Has anybody attempted to repair their ECU?

[Captain Obvious]

The cold start valve is completely independent from the ECU. It's driven solely by a couple relays and the thermotime switch. I'm betting your ECU is stone dead and you're running off the cold start spray for a couple seconds.

And for testing purposes, you don't need a Schottky. Any diode capable of handing the current requirements would work just for a proof of concept test. If the 1N4005 (I'm assuming you meant 1N4005 and not 1N005?) didn't work, you've got problems more significant than just the diode. No surprise there.

[sscanf]

Right 1N4005.

There's a test case for someone that is wondering about their CSV/Thermotime - With a cold motor, unplug your ECU and see if you get a couple of seconds of run time: None is bad (but ambient temp matters) and more than a couple of seconds is bad.

More work to do. I will have to pick at it over time. I'll get that spreadsheet started though. These are the columns I plan:

All tests will be done initially in circuit and redone as necessary out-of-circuit

Resistors Sheet

ID, power rating, marked value, measured Resistance (in circuit), measured Resistance (out of circuit)

Diode Sheet

ID, Marked Type, fwd, rev

Transistors Sheet

ID, Marked Type, B-E fwd, B-E rev, B-C fwd, B-C rev, E-C resistance (maybe more)

Caps Sheet

ID, Type, Marked value, in-circuit measured resistance, Measured value (only if I take it out - I don't have one of those fancy in-circuit capacitance measuring devices - also my experience with capacitance measurement is not good but I haven't done much either - if I take a cap out its usually because its melted or measured as short in-circuit - and there is no good explanation that it isn't melted).

Other Sheet

ID, Type, in-circuit resistance measurements, ?

I'll probably pull my working ECU and compare some measurements if I don't find anything of interest.

Edited June 19, 2014 by sscanf

[Zed Head]

Woof. That's not good... That used to be diode D190 and based on where it's located in the circuit schematic, I'm guessing it's a Schottky.

Supposed to look like this:

It's the main power feed into the ECU and the input side is hot any time the fuel injection is operating. I'm thinking reverse polarity protection for the whole shebang because it's in right at the supply input and feeds just about everything.

So... Yours passed way too much current and went up in smoke. Problem is though... What was it that was demanding so much current that the diode gave up? The diode probably isn't the underlying problem, it's probably just the result of the underlying problem.

Interesting that the resistors in the upper left of your picture are different than the ones in Post #21.

I have several ECU's that I've collected. I'm going to open them up and see how things compare, so if anyone wants a picture I can get it.

I actually fixed one that had the two (or one of the) main injectors go bad by replacing them with my best guess. The failure symptoms, holding the injectors open, seemed to indicate that and I got lucky. I know very little about electronics.

[Captain Obvious]

Interesting that the resistors in the upper left of your picture are different than the ones in Post #21.

What makes you think the resistors are any different?

But before you answer... The fact that mine have a gold stripe on the end while the ones that sscanf posted have green and blue? Take a look at the other end of the resistors in sscanf's pic. Mine were just assembled the other direction. No difference, just mechanical 50/50 pseudo randomness.

So if that's what caught your eye, don't worry about it. Direction on the resistors makes no functional change.

[Captain Obvious]

Before I forget though... It's clear that the two ECU's are from a different run. On mine the feedthrough wire connections are labeled "U sub n" (U1, U2, U3...) You can see U9 and U15 on mine for example while sscanf's are not marked in any way.

It's clear that the silkscreen markings of the two different boards changed along the way, and I can tell you from experience that nobody changes just the silkscreen. It's too expensive. I'm sure there are some copper changes somewhere between the two as well. Might not be extensive, but I'd bet good money that something changed.

[Zed Head]

You're right, I assumed that the green on the ends was a stripe. There's not enough information in your picture to tell.

I wonder if there was enough variation in components that the final parts were chosen based on test results. Add up a bunch of plus tolerances or minuses and maybe the end result is out of product spec. Just a thought. Considering the injector open times are so small, it's incredible that they could build a functional board "solder by number" alone. Who knows.

[Captain Obvious]

I wonder if there was enough variation in components that the final parts were chosen based on test results. Add up a bunch of plus tolerances or minuses and maybe the end result is out of product spec. Just a thought.

I have no doubt the final parts were chosen based on test results. In fact, I guarantee it.

Look at the resistors below the burned diode. See those metal stands with the resistors soldered to them? Notice how most of them have two resistors soldered to each stand (putting the two resistors in parallel)? Notice how one of them is always a significantly higher value (order of magnitude) than the other?

The reason for that is... You put the lower value in place and then tweak the value down a little more by soldering a higher value resistor in parallel with the first based on test results. The lower value is "standard" and is probably the same on all the ECUs of the same generation, but I bet the higher value resistors change from one ECU to the next as determined on a test fixture at the factory.

[Zed Head]

Makes sense. I see also that sccanf's has an extra D315, right below the burned diode. Missing in yours.

Looks like a tough puzzle. I wonder if one of the old Nissan diagnostic testers would help with the project.

[superlen]

sscanf

I think once you dig in to it, you'll find the drift is actually in the multivibrator stage, not in the conditioning circuit from the CLT sensor. Not the entire multivibrator just the section that the CLT conditioning circuit feeds. Note: This is just my gut instinct as I didn't do a lot of digging back when I was investigating. That was several years ago.

As you might guess, I have craploads of old boards. If you want, let me know and I'll send you a care package. This will give you a bunch of spare parts and several copies to do some comparisons with. I've already thrown away about a dozen I bet, but don't worry I have more. I cut the wires soldered to the output transistors & the cable that connect the two so if you wanted to put them back together in your box & actually fire them up, you'll have to do some soldering.

+10 on what Zed, Fast, and Captain said. No electrolytic caps which is one of the reasons these ECUs are still even halfway working today. Electrolytics have there place in the world, but not in automotive applications.

While you are in there, if you wanted to detail and create a schematic of their coil input conditioning circuit, that would be interesting to see as well. Captain and I both did some theorizing and testing on it, but I never traced it out. I'm not sure if Captain did or not.

Lenny

[sscanf]

OK. Will do what I can and bug you guys when I get stuck - I guarantee this will not be an overnight thing. Too much other stuff to do but I will pick at it over time. I may take you up on that care package though. Stay tuned. I'll post my attempts at progress in this thread as time goes on.

[superlen]

10-4.