4 pin ECU doesn't work. Old 5 pin does.

-
moparmandan

moparmandan

FABO Gold Member
FABO Gold Member
Joined
Jun 28, 2017
Messages
2,999
Reaction score
3,009
Location
Deland, FL
Since I'm not the only one, I figured I would state the problem succinctly, and put it out there for the experts.

Have tried several different 4 pin ECU's. And two distributors. Same result's. Nothing. Old 5 pin ECU cranks and run's the engine fine. For both distributors. New 4 pin won't. Swapped coil's also. Same result's.

For discussion sake, let's assume we have a good 4 pin ECU, coil, distributor. With old factory electronic ignition wiring.

Any idea's? Pin's 4 & 5 swapped? Bad connection's? Let's brainstorm. Thanks!!!
 
Last edited:
If I remember correctly, if you wire for the four pin, you can run both, but not the other way round. Five is only five.

I MAY have that backward
 
jos51700 said:
If I remember correctly, if you wire for the four pin, you can run both, but not the other way round. Five is only five.

I MAY have that backward
Click to expand...
You have it backward's. 4 pin ECU should work fine in a factory set-up.
 
Last edited:
moparmandan said:
You have it backward's. 4 pin ECU should work fine in a factory set-up.
Click to expand...

It matters which ballast resistor you have.
Generally the 5 pin ecu takes the 4 terminal ballast, and the 4 pin ecu uses the 2 terminal ballast.
This is why the 4 pin works on both.

Do a google image search and check it out.
 
TrailBeast said:
It matters which ballast resistor you have.
Generally the 5 pin ecu takes the 4 terminal ballast, and the 4 pin ecu uses the 2 terminal ballast.
This is why the 4 pin works on both.

Do a google image search and check it out.
Click to expand...
Thank's man. I'm familiar with the wiring.
Like I said, For discussion sake, let's assume we have a good 4 pin ECU, coil, distributor. With old factory electronic ignition wiring.
Factory would assume a 4 pin ballast.
 
moparmandan said:
Thank's man. I'm familiar with the wiring.
Like I said, For discussion sake, let's assume we have a good 4 pin ECU, coil, distributor. With old factory electronic ignition wiring.
Factory would assume a 4 pin ballast.
Click to expand...

Have you replaced the ballast in all your thrashing?
 
moparmandan said:
While I've got you here what would you guess is the failure rate of the blue ECU's O'reilly sells?
Click to expand...

Master Pro? a lot. They are on par with the Wells stuff Autozone carries. Junk.
 
RustyRatRod said:
Master Pro? a lot. They are on par with the Wells stuff Autozone carries. Junk.
Click to expand...
No lie. I've tried 2 of them (Master Pro), 1 from AutoZone and a chrome one off of e-bay. NONE, but the old 5 pin, will start my car and make it run. Haha

I WILL figure this out.
 
Last edited:
Today I decided to mess with it a little. Cranked right up in the old 5 pin ECU configuration. No go with a new 4 pin. So I had read that maybe if the distributor wires (ECU pins 4 &5) were crossed, an old ECU would fire the coil, but not a new one because of the difference in the waveform. Sort of like a generator that puts out a square wave instead of a true sinewave. OK for a toaster, not for a TV. Anyway swapped the wires with no change. Swapped everthing back and it fired right up.

Laughed and scratched my head..........
Checked voltages with old ECU. 10.5 coil + and 2 volts at coil -
Swapped a 4 pin ecu in got 11 coil + and 0 at coil -
Starting to suspect the old ecu connector is not making contact on pin 2 with these new China ecu's.

Think I'll try a bench test setup like @67Dart273 recommends.
 
moparmandan said:
Today I decided to mess with it a little. Cranked right up in the old 5 pin ECU configuration. No go with a new 4 pin. So I had read that maybe if the distributor wires (ECU pins 4 &5) were crossed, an old ECU would fire the coil, but not a new one because of the difference in the waveform. Sort of like a generator that puts out a square wave instead of a true sinewave. OK for a toaster, not for a TV. Anyway swapped the wires with no change. Swapped everthing back and it fired right up.

Laughed and scratched my head..........
Checked voltages with old ECU. 10.5 coil + and 2 volts at coil -
Swapped a 4 pin ecu in got 11 coil + and 0 at coil -
Starting to suspect the old ecu connector is not making contact on pin 2 with these new China ecu's.

Think I'll try a bench test setup like @67Dart273 recommends.
Click to expand...

Yeah, Del (@67Dart273) is da man with electronics. You're listenin to the right dood.
 
I have a ecu tester if totally stumped I can check it out for you just pay the ride.
 
I have been using nors Kem ones have not found a bad one yet, just FYI
 
TrailBeast said:
It matters which ballast resistor you have.
Generally the 5 pin ecu takes the 4 terminal ballast, and the 4 pin ecu uses the 2 terminal ballast.
This is why the 4 pin works on both.

Do a google image search and check it out.
Click to expand...
The 4-pin should work with a dual ballast as the missing pin is the one that goes to the ballast.

The difference is the 5-pin gets a reduced power from the ballast along with 12v on another pin. The 4-pin gets the reduced voltage internally from the 12v feed.

Alan
 
Cuda Al said:
The 4-pin should work with a dual ballast as the missing pin is the one that goes to the ballast.

The difference is the 5-pin gets a reduced power from the ballast along with 12v on another pin. The 4-pin gets the reduced voltage internally from the 12v feed.

Alan
Click to expand...
Yes. You should be able to swap in a modern 4 pin ECU to a factory set-up and never know the difference. That's why this is a little perplexing.
 
You must log in or register to reply here.
-

Back
Top