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Mechanic retired, now have slight engine miss
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Slip356
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PostPosted: Fri Aug 20, 2021 11:55 am    Post subject: Mechanic retired, now have slight engine miss Reply with quote

Here’s the detail:62 356 B Cab engine professionally rebuilt with big bore kit 10 k miles ago. Rebuilt distributor with new cap & rotor & 6 volt Petronix 3k miles ago. Valves adjusted 200 miles ago, plugs have 4K miles. New rubber fuel ines and viewable in line filter about 3k miles ago.
Here’s the problem. When engine is fully warmed up after 1/2 hr driving in 85 F temp a slight miss fire occurs sporadically.
I cleaned the dist cap internally by polishing the contacts & rotor after a
Just completed 1,400 mile trip in 90F temp and car ran perfectly until about 100 miles from home when the slight misfire started.
I’ve heard petronix ignitors are either working or not? True? Is this likely the issue?
Could it be the coil?
Ideas?
Thanks,
Slip
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60ragtop
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PostPosted: Fri Aug 20, 2021 5:41 pm    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Is this a new problem?
I have read Pertronix doesn't play well with 6 volts. try putting your points back in it.
Also check the continuity for the plug wires especially the coil wire
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Certified Mechanic by the State of Michigan in 1977
ASA certified in 1987
Certified Hunter Wheel Alignment Master Technician 1986

tasb wrote:
I've restored a large number too, but I don't toot my horn quite as loud.


sb001 wrote:
maybe he just snapped cause his car sucked Wink
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Slip356
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PostPosted: Sat Aug 21, 2021 4:48 am    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Thanks Rick,
I purchased new plug wires, cap & rotor from Stoddard, just don’t like throwing new parts at it without knowing the actual problem. As indicated in earlier post, problem just started as I was finishing a 1400 mile drive in 85 F temps. I’ve owned the car for 15+ years and haven’t replaced the plug wires, that might be the problem.
Will check continuity in plug wires including coil wire, looking for abnormalities and put points back in.
Will report back.
Slip
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Starbucket
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PostPosted: Sat Aug 21, 2021 3:24 pm    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Look at your plugs, you might have a slightly plugged jet. Look at the color. Maybe a carb has loosen up and you have a small air leak. What RPM does this happen?
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Slip356
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PostPosted: Sat Aug 28, 2021 4:32 am    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Still working on this problem. Went for a 40 mile lunch ride Tuesday. At steady 50-70 mph on level ground, no slight miss. When accelerating thru the gears, or up a hill the stumbling occurs. Replaced the coil wire with a new one, very slight resistance difference, no change.
Will have time in next few days for a ‘deeper dive’ into it.
Will report back.
Slip
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janerick3
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PostPosted: Sat Aug 28, 2021 7:43 am    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

If you are running Zeniths, check the inlet ports for bits of rotted rubber from the old lines. This will cause stumbling only when the engine is warmed up, so people waste lots of time and money chasing non-existent ignition system problems.
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Starbucket
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PostPosted: Sat Aug 28, 2021 8:09 am    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

If the stumbling happens as you are pressing down on the gas peddle check that the accelerator pump jets are squirting as soon as the carb starts to open, adjust until they do as no squirt or delayed squirt will cause a stumble.
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Slip356
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PostPosted: Sun Aug 29, 2021 5:01 am    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Am running Weber’s that were rebuilt within the last year. Have new rubber fuel lines and in line viewable glass filter under the car. Installed spare points distributor yesterday. Will start & time today & test drive. Will report back.
The 6 V Petronix is two years old with a 30 month warranty. Will have to search for the purchase receipt.
Thanks for the suggestions so far.
Slip
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vwoldbug
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PostPosted: Sun Aug 29, 2021 8:40 pm    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Have you checked the running voltage yet.
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Slip356
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PostPosted: Mon Aug 30, 2021 4:52 am    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Problem fixed, we’ll almost! Installed spare distributor with points, set dwell & timed engine, went on 30 mile drive, no more stumble, yea. Spare is an aluminum 09 distributor that was on my car when I bought it, replaced with correct rebuilt cast iron unit. Need to remove Pertronix unit and install points in correct unit.
Petronix is 24 months old with a 30 month warranty. Purchased from Amazon, will find receipt and send back to them. Ring magnet came off shaft too easily as it’s supposed to snap in. I have a spare ring, will be examining for problems.
Will report back
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Slip356
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PostPosted: Sat Sep 11, 2021 4:59 am    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Making more progress, miss is gone with points distributor however I like the simplicity of electronic module. Called Petronix, tech was very helpful, indicating modules either work or they don’t, like a light switch, so my problem is not the module.
He suggested three electrical tests:
1. Voltage on + terminal on coil should be minimum 4.5 volts when cranking engine with coil wire pulled, cranking only, no start. Mine showed 5.2 volts.
2. Ground, negative bat terminal to base of module should not be over 0.2 ohms.
Mine measured 8.6 ohms on the 200 ohm scale. More work is necessary here as this likely is the problem.
3. Positive to negative on coil should be 3 ohms or less. I have three 6 volt coils,
Readings are 1.7, 1.4 and 1.5 so all good here.
4. Positive to center of coil, where the coil wire attaches should not be over 10K ohms. Mine are 8.2, 8.98 and 8.5K ohms so all good here as well.

Started & timed car yesterday with module but ran out of time so didn’t drive car. Will clean negative battery terminal, both ends and transmission ground strap today and repeat test no. 2 above.
Will drive car and report back.
Fingers crossed.
Slip
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Slip356
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PostPosted: Sat Sep 11, 2021 11:10 am    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Well, good news, found the problem!!! Battery cut off switch which I use on all my cars was slightly corroded, cleaned it up and the negative battery terminal and resistance went from 8.6 ohms to 0.6 ohms. Still a bit high (see test 2 above)but miss is gone. Pertronix tech indicated moduals are very suspatable to voltage especially 6V cars like mine.
Will need to check/clean trans strap to body yet but had the trans out early this year so don’t expect much change.
You know what they say, With new electrical problems, always check grounds first.
Slip
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60ragtop
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PostPosted: Tue Sep 14, 2021 12:45 pm    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Slip356 wrote:
WPertronix tech indicated moduals are very suspatable to voltage especially 6V cars like mine.
Wink
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Certified Mechanic by the State of Michigan in 1977
ASA certified in 1987
Certified Hunter Wheel Alignment Master Technician 1986

tasb wrote:
I've restored a large number too, but I don't toot my horn quite as loud.


sb001 wrote:
maybe he just snapped cause his car sucked Wink
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Slip356
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PostPosted: Tue Sep 21, 2021 2:00 pm    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Problem now fixed, as it was two things:
1. High voltage resistance at battery shut off switch due to what appeared to be minor corrosion. Tested between negative battery terminal and base of Petronix module. See earlier post for readings both with and without bat switch.
Thought that solve problem but when installed cast iron correct distributor with Petronix, timed engine it ran like crap, backfire, hiccups and no power.
2. I had read a while back that coils can fail when heat soaked even if coil resistance checks out when cold. So I changed out the Bosh blue coil that has been on the car for several years with a spare Bosh black coil that was on it when I purchased it 15 yrs ago.
Just came back from a twenty mile drive. Both in town & at highway speeds, no more miss, car ran perfectly. YEA!
Remember, Petronix modules need steady clean voltage, especially 6 volt cars like mine.
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Jon Schmid
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PostPosted: Fri Sep 24, 2021 7:34 pm    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Dude, it's "Pertronix."
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Slip356
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PostPosted: Sat Sep 25, 2021 5:25 am    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Just a test to see if anyone was reading! You are.
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Jon Schmid
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PostPosted: Sat Sep 25, 2021 7:28 am    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Slip356 wrote:
Just a test to see if anyone was reading! You are.
Slip


LOL Very Happy
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roy mawbey
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PostPosted: Sat Oct 02, 2021 7:05 am    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Well that was a most interesting read and pleased you really found the problem and solved it. I had a few years a problem with a slow turn over when hot on my 356A. After checking every earth, changing the bellhousing bush and checking starter brushes in the end, after nearly pulling my hair out it turned out to be the starter solinoid contacts hidden underneath the soldered on cap I have never removed in over 50 years.

I would like to say I was brave enough to remove that soldered on? cap but no a good electrical guy on 356 starters did that and saw the dirty burnt contacts. I had began to think field windings armature problems but no, just dirty contacts.

He replaced the cover with four nuts and bolts and after I re-inserted the starter the difference was unbelievable hot or cold since then the starter speed is perfect.

Mine was not the same problem as yours but in principle it was, as 6volts need perfect clean connections in the circuit to get the best result.

I bet you were as pleased as I was to see that solved !!

Roy
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Slip356
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PostPosted: Sun Oct 03, 2021 5:02 am    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

Good on you for sticking with the problem till you found it.
Well, my problem is not fixed! Went on an 40 mile lunch ride with my buddies, 72 F temps. On the way out car ran perfectly, however on the way home the occasional engine miss occurred again, damn! The problem occurs when engine is heat soaked.
I think I’m done with 6V pertronix and will be replacing with points & condenser.
Will report back.
Slip
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Slip356
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PostPosted: Thu Nov 11, 2021 6:31 am    Post subject: Re: Mechanic retired, now have slight engine miss Reply with quote

UPDATE, after five weeks away from the problem (bought a 2016 Boxster Spyder that took all my car time) I’m back at it. 356 was lonely sitting in shop, looking like it might cry from lack of attention.
I reinstalled battery cut off switch after throughly cleaning it (I have those on my cars & like to shut off battery when car is stored) left Pertronix in because I like them, put in new plugs, dist cap & rotor & went for 25 mile town/highway drive in 40 F temps. No engine miss!!
Due to colder outside temps, engine might not have ‘heat soaked’ when past problem occurred but winter has arrived in No. WI with snow and salt not far behind. It’s raining/sleetingthe next few days. May have to wait till spring for final evaluation.
Love the ‘new to me’ Spyder and the 356, can a guy have two lovers??
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