Re: [DML] Re: End of life for idle ECU's

[Martin Gutkowski - DMUK Ltd <martin@xxxxxxxxxxxxxx>]

  Sounds like it's running lean to me, and is on the limit of the 
control band the lambda system has. Therefore I agree it's probably 
vacuum lrelated

Martin

David Teitelbaum wrote:

>I recently worked on a car for a nearby owner that had a
>hiccup-hunting type problem. It would idle smooth and had a regular
>repeating bump up and down in the idle. Rob Grady tried to smooth it
>out but the owner didn't want to spend a lot of time (read money) on
>it so Rob had to leave it alone. I figured I "knew better" and just
>had to substitute a known good idle ECU and maybe a Lambda ECU. My
>origional theory was some kind of interaction between the different
>control loops. As pointed out the ECU's only communicate with each
>other by their interactions on the motor itself. I figured they were
>chasing each other's tails so-to-speak. Ater swapping the ECU's and
>several other things that we could think of WITH NO EFFECT I had to
>think of something else. I started looking for vacuum leaks. I found
>the "O" ring to the cold start valve under the mixture unit was out
>and the brass piece that holds it in was sliding around on the tube. I
>got the brass piece and the "O" ring back correctly and although it
>made a BIG   difference, it still hunted a little. I still suspect
>multiple vacuum leaks under the intake manifold but we didn't have the
>time to "go digging" in there. In any case the owner was happier with
>the improvement. You would think a vacuum leak would cause a constant
>effect, not a cyclical one but I have seen it with my own eyes. Anyway
>there was nothing wrong with any of the ECU's. The moral here is you
>HAVE to correct ALL vacuum leaks or the control systems cannot work
>right. Vacuum leaks also have a cumulative affect ie, many small ones
>add up, not cancel out. I have done several motors and when you do all
>the seals, "O" rings, and gaskets you can have the idle very smooth.
>For Elvis where he notices a sudden cahnge in the idle it could be as
>the motor warms up and one of the warm-up systems which uses vacuum
>goes on or off he has a vacuum leak which is causing that, not
>anything with the idle ECU. Of course you HAVE to have a tuned up
>motor with clean fuel injectors, good ignition wires and good compression.
>David Teitelbaum
>vin 10757
>
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>--- In dmcnews@xxxxxxxxxxxxxxx, doctorDHD@xxxx wrote:
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>>Dave T or anybody else.  My idle is pretty darn solid when I 
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>disconnect the 
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>>wire going to the idle speed motor.  It hunts bady when  connected.
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> Is this a 
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>>clue as to where the problem is?
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>>D² & 6530
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