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Old 12-24-2018, 11:21 PM   #101
Harry Tuttle
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That was a nice easy fix. Sounds real good.

If you find that you can't resist upgrades, I am kinda lookin' for a complete B20 breakerless ign system...
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Old 12-25-2018, 01:14 AM   #102
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FYI, Volvo still sells that 2 wire harness, but it's pricey at $182.00.

However, Dave Barton has an excellent copy of that harness for $30.00.


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Thanks for the idea...it was sort of acting like fuel starvation, but luckily I think I've solved it without having to break out K-jet tools!

Took some time today to carefully go through the ignition system. I had good incentive to get the car running again, since it was dead in my driveway and blocking all access. I followed the ignition troubleshooting flow chart in the factory service manual, to start with.



Step 1: "Run starter and hold high tension lead from coil approx. 3/4" from engine ground. Spark available?"
>>Result: kinda sorta... spark is "available" sometimes. Although it didn't seem consistent, it would indeed arc from the coil wire to the engine while cranking. I thought maybe the issue was intermittent spark, so I proceeded down the "No" path.

Step 2: "Check if coil terminal 15 is live by connecting voltmeter across it and ground. Coil terminal 15 live?"
>>Result: yes, I got something like 8 volts at terminal 15 (power side of coil) with ignition switch in position 2.

Step 3: "Check the voltage drop across the transistor [resistor?] by connecting voltmeter to coil terminal 1 and ground. Voltmeter reading 0.5 - 2.0 volts?"
>>Result: yes, it was 1.something volts at terminal 15 with switch in pos. 2.

Step 4: "Check impulse sender [inside distributor] resistance by connecting ohmmeter across terminals 7 and 31d in removed connection plug [at the breakerless ignition module connector]. Correct value at 75F is 950 - 1250 ohms for the 240. Impulse sender resistance correct?"
>>Result: yes, I measured 1000 ohms.

Step 5: "Check for grounded circuit in coil of impulse sender by connecting ohmmeter to one of the impulse sender terminals and ground. Reading should be indefinite [open circuit]. Coil grounded (ohmmeter reading not indefinite)?"
>>Result: no, the impulse sender coil wasn't grounded when I checked. But this step did get me interested in the 2-wire harness going to the distributor. Sure enough I found them bare and touching each other right where they go into the connector. I spread them apart thusly:



After this, the B20 fired up and ran fine. No random stalling, no misfiring. So I'm pretty confident it's mystery solved. I should probably figure out a way to heat shrink or otherwise insulate these two wires so they don't short anymore.

In the process of checking all this stuff I removed the ignition module, cleaned behind it, cleaned all the pins in the connector and the module, removed about 5 lbs of dirt from inside the shock tower, cleaned up all the grounds in this area, and reassembled.
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Old 12-28-2018, 12:06 AM   #103
Duder
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Originally Posted by planetman View Post
FYI, Volvo still sells that 2 wire harness, but it's pricey at $182.00.

However, Dave Barton has an excellent copy of that harness for $30.00.
Thanks for the tip, Eric! I had no idea that Dave sold any harnesses for a 75.
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Old 12-28-2018, 12:42 AM   #104
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The same harness fits all 240's with breakerless ignition so it's not specific to '75. I think we have one in stock.

If you want to check the fuel pressure, hit me up. I have the factory tools.

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Old 01-02-2019, 01:22 PM   #105
Duder
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Thank you, Ian. That may come in handy. I drove the 75 today and it's back to the same stalling behavior, so my 2-wire harness theory wasn't quite right. I'll check spark again first. It did seem erratic from the coil when I tested it last time.
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Old 01-03-2019, 02:57 PM   #106
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Seems like it's back on the road now...

Yesterday I verified that all the ignition control connector pins look ok. The car went totally dead after a few more tries. Then remembered that I had another breakerless ignition control module in the garage left over from my '81 242. Went back to the 75 this morning to verify that it was still dead...it cranked over fine but wouldn't start at all. Then swapped to the later -018 module, and it instantly fired up and seems happy. So maybe (fingers crossed) it's fixed for good now. Thanks to Eric and Ian for the pointers!
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Old 01-03-2019, 04:54 PM   #107
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Old -005 box out of the car. Roadmaster to the rescue. Ian suggested that this may have failed due to cold solder fatigue, so I'll open it up and see what I can see. Might be worth trying to repair.



New -018 box dusted off and installed. Case is cracked but the B20 is running great again.



For future reference, there's an interesting page about the breakerless brain box on the cleanflametrap site.
http://cleanflametrap.com/breakerless.htm

Last edited by Duder; 01-03-2019 at 06:14 PM..
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Old 01-09-2019, 01:55 AM   #108
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Ive replaced that box with a GM 4 pin HEI module with success. It bolts right up to a heatsink from an 89-93 240 or an 85-95 7/940. It is made by Bosch for GM.
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Old 01-09-2019, 01:57 AM   #109
Duder
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Ive replaced that box with a GM 4 pin HEI module with success. It bolts right up to a heatsink from an 89-93 240 or an 85-95 7/940. It is made by Bosch for GM.
Interesante. Good to know, and makes sense I guess since the HEI wiring diagram looks very similar to the Volvo / Bosch breakerless system. I'll keep that in mind for next time it dies...
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