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Still Can't Get this Thing to Start #2

(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
 
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?
 
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.
 
I took the ECU home and opened it up. I see small amounts of corrosion, but nothing burnt or anything that seems wildly wrong
 
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.
 
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.
 
OldCarNewTricks said:
I found one thing - a smashed up resistor. Rings are in this order: yellow, grey, silver, gold.
Click to expand...
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).
 
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.
 
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.
 
bobxyz said:
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.
Click to expand...

I took another look at it. I was wrong. The "grey" is actually the second ring that is discolored from heat. This resistor must have split open from heat. It's burnt. On the other side, what's left of ring #2 seems to be sandy brown colored. It seems to be about the size of a 3 watt.
 
Woohoo! It runs. Turns out the ECU was the issue. Thank you to 2manyturbos for getting that replacement to me so quickly. Sounds to run a fair bit better than before, as well.
 
Drove it home finally. Bit sketchy with all the guage cluster lights out and the blower motor that died on me. But its home now, so time to get to work on all those smaller issues.
 
84B23F said:
Might have the ECU for B23F higher compression engine:-)
Click to expand...


LH ECU is the same for high and low compression. 1983 is a 503 number, 1984 is a 510 number, I'm assuming because of the added circuit on 1984 cars for the heated O2 sensor. OP's car is an Aw70 car, if I remember correctly, so it's already a flat top piston B23F engine in there, unless swapped.



Ignition box is different on low compression engines. More aggressive advance curve.
 
John242Ti said:
LH ECU
Click to expand...

ECU table suggests 503 is for NA 1983/1984, but I've wondered if engine program was twitched between AW70 and stick versions...since engines mated to AW70 were higher compression on 1984 (on engine I own).

Increasing the compression ratio changes the mixture density, but knock sensor may compensate so lower/higher compression engines work ok with 503 LH ECU.

I do know a rebuilt 1984 B23F that was mated originally to AW70 works just fine when installed in a 1993-940 with Rex-Regina, using Bosch 0 280 155 746 injectors ; of course, a CPS was installed on B23F.
 
84B23F said:
ECU table suggests 503 is for NA 1983/1984, but I've wondered if engine program was twitched between AW70 and stick versions...since engines mated to AW70 were higher compression on 1984 (on engine I own).

Increasing the compression ratio changes the mixture density, but knock sensor may compensate so lower/higher compression engines work ok with 503 LH ECU.

I do know a rebuilt 1984 B23F that was mated originally to AW70 works just fine when installed in a 1993-940 with Rex-Regina, using Bosch 0 280 155 746 injectors ; of course, a CPS was installed on B23F.
Click to expand...


Suggests is a good term. That ECU table is a crap shoot. Here is just one example of what I mean.

LH 2.4 -016 0 280 000-556 B230FD 1989 (EGR) 1989-1990 (EGR) - California / EGR Model: -937, -967 and -954 are suitable.

The B230FD didn't appear until 1993. A 556 is an NA 240-740 ECU with EGR. The suggested replacement ECUs are all 740-940 Turbo ECUs. The 937 and 967 are both non-EGR turbo ECUs. Suitable replacements would be a 933 or 946 NA ECU with EGR function. John is correct. 1983 US market NA 240s got the 503 ECU and 1984 got the 510.
 
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