ecu float

[rcb280z]

Okay, before I go into detail of my new F.I. issue I'm posting a question:

Anyone with the so called "ecu float" issue, can you describe symptom(s) or reason(s) you believe that is what's happening.

[Captain Obvious]

The ECU output stage uses open collector Darlington transistor drivers to pull the low side of the injectors toward ground in order to open them. That open collector style of driver is sometimes referred to as "floating" when it's OFF.

Ummm... I'm assuming that has absolutely nothing to do with what you're talking about?

If that's the case, then I've never heard of it. Give me just a little hint (PM if you don't want to influence the results from others) and I'll see if it rings any other bells?

[Zed Head]

I think he might be talking about FastWoman's theory of "lean mixture drift". Aging electronic components causing a shorter injector open time. Typically fixed by adding resistance to the coolant temperature sensor circuit.

If that's the case, then the signs would be slight hesitation and surging during driving. The engine doesn't get enough gas for the amount of air it's pulling in.

[siteunseen]

Yea it's drifted out of spec is what I read. Mine ran terrible between idle and 2500 RPM, it wouldn't even spin the tires from a dead stop. I first thought it was the TPS though. I did what Fastwoman and Zed Head suggested, also on Atlantic Z's tips for fuel. I'm so glad I did too, made mine run like it should. Cheap and easy to do, the way I like it!

http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

Edited February 25, 2013 by siteunseen

[rcb280z]

Yes I am speaking of FastWomens lean mixture drift. My 77 is running similar to siteunseen's did but I was under the impression that it only happens with the 78 model. I haven't had a chance to trouble shoot anything yet. Has anyone experienced the same thing with a bad altitude switch which is a CA only sensor, supposedly. Damn, everything had been replaced when I was putting it back together a year ago. CTS, TTS, and harness to those, injectors (new) and connectors, TPS, AAR, CSV, Iv'e had all these new parts for quit some time and when I was installing my header I went ahead and replaced these items. Oh and a refurbished AFM. I swapped my old one in and it ran like crap also so I put the rebuilt one back on with the new setting and it runs good. So Far mileage hasn't gotten any worse either, plugs look good. I could keep on and on but I don't want to do that yet and waste peoples time here. It seems to have had the symptoms of "lean mixture drift". And I wanted to know what the symptoms are. Thanks

[black gold man]

pop out the intake .

[Captain Obvious]

Yes I am speaking of FastWomens lean mixture drift.

"Oh, that's very different.... Never mind."

[Powerglide]

Pure BS. Solid state components don't drift. Vacuum tubes drift as do oil filled paper capacitors. Neither of which exist in an S30 ECU. The ethanol in today's gas and or fuel delivery issues are far more like the culprit causing your off idle/low rpm stumble.

[rcb280z]

That's why I posted the question. I'm no electrician but I didn't think it was possible. Interesting Powerglide...that you would say fuel type related. Never gave it any thought. Why would it have been all of a sudden. My curiosity is up now about fuel additives is SoCal. Didn't think it got cold enough for it. As far as fuel delivery, no problem there. Observed no change in fuel pressure at all. I can see my inline gauge under the hood scope from inside the car.

[siteunseen]

I get my fuel for my 4 vehicles from the same Gas Station. The '77 280 had a problem that was fixed by putting the potentiometer in line with the coolant sensor. I've actually done this. Maybe "drift" wasn't the right choice for a word so I'll just say it was broken and now it's not.

[Captain Obvious]

Pure BS. Solid state components don't drift.

Haha! You must be in Marketing or Sales. :laugh:

Seriously though... There's no way I would guarantee the performance of the ECU would be dead-nuts identical today as it was the day it left the plant almost forty years ago. No way.

Things are better than vacuum tubes and oil filled paper caps, but we haven't figured out how to get all the long term drift out of everything yet.

[rcb280z]

I still say putting a potentiometer inline is not "a fix" rather a mask to cover the problem. No different than making adjustments to the AFM IMHO. The problem is still there.