All of a sudden low rough idle and no acceleration

[Russell Petry]

Good afternoon, Everyone!

I drove my 1977 NYB two weekends ago and it ran great, no issues. It has a 400 in it with only a little over 60k miles. Parked it in the garage for a week. I got in in Saturday to back it out of the garage and it started but the idle is very low and rough. Sometimes it runs a little rough until the engine warms. But this time it continues and when give it some gas, the engine will not accelerate, and just sputters as it tries but will not accelerate. I tried this at the edelbrock carb linkage and same result. Any cues as to what might cause this? I am going to get into it this evening but wanted to know what some of you experts might think ahead of time. Since it happened just from being parked for a week, I am thinking maybe the coil is bad?

Thanks in advance!

 

[thrashingcows]

I'd start with looking for vacuum leaks...Check all hoses and make sure they are hooked up tight and if they all look good with no cracks or worn through holes on the backs of the lines then check for a loose carb or damaged carb gasket.

 

[CBODY67]

Check exhaust flow at the end of the tailpipe. If none, loosen the pipe on the inlet side of the catalytic converter.

 

[david hill]

Let's start w/ the easy eliminations. Spray around the carb, EGR & intake gaskets w/ carb cleaner to check for vac leaks. Inspect vac hoses for cracks or splits, replace if found. Another possibility is a sticking PCV valve and or collapsed PCV hose. Next would be drop the exhaust at the manifolds to check for a plugged catalytic converter.

 

[Davea Lux]

Also check the base timing, if it has gone way out of spec, that is a sure sign that the timing chain has jumped a tooth. Another possibility is that EGR valves do not play well with moonshine blend oxygenated fuels, the EGR carbons up and sticks open. This drops the manifold vacuum thru the floor resulting in very poor performance.

Dave

 

[CBODY67]

Few things can have a sudden failure mode once the engine stops. With age (and probably mileage), the timing chain might be a prime suspect. Loosen the distributor hold-down bolt and rotate the distributor in the "advance direction". If things get better by about 1 spark plug wire's amount of additional advance, the timing chain becomes a prime susoect. I saw that happen on a '72 police car at the local Chrysler dealership, in the earlier 1970s. It was not running as poorly as you describe yours, but it was not right. The service manager got a wrench and loosened the hold-down bolt, then put more advance in the base timing and things cleared up almost completely.

A loose muffler internal baffle which has come loose should result in a rattle when the muffler case is tapped on with the side of your fist, usually.

Might even be a failed ignition module or computer.

Vacuum leaks can be contributing variables, but not usually enough to result in what you describe, typically. When the pcv line on my '80 Newport 360 gets clogged in the winter time (crankcase vapors combined with fuel vapors form gunk in the low part of the hose routing, clogging the line), the engine idles a bit funny but still runs fine other than that.

Might even be some carb stud nuts which finally loosened off enough to cause problems, too?

Hoping it's something inexpensive and easy to fix! Please keep us posted on what you find.

Take care,
CBODY67

 

[Gerald Morris]

Also check the base timing, if it has gone way out of spec, that is a sure sign that the timing chain has jumped a tooth. Another possibility is that EGR valves do not play well with moonshine blend oxygenated fuels, the EGR carbons up and sticks open. This drops the manifold vacuum thru the floor resulting in very poor performance.

Dave

WISE WORDS! I learned about THAT EXECRABLE FACT on my '83 Dodge Miser w the /6. I copped a new EGR, deleted the Lean Burn, popped a 1974 type Holley 1945 on w old fashioned thermal choke and a standard 70s style electronic ignition and All was Well, for awhile. NOW my EGR valve, and the damned gasoline return vacuum crap is again starting to diddle up things a little. Am fixin to put a simple vacuum valve on the gas return lines to control them better.....

I HATE post 1972 additions! Un gran dolor del fundio!

 

[Gerald Morris]

Few things can have a sudden failure mode once the engine stops. With age (and probably mileage), the timing chain might be a prime suspect. Loosen the distributor hold-down bolt and rotate the distributor in the "advance hat ....

Might even be some carb stud nuts which finally loosened off enough to cause problems, too?

Hoping it's something inexpensive and easy to fix! Please keep us posted on what you find.

Take care,
CBODY67

Had THAT happen last week, after replacing a badly leaky Stromberg WWC w a reman Carter BBD. It's more difficult to tighten the stud nuts down properly on the Carter, and I failed to get one properly. Finally SAW that the nut had worked UP enough to show. Tightened it down, improving things a fair bit, though the idle circuit on these Carters isn't as nicely done as the Bendix carbs.....

 

[Russell Petry]

Good morning, Everyone!

Well, I found out the issue on my NYB. A while back, I removed the old Chrysler electronic ignition system that was failing and replaced it all with a Pertronix distributor with the Ignitor II chip. Along with that, I added the Pertronix HP digital 510 electronic ignition system and removed the resistor on the firewall. I found in one little web thread that mentioned if the ignitor II module does not get enough power, it will cause the very same issue I was experiencing. I tested the leads to the coil and sure enough, it was only getting about 7.2 volts. Since the Pertronix HP module controls that, I got another one and swapped it out. The car runs like new again! I believe mounting it on the firewall might be too hot for the module so I will re-route the wiring and mount it on the passenger fender well where the old Chrysler module was mounted.

Thank you again for all the advice, it did help me troubleshoot and rule out some things.

 

[Gerald Morris]

Good morning, Everyone!

Well, I found out the issue on my NYB. A while back, I removed the old Chrysler electronic ignition system that was failing and replaced it all with a Pertronix distributor with the Ignitor II chip. Along with that, I added the Pertronix HP digital 510 electronic ignition system and removed the resistor on the firewall. I found in one little web thread that mentioned if the ignitor II module does not get enough power, it will cause the very same issue I was experiencing. I tested the leads to the coil and sure enough, it was only getting about 7.2 volts. Since the Pertronix HP module controls that, I got another one and swapped it out. The car runs like new again! I believe mounting it on the firewall might be too hot for the module so I will re-route the wiring and mount it on the passenger fender well where the old Chrysler module was mounted.

Thank you again for all the advice, it did help me troubleshoot and rule out some things.

I'm delighted to see this good news! I'd say the old ballast resistor certainly has no place in a modern designed circuit, unless it was specifically designed with it accounted for. Ballast resistors, like the rest of the electrical circuit elements in C body Mopar products really were designed with 19th century THERMAL FLUID electrical thinking in mind. The Field Effect hadn't yet penetrated the minds of leading engineers until circa 1980, and not fully for at least another decade. So, to regulate current, crude resistive heaters would lay in series with the elements they were meant to protect. It worked, at the cost of electrical efficiency. Incandescent light bulbs used resistance to heat metal filaments until they glowed. Turn signals switched off and on as the blinker elements would heat up, then cool as they repeated their cycle. Regulators vibrated at cycles approximating the factor needed for the desired output voltage, from a given input. Bipolar Junction Transistors improved on things a bit, but still required some serious heat sinking if they did much work, for the state of the art then....

We can thank the likes of Tommy Edison for a lot of this, as his notions would dominate the industry despite Better Folk (Nicola Tesla, George Westinghouse, et cetera...) knowing what paleolithic crap this was. The British were WORSE, retaining Fluid on the Brain to the degree that called vacuum tubes "valves" as they were using heat to effect primitive amplification and switching. Well, Fire and Iron won folks many wars for a long time, and it will take a long time to fully grasp better ways to do things.

I run a Kettering ignition myself, as they're fun and easy to tune. Also, primitive as the Old School stuff is, there is THIS to be noted in its favor: an EMP won't cripple such a system nearly as badly as it will a fancy, airy fairy, digital dildo system. To wit, you can't program a chip with a matchbook.

ENJOY!