU, just and orange one.

[the_engineers]

What's FBO? 

[MEK-Dangerfield]

What's FBO? 

They have their own ignition system that looks like Mopar's. I'm not sure anyone knows what FBO stands for though.   

[LAA66]

FBO = Fat, Bald, Oldguy. 

[the_engineers]

FBO = Fat, Bald, Oldguy. 

Am I selling ignition systems?

[LAA66]

Am I selling ignition systems?

 Try this one on for size....

http://www.4secondsflat.com/Realitycheck.html

  

[the_engineers]

I like!