62 Fuelie with Pertronix troubles

[Duke W.]

See next post

[Duke W.]

I suggest you follow a logical troubleshooting procedure.

Old ignition coils are known to get "flaky" when hot. Borrow a known good one if you can and test.

Non-ethanol fuel probably has less tendency to percolate than E10, but if you've owned this car for some time in the same location and this is a new problem then I doubt it's percolation.

Don't think that a carburetor is a solution. They, too, are prone to percolation, maybe more so than FI engines because carburetor/manifold systems have heat riser systems. FI engines do not.

A 160 thermostat likely won't help as it only controls the lowest engine temperature, and 180 thermostats will better purge blowby from the crankcase. If your engine just has a road draft tube, it already has more tendency to retain blowby and contaminate the oil more quickly than engines with properly designed and functioning PCV systems.

Use some long test leads to rig up a voltmeter or dwell meter in the cockpit that you can read while driving. Connect the positive voltmeter lead to the ignition coil and the common lead to any good ground. If you use a dwell meter follow the instructions.

If the voltage dwell remains constant when the engine acts up, the problem is likely a fuel system issue, but could still be the coil. If the voltage or dwell start jumping around, it's likely an ignition circuit problem.

Duke

[Richard L.]

Coil is good because I already changed the original one for a known quantity. Nevertheless, I'll rig up a dwell meter that I can read while driving and note any change in the readings.
Aviation gas price is not the issue, getting it from the closest airport is--miles away, tail number required, pumping it into 5-gallon cans, dirty looks from nosey individuals, questions from less-than-helpful airport attendants. However, I'll do it if it means leaving the Injector on, although it does effectively limit my driving range.
For my own peace of mind I'll check and see what thermostat is now installed, fan belt tension, radiator hose condition and any airflow obstruction.
I doubt that my electric fuel pump installation has anything to do with this.
I will also check/change the FI fuel filter and the in-line fuel filter installed in front of the electric pump.
All will be done sequentially, of course, to be scientific about it.
What else can I do?

[Jim L.]

The bad part is that the initial issue persists--runs good for 10 to 11 miles, till it warms up (180 degrees) and then it begins missing, won't idle and dies without working the gas pedal. A fellow FI owner who currently converted his to carburetor assures me that our winter fuel blend is percolating and causing my troubles, that May 15th is the start of Colorado's fuel summer gasoline and that should make all of the difference. I neither want to put my Injector on a shelf nor wait for our summer gas blend.

Any ideas that will extend my driving range from 10 miles to 110, LOL?

Here are some useful things to know about fuel perc in Rochester FI:

1. Perc is possible ONLY when the engine is idling.

2. As long as the engine is under a load (i.e. causing the car to move) fuel perc can NOT happen. If your engine acts up while under load, you do NOT have a fuel perc problem.

3. When fuel perc happens with a carbureted engine, you are stuck until the engine and fuel cools. With a fuelie, if perc happens, start driving and perc will immediately stop. Immediately, as if someone flipped a switch. Switching to a carburetor would be a step backward in the battle against fuel perc.

4. With the winter blend of CA motor fuel, FI fuel perc can happen at engine idle at ambient temps as low as 65F. Colorado winter motor fuel might be similar. I don't know.

With these facts in mind, what is the engine doing when it acts up? Idling only? Under way? What has been the ambient temperature when the engine acted up?

Expiring minds want to know......

[Richard L.]

Here are some useful things to know about fuel perc in Rochester FI:

1. Perc is possible ONLY when the engine is idling.

2. As long as the engine is under a load (i.e. causing the car to move) fuel perc can NOT happen. If your engine acts up while under load, you do NOT have a fuel perc problem.

3. When fuel perc happens with a carbureted engine, you are stuck until the engine and fuel cools. With a fuelie, if perc happens, start driving and perc will immediately stop. Immediately, as if someone flipped a switch. Switching to a carburetor would be a step backward in the battle against fuel perc.

4. With the winter blend of CA motor fuel, FI fuel perc can happen at engine idle at ambient temps as low as 65F. Colorado winter motor fuel might be similar. I don't know.

With these facts in mind, what is the engine doing when it acts up? Idling only? Under way? What has been the ambient temperature when the engine acted up?

Expiring minds want to know......

Jim, Under your #2, the second sentence contradicts the first one. Could you clarify please?
ric

[Jim L.]

Jim, Under your #2, the second sentence contradicts the first one. Could you clarify please?
ric

The ONLY time fuel perc can happen is when the engine is idling, say, at a stop light.

Once you put the engine under load by driving away from that stop light, fuel perc is NOT possible. Not even a little bit.

I can explain why, if you are interested, but my main point is that statements #1 and #2 are not contradictory.

[David H.]

... The bad part is that the initial issue persists--runs good for 10 to 11 miles, till it warms up (180 degrees) and then it begins missing, won't idle and dies without working the gas pedal. ...

Richard

How is your ignition wired?

Specifically, your resistor that runs to your coil.

Have you checked resistance of that resistor?

Has many have indicated, sounds like coil is heating up. e.g. 12 volts to coil at all times as opposed to 12 volts only when starter is engaged.

Dave

[Jim L.]

Jim, Under your #2, the second sentence contradicts the first one. Could you clarify please?
ric

I think I've realized what seems contradictory about my statements in #2. So let me try again.

Since fuel perc CAN NOT HAPPEN while you are driving, if your engine runs poorly or dies while you are driving, the cause is something OTHER THAN fuel perc.

Is that more clear?

Now back to the questions I asked you.....

[Richard L.]

After the latest test with the same disappointing results (160 thermostat already in place, tightened fan belt) I have to agree with most of you (Jim, Dave, Mark, Duke) that it's unlikely a fuel (no hesitation during acceleration but bought 10 gal of av gas for next test) or a temperature (was 45 degrees outside) issue.
Now as to the electrics: coil believed to be good (I'll recheck it), coil+ connected to 7-9v end of resistor, coil- connected to distributor points. Ballast resistor is an unknown quantity since it looks original but it was used for the prior (Pertronix now removed) application which could have required 12v at the coil+.
Today I will:
1) test the resistor at both ends to ensure that the coil is only getting 7-9v (except when cranking).
2) feel the coil to see if it's inordinately hot to the touch or use a laser thermometer.
3) I have a brand new MSD coil that requires an additional resistor that I can install if #2 above proves to be abnormally hot.
4) Remove and replace fuel filters.
5) Remove electric fuel pump and go back to original mechanical fuel pump.
6) Borrow Elvis' gun that he shot his Pantera with and do likewise to my 62.
I really appreciate the recommendations and advice, all are most helpful to me.
Ric

[Duke W.]

Have you done the road test with a voltmeter or dwell meter that I recommended in Post # 17.

There's an old adage among knowledgeable vintage Corvette owners: " Ninety percent of fuel injection problems are the ignition system", and I can say the same for carburetors.

Duke

[Richard L.]

Have you done the road test with a voltmeter or dwell meter that I recommended in Post # 17.

There's an old adage among knowledgeable vintage Corvette owners: " Ninety percent of fuel injection problems are the ignition system", and I can say the same for carburetors.

Duke

Yes, did the dwell meter test and no variations registered.
This morning I tested the ballast resistor with ignition on but the engine off: 12.9v at one end and 5.34v at the other end where the wire to the coil- minus terminal attaches. I was under the impression that the low voltage side should read 7-9v, so the 5.34 seems low.
I will next start the engine, get a reading of the resistor low side and let it run at idle to see how long it takes for the engine to warm up and when it starts to run rough, read voltage again and take a reading of the coil temperature as well.

[Jim L.]

Richard the conditions that exist which your engine acts up are not yet clear.

You've mentioned the 10 minute time threshold multiple times. When you cross that threshold and the engine begins to act up, what was the engine doing immediately prior to acting up? Was it just idling? Were you driving?

And another question for good measure: How long does it take for the choke on your FI unit to turn compleatly off?

[Duke W.]

There are two ballast resistors used during the C1/2 era, 0.3 ohm and 1.8 ohm. They are visually identical. Many say that the 0.3 ohm ballast has a "black dot" and the 1.8 ohm type a "blue stripe" (I might have this reversed), both applied with what looks like a marker pen. It is my belief that these identifying marks apply only to service replacements, not plant installed parts.

In any event, all C1 Corvettes were originally built with the 0.3 ohm unit. This allowed higher primary current for more spark energy than the 1.8 ohm unit, although this could be tough on points, especially in cold weather since the special ballast resistor resistance wire alloy varied in resistance with temperature, the colder the temp. the lower the resistance. The nominal values I quoted are at room temperature.

In any event, Chevrolet wrote a TSB on the issue recommending that the 0.3 ohm resistor be replaced during cold winter months with a 1.8 ohm unit. I wonder how many owners even knew about this. Chevrolet also modified '63 production to use the 1.8 ohm unit on 250/300 HP engines while retaining the 0.3 ohm unit for SHP/FI engines about halfway through '63 production. This continued for '64, but for '65 all engines with single point ignition systems got the 1.8 ohm unit for '65 and beyond.

Measure the resistance across your ballast resistor and also across the coil + and - terminals, engine OFF. It can be tough to measure such low resistance values, but tell us what you get.

The ballast and coil primary resistance form a voltage divider circuit, and the voltage across each resistance is given by the formula:

Voltage across resistor 1 = input voltage X (resistor 1 value divided by the sum of both resistances) , and similarly for resistor 2.

If you still have the OE ...107 coil the primary resistance value might be in ST-12, but measure it anyway.

With the points CLOSED and ignition on measure input voltage and voltage across the ballast and coil along with your computed results.

lf the dwell did not vary when the engine acted up during your test drive, that would tend to exonerate the ignition system leaving the fuel system as the culprit, but more testing including more details and data is needed.

Duke

[Richard L.]

Richard the conditions that exist which your engine acts up are not yet clear.

You've mentioned the 10 minute time threshold multiple times. When you cross that threshold and the engine begins to act up, what was the engine doing immediately prior to acting up? Was it just idling? Were you driving?

And another question for good measure: How long does it take for the choke on your FI unit to turn compleatly off?

Makes no difference whether it sits idling like it did a little bit ago or driving, it's always around the 10 minute mark, and it runs fine clear up until it starts missing, refuses to idle and then dies unless prompted by the gas pedal to keep it going--barely--otherwise it just dies. The temperature gauge reads anywhere between 180 and 190 degrees.
Today I took the following measurements:
--Ballast resistor: Cold, ignition on, engine off, read 12.19v and 5.32v (terminal with wire going to coil+)
--Ballast resistor: Hot, engine running, read 15.2v and 10.7v (terminal with wire going to coil+)
I did not drive it but simply let it idle in my driveway and the symptoms were EXACTLTY the same as when I road test it, same number of minutes, no more than 10.
I am truly stumped.

[Richard L.]

There are two ballast resistors used during the C1/2 era, 0.3 ohm and 1.8 ohm. They are visually identical. Many say that the 0.3 ohm ballast has a "black dot" and the 1.8 ohm type a "blue stripe" (I might have this reversed), both applied with what looks like a marker pen. It is my belief that these identifying marks apply only to service replacements, not plant installed parts.

In any event, all C1 Corvettes were originally built with the 0.3 ohm unit. This allowed higher primary current for more spark energy than the 1.8 ohm unit, although this could be tough on points, especially in cold weather since the special ballast resistor resistance wire alloy varied in resistance with temperature, the colder the temp. the lower the resistance. The nominal values I quoted are at room temperature.

In any event, Chevrolet wrote a TSB on the issue recommending that the 0.3 ohm resistor be replaced during cold winter months with a 1.8 ohm unit. I wonder how many owners even knew about this. Chevrolet also modified '63 production to use the 1.8 ohm unit on 250/300 HP engines while retaining the 0.3 ohm unit for SHP/FI engines about halfway through '63 production. This continued for '64, but for '65 all engines with single point ignition systems got the 1.8 ohm unit for '65 and beyond.

Measure the resistance across your ballast resistor and also across the coil + and - terminals, engine OFF. It can be tough to measure such low resistance values, but tell us what you get.

The ballast and coil primary resistance form a voltage divider circuit, and the voltage across each resistance is given by the formula:

Voltage across resistor 1 = input voltage X (resistor 1 value divided by the sum of both resistances) , and similarly for resistor 2.

If you still have the OE ...107 coil the primary resistance value might be in ST-12, but measure it anyway.

With the points CLOSED and ignition on measure input voltage and voltage across the ballast and coil along with your computed results.

lf the dwell did not vary when the engine acted up during your test drive, that would tend to exonerate the ignition system leaving the fuel system as the culprit, but more testing including more details and data is needed.

Duke

At this point I'm willing to reconsider the fuel option once again.
1. Replace both the inline filter and the f.i. filter and--very carefully--test to see the amount of fuel being pumped by the electric pump.
2. run again with new filters installed and if no difference retire the electric pump and reinstall the original mechanical one.