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Discussion Starter #1
As per my "is this as bad as I think it is" thread, so far I've found no mechanical issues. Timing marks line up, valves appear intact, crank turns freely and with no crunching our other sounds of internal distress. It was suggested I might be experiencing a critical ignition problem and I just got to wondering if MAYBE the fact I was under the hood working on timing when this happened wasn't just a coincidence, and that actually my ECU chose that moment to go belly up?

My question is, is there any way to test the ECU without just straight up swapping it? I'd rather get that out of the way before I proceed with further tear down, ie in situ head removal or even full engine removal. My herniated discs thank you for your response.
 

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No simple way that I know of. Generally, one tests all the input devices, makes sure their signals get to the ECU until the only fault remaining is the ECU itself. Then one replaces the ECU.

I have heard good reports (but no personal experience) about ECU Doctors. Both in that they can test and, if needed, repair our ECU's.
 

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There is no way that mechanical knocking noise is electric/fuel related. Though it does sound like a top end noise, don't be surprised if you have another major issue. It's easier to pull entire motor, I think, than to pull both heads. You can R/R motor without removing booster/master cyl. But to pull driver side head, you have to remove master/booster assembly which requires contorting under dash. If your back is bothering you, better get help. Either way it's tough.

It's possible your valves could still be "in place" and yet a chunk of guide could have fallen through. How did you check/test valves and valvetrain? Did you check for broken pushrods by loosening locking nuts and examining? Tappets still free in bores? Any cam lobes show excessive, recent scoring?

Compression test is still next step.

But to answer your question - the ECU in my experience is very, very reliable. It either works or it doesn't. Even though your car sounds terrible, it still "started" rather quickly and thus the injectors and ignition system (which uses a separate ECU/control by the way) is working. If you want to swap in an ECU be sure to get an early (81-83) spec. I can't remember the difference offhand but the later cars are different. It's possible each will run the car but not sure.
 

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The GTV6 ECU change 3 times: 81-82, 83, 84-86. The one you want is 0 280 001 113. You might be able to get away with an 83: 0 280 001 131. Bosch made a special testing meter for checking ECUs. Don't know how often they pop up on EBay.
 

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I have seen pictures of the Bosch tester. I don't believe it actually tests the ECU itself. It plugs in between the wire harness & the ECU & allows the technician to test the various inputs (and perhaps the outputs?) but it doesn't really 'test' the ECU the way I'd define it as a tester. Basically it does the same as one can do with a volt-ohm meter.
 

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Mr Chairman: I agree with the others that pulling your motor should be a last resort. Like Rob says, verify your valve train integrity topside before taking drastic action.

I suggest you do a compression test next. But even before that, check the intake rubber hoses for cracks or breaks. Did you inadvertently pull one off maybe when you were working?

Big bad air leaks on the intake side makes some God-awful noises, and shakes the works something scary. It's worth a look, right?
 

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Discussion Starter #7
I'd actually gone through all of the hoses, vacuum lines, and clamps, which knocked out a bad idle shudder I'd been experiencing. I was in the process of adjusting timing when this all went down.

I found a sweet little USB endoscope on Amazon for $20. Plugs into my shop laptop. Has 4 tiny LEDs. Hopefully if there's any junk in the cylinders this'll help me find it. That's coming Monday. I'll put off the compression test until then. Better safe than sorry.
 

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I have seen pictures of the Bosch tester. I don't believe it actually tests the ECU itself. It plugs in between the wire harness & the ECU & allows the technician to test the various inputs (and perhaps the outputs?) but it doesn't really 'test' the ECU the way I'd define it as a tester. Basically it does the same as one can do with a volt-ohm meter.
I've got one version of that tool called an "Autoforce Tester" and yes, pretty much all it does is let you simulate settings on various sensors. Very handy for testing whether the CTS, TTM etc. are bad.

Kevin
 

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I've got one version of that tool called an "Autoforce Tester" and yes, pretty much all it does is let you simulate settings on various sensors. Very handy for testing whether the CTS, TTM etc. are bad.

Kevin
Yes, my Bosch L-Jetronic manual basically says don't attempt to test the ECU. It should be only be judged faulty if compression, ignition system, and EFI components (including wiring) have been thoroughly tested and found good.
 

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Discussion Starter #10
Well, I'm still going through mechanical checks. Have a USB endoscopic camera coming tomorrow (UPS delivers on Sunday now?) so I can make sure there's no junk in the cylinders or damage to the pistons. Then compression check. Then I start actually disassembling the valvetrain.
 
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