Random stalling, please help.

[1971 300 Alvah]

'71 Chrysler 300. Generally runs great, however I'm having common intermittent stalling.
No sputtering, the engine just stops.
This started happening after I changed the carb to an AVS2 with electric choke. Not sure if the electric load of the choke is enough to cause ignition issues? I wired the electric choke into the pigtail plug on my engine harness I got from Evans wiring a few years back, one female spade connector for the ballast resistor, another one unused previously.
When this happened recently I was able to correct the issue with a wiggle of the ignition key... made me think it was a bad ignition switch (tilt telescope), there seemed to be a spot in the switch in between both the accessory power and ignition power being on at the same time. I put a NOS switch in, looks like I'm still having the issue, and I still have vague positions on the ignition key.

I need a grown up! Help!

 

[Ross Wooldridge]

Please check the 12V feed to the coil - the wire runs along the valve cover and is held down by bend-over tabs, which can rub the insulation away and short the wire to ground.

I had the EXACT same symptoms as you, and it was hard to diagnose. Found it, and it's solved the issue.

 

[65Port]

You can also get the engine up to temp on a warm day and then disconnect the wire to the electric choke. The coil in the choke should have enough underhood heat to keep the choke open. Then you can see if it is still stalling with the electric connection omitted.

Other than that, check anything you may have moved or touched during your carb swap.

 

[CBODY67]

The electric choke is not the issue. I had a TQuad 9801, w/electric choke, on my '67 Newport 383 4bbl with no issues at all. With the stock a/c alternator. ONLY thing is that the power to the elec choke has to be "switched" rather than "direct".

How old is the fuel in the tank? Are you buying fuel from a location which is "higher volume" rather than a small station? Did the performance issues start with a temperature swing of the weather?

Might try adjusting the elec choke thermostat a notch leaner than it is now. When the ambient temp, with the engine completely cold, as about 70 degrees F, adjust the electric choke thermstat until it barely closes. Tighten the choke coil screws down at that point. Probably will be a notch or two leaner than it now is, I suspect.

Might even be a worn fuel pump pushrod.

Just some thoughts,
CBODT67

 

[1971 300 Alvah]

The electric choke is not the issue. I had a TQuad 9801, w/electric choke, on my '67 Newport 383 4bbl with no issues at all. With the stock a/c alternator. ONLY thing is that the power to the elec choke has to be "switched" rather than "direct".

How old is the fuel in the tank? Are you buying fuel from a location which is "higher volume" rather than a small station? Did the performance issues start with a temperature swing of the weather?

Might try adjusting the elec choke thermostat a notch leaner than it is now. When the ambient temp, with the engine completely cold, as about 70 degrees F, adjust the electric choke thermstat until it barely closes. Tighten the choke coil screws down at that point. Probably will be a notch or two leaner than it now is, I suspect.

Might even be a worn fuel pump pushrod.

Just some thoughts,
CBODT67

The fuel is new, and the issue has persisted across multiple tanks purchased from different locations.
The issue does not present itself when cold, it happens after warm up when the engine is running smoothly. The engine speed doesn't slow or stumble, it just shuts off.
I wonder about the fuel pump, as it is hard to start after it shuts off.

 

[3C's & a D?]

How's your coil? Old/bad ones don't like heat and will behave as you've described.

 

[CBODY67]

Condensers, if equipped, can fail too. Only buy NOS items, if possible.

CBODY67

 

[Bucket]

Sounds like a fuel issue to me .

 

[halifaxhops]

Points or electronic ign? Only when hot sounds like a bad pick up or ecu from what you posted especially if it starts right up after it cools down.

 

[Boydsdodge]

Also check the main power from ignition switch to coil and ballast resistor, the connection under dash could have gotten hot and now loose. But if you have electronic ignition, I would start with ECU and also grounds.

 

[halifaxhops]

If it was a newer MP kit I would suspect the orange ecu. New ones are terrible.

 

[Ross Wooldridge]

A fuel issue would likely have the motor gasping as it stopped.

A loss of spark has the engine stopping immediately.

I still lean towards ignition - loss of coil, ECU failure, that sort of thing.

A car needs spark, fuel, and air to run.

So start at the beginning:

AIR
Well, it's obvious it's getting air...

SPARK
Check the feed wire to the coil for worn insulation.
Check the ignition wire from the coil to the distributor to see if it's loose.
Try a known good ECU (FWIW, I don't like the orange boxes either) if it's an upgrade to modern electronic ignition
Try a known good coil

You didn't say anything about replacing the ignition system with a new version - so check the components of the ignition system - it it's still running points, look at the condensor and points.

FUEL
Make sure that fuel is squirting into the carb when manually opening the throttle and watching for it.

 

[1971 300 Alvah]

Lots of good advice here. It may be a while before I get an opportunity to dig deep into this to find the solution. In the meantime I am driving the car, no stalls this morning...
I did replace the original distributer for the Mopar electronic, I did this when I 1st bought the car 8 years ago, so I'm not sure if this should be a "suspect" unit or not. The coil was also replaced in the 1st few years of ownership as well.
The spade connection from the wiring harness to the ballast resistor seems a little lose...

 

[Sixpactogo]

The first thing I would do is check the case ground on the ECU. A poor ground (more than .08 ohms) causes a transistor to open because of being overheated and will close the circuit back up when cooled down. People always blame the orange box when many times it is their own doing. The Chinese units are more apt to have the issue due to inferior components but even the better ones will fail because of a bad ground. You could have other problems but that is where I would start.

 

[halifaxhops]

If it has a real transistor on a heat sink instead of buried in the potting. We beat the hell out of it here

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Was heading out to a local car gathering a couple weeks ago, and a no start on my '76 Truck. Turns out the 1 year old replacement brain box failed. I had a well used 1974 5 pin brain box from my '74 Dart that I had replaced because all the goo on the back had melted out from the hot sun in...

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[1971 300 Alvah]

The first thing I would do is check the case ground on the ECU. A poor ground (more than .08 ohms) causes a transistor to open because of being overheated and will close the circuit back up when cooled down. People always blame the orange box when many times it is their own doing. The Chinese units are more apt to have the issue due to inferior components but even the better ones will fail because of a bad ground. You could have other problems but that is where I would start.

I've got a very high quality multimeter, with a very low quality operator... I'm excellent at checking voltage, other than changing the dial to ohms, where do I measure the grounded resistance from?

 

[Big_John]

The spade connection from the wiring harness to the ballast resistor seems a little lose...

The very first thing to do is repair that.

With any intermittent problems, you want to eliminate the easy stuff first.

 

[Sixpactogo]

I've got a very high quality multimeter, with a very low quality operator... I'm excellent at checking voltage, other than changing the dial to ohms, where do I measure the grounded resistance from?

One probe on Neg post of the battery and one probe on the case of the ECU. If it has a good ground, it will show .03 ohms or less. If you get a bad or high resistance, try scraping a little paint off the firewall around the mounting bolt. Better yet, put a star washer between the firewall and ECU. Some guys have added a designated ground wire from the engine to the ECU mounting bolt.

 

[CBODY67]

One probe on Neg post of the battery and one probe on the case of the ECU. If it has a good ground, it will show .03 ohms or less. If you get a bad or high resistance, try scraping a little paint off the firewall around the mounting bolt. Better yet, put a star washer between the firewall and ECU. Some guys have added a designated ground wire from the engine to the ECU mounting bolt.

In one respect, using a star lock washer under the existing flanged-head bolt and then one between the ECU and the body might even be better?

 

[1971 300 Alvah]

I have now replaced the ECU. I am interested in the HEI conversion, but for now I just ordered a replacement box (the blue one) from Summit Racing. The car seems to run better than it has for a long time now, but then again it ran fine before except for the more than occasional failures...