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Thread: Intermittent hesitation

  1. #1
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    Intermittent hesitation

    I have a 1950 Studebaker Commander with a 4.0 L straight six. Engine was rebuilt by PO and starts up and runs without issue. Unfortunately, the engine hesitates/misses intermittently. I've installed a new carburator, electronic ignition, new coil, new high-voltage cable from distributor to coil. Is there a way to figure out the source of this issue without replacing every component on the engine? I can continue and replace all the spark plug wires but I'm concerned I might be missing something. How do I troubleshoot this issue>
    Chuck

    1950 Commander Starlight Regal Deluxe
    1954 Ford Custom Coupe
    1969 Datsun Roadster 2000

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    Did the car misbehave "before" you installed the new components ??

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    I would suspect the electronic after market unit first. I would investigate the user responses on line as to any negative issues related to this product if you haven't already done so. If satisfied move on to engine timing, vacuum leaks and the usual suspects. Start with the basics.

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    I installed electronic ignition in an effort to eliminate the hesitation. Just received a new distributor cap and rotor in the mail today. I'll install them and see if the issue is resolved. I was hoping for an "aha" moment from someone who has experienced the same.
    Chuck

    1950 Commander Starlight Regal Deluxe
    1954 Ford Custom Coupe
    1969 Datsun Roadster 2000

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    Without experiencing it, it is hard to say. You seem to be mainly focused on electrical issues. Have you considered fuel issues - insufficient volume, air entering the lines, insufficient pressure (bad pump or clogged filter), etc.?
    Gary L.
    Wappinger, NY

    SDC member since 1968
    Studebaker enthusiast much longer

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    A vacuum leak can drive you grazy. spray around carb and manifold with carb cleaner or safer wd40 and listen for engine speed changes. Luck Doofus

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    Golden Hawk Member jclary's Avatar
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    Perhaps not an "AH HA" moment, but something to consider. For fuel related, check carburetor accelerator pump for wear. Others have already addressed vacuum issues. Electrical can drive you nuts if you have something like an intermittent plug wire leakage. It only takes one. An additional thing, often overlooked, is a fouled spark plug. When I say fouled, there are conditions where a plug can foul intermittently too. I have seen plugs with good appearance at the tip, with good gap, etc. However, on close examination, carbon buildup combined with an imperceptible crack in the ceramic center electrode insulator, can provide a path for an electrical short internally in the spark plug. Especially, if the carbon deposit becomes wet with gas & oil. I have a six cylinder where this occurs in the back cylinder, and I have to keep an eye on it. The older and more worn an engine is, the more likely this will occur.

    When chasing such a problem, check the function of accelerator pump, and when examining the condition of spark plugs, be sure to use a good light, and examine closely for crusty oily carbon buildup between the wall and center electrode insulator. If (& when) you resolve the issue, please post your solution.
    John Clary
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    "the engine hesitates/misses intermittently. "

    When idling, when accelerating, when croozin' on the highway ??
    Only when warmed up, going up hill, etc, etc.

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    It is 1) fuel or 2) spark. You have eliminated spark issue ergo the problem is fuel delivery. Check fuel pump pressure. if OK could still be a tiny bit of crud intermittantly getting stuck in on of those 2 little valves in there. The needle valve could be sticking(quite likely, as we don't drive our old cars much and modern gas is crap) Often rebuilders take short cuts so replace needle and seat and adjust. It would be a good idea to install a back up electric fuel pump. That oughta do it ! Good luck!

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    Quote Originally Posted by chlenz62 View Post
    I have a 1950 Studebaker Commander with a 4.0 L straight six. Engine was rebuilt by PO and starts up and runs without issue. Unfortunately, the engine hesitates/misses intermittently. I've installed a new carburator, electronic ignition, new coil, new high-voltage cable from distributor to coil. Is there a way to figure out the source of this issue without replacing every component on the engine? I can continue and replace all the spark plug wires but I'm concerned I might be missing something. How do I troubleshoot this issue>
    Random misfire? Worse at higher revs, more throttle? Plug wires. Been there, done that. Twice.

  11. #11
    President Member TWChamp's Avatar
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    Here's a tool I made last month to check for a hot blue spark. I used a pair of alligator clips, 9" of 10 gauge "Monster Cable", and 3" of rigid clear plastic tube 1/4" ID. After installing a short piece of heat shrink on the 10 gauge wire, it gives it enough drag to stay in place while the wire is pushed in or out to check the spark. I used a few drops of 2 part Permatex Marine Epoxy to fasten the alligator clip to the plastic tube. I soldered a short piece of brass rod with a point to this alligator clip.

    Another advantage of using a spark tester like this is that it can often be used to fire a wet fouled plug. Set the gap to 1/8" to 1/4" and the coil needs to build to a higher voltage to jump the gap of the tool and spark plug. This higher energy will often fire a wet fouled plug. Once the plug fires for a minute or so it's hot enough to burn clean, and the tool can be removed

    Homemade Tools Spark Tester.jpg

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    To answer a question on when the engine hesitates, it's during idle and also when steady-state while driving down the road. I don't feel it during acceleration but it's probably still there but not perceptible. Now the car won't start at all. I've put a cheap digital scope on the low voltage wire to the coil and I see a 6 volt pulse.


    IMG_20180317_161115031.jpg.

    But my timing light does not trigger when clamped on the high voltage wire from the coil to the distributor cap. So it appears I've got no spark. I've measured the resistance from ground through the coil to the center of the distributor cap and I measure about 13.5 K-ohms. My brand new coil measures about 8.5 K-ohms on the secondary winding and when I measure the high voltage wire from the distributor cap to the coil I measure about 5 K-ohms. So everything adds up correctly. The primary winding of the coil measures about 1.5 ohms.
    Chuck

    1950 Commander Starlight Regal Deluxe
    1954 Ford Custom Coupe
    1969 Datsun Roadster 2000

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    I don't know what components are different with electronic ignition, however I had experienced an intermittent misfire up to total failure, I had power up to the points, sometimes, as I was probing around I noticed a spark jump inside the braded wire at the points and the brading was perfect with no evidence of a separation. To continue enroute I removed the vacuum advance hose to avoid any movement of the advance device and completed my destination. The constant movement of the vacuum spark advance caused the wire to fatigue and break, however did not affect the braded cover. It was dark and I was able to see the spark, I may not have been so lucky in the daylight.

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    Quote Originally Posted by chlenz62 View Post
    when I measure the high voltage wire from the distributor cap to the coil I measure about 5 K-ohms. So everything adds up correctly. The primary winding of the coil measures about 1.5 ohms.
    The wire from coil to center of distributor cap should be very low resistance, not more than a few ohms. Ditto for wires from distributor cap to spark plugs.

    It's cheap and quick to replace those wires. See if you can get some copper core wires, not modern coil and plug wires which have built in high resistance. You local FLAPS should have some generic low resistance wires and terminals. Take your Ohm meter along.

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    I'm reading up on spark plug wires this morning but the car was running and now it won't. I'm hesitant to change anything until I find out why it stopped running. I don't want to increase the number of variables in the equation I'm trying to solve.
    Chuck

    1950 Commander Starlight Regal Deluxe
    1954 Ford Custom Coupe
    1969 Datsun Roadster 2000

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    President Member TWChamp's Avatar
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    Won't start now, so check for a hot blue spark at the end of the coil wire while the engine is being cranked.
    Got spark, then squirt a shot of gas into the carb and see if it fires up.

    My restored 50 Champion was giving me problems due to the tank liner coming off and plugging up the tank intake line.
    I stripped the tank clean by tumbling it with a handful of wood screws and lag bolts, and now it's fine.

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    I purchased a spark tester and I do have spark. The timing light I was using to validate spark is not reliable for a 6 volt system. The car is now running. I changed the spark plug wires but it's still hesitating and when it warms up, the engine power drops off above a few hundred RPM (no tach available so I'm guessing on the RPM's). But my point is that the engine just loses all power as I accelerate. I can limp home and it idles without issue. But as soon as I accelerate, it hesitates then as the engine RPM increases, the power just drops to nothing. I sprayed some air flow sensor cleaner around the base of the carb and the engine speed increased. So I tightened the nuts. I'll keep whacking away at this issue until I get it solved and I'll update as I gain ground on this ongoing issue. Shouldn't be this hard . . .
    Chuck

    1950 Commander Starlight Regal Deluxe
    1954 Ford Custom Coupe
    1969 Datsun Roadster 2000

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    President Member BRUCESTUDE's Avatar
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    As TW Champ said, maybe crud in fuel tank. I had a '52 Champion that ran fine for awhile then sputtered, but if I slowed down it ran OK. Turned out to be rust flakes that slowly plugged up the fuel intake line, when I let off the gas the rust fell or sloshed off enough to get home. FWIW

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    Golden Hawk Member jclary's Avatar
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    Quote Originally Posted by BRUCESTUDE View Post
    As TW Champ said, maybe crud in fuel tank. I had a '52 Champion that ran fine for awhile then sputtered, but if I slowed down it ran OK. Turned out to be rust flakes that slowly plugged up the fuel intake line, when I let off the gas the rust fell or sloshed off enough to get home. FWIW
    Don't forget the tiny screen wire like filter at the carburetor inlet fitting. After all these years, many have already been removed. However, I have had these often "overlooked" strainers to drive me nuts when searching for the cause of exactly what you are describing. Everything checks out like the carburetor accelerator pump in the carb, electrical (points, plugs, coil, etc.) and the engine runs great in your driveway. However, once you actually take off down the road, with the true demands of fuel for driving, performance just isn't there. What's happening, is that the engine is starving for fuel flow due to a restriction somewhere in the plumbing.
    John Clary
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  20. #20
    President Member TWChamp's Avatar
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    Unfortunately the shot gun approach was an expensive mistake. Before replacing any parts be sure to do a complete diagnostic test to determine which part is causing the problem. At this point I'd run a flow and pressure check at the fuel line going into the carb. Even better would be to install a tee at the carb and monitor the pressure as you drive. That's what I did on my 50 Champion after I solved the bad tank liner problem and installed an electric fuel pump to replace the original pump destroyed by this new crap gas.

    I could remove the pressure gauge, but still have it in place, and my car runs fine as long as I see at least 1 PSI while driving. I've been adjusting the pressure by using various ohms resistors on the power line to the fuel pump. Right now I'm using a 12 volt Holley pump on my car's 6 volts, and it does fine. At 12 volts the pump puts out 15 PSI when I bench tested it.

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    Everything definitely points to a lean situation. Engine backfires through carb. I replaced the fuel filter and when I turned on the pump, there was very good flow. I pulled the top of the carb off and the fuel bowl was about half full. I bent the float arm to allow the bowl to fill with more fuel. Neither of these two things changed the situation. When I continuously pump the accelerator I can get the engine to speed up but as soon as I stop pumping and try to hold some level of RPM the engine drops down in speed. If I open the throttle until the engine begins to drop in RPM, and then with my other hand I slowly close the choke butterfly valve, the engine speeds up with a lot of power. So I sprayed more brake cleaner around the base of the carb and the engine dropped in speed. It appears I definitely have an air leak at the base of the carb. When the engine cools I will pull the carb and slap another gasket on it. Feels like I'm getting closer. Appreciate all the feedback!
    Chuck

    1950 Commander Starlight Regal Deluxe
    1954 Ford Custom Coupe
    1969 Datsun Roadster 2000

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    Again, for me, just back from a cold AM drive, my Commander 6 wants to run on a slightly choked air valve setting. Does this all year round regardless of temps. When I slightly pull the manual choke handle out (1/8th inch) the engine runs perfectly, without hesitation. Whenever I push the choke handle to the dash (open valve on carb) it will "always" hesitate no matter what gear, except "in" gear. With the slightly choked setting, I will get a slight "bogging" on acceleration..... BTW: when you spray around the carb or manifold base, a leak will temporarily "speed up" the RPMS, not slow it down....

  23. #23
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    you've got a vacuum leak. Likely at the throttle shaft to body. caused by wear over the years. I won't rebuild a carburetor without having bushings installed between the throttle shaft and body. It does wonders for drivability results.

    Quote Originally Posted by jackb View Post
    Again, for me, just back from a cold AM drive, my Commander 6 wants to run on a slightly choked air valve setting. Does this all year round regardless of temps. When I slightly pull the manual choke handle out (1/8th inch) the engine runs perfectly, without hesitation. Whenever I push the choke handle to the dash (open valve on carb) it will "always" hesitate no matter what gear, except "in" gear. With the slightly choked setting, I will get a slight "bogging" on acceleration..... BTW: when you spray around the carb or manifold base, a leak will temporarily "speed up" the RPMS, not slow it down....

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    The carb is brand new so it is unlikely there is a leak around the throttle shaft to body. I pulled the carb and replaced the factory gasket with a hand-cut oversized gasket to ensure no leakage at the base of the throttle body. The car is now running better but still a lot of back-firing through the carb and significant loss of power. I removed the choke linkage and I partially close the choke butterfly valve using some hangar wire. This seemed like it helped so everything points to a lean situation. I may try installing the old OEM carb just to see if there is a difference. I will quadruple check the timing as well but every time I check it, it's spot on. (It's now electronic.) Is it possible the new carbs just don't put out enough fuel for these old engines?
    Chuck

    1950 Commander Starlight Regal Deluxe
    1954 Ford Custom Coupe
    1969 Datsun Roadster 2000

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    After all you've done, it sounds like it's sucking air somewhere. Manifold gasket? Vacuum port? Does it have vacuum powered wipers?

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    Success! I had already plugged all the vacuum ports: choke, windshield wipers. But you guessed right. I was staring at the engine this evening and decided to spray some brake cleaner at the intake manifold and the engine instantly responded. So I checked the bolts and one of them was not even finger tight while the one next to it was snug but not torqued. (Apparently ALL the bolts on your engine are supposed to be torqued down!) It was the only thing I had not yet checked. Feel incredibly stupid to have overlooked something so obvious. I may still need to replace the gasket but I drove it around the block and it has much more power. Not sure the hesitation is gone but this is the first time the car feels drivable. I sincerely appreciate everyone's persistence and great input. The collective wisdom of the team always wins out over the lone genius. And I'm no genius!
    Chuck

    1950 Commander Starlight Regal Deluxe
    1954 Ford Custom Coupe
    1969 Datsun Roadster 2000

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    President Member BRUCESTUDE's Avatar
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    Congrats! File it away in your brain for future use....

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