tylerrogers

I have a 1973 plymouth duster inline 6 225, I did a complete tune up not to long ago, but recently every time I drive the car for a while or drive on the free way for a while, the car wants to die when I either get off or hit traffic, when it dies I try to turn it on and the starter sounds differnt like barley trying to crank, and the car barley turns on and sounds like it's back firing when it finally Comes on, i need some advice please sincerely - Tyler rogers

Mr.4spd

Sounds like an ignition timing issue (too much advance), vacuum or mechanical mechanism could be sticky.

Coronet 500

Welcome.

I wonder what condition is the battery and charging system.

Lower voltage can cause stalling and back fire.

Sangetsu

Check the charging system, a simple check is to start the car and then disconnect a battery cable. If the engine dies, then there may not be sufficient power to properly recharge the battery, or run the electronic ignition.

Look at the spark plugs, if they are very white, then your engine might be running lean, causing it to run hotter than usual. They should be a light brown color.

Check the timing with a timing light, make sure it is correct. Don't forget to disconnect the vacuum line to the distributor and plug the vacuum port before checking the timing. Also make sure that there are no vacuum leaks from cracks in the hoses, etc.

Also check for exhaust restrictions, especially the catalytic converter. The original converters are crap, and are full of platinum coated pellets, which can get gummy and stick together, clogging up the exhaust system. You can either get rid of the catalytic converter altogether (if possible), or replace it with a more modern one.

440roadrunner

!!!NO!!!! !!! ABSOLUTELY NOT !!!!

I wish to HELL I could put this old wive's tale underground

1.......You are very likely to kill something like your stereo, IE electronics. Disconnecting the cable IF is charging generates a huge electrical spike

2........This test will NEVER EVER be found in any automotive text, service manual, or found being taught in any automotive mechanics course. This so called "test" is not legitimate, and should be buried forever

3......Possibly most important, THIS TEST PROVES NOTHING and may lead you to incorrect conclusions, and here is WHY

Situation A......The charging system is working "just fine." Maybe the engine is idling a little slow. Maybe you left the heater on. Maybe you have an electric pump. The point is, you are in "situation A" at a point where the alternator is not quite "up." you remove the cable and it dies, and you INCORRECTLY conclude that it is not working

Situation B......The alternator has two or more blown diodes or some other problem that has REDUCED it's output. Maybe it puts out enough to keep the ignition system happy in the daytime, but not enough to run lights at night. You have it idling, all accessories off. You pull the cable and it continues to run and again, you INCORRECTLY conclude that the charging system is OK

DO NOT DO THIS

440roadrunner

I would first attempt to determine if this is electrical, carburation, engine overheating etc, that is at least figure out what section

1..........Is it overheating? Do NOT believe the factory gauge. Get / buy / borrow an alternative device, it can even be a known good thermometer taped to the top rad hose with a rag around the outside. You can check a thermometer for boiling by simply boiling water on the stove....near 212 F unless you live at some extreme altitude. You can also, nowadays, get infra red temp "guns."

2........Is it electrical? This covers a LOT of ground. Also, you could have a COMBINATION of problems, such as flooding when hot, and an electrical problem. Get yourself some electrical tools which are a MUST on these old girls. Get a bag of clip leads at Radio Shack, get an automotive 12V test lamp, a spark testing gap device, and a multimeter. You can buy multimeters at MANY sources, including Sears, automotive, hardware, Lowes, etc

A....Check RUNNING battery voltage at fast idle right at the battery, all accessories off, and repeat with headlights, heater, etc on. Running voltage accessories off, fast idle, engine warm should be 13.8--14.2, and in no case below 13.5 or above 14.5

With all accessories on, good fast idle or "low cruise" RPM should not be below 13. V at absolute minimum.

B....Have the battery LOAD TESTED. You want to be sure it's charged, and that whoever does this knows what they are doing. Google it. Carbon pile load tester

C....If you can find a friend who has one of these testers, you can also have STARTER DRAW tested. This can lead you in a couple of directions. Is it a bad starter, or has the engine some internal problem, IE bad bearings, causing it to tighten up when hot, or is the starter dragging when hot?

D.....Is it losing ignition voltage? Coil failing when hot? There's lots of room for problems here. If you can go out on a country road and duplicate the problem away from traffic, check the starting spark with your spark tester. You should have at least a 3/8 or better 1/2" long nice blue spark. Don't use the resistor coil wire to test, use a solid core wire. Make sure to USE THE KEY when cranking the engine, as this sets up a hotter spark than when jumpering the start relay

How about primary voltage? Check voltage key on/ engine off under the hood at the ballast resistor. You should have within .3V (three tenths of one volt) "same as battery." Lower means that you have a bad connection in the harness, most likely at the bulkhead connector, or in the ignition switch or switch connector

Mr.4spd

X2 on the overheating theory. And I still think the timing is suspect...

Sangetsu

I recommended this because it is not an "old wive's tale". I learned this from my high school shop teacher, and he was as knowledgeable as anyone I have known. He had been an engineer for GM since the end of the second war. Having owned 60-odd old cars (including no less that three 440 Roadrunners) and having fixed hundreds more, I have found this to be a quick test to see if the alternator is putting out enough power to run the electrical system without the battery assisting it. Of course other accessories must be switched off, just as they would have to be if you were testing with a meter.

The voltage spike does occur, but it is no greater than the spike which occurs when turning the starter, or switching on a high-amp accessory. It certainly won't damage your stereo or anything else.

440roadrunner

I proved all this to be wrong on a bet on one of my own cars. You are incorrect, and just plain full of crap. YOU WILL NEVER find this in any legitimate service manual or anywhere else. THIS IS NOT an accepted nor an acceptable test method, and it WILL damage electronics if you do this often enough.

On my old 64 Dodge, at the time, had NO electronics except an AM radio, so we used it as a guinea pig. I was a NAVY ET and have been in electronics all my life. We used an HP oscilloscope to run this test. The stock alternator when disconnected on my 64 generated MORE THAN 100 volts as I recall the peak spike was in the neighborhood of 140 volts. This was in about 1971 or so.

THIS IS NOT a legitimate test. IT DOES NOT prove a thing for the reasons I already outlined.

THERE ARE already accepted test methods for checking out charging systems and THAT IS THE WAY it is done.

A starter DOES NOT generate anywhere near this kind of spike for the following reason

The really big spike is on the STARTER side of the solenoid contacts. These are disconnected when the solenoid "breaks."

The remaining spike is generated by the inductance and current flow in the main battery cable. This is LIMITED by the low impedance of the BATTERY ITSELF

When you DISCONNECT the battery from a HARD CHARGING alternator, one that is putting out some 40A or so after an engine start, the split second that takes the ROTOR INDUCTANCE to die, even if the regulator shuts off quickly enough, causes an enormous spike on the main system buss. If "everything" is turned off such as headlights and other loads, only what "operates the car" then there is not much to absorb that huge spike

Many (most) modern stereos and other equipment is constantly connected to what might be called the main system buss. WITHOUT the battery as a low impedance sink, the malfeasance is worse that what went on in Fargo