Strange Electrical Behavior (2 Viewers)

[Freeborn]

Team, I'm struggling...

Context:
I have a '78 with the original 2f, Sniper TBI, and a HEI distributor. I've been chasing a misfire under load for a long time. I think it's finally come down to just not having enough juice to the coil. When I ran a bigger "bat" wire to the dizzy I got a big leap forward, but not 100% of the time. 80% of the time 3rd gear acceleration is smooth and maybe 10% of the time in 4th gear. I feel it in the stick under load when it's running rough.

Symptoms and observations:
- max voltage is 13.1, average is maybe 12.9
- changing the voltage regulator to any aftermarket unit gives me >= 16V unless I turn on the headlights, at which point it might get below 14.5V
- I tried running a dedicated ground wire from the voltage regulator to battery (-) with no difference
- new alternator has made a very minor improvement to the misfire condition
- ammeter is at 0 with the ignition off, and constantly around +5-8 when running - like always
- changing the battery doesn't seem to change much with the original voltage regulator or new (i.e. ~13V and 16V respectively)
- when I get the misfire condition, the Sniper is running about -17% closed loop compensation (i.e. 1/6 less fuel, like a cylinder isn't burning gas)

So what would you do to diagnose the issue?

 

[1911]

Where are you measuring the voltage?

A good and charged battery should read 12.6 volts or more at rest (nothing on).

Staring the engine (and running it above idle) should be close to 14 volts at the battery, usually 14.6 or more at the alternator.

 

[zerotreedelta]

Running with logging enabled on the Sniper (with an SD card in the slot) might give you some concrete data to poke at - O2 readings, battery voltage, etc. Might be able to hone in on what might be related - seems likely to be voltage related, but it's always nice to remove some of the guesswork for something definitive.

 

[Freeborn]

Where are you measuring the voltage?

A good and charged battery should read 12.6 volts or more at rest (nothing on).

Staring the engine (and running it above idle) should be close to 14 volts at the battery, usually 14.6 or more at the alternator.

Voltage reading is coming from the Sniper, which is just across the battery terminals.

 

[Freeborn]

FWIW I also just went and checked voltage for all the inputs/outputs to the alternator and voltage regulator (key on, engine off) and nothing unexpected.

 

[charliemeyer007]

Just a thought, Volts are pressure, but work is accomplished by flow as in Amps.

 

[Freeborn]

Reference image… new alternator, new battery, old voltage regulator

 

[sggoat]

First law of troubleshooting is: what changed? Seems earlier the rig was running ok and now it's not--what changed? Did it just suddenly start the misfire? that would indicate a 'wear' issue. what do the plugs look like? Do they all look the same?-if one is cruddy, could prob be the plug or the wire. the coil would seem to be out of the question--if it's bad all the plugs would be misfireing-prob wouldn't even start--go back to the plug route - if one is cruddy-gap ok? or wire resistance all ok? if so, look at the dizzy-cap, any burn marks on the suspect cap connection? is the cap cracked anywhere? If all this is ok, now look at cylinder compression- are all within spec--if you have a vac gauge installed what does it do under the heavy load--do you see a flicker down when the engine mis-fires?--indicates a vlv adj is needed---just some things to check

 

[Freeborn]

First law of troubleshooting is: what changed? Seems earlier the rig was running ok and now it's not--what changed? Did it just suddenly start the misfire? that would indicate a 'wear' issue. what do the plugs look like? Do they all look the same?-if one is cruddy, could prob be the plug or the wire. the coil would seem to be out of the question--if it's bad all the plugs would be misfireing-prob wouldn't even start--go back to the plug route - if one is cruddy-gap ok? or wire resistance all ok? if so, look at the dizzy-cap, any burn marks on the suspect cap connection? is the cap cracked anywhere? If all this is ok, now look at cylinder compression- are all within spec--if you have a vac gauge installed what does it do under the heavy load--do you see a flicker down when the engine mis-fires?--indicates a vlv adj is needed---just some things to check

Right…more back story…
- new plugs, gapped
- new wires
- new cap
- new coil
- rebuilt motor (4 yrs ago)
- rebuilt transmission last year
- rebuilt rear diff last year
- fresh u joints

Nothing really changed recently other than changing the battery wire to the distributor to 10 gauge and realizing that it isn’t normal for the stick to rattle in third gear under load.

 

[Freeborn]

After spending lot of time studying wiring diagrams and measuring resistance across the wiring harness, I'm 90% sure that my wiring is just fubar'd. I think my path of least resistance (see what I did there?) is to just fashion my own harness for the voltage regulator.

Questions:
1. Does anyone have a resource for wiring connections? The 6-pin voltage regulator connection looks pretty unique to me. The 3-pin alternator less unique, but still not easily found with a quick search. (reference images below)
2. Am I better off just finding an aftermarket 6-pin and replacing the connector on the VR?
3. Does anyone know where the "charge warning light" is located? I haven't found anything yet.

 

[AlaskanWheeler]

@Coolerman will have all the OEM wire and connectors you'll need.

 

[peesalot]

PM firemedic831 on here, he has the trouble shooting thing down on these.

 

[Freeborn]

Follow-up question:
Is there a compatible alternator with an internal voltage regulator? It seems like that could save me a LOT of time and frustration.

 

[charliemeyer007]

Not a purest, but I am going to a one wire when the OEM dies. 105A for like $80 on amoron

 

[AlaskanWheeler]

Follow-up question:
Is there a compatible alternator with an internal voltage regulator? It seems like that could save me a LOT of time and frustration.

Yes, anything later model Land Cruiser will work.

 

[Freeborn]

Not a purest, but I am going to a one wire when the OEM dies. 105A for like $80 on amoron

Link? I didn't see anything obvious.

 

[charliemeyer007]

https://www.amazon.com/Alternator-Output-1-Wire-Self-exciting-ADR0151/dp/B07WY42G8X

 

[Firemedic831]

your IAC is high first get it up to temp 160 and then lets see where its at at idle

 

[Freeborn]

your IAC is high first get it up to temp 160 and then lets see where its at at idle

Good point. That’s exactly what the voltage and ammeter look like regardless of temp, though.

 

[POTATO LAUNCHER]

Look down the Sniper throttle body at the venturies with it running. Make sure both barrels are flowing a steady stream of fuel.
I had a similar issue with a customer's 40. The barrel closest to the engine / valve cover had a clogged injector. Cleaned it and it runs like a champ. I chased electrical for several days. Turned out real simple.