351C issues

[DRZ 0]

I have a 1970 Mustang I restored. Engine is a 351C mated to a 4 speed. The engine has given me fits now for two years. It starts and runs smooth when cold. If I drive it after about ten miles or so it dies. After much trying it starts and a mile later we go through the whole thing again. When I get back home it will not even idle. It will start run for a minute or so then die. I have changed the coil the distributer the carb and the fuel pump. I think it is a fuel problem but not sure. I have checked the tank and changed fuel filters. The fuel lines are new as well. Do these engines vapor lock? That is what it acts like to me. I am not a stranger to a Mustang. I have owned and restored a 65 a 67 convert and a 71 429CJ Mach1. But have never had an issue like this. 

Also on another note does the 70"s mustang have the blinkers hooked up so the side marker lights for the side markers blink when turn signal on that side is used? When you turn left or right that side of the marker lights blink also.  

[RPM 1,242]

Vapor lock after ten miles, I doubt it. 

What ignition system you using? If points, have you checked the points and condenser? You can disconnect the condenser to test if it's the cause. Not using the condenser for a period of time will fry the points though. 

 

[Vicfreg 790]

If you let it idle for 30 minutes sitting in the driveway, does it die, or continue to run?

RPM has a good point, the condenser might be the issue.  The are essentially a capacitor, and have a finite lifetime (like 7 to 8 years).  I would get one from NAPA or a reputable on-line supplier (not Amazon-Chinese supply).  They are cheap.

Other potential issues:

 - Are you using a stock coil or aftermarket (like Flamethrower) coil?  The newer coils are much lower resistance (about 1/3) than the original coils.  

 - Is your "pink"  wire to the coil in good shape?.  This is the pink "resistor wire" that is used to supply less than 12 v to the coil.  Not sure what the resistance is supposed to be, MidLife would know.

 - Did you replace the ignition switch when you restored the car?  Did you rebuild the steering column?  The 1970's have that funky column mounted ignition switch, where the wires are kind of riveted on to the switch housing. Could be an intermittent connection there.

Hope you find the issue.

Vic

[DRZ 0]

4 hours ago, RPM said:

Vapor lock after ten miles, I doubt it. 

What ignition system you using? If points, have you checked the points and condenser? You can disconnect the condenser to test if it's the cause. Not using the condenser for a period of time will fry the points though. 

 

I have had two different pointless systems in the car. It did the same thing with both.

[DRZ 0]

22 minutes ago, Vicfreg said:

If you let it idle for 30 minutes sitting in the driveway, does it die, or continue to run?

RPM has a good point, the condenser might be the issue.  The are essentially a capacitor, and have a finite lifetime (like 7 to 8 years).  I would get one from NAPA or a reputable on-line supplier (not Amazon-Chinese supply).  They are cheap.

Other potential issues:

 - Are you using a stock coil or aftermarket (like Flamethrower) coil?  The newer coils are much lower resistance (about 1/3) than the original coils.  

 - Is your "pink"  wire to the coil in good shape?.  This is the pink "resistor wire" that is used to supply less than 12 v to the coil.  Not sure what the resistance is supposed to be, MidLife would know.

 - Did you replace the ignition switch when you restored the car?  Did you rebuild the steering column?  The 1970's have that funky column mounted ignition switch, where the wires are kind of riveted on to the switch housing. Could be an intermittent connection there.

Hope you find the issue.

Vic

New ignition switch and I have tried two original coils also using one of the pointless distributors. It acts like it is a fuel issue. Never seen this in my 50 years of doing this. I have always considered the 351C a boat anchor but I really want this to work. The car was 351C 4 speed Factory A/C tilt wheel AM/FM 8 track power steering power brakes trac loc  car. The wiring was original and like new as it was out of the car in a box for 20 years (so I was told). Still has most of the ford tags on it.

[Vicfreg 790]

Ok. If you use the pointless systems, and the lower resistance coil, you probably need to bypass the pink wire so you get 12volts to the coil. I did this on my '68.

 

 

 

 

[DRZ 0]

32 minutes ago, Vicfreg said:

If you let it idle for 30 minutes sitting in the driveway, does it die, or continue to run?

RPM has a good point, the condenser might be the issue.  The are essentially a capacitor, and have a finite lifetime (like 7 to 8 years).  I would get one from NAPA or a reputable on-line supplier (not Amazon-Chinese supply).  They are cheap.

Other potential issues:

 - Are you using a stock coil or aftermarket (like Flamethrower) coil?  The newer coils are much lower resistance (about 1/3) than the original coils.  

 - Is your "pink"  wire to the coil in good shape?.  This is the pink "resistor wire" that is used to supply less than 12 v to the coil.  Not sure what the resistance is supposed to be, MidLife would know.

 - Did you replace the ignition switch when you restored the car?  Did you rebuild the steering column?  The 1970's have that funky column mounted ignition switch, where the wires are kind of riveted on to the switch housing. Could be an intermittent connection there.

Hope you find the issue.

Vic

New ignition switch and I have tried two original coils also using one of the pointless distributors. It acts like it is a fuel issue. Never seen this in my 50 years of doing this. I have always considered the 351C a boat anchor but I really want this to work. The car was 351C 4 speed Factory A/C tilt wheel AM/FM 8 track power steering power brakes trac loc  car. The wiring was original and like new as it was out of the car in a box for 20 years (so I was told). Still has most of the ford tags on it. And yes 30 minutes or less it stumbles and dies.

[Vicfreg 790]

Oh, ok. Sounds like you have covered all the bases.   Not sure what else to check.

[DRZ 0]

3 minutes ago, Vicfreg said:

Ok. If you use the pointless systems, and the lower resistance coil, you probably need to bypass the pink wire so you get 12volts to the coil. I did this on my '68.

 

 

 

 

I will check that out. Thanks

[Vicfreg 790]

I was trying to find my Pertronix instructions, but I remember ditching the pink wire as there was only like 9 volts going to the coil, and I am pretty sure that it needs 12 volts.  

Not sure why that would cause these intermittent problems.  Good luck. Sounds like a really nice car.

Vic

[69RavenConv 302]

Confirm the choke is opening? Any evidence of running rich or lean? I agree about bypassing the resistor wire.

[DRZ 0]

Yes choke is open seems lean have tried two carbs and also new fuel pump.

[kblagron 28]

I had an issue with the Pertronix III and the rev limiter - Once I turned it off, everything worked fine.

[Mach1 Driver 596]

In case you are wondering how to get "keyed" power into the engine compartment, see below. You need power that is on in "Start and ON". The yellow shows the resistor wire going through the firewall, but I'm assuming you don't want to run another wire through the firewall. There is also a line that goes to the voltage regulator. The non-tach car looks like below. 

This line can't drive a coil, it's too much amperage, but you can add a relay that gets it's power directly from the battery. Note that the example on the right with the starter solenoid does not work in your case.

[Vicfreg 790]

Oh, that’s very interesting with your rev limiter, good job troubleshooting that
 

[RogerC 147]

Before I parked my 69 with a fresh 351C, I could drive around town for maybe a half hour then it would start running rough and vapor lock. I later figured out I had a windsor thermostat instead of the cleveland specific one. The engine would get too hot and cause vapor lock. It did run better at highway speeds but only because enough airflow was passing through. These are great engines if built right, unfortunately the parts stores contributed to this issue, especially in the past, due to supplying windsor thermostats for clevelands.

[DRZ 0]

Thank you all. I am still working on this issue. I have had trouble getting into this site. Seems good now. I have driven the car now in cooler weather and it is doing ok. But now having trouble getting it to start after driving a while and shutting it off. I have to turn it over for several times and longer periods of running the starter then it starts and seems fine. Not running rich at least when it starts no black smoke. I have jetted up the Eddlebrock carb to 100 jets as it seemed lean before. I have never in 40+ years seen anything like this that I cant figure out. But this is going on 2 years now. Although I have a lot of other cars I work on as well.

[RPM 1,242]

Ya, this site has been running out of bandwidth towards the end of the month, but it seems to be shorter periods of time. 

 

[Vicfreg 790]

This is a very elusive cause you are chasing here. The only other thing I can think of is perhaps a vacuum leak.....

[BobW70Mach1 29]

Pertronix points needs 12 volts.  They sell this simple kit to bypass the resistor wire without having to cut the wire. I would also make sure you have the Robert Shaw 180-333 thermostat.  99% of Cleveland problems are because people are using a Windsor thermostat.

https://www.amazon.com/gp/product/B004OXT3X4/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

[det0326 191]

A stupid question I guess (you seem very knowledgeable ) but when you drive it and it dies have you looked down the carb throat to confirm it is squirting fuel. 

[bigmal 229]

Try running with the gas cap open/off. This will eliminate fuel tank venting as the cause.