Now, how to fix it?

This engine has had an electronic run-on problem for a long time. Here is the story. The Accel ECU is hooked up to the battery, and grounded full time, and is also switched on/off with the ignition switch by a seperate lead. There is a third lead that switches ign voltage to the fuel pump relay. The problem stems from the ECU itself, which allows a slight bleed through from the battery side to the switched ignition lead that is designed to turn the ECU on/off with the key.

As I have stated elsewhere, I am an electronic dunce. When the 12v switched connection was temporarily gone earlier this week, I still read 1.75 volts or so on the switched fuse blocks. Even though there was no existing connection any longer between the ignition key output blue wire, and the switched fuse block. NONE. HMMM! A mystery, but not a surprise, as I have had problems with this engine running on after the key was turned off. Once I got the ignition 12v restored as detailed in another thread, I decided to track down this mystery. So, with the battery ground unhooked, I put my ohm meter between the switched fuse block and the battery fuse block under the hood. No surprise, the ohm meter reads .07 on the 20K scale. I'm not enough of an electronics guy to understand anything about this except that there is a connection here where there should not be, even though small. It was enough to just barely make the buzzer sound when the ohm meter was set to buzzer.

So I set about pulling fuses from the fuse blocks to see which circuit was producing this crossover connection, and the continuity disappeared when I pulled the fuse for the ECU. This effectively disconnected the on/off lead from the switched circuit, and at this point the continuity between the switched and battery fuse blocks was gone. I do have the fuel pump on a seperate toggle in an attempt to get the engine to cut off , but that was still not doing the job of stopping the engine. The cross over connection is so slight that there is not enough voltage on leaked to the switched side to start things up when starting the engine, but it is enough to keep it running once the engine is going.

So now I must find a way to block this bleed through the ECU from the battery to the switched fuse block. The simplest thing perhaps would be to put another toggle switch in that lead to simply shut it off too. I have another available toggle on the dash board with no intended purpose yet. Another fix would be to put a relay in the line and have it turn on the ECU, but there is a relay in there somewhere already by ACcel's design, so I am not sure why another one would fix the problem. The fact is, as long as the ECU on/off lead is hooked up to the switched fuse block, something gets through there from the battery. Even this mystifies me, as there should be no connection between the relay coil and the ECU when things are turned off. I am suspecting some kind of obscure ground path of some kind that is causing all of this. But, I dont; see it. Is it possible that the relay is defective, and not breaking the contact entirely, but leaving a very small connection that is high resitance but still there?

Another fix would be a diode in the on/off wire, but then, as I have said before, this would be an electronic device, which I really don;t understand. A toggle switch I can conceptualize, but the diode is a little more mysterious to me, and requires a little more faith than a switch that will cut things off at the source. Any thoughts on any of this? Any ideas on the cause, or the cure? I am just glad I am on the track of solving this now. Thanks in advance for any ideas.

Sam

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Could you post some sort of diagram of how the wires are set up? I'm having trouble following some of the details. But I'm wondering if a relay would work as a substitute for a toggle switch - just have it come on with a switched 12V source. Relays are like electronically operated toggle switches, pretty simple as far as electronics go.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Sorry Matt, I'm not that web literate. Let's see if I can break this down simply.

1. Switched fuses.
2 Battery power fuses.
3. ECU is hooked directly to the pattery posts, and also to a switched fuse. When I check for continuity between the batt fuses and the switched fuses, it shows a low level of continuity, enough to read 1.75 volts on the switched fuses panel even when the key is turned off.

When I remove the fuse from the ECU switched fuse panel this feedback goes away, and the switched panel no longer has the continuity between it and the batt with the key turned off.

Maybe I will use the relay. I still have an extra toggle on the dash though.

Sam

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Ok, I get what's going on here. One way to solve this might be to take a diode - just about any diode is likely to work - and wire it so that the banded end points towards the wire going to the ECU. Diodes are like electronic one-way valves; electricity can go from the non-banded end to the banded one, but not the other way around.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Is the purpose of the switched fuse to the ECU to tell it when to turn on?
(I think it is)

I think the ECU is using a transistor internally, and you're getting leakage from the battery to the switched fuse thru the ECU.

That being the case, the diode on the switched fuse line to the ECU should do the trick.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

To me this seems super simple. The switched 12V items need to be on the accessory output of the ignition switch and the ECU and fuel pump need to be on the ignition (Ign 1 and Ign 2) output of the switch. When the ignition switch is off the accessory loads will be isolated from the ECU.

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Joshua

I can also think of a way to fix the problem with a relay installed in one of several locations. At least, I think I can think of such a way. I just got back from Germany, so I think I'll sit this one out til the jetlag wears off.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

The thing is, the way Josh is suggesting, is the way it is wired. The wire to turn the ECU on is run off the blue wire. When the ignitiion switch is turned off, there is still a bleed back from the battery side for some reason, even though all the hard wires you can see are isolated between the battery side and the ignition voltage side. The more I ponder this, the more I think the relay Accel has in the ON/OFF wire must be the source of the leak. Is there any other part of the EFI that will bring the switched 12 and Batt 12 in some kind of electronic proximity? I can think of nothing in the system except the ECU that has both sources present.

Dan, I hope you had a good time. Germany should be nice this time of year. What city did you go to?

Sam

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Does Accel have directions on a web site (and wiring diagram)?

If so, got link?

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

This is it:

http://www.accel-dfi.com/pdf/gen7_instructions.pdf

Sam

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no wiring diagrams in there that I could find....

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Try looking from the home page of their site. At;

http://www.accel-dfi.com/


I went back and looked, and you are right. Now you remember why I felt so annoyed at the support from Accel. Can you imagine writing instructions without wiring diagrams. They are indeed on the CD they include with the kit, and are so small you cannot read the print without a 21" screen. Or click out which lets you see only a tiny part of the screen at a time. They are very hard to use. Maybe that is the only place the wiring diagrams exist. Anyway, see what you can find from their home page if you would like. And thanks.

Sam

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Was in Frankfurt and Darmstadt. I like the former better than the latter, but the food's good in both places!

Without seeing wiring diagrams, I have a question for you: What happens if you disable the alternator (remove the main wire from B+, for example)? Will that stop the run-on?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Is the switched fuse wire pink?

Found something here (pg 11):

http://www.accel-dfi.com/pdf/ProRamBig.pdf



If you remove this wire, it doesn't run right?

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Is it similiar to this:

http://www.msdignition.com/1troub1.htm#runon

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes