ecu float

[FastWoman]

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.

Just speaking for myself, I bought the car running lean, and I fixed/replaced/verified/reconditioned EVERY part of the EFI, bringing EVERYTHING up to spec. And still I was running lean. And yes, I even tried real, non-ethanol gas, which makes a small difference, but doesn't really solve the problem. All that was left was the ECU. I bought another '78 ECU off of ebay, and the engine ran pretty much the same.

Then I thought about all the old electronics I've fixed/adjusted/restored in my lifetime, including tube-type, component transistor, and early linear IC. And I thought about the hostile conditions (lots of heat!) under which the ECU had to operate for decades. I've seen lots of drift in lots of components manifested in wonky calibration, as viewed on an oscilloscope. Components do drift, and semiconductors do break down. Even a linear IC, with its numerous feedback circuits, will ultimately break down. More significantly, add to that that capacitors lose their capacitance, and therefore charge faster than they should, hence faster voltage ramps and shorter trigger times. It made sense to me that the base pulse might be shortened, and so I took measures to lengthen it.

[rcb280z]

I guess its once again time to break out the diagnostic equipment and start trouble shooting the fuel injection AGAIN! Would be nice to go more than a year without problems.

So the reason I asked about the lean drift is because my Z has been running really good, great mileage and all. Was getting around 17 or 18 mpg in city and around 25 on the freeway. Anyone that lives in Southern CA knows that is good mileage. On a trip out one day recently I noticed surging on acceleration, and a rough idle. So when I got back to the house I popped the hood, its a 77 280, and looked at my fuel pressure gauge and fuel pressure is good. Checked timing, checked for vacuum leaks (pulling 18in), everything seemed fine until I pulled the plugs. They are usually a nice tan color and this time they look almost white! I'm assuming lean. So I started adjusting the bypass screw on the AFM and no change! I turned it all the way in and no change. I shut the car down and set the set screw back to where it was, I removed the cover from the AFM and loosened the screw holding the large "geared" wheel. Started the car and began inching the wheel counter clockwise and it was nearly a half turn (180 degrees) before I started noticing a change. Then it was running good. Plugs were back to normal, all seemed good until today. Now I think its running really rich! I did some running around town today and I can smell its rich now. Plus I burned through 1/4 tank of gas with a total of 35 miles. Not good. This is why I was asking about the lean drift issue. But, I don't see where anyone has had the same problem with it drifting out and then back. Which is what it seems like with mine. The only parts that haven't been replaced would be the ecu, EFI harness, dropping resisters, things you wouldn't normally have to replace. Here is what I replaced just over a year ago, the TTS, CTS, TPS, AAR, and their harness's and or connectors, injectors and injector connectors. She has been running really good until now. I have had injection issues with this car a few times now and they weren't easy ones to fix. I really haven't had the time to diagnose it this time not to mention I'm tired of having to diagnose injection problems. This was a quick run down of whats going on now. has anyone else experienced this before?

[FastWoman]

It doesn't sound like drift to me. Drift never goes back. It just keeps drifting in the same direction. It also happens gradually, not suddenly.

It sounds to me like an intermittent sensor problem -- perhaps a shorted air temp sensor, shorted coolant temp sensor, or some weird problem with your AFM. I suppose you could also have an intermittent vacuum leak, although it seems rather unlikely. Perhaps it relates to mode settings on your HVAC system? (One of your pneumatic control tubes could have broken or come loose.)

[rcb280z]

Forgot about the HVAC system. Better check that first. However, I don't ever use it here on the beach. Never need any of it. I think I'll get everything ready (Diagnostic equip and tools) and the next time it "drifts" for lack of a better description I will check everything and log results. I should go ahead and run through everything tonight so I have something to compare to later....to see if there are differences.