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Hello Friends,
1934 836a has a high speed miss under light throttle. No missing under acceleration at any speed, misses only with light throttle.
I have installed new plugs, wires and coil recently.
Any ideas on where to start?
thanks,
Blaine
E
Blane,
I don’t envy you. I hate electrical problems if that ends up what your problem is.
I would start with making sure you have the plug wires correct. If you have 2 switched that might do it. Check both at the plugs and at the cap. Speaking of the cap, you didn’t mention it. Is it used or new. If used, is there any carbon tracking or cracks on the underside? Condenser? Check the plug gaps. What condition is the rotor? The carbon electrode?
Recheck point gap/setup, make sure there is no play in the dizzy shaft (worm bushings)
I would check the resistance on the plug wire to see if the were all the same, if not that might be it.
It just takes a disciplined approach and eliminate the potential problems one at a time.
Let us know what you find. Good luck.
Bill
At what ‘high speed’ is the miss? What are the characteristics of the miss? A bit of vibration felt through the gas pedal? or a noticeable drop of a couple of cylinders with maybe even a backfire?
The EE-3 carburetor can get a bit of dirt under the power valve needle. The result is that the carb is feeding a rich mixture to the engine even under light throttle. The power valve is located at the bottom of the accelerator pump piston. Since the power valve is part of the accelerator pump circuit, you can see if it is actually leaking by looking down the throats of the carburetor while the engine is running.
The procedure is to remove the air cleaner, without the engine running, hold the choke open, and look down the carburetor. Stroke the throttle linkage, and you will see gasoline squirt out of the accelerator pump nozzles. The short brass tubes that poke our of the venturi are the accelerator pump nozzles. Once you have identified the nozzles, start the engine, and look down the throats of the carburetor while the engine is running. You should NOT see any gasoline coming out of the nozzles, except when you stroke the throttle.
OK, that will cover the possible too-rich mixture diagnosis.
Next is a possible too-lean miss. Since the power valve adds extra fuel under acceleration and heavy load/ wide throttle use, it can mask a lean running situation under light throttle. The most common cause of a too lean mixture is a manifold gasket leak. Check the 9/16″ manifold nuts. Snug to tight is ok, don’t over tighten them. But barely snug might be allowing air to enter the intake without going through the carburetor, so those cylinders run lean.
You can take a propane torch to test for intake leaks. Without lighting the torch open the valve and direct the torch end at the manifold/engine/gasket area with the engine idling, if there is a gasket leak, the engine will pickup speed when the propane gas is pulled into the leak.
Some people use an oil squirt can, filled with gasoline to do the same test for a leaking head gasket.. obviously this is rather dangerous, since you are squirting a flammable liquid all over the side of the engine. if this gasoline ignites, you have a significant fire. With the propane gas test, you will just get your torch lit, and a bit of a pop from the propane igniting.
If you choose to use gasoline, HAVE A HELPER WITH A FIRE EXTINGUISHER. Don’t do the test on your own.
The ‘old saying’ actually is that ‘most fuel and carburetor problems are a set of points or a condenser’.. This miss with your engine is the opposite. Having a light throttle miss is a bit difficult to diagnose. I’ll assume you do have copper-core spark plug wires, and as mentioned above, a good cap and rotor, and properly set points and timing.
Let us know what you discover, so we all can learn about the cause.
Greg Long
Another thing to consider is the distributor shaft that turns the rotor. If the bearing in the distributor that holds the shaft true has excessive wear, you will get an asymmetrical rotation of the rotor that will cause intermittent misfire.
I experienced this condition once and under acceleration, the car seemed fine, but would buck at cruising speed with a tap on the gas.
Best of luck Blaine
Thanks so much for the tips and advice so far. I’ll get to work running down these options and let you know!!
I dated a High Speed Miss when I was in college. Couldn’t keep up with her. And, the sad part of the “joke”, I’m serious, she was a cheerleader for the Nawlin’s Saints in the early 1970’s, I even remember her name. But, to protect the guilty, I won’t mention it here.
In all seriousness, my ’31 had a funny miss, all else was well and we tracked it down to a worn bushing in distributor, as John mentioned. It’s just not something you think of offhand, but it can affect performance.
Good stuff David!
As usual, Greg comes through with some great advice and real world experience.
Thanks for always chiming in, I learn a ton from guys like you and the other experts in the PAS.
Every marque has their quirks and most of my Pierce experience with our ’29 so I love learning about all the other Pierces.
todays update :
Before setting out for home with the 836, I gave the battery a good charge and noticed the negative lead laying across the metal bracket of the battery box, and was rubbed bare. I zip tied a piece of inner tube on it as a temp fix and drove the car between 55 and 60 mph 25 miles to my house.
Car ran with no miss. Would the battery lead shorting effect ignition? or was the fully charged battery making a difference? I will still go through all the suggestions when i get some time.
On another note, I got to change a tire in the heat thanks to one of my pristine vintage tires completely loosing the tread. Checked the other tires after changing, and all of them are deeply split, even though the tread still has nubbies on them. I thought i would b able to drive on them a while, but no.
Now that I am tire shopping for 7.0-17’s, any good deals out there??
thanks,
Blaine
Check your valve springs. If you have hydraulic lifters it could also be high oil pressure lifting the valve up off the seat. A common problem with the eights.
I started my ’36 1601 without the air cleaner. The car backfired,
puking gas that caught on fire. A quick thinking helper beat out the
fire with his shirt. No damage resulted, but I still have nightmares.
Blaine,
The short answer is yes, the bare lead could have some effect on the ignition as this is a positive ground system. The charging could likewise cause this, but it is less likely. If it does, it is telling you to clean all the terminals in the ignition system, as there is a poor connection somewhere, or the earlier suggestions to check the continuity through the system will find an issue in the wiring, coil, or another component.
Blaine, you have found the problem. The negative battery terminal is delivering power at 6V nominal while the generator is charging the same terminal at that voltage. If the terminal is grounded (6V turned to 0V instantly),ignition and the generator will stop working and be extremely stressed. Not the best for the battery either.
Fix that problem right away and keep an eye on the charge gauge to confirm your generator is ok.
A few comments and concerns:
Hi Blaine, it is quite likely that you have found your miss. But I’m a bit confused as to how or why the miss did not occur at low speeds, like 20-30mph? I would think that at low speeds, if you hit a bump in the road, that the battery cable would jiggle and short or arc against the battery box, and create the same miss.
Two scenarios I”ve conjured up: 1. Is there somehow that the throttle linkage is rubbing against something or forcing the cable closer to the battery box when a lot of throttle pedal is in use? Yet, this would be contradictory to the lack of a miss when accelerating hard. 2. Is the negative battery cable routed such that high air-flow from the engine fan and air from under the car able to push the cable closer to where it shorts against the box?
The element of the miss being at higher speeds doesn’t seem to support this chaffed cable as being the source of the miss. BUT, lots of times the oddest darn thing can cause symptoms that just don’t make sense.
This is the reason that I did not suggest the distributor bushings being worn as a cause. There is nothing in our Pierce distributors that cause a side force with either throttle, or engine speed that could force the shaft to close up a set of points.. if our cars had a vacuum advance mechanism, that pulled and moved the points-plate, then I could see the speed or throttle position having an effect..
Probably, I’m WAY over-thinking this..
Greg Long
Good point Greg, you would think an intermittent shorted battery terminal would be independent of rpm/speed.
Thanks to all for bringing to light the possible fault problems and solutions. I am not yet convinced myself that the problem is solved, although I drove it out to breakfast today and no symptoms appeared.
Just to clarify, the miss occurred under the lightest throttle at mid range RPM’s. I should not have said “high speed” because it would occur in any gear, as long as the rpms were near the shifting point, and only under light throttle. As long as you were accelerating, it was right on.
The value of the thoughts and suggestions offered is that when it reappears, I will have some directions to go in chasing down a solution. I have printed out this thread so far and stuffed it in the glove box for roadside reference if necessary, and will be quite happy to work through each offering, since it will either reveal a problem or enlighten the owner/mechanic.
I am grateful for the input!!!!
Blaine
While it would be nice to find and know what the culprit is/was, if you go ahead and perform a few of the checks suggested, you might not find a ‘smoking-gun’ but you might do enough that the problem does not reoccur.
Was there any correlation between the miss and how long you had been driving the car? If the problem does seem to occur only when the engine is fully warmed up, this would be a valuable additional clue.
Greg Long
Hello Greg,
Good question – the miss was consistent at all temps.
If it was heat related, would the most common suspect be coil related??
Blaine,
You mention the new coil as a potential. One thing I leaned the hard way, just because it is new doesn’t mean it will work (particularly in this age of the finest China can offer). Check each item and don’t assume they are ok.
Bill
Back in the days I was fixing tube type TV’s and radios, we used to buy at least two of the same type tubes we thought were defective when diagnosing a TV problem. We found that approximately 10% of the new tubes were defective out of the box. That did not change with the early transistors. Nowadays, we throw out defective TV’s as it is more cost effective to replace than repair. The brain trust that can diagnose a problem has slowly died out. We, in effect, are dinosaurs…