It's not fun anymore.

[DonaldSmith]

I love the forum. 

I love showing off the car, but I can't keep it running right.   

 

We are signed up for the National DeSoto Club Convention in Chatham, Ontario, in July, but I'm having trouble getting the car to run right, and I have fears of the car misbehaving and having to be flat-bedded home, if it even makes it to the convention.   

 

The car starts.  It runs rough for a few minutes -  lup   lup   lup.  Then it smooths out and runs sweet.  I take it for a drive.  Randomly, it decides to lup   lup   again, and it's all I can do to goose it and keep it running.   (Hint: this is when it is in idle mode.)  Something loose, that changes things?   

 

After sixty-some years of trying to keep cars running, I still don't have a handle on diagnostic procedures.  One year of experience, sixty times over.

 

Put a neon thing in line with a plug wire, to see if the ignition falters?   Pull the plugs to see if one cylinder might have intermittent valve problems? At least I'll be doing something, "Ruling out" this or that. 

 

The vacuum gauge usually runs at 18 or so.  When the engine lups, it drops to 14.  But no wild fluctuations.   

 

Maybe you guys can advise a diagnostic procedure.  Or maybe it's just got to be the disgronificator.   

 

[Sniper]

Did you check the choke? It might be acting up specially since it seems to do it when the engine's cold. Most of the time anyway.

[Dave72dt]

Use a timing light to verify consistent spark when it's misbehaving.  You can move from cylinder to cylinder watching the flashes.  If all the cylinders have a noticable misfire, hang the pickup lead on coil wire.  If spark is consistent, you're down to fuel and air.  You may want to try a remote fuel source.  Electric fuel pump? check power and ground, terminals.  Exhaust can also get plugged and baffles in mufflers can come loose

[Plymouthy Adams]

many small things could be wrong leading up to the problem you have.  Fuel, ignition, exhaust (don't forget the manifold heat control vavle)  Maybe not much help here but when you do not readily know what is wrong, prove what is right.  By that, go over your state of tune, delivery of fuel, ability to exhaust and ensure the components are up to the task.  When is the last time a compression test, valve adjust etc was made on the engine.  Small things....prove them one way or another.

[DonaldSmith]

I'll check the choke.  Lots of little pieces to move around and wind up in the wrong place. 

 

I'll check the spark.  I'll check the manifold heat control vavle.  (Is that something like the disgronificator?) 

 

I do have the time to go over everything.   Things are looking brighter.    Thanks, guys. 

 

[Booger]

I dont like automatic chokes for all the above reasons.

Booger started running rough suddenly. Made no sense. Turned out something as simply as a bad condenser

[keithb7]

There could be lot going on here as many things may cause the symptoms. There could be a long list of instructions to find the problem and fix it.

The best thing anyone can do for themselves become proficient at diagnostics and troubleshooting is to study the fundamentals automotive systems.

One year of reading in your spare time would give you tremendous knowledge to fix this.  Saying that, it won't fix the problem before the National Desoto Convention.

 

Based on my experience I'll pass along some things to check. If you report back we can get to bottom of this. I am not trying to hone in on your specific symptom. I 

am will mention things that will effect overall engine performance.

-Perform a wet & dry compression test. Post results

-Test fuel pump pressure. Post results.

-Any fuel filters? When were they last replaced?

- Drive around the block with no filter and choke rigged fully open. -Take the top off carb. How's the bowl looking? Clean or rusty scale looking down in there?

-Check & set float level

-Hook up vacuum gauge at intake manifold. At idle does adjusting your air/fuel mixture screw make any difference to vacuum readings?

- When was carb last disassembled or deep cleaned? Are the paper separator gaskets sealing?

- Throttle plate linkage sloppy at the shafts? Worn carb body bores at the throttle shaft? 

-Spark plug wires. Age and condition? Start up engine in the dark, watch for sparks around the ignition system under the hood

- Remove spark plugs and clean/gap

-Remove distributor cap. Clean inside for possible carbon tracking. Clean lugs where spark jumps. Clean rotor. Both with emery cloth.

- Inspect points and all related wire inside distributor cap. File and gap points. If anything is questionable replace.  Wire mounting screws all tight.  Rubber isolators in place? 

-Points squared off all related anchors tight? Condenser age?

- Set points gap. Set dwell with a dwell meter. Set timing. Recheck dwell and set again. Double check timing after setting the dwell. 

-Set Air Fuel mixture to maximum vacuum. Set engine idle RPM.

- Break plate able to rotate as needed? Test vacuum advance pot. Is it working? Pull a vacuum on it.

- Wire from coil to distributor. Nice new, clean and fastened securely at both ends?

- Wire from ignition switch to coil. Snug tight, clean. Test continuity while wiggling wire. Solid firm connection?

- All wires at ignition switch: soft, clean, not crunchy and snug at all ends?

-When were valves last set?

 

If you are going on a longer-ish trip all these items should be in good, maintained condition.

A few ideas. Looking forward to you reporting back.

 

 

 

Edited April 15, 2023 by keithb7

[greg g]

The manual has a simple test to check fuel flow.  Do that test and you can rule out the pump.  I had a situation with a piece of debris in the suction side fitting.  It acted like a rev limiter.  It would pass enough fuel to idle and drive gently up to 30 mph or so. Then the flow would move the chunk to choke itself. When the flow lessened, it would drive at 30 and idle all day but not want to go above 30.  Check your rubber line going into the pump. With age they will look OK on the out side but inside will collapse under suction and cause insufficient flow.  

[plymouthcranbrook]

A few years ago my 52 Plymouth slowly began running worse and worse.. I checked everywhere I could but it all pointed to a fuel problem.  The pump worked well but the problem seemed to be a lack of fuel when accelerating . Idle and steady speeds seemed ok. The carb had had a major rebuild several years ago and a couple of minor tuneups recently.  I finally decided the old carb was acting up. I bought a two barrel kit from Langdons(which is apparently no longer available) and the problem was solved. Car now runs excellently.

[nonstop]

All above is good advice.  The only other advice I can add is to check one item at a time.  It is too easy to jump around and next thing you know is you have fiddled with a few different things and not sure what will get you back to baseline, or what actually fixed the problem.  A lot harder to go back and make the permanent fix.  This is especially true when checking fuel and ignition problems, as symptoms can be mistaken for one or the other.  I have been down that rabbit hole.  It can get frustrating.

[Doug&Deb]

I feel your pain. My diagnostic skills are atrocious and my mechanical abilities are sketchy at best. All of the advice given is good advice. One thing at a time and don’t be afraid to walk away for a bit if you’re frustrated. Keep going and you’ll get it fixed.

[SteveR]

I would add if you make an adjustment and see no change, Put it back. I have see people put additional problems in and then they start chasing their tail. Good luck and keep us posted.

[dpollo]

check and/or replace the flexible wires inside the distributor.

[DonaldSmith]

Spark test:  I put a neon test light in series with each spark plug, and noted even firing, even when the engine would lope. That would seem to rule out ignition problems. 

 

Choke:  Functioning normally.  Closed when cranking, partially open when the manifold is cold, opens fully as the manifold heats up.  If I push it full open, the engine idles a little faster.   

 

Fuel pump test?  The manual says to "insert a tee in the line at the carburetor and connect a pressure gauge...  reading ... between 3-1/2 and 5 lbs ... remain constant ... drop slowly ..."  OK, it doesn't say crank the engine with ignition off, or run the engine.  Does it matter?  I would crank it with ignition off.   Challenge:  Fit a tee in a line with flared tubing.   (I could cobble something.)  I have heard of another test, where the fuel line pours into a container, and there should be a certain volume pumped out in so many seconds.  (This would be cranking with the ignition off, of course.)  Comments on what would make sense?  

 

And I still have Keithb7's checklist of things to took for, and other odd things that could affect a smooth idle.   

 

This is all while I'm not feeling so hot.  Chronic back problems.  Now the foot arch.  Facial nerves  mimicking a toothache.  But the weather is getting better, and I can do a little at a time.  Frequently I have to take what the family calls my "Wert Gunnell" breaks. 

 

Wert was an old mechanic that lived next door to my friend Jimmy and treated him as a son. My dad hired Wert to do a valve job on a tractor, and I went along as the go-fer.  Wert would wrench for twenty minutes or so, and then take a twenty-minute break, while he did justice to a cold beer.  I was the anxious get-it-done kid, and I didn't understand the pause.  Now I understand the pause, but with a Mountain Dew instead of a brewski.     

[greg g]

Fuel flow test.  You need an assistant.

Pull the coil wire, car in neutral park brake on.

Disconnect fuel line at carb

Direct discharge into a suitable container, a 20 Oz beverage bottle works fine

Have an assistant crank the starter

Count pulses as you direct flow into the bottle

12 pulses should yield 8 or more ounces of fuel

Less than 8 won't support proper operation. 

Low flow suggests worn pump, obstructed fuel line, clogged filter/s, clogged pickup in tank, or small air leaks in the line/s on the suction side of the pump.

 

Have you given any thought to rigging a temporary fuel supply with either gravity feed or an electric pump?

[DonaldSmith]

Thanks, greg g,  for the fuel flow test procedure.  I have a remote starter with optional ignition switch, so I can crank the engine while holding a receptacle at the end of the fuel line.  Better yet, secure the receptacle, to avoid clumsy episodes.  12 pulses, 8 or more ounces.  got it. 

 

I don't suspect the fuel pump is causing the loping, but I want to rule it out anyway.  (I do have the stalling at speed problem, which will get into investigating the condition of the tank, for possible sediment blocking.  I already replaced the fuel filter "in front of" (on the inlet side of) the electric fuel pump.  As I understand it, the main purpose of that filter is to protect the electric fuel pump.)  

[Sniper]

Wish I were closer and could help, I love these kinds of troubleshooting things, it;s what I do.

[greg g]

Mtn Dew has lots of caffeine.  I know my hands get jittery after two cups of coffee.  Jittery hands and tools don't work for me. Iced tea or lemon aide are my garage go to bevs. At least till 4 pm when I might treat my self with a wobble pop or 2.

Hope you can track this down.  Have you checked the spring on the points and the thin wire to the points.

[DonaldSmith]

No points.  Pertronix.  There is still a ground wire from the breaker plate to the shell.  Maybe Pertronix needs the ground. I'll check that wire. 

 

Does the Pertronix get screwy?  Anyone having problems with Pertronix?  I've heard of failures, but that may have to do with not having a resistor in the semi-auto transmission circuit. 

 

(I pace myself with the Mountain Dew - one can in the morning, and one can in the afternoon.  Usually.)   

[Plymouthy Adams]

I pace myself with coffee, one pot in the morning, one pot in the afternoon and often, another before going to bed at night.....rarely ever less that two pots a day even in summer.   I rarely will drink a soda....usually treat myself to one from the Mennonite country store on the way home from the wrecking yard pick and pull runs.  I remember well when Mountain dew first came out with the hillbilly ad....my how times have changed.....lol

[JerseyHarold]

16 minutes ago, Plymouthy Adams said:

I pace myself with coffee, one pot in the morning, one pot in the afternoon and often, another before going to bed at night.....rarely ever less that two pots a day even in summer.   I rarely will drink a soda....usually treat myself to one from the Mennonite country store on the way home from the wrecking yard pick and pull runs.  I remember well when Mountain dew first came out with the hillbilly ad....my how times have changed.....lol

The first time I heard about Mountain Dew was on a billboard ad in Maryland in 1965.  The slogan was "It'll tickle your innards"!  Don't know why I remember this stuff....

[Sniper]

Since my triple bypass some years ago I quit caffeine, cut way back on sodium (last time I had blood work that level was just below the low of the normal range) and other deleterious things, lol.  Even red heads.

[rallyace]

My friends that worked for Pepsi told me that Mountain Dew was first developed for the US military as back in the Viet Nam days they had lots of folks who would not drink coffee but would guzzle a couple gallons of soft drinks. Thus the high amount of caffeine in Mountain Dew to keep them awake.

[Young Ed]

3 hours ago, rallyace said:

My friends that worked for Pepsi told me that Mountain Dew was first developed for the US military as back in the Viet Nam days they had lots of folks who would not drink coffee but would guzzle a couple gallons of soft drinks. Thus the high amount of caffeine in Mountain Dew to keep them awake.

Pretty sure MT dew is older than that. 

[Young Ed]

7 hours ago, Plymouthy Adams said:

I pace myself with coffee, one pot in the morning, one pot in the afternoon and often, another before going to bed at night.....rarely ever less that two pots a day even in summer.   I rarely will drink a soda....usually treat myself to one from the Mennonite country store on the way home from the wrecking yard pick and pull runs.  I remember well when Mountain dew first came out with the hillbilly ad....my how times have changed.....lol

Few years back when they reintroduced real sugar Mt dew the hillbilly guy was on the cans