68 GTS won't stay running

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Jimmy428

Jimmy428

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Hi guys. I'm new here and in desperate need of help with my dart GTS. It has a 340, 727, 8 3/4 with 3.55. It was a fantastic running car but now for some reason it won't stay running especially after it has warmed up. I am at a total loss. I put a new battery, voltage regulator, coil, spark plugs, wires, carburetor, ballast resistor, and no change. Same thing happens. Starts fine, runs until sufficiently warm and cuts out, then will not restart with vapor lock or flooding symptoms. Will only restart after sitting for some time. Car has electronic ignition and was converted by the previous owner. Have had no issues for the last ten years. Never did anything but oil changes. I do not know what to look at next. It has to be something simple. It will even cut off as I am giving it gas (hold gas to raise rpm at a steady high pace and still cuts out). Any help is greatly appreciated. Thank you.
 
Sounds like the fuel tank sock filter is clogged. Fuel starvation....takes a while for the gas to seep back through it.
 
Very first thing to do is try to separate into spark? / other electric or fuel?

When it dies, IMMEDIATELY check for spark. A wrench in this gearworks is that you need to use the key, not jumpering the start relay to do this, so that you bypass the coil bypass resistor. Easiest way would be to rig a spark gap out of a spark plug, or buy a spark tester.

If that checks out, pull the air filter, look down the carb throats and work the throttle. It should immediately produce a shot of fuel from the accelerator pump.

I'm playing with EFI (last fall) but best thing I did with my Dart for poor hot start/ vapor lock was to install a rear mount electric pump, use a carb isolator, and rig a vapor return system.
 
If I can say one good thing about the see thru fuel filters... you can see fuel delivery issues. :)
I would like to know if you have a dual or single ballast resistor, 4 pin or 5 pin ignition module. Doesn't make a whole lot of difference though. Either of the ignition module types can fail just as you describe. Sometimes we find the gel coat running off the back of them too. Overheat and fail, cool and run again.
 
if it's electrical, might be coil. had balast hooked up wrong once and had too much voltage going to coil, was doing same thing your describing. I keep an old plug and
when mine won't start I pull the wire off one of the plugs, put on the old one and
sit it on something metal like the brake master cylinder, leave the key on and use a
screwdriver on solinoid to crank it over
 
Sounds like a fuel issue to me....fuel pump or fuel filter......Get a clear filter and put it inline and then you can see if you are getting fuel...When it dies, check the fuel filter if no gas in it then it is a fuel delivery problem.....Also a fuel pressure gauge inline is a good idea....
 
bbrroowwnn said:
sounds like a fuel issue to me....fuel pump or fuel filter......get a clear filter and put it inline and then you can see if you are getting fuel...when it dies, check the fuel filter if no gas in it then it is a fuel delivery problem.....also a fuel pressure gauge inline is a good idea....
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x2
 
Thanks for all the replies. Lots of fresh ideas to work with. To the best of my knowledge, the electronic ignition in the car now resembles a mid 70s electronic ignition setup, so not sure if someone had used a donor car and swapped it all over. It looks like a dual ballast on there.

I have a see through filter on it and when it dies, it does not crank any gas into it. I have one question though, although it seems fuel starved, why would the accelerator pump shoot gas still as though it is not? Maybe that's not enough to start it? I know the tank has a lot of crap since I have always replaced a lot of filters so I'll start with that today. I can drop the tank and clean it out real well. Worth a shot. If it does it again, I will check for spark immediately after it dies.

My dad thinks I'm crazy working in this cold! Haha he said it reminds him of his youth. I also replaced popped wheel cylinders and bled the brakes yesterday. Man this car is a nightmare right now. I guess when it rains it pours.
 
The fuel in the accerator pump cavity is seperate from the fuel in the bowl.
If you are sure the bowl vent is opening.. delivery from the tank may be the problem.
The fuel pump needs to both pull and push. The 2 small sections of rubber line can deteriorate and fault the pull side.
 
Check the rubber hose going from the sending unit at the tank to the fuel line,I had one go sour once did just what your going through.The fuel pump,sucking hard like a crack hore would colaspe it after not running it would allow some opening.Just my 2 cents,lol seams our 1 cent is going out of circulation so that word penny will not apply any more.
 
im voting on fuel delivery as well only because ive had pretty much the exact same issue before. mine was water that had gotten in the tank and caused a rust issue that clogged up the lines . i definately dont think it would to clean the fuel tank on any 25+ year old car
 
That sounds EXACTLY like a plugged filter as mentioned above.
The separate cavity for the accelerator pump is a great call also.

Look for another filter underneath.

You can also run the car off of a seperate container bypassing the tank and pump all together and see how it runs. (gravity feed to the carb)

Or run it off a separate container and run your normal fuel line into a container to watch the flow.

It's kind of a pain, but it sure will tell you alot.
 
TrailBeast said:
Or run it off a separate container and run your normal fuel line into a container to watch the flow.

It's kind of a pain, but it sure will tell you alot.
Click to expand...

I would try this ^^^. Hook a fuel line to your pump and into a gas can. If it starts and runs you know your pump is good and your problem is from the pump back.
 
As stated above, while you are under there, pull the sender and look at the fuel sock since you noted there was "crap" in your fuel tank.
 
check ur wiring under dash and fuse box , If u have good fuel pressure using a gauge at least 5 psi that's a problem is ruled out .. if no spark after the stall n cut off then its electrical issue .. Where talking about a 30 year old wire harness correct ? u converted to ECU ignition u need more amp's to power it 60 amp alternator a constant output regulator the blue box .. check ur fuse box turn up side down , may need a new one for that set up.
 
Some updates, the gas tank is completely clean with zero rust. A shocker, but true.

Did not test the fuel pump because when I saw this i assumed its bad. Will replace that tomorrow.

Also realized my fuel gauge is completely wrong. It was registering empty with a half tank. I always thought it drank gas too fast and never took as much to fill it.

The sending unit is new and unclogged. Looks 100% good.

Only other factor is the fuel lines may be clogged if its not the pump. But my thing is, if the tank is perfect, the lines shouldn't be bad, so hoping it's the pump unless its the lines that rusted causing the filter to crap up. Either way, my new fuel filter never filled all the way so it's gotta be starving for gas.

I also noticed that a hole at the top of the tank above the sending unit hole is plugged. Looks like a spot for a vapor line?

Any suggestions on the gas gauge and missing line would be appreciated. I will let you know how the car turns out tomorrow.
 
Ok I saw the filler neck has a vent tube attached, but the bottom half is not there. Maybe it rusted off and fell and was plugged at the tank some time ago before I acquired the car. Will there be any adverse effects with no vent tube?

I did have a vacuum gauge on the car and was reading very low. I believe 5-6" at idle in drive. I also recall the po saying "I stuck the biggest cam in there I could since there is no power brakes or anything running off vacuum to worry about"

I could not locate a vacuum leak.
 
............Ur fuel filter will not befull all the time, in fact it will be empty at times as the fuel pump pulsates as it pumps,...........kim............
 
Sometimes the second try but most times it's a while. 15-30 min before it'll want to go again. Also, immediately after dying, I checked for spark with the key in the ignition, not jumpering it and it gave plenty of strong spark. They told me Monday for the new pump, so I guess I'll give it a shot. I fitted a nipple to the tank and attached the vent tube, so that's good now.
 
My '74 did this to me a lot in 2006 and I was pulling my hair out.

Turns out, the rubber fuel hose between the sending unit and the fuel line was collapsing/sucking shut (new but defective) after I ran the car for a while. Replaced that hose and didn't have that problem again.
 
After you replace the pump, and it still does it, I would look at the possibilty of vapor lock, try an phenolic spacer under the carb.
 
Mine was doing something like that

The lower radiator hose was too close to the fuel pump and causing issues

Had electric pump installed and solved most of the issues

Sounds like fuel issue to me
 
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