318 stalling while driving

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Dion Light

Dion Light

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Nearly every day for a week I start my ‘76 Dart w/318 2BBL and drive about 6 miles. While cruising along at 55 mph it will die. I slap it in neutral fire it back up and continue on my way without any issues the rest of the day. Yesterday it wouldn’t restart, pulled off the road, I could get it to start but wouldn’t stay running. Fuel line is clean
Any ideas where to start?
 
Check all the jumpers in the fuel line, they tend to collapse and starve the engine



also check for loose wiring
 
When cruising along does it stumble and then die or just die?
Running a mopar ECU?
Almost sounds like an electrical thing to me...
 
If it stalls when driving, then don't drive it so it won't stall... :steering:
 
Dion Light said:
Nearly every day for a week I start my ‘76 Dart w/318 2BBL and drive about 6 miles. While cruising along at 55 mph it will die. I slap it in neutral fire it back up and continue on my way without any issues the rest of the day. Yesterday it wouldn’t restart, pulled off the road, I could get it to start but wouldn’t stay running. Fuel line is clean
Any ideas where to start?
Click to expand...


Check the reluctor gap in the distributor... It should be .007" with a brass feeler gauge...
 
I had an ECU that would fail this way. Get hot and quit. I used the same process you did, put it in neutral and restart. The ECU box case needs grounded well too and sometimes poor grounding can causes issues.

Starting and not staying running might be a different issue like ballast resistor, fuel, or other electrical issue. Every old car my dad and I messed with has needed a new ignition switch.
 
Yeah if it's just dying then I'd be looking at electrical. As stated make sure the ECU is well grounded. I run a wire to a good ground to one of the mounting screws.

Also, as dano said; possibly you are losing voltage to ignition from bad ignition switch / bulkhead connector.

Quickest thing to try is when it is not starting, check for spark and then start measuring voltage at ballast etc with key in "run position"
 
If the dist has done a lot of miles AND the vac adv is hooked up [ & working ], the p/up wires may have finally broken from constant flexing. Disconnect plug & while wiggling the wires, check resistance. Should be 150-600 ohms & STEADY.
Other possibilities: plugged fuel filter, sock in the fuel tank blocked with debris.
 
Sounds like a ECU or pickup coil to me. They get hot internally and seem to fail, cool down work fine for a bit. Then if it has a fake transistor on top it is a nowere one and they have issues no mater who manufactured them.
 
Thanks everyone for the input
Educate me on 4 pin versus 5 pin ECU’s
Mine is running a 4 pin with a Malaysian made chip
But the spec sheet calls for a 5 pin
Thanks in advance
 
Dion Light said:
Educate me on 4 pin versus 5 pin ECU’s
Click to expand...
4 & 5 pin ECUs
Kit's explanation as to the internal regulation of the ECU's power.
Chrysler's introduction of the factory system 1972 Imperial & Chrysler Ignition System Service Book (Session 292)

Dion Light said:
Yesterday it wouldn’t restart, pulled off the road, I could get it to start but wouldn’t stay running. Fuel line is clean
Click to expand...
Good clue here...
Start and Run have seperate routes to the power the ECU and Coil
Ignition Start provides power to coil without going through the 0.5 ohm resistor.
Ignition Run is J2 (blue)

Factory Ignition wiring for 1976
upload_2022-6-28_8-44-58.png


A 4pin replacement ECu doesn't use the 5 ohm resistor for regulating its power.
The ECU gets its power only through the top pin.
upload_2022-6-28_8-50-42.png
 
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Dion Light said:
Nearly every day for a week I start my ‘76 Dart w/318 2BBL and drive about 6 miles. While cruising along at 55 mph it will die. I slap it in neutral fire it back up and continue on my way without any issues the rest of the day. Yesterday it wouldn’t restart, pulled off the road, I could get it to start but wouldn’t stay running. Fuel line is clean
Any ideas where to start?
Click to expand...

having the same issues with a big block and an msd ignition , complete rewire , new ign. switch, new coil, new relays, new starter, and wiring to it , new battery, wondering about the msd 6al , but it fires when tested-----------???
ANY AND ALL SUGESTIONS APPRECIATED !!!!!!!!!!
 
Mattax said:
4 & 5 pin ECUs
Kit's explanation as to the internal regulation of the ECU's power.
Chrysler's introduction of the factory system 1972 Imperial & Chrysler Ignition System Service Book (Session 292)


Good clue here...
Start and Run have seperate routes to the power the ECU and Coil
Ignition Start provides power to coil without going through the 0.5 ohm resistor.
Ignition Run is J2 (blue)

Factory Ignition wiring for 1976
View attachment 1715948429

A 4pin replacement ECu doesn't use the 5 ohm resistor for regulating its power.
The ECU gets its power only through the top pin.
View attachment 1715948436
Click to expand...
Thanks again for the info.
So if I'm reading correctly, wouldn't I need a 5 pin ECU?
I have a 4 post Ballast resistor and my ECU harness has 5 wires
 
Yes I'm asking you to explain how you came to that conclusion.
That way I and others can perhaps phrase it or specificially address the point of misunderstanding.
 
Sorry I don't have a technical explanation. After reading the Chrysler article you posted above, it seems the 5th pin does protect the ECU by limiting current flow. Is it possible I'm damaging the ECU by not utilizing the 5 ohm resistor on the Ballast?
Again, I'm just assuming I need the 5 pin based on the parts and harness I have. Thanks again
 
The 5th wire on original factory ECUs was a part of the internal power control. Later the factory and aftermarket was able to incorporate solid state control into the units without using that. The 5th wire is just along for the ride and available if you ever install an original ECU.

The ECU draws only a little power as all it does is amplify the magnetic pulse (wires from the distributor).
That amplified magnetic pulse signals when to make and break the primary coil circuit. Its just an electronic version of points opening and closing.

When the key is in run, the power available in the J2 wire is approximately 14 Volts (engine running).
upload_2022-6-28_11-16-50.png

The coil doesn't need power supplied at 14 Volts. It will draw more current and get too hot if given power at that voltage. So it draws power through the half ohm resistor. This reduces the voltage the coil sees while running to something less than 14 volts..
 
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My point was that power has been getting to the ECU and the coil when the key is in start.
It only intermittantly works with key in run.
Its possible there is a poor connection in the run circuit - some place between the key switch and the splice.
This poor connection or wire either vibrates loose and/or gets hot while running. (The hotter it gets the the more resistance to flow)
It is also possible that ECU is failing hot, or that the coil is failing hot. The coil's primary and secondary windings can be checked with an ohmmeter.
The ECU is not easy to test without a tester.
 
Mattax said:
It is also possible that ECU is failing hot, or that the coil is failing hot. The coil's primary and secondary windings can be checked with an ohmmeter.
Click to expand...

ECU failing hot is a real possibility as the days I've had this issue (engine shuts off while cruising along) temps here in the Charlotte area were high 90's?
 
Vapor lock... does it have headers? is the fuel line close to the exhaust on the passenger side? also...next time it dies, carry some carb cleaner, spray it down the carb, see if it fires... This will immediately tell you wether to chase after a spark or fuel concern...
 
Dartswinger70 said:
Vapor lock... does it have headers? is the fuel line close to the exhaust on the passenger side? also...next time it dies, carry some carb cleaner, spray it down the carb, see if it fires... This will immediately tell you wether to chase after a spark or fuel concern...
Click to expand...
No headers.
It is getting fuel
Thanks
 
Mattax,
Looking at post #12, how does the 4 pin ECU get power during cranking [ start ]?
 
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