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ECU box testing??

XCELLR8

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I have a 77 400 in my Cordoba and it runs and drives. It has had the electronic conversion done to remove the lean burn set up years ago. I noticed that the ECU box was losing the epoxy in the back of the unit and running down my firewall. I bought the Jegs HI-REV 7500 ECU unit as it was made in America and with all of the other ones being made overseas I thought I would be fine. Well I'm not. The car runs with the stock ECU but when I install the new ECU it will not fire. I have even wire brushed the firewall and ran a ground wire, still no fire. I have changed out the stock ECU with the new ECU 3 times and the car will run with the stock ECU but not with the new ECU. My car is not stock, so that is why I went with the Jegs ECU. Is there a way to test the ECU on a bench to see if it is good? My stock ECU is the 5 pin and the new one is 4 pin and my ballast is the 4 tab style. Am I missing something that needs to be done to run the new ECU? I have read that this should be a plug and play switch.
 
Anybody ever run into this problem? If so, how did you fix it? I don't know, maybe I got a box that was DOA.
 
Could be....

Is the coil the stock type coil? Per the instructions, it has to be that type.

If you have a volt-ohmmeter, then check the resistance of the section of the ballast resistor used for this setup (the section that still connects to the coil +); do this with at least one end disconnected. See if it is per the instruction sheet (1 ohm or more; measure the leads of you meter alone by shorting them together and noting the resistance; then subtract that reading from the reading of the ballast section that you are testing).

Here is a link to the ignition systems; the difference is the elimination of the extra ballast section feed to the 4 pin unit; since the pin at the ECU is not there, it should not matter if the 2nd ballast resistor section is ther or not. Just be sure that the ballast section that feeds the coil + is the low resitance section and is in the 1 to 1.2 ohms resistance range.

For grins, disconnect the lead to the 4 lug ballast resistor that is by itself to the missing conector in the new 4 pin ECU. Should not make any difference whatsoever.....

Check the reluctor gap in the distributor to be .008"; could be that the adjustment is more critical fore the new box.

http://www.chargerr.com/Ignition/Ignition.htm
 
Could be....

Is the coil the stock type coil? Per the instructions, it has to be that type.

If you have a volt-ohmmeter, then check the resistance of the section of the ballast resistor used for this setup (the section that still connects to the coil +); do this with at least one end disconnected. See if it is per the instruction sheet (1 ohm or more; measure the leads of you meter alone by shorting them together and noting the resistance; then subtract that reading from the reading of the ballast section that you are testing).

Here is a link to the ignition systems; the difference is the elimination of the extra ballast section feed to the 4 pin unit; since the pin at the ECU is not there, it should not matter if the 2nd ballast resistor section is ther or not. Just be sure that the ballast section that feeds the coil + is the low resitance section and is in the 1 to 1.2 ohms resistance range.

For grins, disconnect the lead to the 4 lug ballast resistor that is by itself to the missing conector in the new 4 pin ECU. Should not make any difference whatsoever.....

Check the reluctor gap in the distributor to be .008"; could be that the adjustment is more critical fore the new box.

http://www.chargerr.com/Ignition/Ignition.htm

Thanks for the link and ideas. I am using the stock coil. The only thing not stock with the ignition is the dizzy which is a MP unit. It runs with the stock 5 pin ECU but wont fire with the 4 pin after market ECU. I will check the ohms of each side of my 4 prong ballast to make sure the wires are on the right side. The distributor was checked and is at .008" before I installed it in my motor.

super77se: That is the ECU I bought, but from JEGS at $40 shipped. I am thinking about buying a stock ECU from the local auto parts store to see if the ECU is bad or the wiring. It would be a spare unit to put in the trunk. Are you running a 4 prong or 2 prong ballast?
 
super77se: That is the ECU I bought, but from JEGS at $40 shipped. I am thinking about buying a stock ECU from the local auto parts store to see if the ECU is bad or the wiring. It would be a spare unit to put in the trunk. Are you running a 4 prong or 2 prong ballast?

my ballast is a 4 prong plug in. I ran this on my 77 charger which is the 5 pin harness just like yours. I put it on my 74 charger which has a 4 pin harness and same ballast set-up, it works great on both. I don't know why you are having issues with the same ignition box. I guess its possible you got a bad one.

also, be sure you are plugging in the ballast with the connectors the right way. they are supposed to have locating pins on the connector to locate them on the ballast. sometimes these pins get broken off and plugged in upside down. this will cause a weak/no spark condition. I found this out the hard way lol

the distributors are bone stock. the 77 charger did not have the lean burn to begin with. I used both a standard and Mallory coil. no other ignition upgrades other than wires
 
You can check the standaed ECU's response to the reluctor by disconnecting the 2 wire harness to the distributor and momentarily grounding one lead to the ECU and then the other while looking for spark. One or the other should produce a spark each time it is grounded/ungrounded. I assume that you can do the same for the new box....

Also check the resistance through the 2 pins of the reluctor lead to the distributor; a stock unit would read in the 150-900 ohm range...I have also read that it should be bewteen 350 and 550 ohms...not sure which is correct. But if your reluctor is in the high end of the 150-900 ohm range, then it could be that it will not quite fire the new ECU.
 
One time I ran into this where the stock ECU worked and the car ran but it would not run when I bolted the orange MP ECU on it. The car was an original 318 and had been changed to a bigblock. What I found was the two wires to the dist pick-up got crossed. The Standard ECU would run with the pick-up wires backwards but it would not run with the orange ECU until I reversed the pick-up wires and then it ran with both. The harness on this had been modified for the bigblock and the wires got crossed in the change. If your harness has been changed or worked on I would check it for this.

Easy way to tell is to unplug the dist 2 wire pick-up plug. Then turn the key on and hold the coil wire about 1/4" from ground. While doing this with the key on take the wire harness side of the pick-up connector and touch or scrape the male terminal in the wire harness side of dist pick-up to ground and it should spark. If it does not put a cotter pin in the female terminal of the same connector and try it. When I did this I got the coil to spark when I did this with the cotter pin in the female terminal on the connector which is wrong as it should spark when you scrape the male terminal to ground. If it does spark using the female terminal the pick-up wires are crossed and need to be switched. Its funny but some ECU's will still spark with the pick-up wires crossed but not all will. Ron
 
One time I ran into this where the stock ECU worked and the car ran but it would not run when I bolted the orange MP ECU on it. The car was an original 318 and had been changed to a bigblock. What I found was the two wires to the dist pick-up got crossed. The Standard ECU would run with the pick-up wires backwards but it would not run with the orange ECU until I reversed the pick-up wires and then it ran with both. The harness on this had been modified for the bigblock and the wires got crossed in the change. If your harness has been changed or worked on I would check it for this.

Easy way to tell is to unplug the dist 2 wire pick-up plug. Then turn the key on and hold the coil wire about 1/4" from ground. While doing this with the key on take the wire harness side of the pick-up connector and touch or scrape the male terminal in the wire harness side of dist pick-up to ground and it should spark. If it does not put a cotter pin in the female terminal of the same connector and try it. When I did this I got the coil to spark when I did this with the cotter pin in the female terminal on the connector which is wrong as it should spark when you scrape the male terminal to ground. If it does spark using the female terminal the pick-up wires are crossed and need to be switched. Its funny but some ECU's will still spark with the pick-up wires crossed but not all will. Ron

Thank you for the info, as this is my problem. I get no spark on the male side, but when I put a 16 penny nail in the female side I can jump a 1/2" spark. So, I must be backwards somewhere in my wiring. Is it just the two wires going to the distributor or could I be crossed somewhere up the line, like the ballast maybe? So 383man did you have a 2 or 4 prong ballast? I'm wondering if the ballast wires are on the wrong side.
 
Adn BTW, the reason that some units wil fire with the wires crossed and others won't has to do with the internal design. The reluctor produces what is similar to a cycle of alternating current with one of the current edges being a quick edge and of the right polarity that should trigger the ECU. If the wires are reversed, then then edge polarites are reversed and one of the other edges will have to trigger the ECU but they are 'lazy' edges; some ECU's will respond to these lazy edges and others won't.

You can read here in the section for variable reluctors for a better explanation:
http://www.megamanual.com/ms2/pickups.htm

Even if the ECU will trigger off of the 'lazy' edges, the timing of these edges can jump around. I bet the OP's car will idle better when this is sorted out.
 
Adn BTW, the reason that some units wil fire with the wires crossed and others won't has to do with the internal design. The reluctor produces what is similar to a cycle of alternating current with one of the current edges being a quick edge and of the right polarity that should trigger the ECU. If the wires are reversed, then then edge polarites are reversed and one of the other edges will have to trigger the ECU but they are 'lazy' edges; some ECU's will respond to these lazy edges and others won't.

You can read here in the section for variable reluctors for a better explanation:
http://www.megamanual.com/ms2/pickups.htm

Even if the ECU will trigger off of the 'lazy' edges, the timing of these edges can jump around. I bet the OP's car will idle better when this is sorted out.

Thank you for the explanation of why the wires being crossed causes problems. Yes, my car does not idle very well.
 
Thank you 383man and nm9stheham as the car is running on the old and new ECU box. I switched the 2 wires going to the Dizzy and now have spark on the male side.
 
Thats great as I am glad you got it fixed. It was the last thing I would have thought when mine would not run on the orange ECU. I thought I had a bad orange ECU but after another did the same thing I found out when looking to see how strong the spark with the old box and thats when I found out the female side would spark and not the male side. I learn't something that day. And thanks for the info " nm9stheham" Ron

- - - Updated - - -

Adn BTW, the reason that some units wil fire with the wires crossed and others won't has to do with the internal design. The reluctor produces what is similar to a cycle of alternating current with one of the current edges being a quick edge and of the right polarity that should trigger the ECU. If the wires are reversed, then then edge polarites are reversed and one of the other edges will have to trigger the ECU but they are 'lazy' edges; some ECU's will respond to these lazy edges and others won't.

You can read here in the section for variable reluctors for a better explanation:
http://www.megamanual.com/ms2/pickups.htm

Even if the ECU will trigger off of the 'lazy' edges, the timing of these edges can jump around. I bet the OP's car will idle better when this is sorted out.



That was one thing as my old Dart with the wires crossed and the after market ECU ran great. I mean it ran very good but no spark with the orange until I figured out the wires were switched. Ron
 
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