Need some expert opinions on a weird situation I’ve discovered with a 60 2F stalling when I push the clutch in at HWY speeds (only with the AC on)

[fjc-man]

I know you’re desmogged under the hood, but the little emissions control circuit board could be malfunctioning or just needs the electrical pin connectors on the board resoldered. This “computer “ does turn the idle solenoid on and off on decel in conjunction air injection control. Been there, done that.

 

[CenTXFJ60]

I know you’re desmogged under the hood, but the little emissions control circuit board could be malfunctioning or just needs the electrical pin connectors on the board resoldered. This “computer “ does turn the idle solenoid on and off on decel in conjunction air injection control. Been there, done that.

Absolutely. Great suggestion. Actually have a bunch of notes written on a page back at the house and will add this one to it. Have one of those in my tote with 60 harnesses which is where I pulled the spare AC amplifier.

 

[Engineer8000]

I think the connection with the AC system is the compressor adds extra load, making the problem worse than when AC is not on. The only system affected by vehicle speed is air injection. I assume you have verified you don't have a legacy VSV opening giving you a vacuum leak when > 50mph?

Is your FCS hot wired or is it still controlled by the emissions computer? The decel/fuel cut comes in >1800 rpm and high intake vacuum (throttle closed). The 81+ emissions controllers are pretty reliable (except solder connections) but you never know. If you are still running the emissions computer, check the connector solder connections on the board.

 

[CenTXFJ60]

I think the connection with the AC system is the compressor adds extra load, making the problem worse than when AC is not on. The only system affected by vehicle speed is air injection. I assume you have verified you don't have a legacy VSV opening giving you a vacuum leak when > 50mph?

Is your FCS hot wired or is it still controlled by the emissions computer? The decel/fuel cut comes in >1800 rpm and high intake vacuum (throttle closed). The 81+ emissions controllers are pretty reliable (except solder connections) but you never know. If you are still running the emissions computer, check the connector solder connections on the board.

I appreciate your input and some good points. Your question about vacuum leak sparked an idea. I extended my vac gauge through the firewall yesterday so I could read it while driving. Everything seems good. At full throttle vac drops all the way down. Cruising it holds steady and as soon as I push the clutch in (at HWY speeds) vac jumps up to 17+. Of course while doing this my AC idle up is disconnected since I mount the vac line onto its port source on the intake manifold. Therefore the truck dies even easier than before. The FCS is not hot wired. Stock wiring still in place. I pulled the emission computer from the kick panel. Very clean in the A-pillar as well. I’m not an electrical expert but the board looks very clean as well.

 

[fjc-man]

Get a tested unit from Engineer 8000 or hard wire the solenoid circuit.

 

[Engineer8000]

Cracked solder joints can be hard to see without a magnifier. I always re-solder all of the connector joints just because of that.

I got out my test harness

These are your relevant connections

 

[CenTXFJ60]

Get a tested unit from Engineer 8000 or hard wire the solenoid circuit.

I assume you’re referring to the fuel cut solenoid. If it performs well being hard wired then where would that point me to as an issue to resolve? Is that controlled on the emissions computer board? And thank you for your input

 

[CenTXFJ60]

Cracked solder joints can be hard to see without a magnifier. I always re-solder all of the connector joints just because of that.

I got out my test harness

View attachment 4175432
This is awesome information. I hardwired the FCS and the truck performed correctly. This is good progress. I’ll send you a PM to find out next steps getting this computer board to you. Are there any other tests I should do prior to sending this unit to you? I believe I can find an emissions board somewhere around here and swap it in to validate it’s not a connection down or upstream. Can’t tell you all how much I appreciate the great insight and willingness to help


These are your relevant connections


View attachment 4175431

 

[Spike Strip]

If your engine is de-smog'd, and If your Idle Solenoid is 'Hard Wired' meaning the WHITE wire from the solenoid is grounded to the carb, then the emissions computer is by-passed, for the ICS. The ICS controls thru a ground switch. Key On, Engine Running should be constant 12v to the Green wire of ICS. You've posted no pix, but I'm assuming the Decel Cut switch that was on the fender with the ABV assy was removed.

I believe the A/C Amp gets an input signal from the Tach. The tach signal wire is the YELLOW wire of the TWO wire bundle to the coil. Just spit-balling here, but here but there may be something in the wiring that's killing juice or feed to the Coil/Igniter/Distributor when A/C switched on at speed. Does the engine stall when A/C turned on at idle ? (sorry too lazy to read back thru everything)

Try disconnecting the TACH wire and run the truck and see if there's a change.

 

[Lead Head]

Ah yes. It’s still on both the carbs involved. Thank you for clarifying.

View attachment 4173640

Does it work though? It should damp and slow the throttle closing.

 

[CenTXFJ60]

Quick recap and apologize for the slow responses. My day job takes a lot of time so I get very few hours in the shop and on MUD. This is a good thing as it’s my own business and it’s been rocking the last year or more. Hence this being my first thread activity since maybe September of last year. So I swapped the emissions computer with one in a spare harness tote. Truck works as it should. I ran it hard for about 25 miles and never died once. Before the switch it would die 80-90% of the time I took the load off the drivetrain at HWY speeds with the AC on. All of you have been invaluable helping me inch down the path to find the issue. Truly appreciate it

 

[CruiserTrash]

@Engineer8000 It's so difficult to tell looking at photos, but are these solder joints cracked? Circled in red...

Those don't pertain to the FCS as you showed above, but ... are these traces cracked? Hard to tell if it's just the edge of some pooled flux or what. Again, circled in red - and at least one of those pertains to the FCS portion of the circuit.

I used to fix tube amplifiers for a long time and I had a 60s Ampeg that took me forever to figure out, it was my white whale. It ended up being hairline cracks in the PC board that made traces intermittent. I pulled my hair out over that one, but when I finally spotted it and jumpered over the cracks everything worked perfectly.

 

[Engineer8000]

Hard to tell, worth touching up anyway. I have never seen a cracked or broken trace on a denso board. You usually see that on larger boards with heavy components, like a flyback transformer on a portable TV set board. Your TV would work fine when first turned on then act up when things get warmed up. I have an LCD magnifier that helps a lot searching for things like that on circuit boards. Cold spray and a hot air blower come in handy too.

You see crazy stuff sometimes, like glue or heat sink compound becoming conductive over time. I always remove the original glue they used to hold components in place during wave soldering.

 

[CruiserTrash]

Hard to tell, worth touching up anyway. I have never seen a cracked or broken trace on a denso board. You usually see that on larger boards with heavy components, like a flyback transformer on a portable TV set board. Your TV would work fine when first turned on then act up when things get warmed up. I have an LCD magnifier that helps a lot searching for things like that on circuit boards. Cold spray and a hot air blower come in handy too.

You see crazy stuff sometimes, like glue or heat sink compound becoming conductive over time. I always remove the original glue they used to hold components in place during wave soldering.

Sorry to get off topic, but I've had boards go conductive before from heat. Again, big B+ tube circuits, the dropping resistors get HOT and char the board. Now adjacent traces conduct through the charred area. Had that on the same Ampeg as well as several other amps over the years. Non-conductive stuff getting conductive is a fun one to solve!

 

[Couvi79]

Sorry to get off topic, but I've had boards go conductive before from heat. Again, big B+ tube circuits, the dropping resistors get HOT and char the board. Now adjacent traces conduct through the charred area. Had that on the same Ampeg as well as several other amps over the years. Non-conductive stuff getting conductive is a fun one to solve!

I am having a very similar problem on our 85. My truck intermittently dies when shifting into neutral from highway speeds and slowing down from normal in town driving. It generally fires back up but sometimes needs to sit a bit before it will. Seems to be more of an issue when it has rained, but that could just be coincidence. Not sure if it is related to AC being on or not, but will pay attention more. I have checked for vacuum leaks and everything seems fine there. I am checking the fuel cut off solenoid this morning.

 

[CenTXFJ60]

Problem is finally fixed. I sent the computer board to @Engineer8000 and he gave it a clean bill of health so unfortunately that was not the issue. I have not been on mud the last week or so but the truck started dying again. Exact same symptoms. So Russ recommended I clean the terminals and they were already as clean as everything else on this truck. My oldest son (he’s a Toyota tech in CO and has several cruisers of his own) and I were brainstorming on this last night and we concluded this is happening at operating temps and not when the engine is cold. So I ohmed (spelling???) the ground wire going to the FCS when cold and it was not perfect, but it was close enough for continuity. Ran the truck and it died several times once temps were up. Ohmed the wire when hot and the #’s were haywire. Bypassed the ground and truck runs awesome. If I feel energetic enough I may go through the harness and find the weak spot but for now it’s grounded to the carb fan bolt on the wheel well. Idle never drops below the carb settings no matter how hard I run it. Chasing a solution is at times like using the funnel process. Everyone here and Nate @mattressking along with my son were a big part of working the funnel. Truly appreciate everyone’s input.