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Old 02-18-2021, 12:31 AM   #26
ZVOLV
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Get a test lamp
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Old 02-18-2021, 10:32 AM   #27
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Originally Posted by OldCarNewTricks View Post
ECU is receiving RPM signal
Jumper wire test at fuel-relay's receptacle that I mentioned above does not require a RPM signal. Relay is removed, and jumper wire inserted between Red and Yellow-Red wires. Fuel pumps will engage. I'd have to see this receptacle again, but I think I did this test to check fuel pump engagement.
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Old 02-18-2021, 11:32 AM   #28
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Jumper wire test at fuel-relay's receptacle that I mentioned above does not require a RPM signal. Relay is removed, and jumper wire inserted between Red and Yellow-Red wires. Fuel pumps will engage. I'd have to see this receptacle again, but I think I did this test to check fuel pump engagement.
Yes, if the bridge is gapped between the YR & R main power wires, the fuel pumps engage. Everything is receiving power as it should. The injectors are not receiving ground signal from the ECU (WH-GRN wire) as they should.

ZVOLV, I might have a test lamp somewhere, but I've mainly been using Fluke DMM, which is plenty sensitive enough to give me indication of issues.
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Old 02-18-2021, 05:29 PM   #29
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injectors are not receiving ground signal from the ECU...test lamp...
Ok...earlier it was about zero voltage at injectors.

6/12/24V CIRCUIT TESTER
ET112X
; used it for years....may be cheaper elsewhere.
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Old 02-18-2021, 06:10 PM   #30
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Ok...earlier it was about zero voltage at injectors.

6/12/24V CIRCUIT TESTER
ET112X
; used it for years....may be cheaper elsewhere.
Yeah, you were right in saying that the engine has to crank for the ECM to trigger the relays open.

Thank you for the link. That's a nice one, especially because it has the extra lead required to be hands free.

Does anyone know if the LH ECUs are repairable? I opened mine up and cleaned small corrosion spots off it, before I got it running. And the car isnt super watertight, so I'm thinking maybe moisture got back in or something. I'll have to test the RPM wire next weekend to make sure.
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Old 02-18-2021, 09:20 PM   #31
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..LH ECUs are repairable?
If the board's fitness is in tact, an old school Radio/TV tech should be able to do it. Capacitors tend to fail. There are shops repairing LH 2.3/4s overseas....don't know if one exists stateside.
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Old 02-18-2021, 09:21 PM   #32
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I think I have 4 LH 2.0 ECUs. Send me a PM if you would like to buy one. I’ll let one go cheap.
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Old 02-18-2021, 11:02 PM   #33
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So the test in the Bentley calls for the gray wire (RPM signal) to carry +8v to the ECM, but I did already test it at as 2manyturbos described, to check for continuity, then I also checked for resistance. Less than an Ohm, if i remember correctly. When I have time, I'll check for voltage.

It would honestly make sense, being the ECU, though. To go more into depth, the car had ants crawling through it. I actually saw what looked like a tiny ant nest in one of the holes of the ECU casing. So I bent back the tabs and removed the board. There was corrosion spots and moisture in a few small spots. I did my best to gently clean it with QD cleaner and a microfiber cloth. After putting it back together, new relays and spinning the fuses, it ran. I let it sit for the week, and I was going to take it home. Last week there was the ice storm in OR, and my 242 was in the open. There was moisture in the car again. The car ran sitting still for 20 minutes then died. So that's why I'm pretty sure the ECU is faulty.

If I get it running on a different ECU (fingers crossed), I'm interested to take the old one apart again and take a closer look at what's happened.
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Old 02-19-2021, 12:02 AM   #34
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The gray wire connects to the - spade on the coil. It's driven by the ignition box. It will be less than 1volt when the coil is charging (during the dwell time), and 12volts (battery voltage) when the coil is not charging. It will pulse between the 2 voltages twice per rev (i.e. 2 sparks per rev), so your meter may show something other than a simple 8volts.

If you have a tachometer, the gray wire goes to it too. If it's easy to get to, you could try unplugging the tachometer to see if the signal improves enough for LH ECM to detect cranking.
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Old 02-19-2021, 12:50 AM   #35
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The gray wire connects to the - spade on the coil. It's driven by the ignition box. It will be less than 1volt when the coil is charging (during the dwell time), and 12volts (battery voltage) when the coil is not charging. It will pulse between the 2 voltages twice per rev (i.e. 2 sparks per rev), so your meter may show something other than a simple 8volts.

If you have a tachometer, the gray wire goes to it too. If it's easy to get to, you could try unplugging the tachometer to see if the signal improves enough for LH ECM to detect cranking.
Good to know. I suppose I didn't relay the correct info. The manual says a minimum of 8v.

I don't have my tach installed yet.
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Old 02-19-2021, 03:13 AM   #36
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Default Injector pulse

Install a test lamp between a positive voltage source and an injector ground terminal. Crank. Blink?

Put a screwdriver handle to your ear and the tip to the injector. Crank. Click?

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Old 02-19-2021, 10:37 AM   #37
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"Runs on starting fluid". Make sure you have a working fuel gauge. Got gas?
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Old 02-19-2021, 11:49 AM   #38
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The injectors are out of the intake so I know they are not pulsing.

As for fuel, I did open the tank a few weeks ago to check condition of the in tank pump. It looked to have a good amount of fuel, but I can double check.
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Old 02-19-2021, 12:17 PM   #39
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The injectors are out of the intake....
At relay's receptacle, I would have tested, with that circuit tester I mentioned, the Blue-Green wire for a ground when engine was cranked.

Then tested coil's positive terminal for a pulsation voltage when cranked
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Old 02-19-2021, 12:51 PM   #40
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It sure sounds like the ECM isn't working. If it was working, it would turn on power to the injectors and fuel pumps, via the fuel pump relay #15, when cranking was detected. The problem could be the ECM is powered up OK, but not detecting the coil pulse. Or, it could be that the ECM isn't powering up.

With key on, have you checked for +12v power at the MAF? The ECM should see Key on, and should turn on the System Relay #9, which supplies power to the MAF. You can also check the intake manifold ground wires to make sure the ECM is properly grounded (not corroded).
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Old 02-19-2021, 04:35 PM   #41
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(Runs on starting fluid and NO injector pulse.)

You need to confirm good power, ground and RPM signal to the LH box at this point.

For testing power circuits, USE AN INCANDESCENT TEST LAMP. A meter is the incorrect tool. It can show 12v, but one strand of wire, or a corroded fuse, could pass 12V, but wouldn't pass enough CURRENT to illuminate a test lamp or operate the component
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Old 02-19-2021, 11:04 PM   #42
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After work, I chose to rip into town and purchase a test light. I then went to where my 242 sits. In the rain and dark, I went ahead and took all your suggestions and tested everything I could.

The MAF receives 12v (MAF pin 9)
The ECU is receiving 12v (pins 18 & 9)
The ECU is receiving good ground (pins 11 & 25, tested with test lamp, as well)
There is a good engine cranking signal (pin 4; minimum of 8 volts, receives ~9.37 volts)
There is RPM signal present (pin 1; any amount of voltage, recieved ~12.13 volts)
The fuel rail is receiving fuel (I gently pulled off injector clip, and pushed an injector to the side. It sprayed fuel out the side)

The things I found that did not test OK:
The O2 and RPM signal shielding showed continuity with ground, it should not.
The ECU is not providing the injectors with a ground.

I'm not sure why the shielding tested wrong, I will have to look into this further. I'm still leaning towards a faulty ECU at this point. Any thoughts?
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Old 02-19-2021, 11:28 PM   #43
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Was the ECU plugged in when checking the shielding continuity to ground? If so, your measurement is OK -- the shields are connected to ground within the ECU box. I think Bentley assumes that the ECU is unplugged and that you're checking at the harness connector.

Sure seems like trying a different ECU is the next step, but first, make sure that the RPM wire is connected to the - terminal on the coil (I know you said it ran briefly, but wires do have a habit of getting moved around during troubleshooting).

If you want, post high-res pictures of the circuits around pin 1 of the ECU circuit board (both sides), and I can try to guess what part may have gone bad.
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Old 02-19-2021, 11:32 PM   #44
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I took the ECU home and opened it up. I see small amounts of corrosion, but nothing burnt or anything that seems wildly wrong
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Old 02-19-2021, 11:38 PM   #45
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I have not moved the coil wires since it ran. I will check them again when I am around that.

Good to know about the shielded wire. Yes, it was when connected to the ECU.

I'll try to take a couple of photos of the board soon.
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Old 02-20-2021, 12:06 AM   #46
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I found one thing - a smashed up resistor. Rings are in this order: yellow, grey, silver, gold.
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Old 02-20-2021, 02:26 AM   #47
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Good! It sounds like you have diagnosed a failed LH box. You have power, ground, and some type of RPM signal. An oscilloscope would show you what that 8-9V signal REALLY looks like. Square wave/sine wave, glitchy pattern/good pattern etc.

I am glad you got a test lamp. I have a Fluke 87 V which I use for accurate parasitic drain measurements, accurate resistance measurements, MIN/MAX measurements, and the powerful VOLTAGE DROP TEST. For confirming power to a component, I use a test lamp and the proper terminal test probe. Be careful stuffing test equipment into female terminals, you can spread the terminal and cause a loss of terminal tension.

I would fire a fuel computer at it. 2ManyTurbos sounds like he can set you up with one.
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Old 02-20-2021, 11:07 AM   #48
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I found one thing - a smashed up resistor. Rings are in this order: yellow, grey, silver, gold.
Great, glad you found something wrong. Can you post a picture showing the bad resistor and some resistors around it? The colors you list don't match anything sensible for a 4-band color code (and it's often hard to decipher old faded markings). See wikipedia "resistor color code" for normal 4-band and 5-band codes. Alternately, you can measure the resistance on a good ECU (and the non-damaged one may be easier to read).
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Old 02-20-2021, 12:58 PM   #49
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The suggestion for use of a test lamp was very helpful, thank you. It simplified the process.

I'll try to snap a picture tonight, before it gets too dark (power is out right now). I was looking at that, and, yeah, its definitely uncommon. It's a rather large brown bodied resistor, so definitely 3-5w if I had to guess. It's one of the internal wire wound ones, from the look of it. It sits vertical to the board, free to move around, so I wonder if vibration did it's worst over time.
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Old 02-20-2021, 02:19 PM   #50
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Oh, I was thinking it was a little resistor, instead of a bigger wire wound resistor. I'd guess that the colors are yellow, violet (instead of grey), silver, gold, which would be 0.47ohms. This is still a pretty tiny resistance to be used in old designs. 4.7ohms (yellow violet gold gold) would be more common. I'd still get another ECU, and make the original a spare if you want to repair it later.
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