Running Rough

[BLPONY]

My son has a 1976 Maverick with a inline six 250. We have put a new carb on it with gasket, new plugs, wires, vac hoses, etc. It starts great and runs fine most of the time. Here is my problem. One day it will run great, then later that day, or the next day it will run rough, die at a stop light, or in general be a pain. I have checked the vac on it and can not find a leak, and the gauge hold at 20 which is what the manual says it should. The other day it would not run or idle and he called me. I popped the hood and all I did was touch the vac hoses, and then the plug wires. It started and ran great!! So we thought it was bad (but new) plug wires. We put on new ones and again it ran great. He drove it to football practice today and it was great. When he came out a few hours later it ran rough and would not idle. Again I popped the hood and touched and moved wires and hoses and it ran fine.
New hoses, checked and rechecked, new wires, checked and recheck, I am out of answers .
Does this make head or tails to anyone? Any help or thoughts will be great. He is only 16 and really loves this car, but I am afraid he is going to get discouraged with it all.
Thanks for any help, BLPONY

 

[mannella]

Did you replace the distributor cap? The next time it won't start or runs rough spray some WD40 on the cap. Also if its not a new cap look inside for any cracks or carbon tracks.

 

[rbohm]

8) it sounds to me like you have an issue with the vacuum hoses, and perhaps not getting the plug wires fully on the plug. you should feel a noticeable click when you push the boots on the plugs.

 

[BLPONY]

It is a new distributor cap but that doesn't always mean anything. But it is super clean inside. And all of the vacuum hoses are also new, but again that might not mean anything either. Since we are on our second set of plug wire I don't think that is the problem. And we are going over the vacuum hoses again with a fine tooth comb, I just have to think that if it was avacuum problem we would have it all of the time.
The only thing that we have not changed is the coil. Do you think that would make it run rough at times and not at others? I did clean the clips on connector and made sure it was making good contact, but have not changed the ciol itself. They are $30.00 at O'Reilly Auto and we hate to spend that on something that doesn't fix it (16 years old on a budget........ but who isn't these days??).
THANKS for the help so far, and any additional help.
THANKS,
BLPONY

 

[JackFish]

I was just having an intermittent problem with the electrical.
Traced it to a loose - ground from the battery. I think a coil problem would manifest itself more when the engine is hot, so I doubt that's the problem.
Have you checked the status of the choke operation?

 

[BLPONY]

I have checked the choke and everything seems to be working great there. It is a brand new carb, and we had this same problem with the old card (which was old and leaking). The problem happens both cold and hot, but most of the time when it has been driven, then sits a couple of hours or so. Then it will start fine, but run rough, and will die when you put it in gear.
THANKS in advance for any other ideas.

 

[CZLN6]

Howdy BL:

And welcome. How many miles on the engine? Is it an auto trans or manual? Is it using any oil? Is it missing any auto trans fluid? Does it act like an electrical miss or lack of fuel? I know, sometimes it's hard to tell. Why did you buy a new carb? Have any of the parts you've replaced seemed to make any differences? Does it act up more when it is cold? hot? Do you know anything about the fuel pump? How long it has been on the engine?

It could be a short somewhere, or a fuel supply problem. How old are the fuel filters? I once had a similar problem with a Comet 250 auto. It turned out that the eccentric on the cam that drives the fuel pump had gone flat- well not entirely. It would start cold and run fine, but once warmed up it would sputter like it was running out of gas. We tried replacing the fuel pump- even several different rebuilds and even a new one. There were only minor differences in the new pumps. So the problem was not the ability of the pump to pump, but a lack of actuation on the pump lever because the eccentric was not giving enough action. We finally solved it by installing a pressure switched electric fuel pump, wired into the key.

Just a thought- for what it's worth.

Adios, David

 

[BLPONY]

Thanks for the welcome and the input CZLN6. It is an auto trans, and is not using or leaking any trans fluid or oil. At first we thought it was a vacuum type miss, but after checking all of the lines and putting a vacuum gauge on it I don't see any problems there. I would think if it was avacuum problem it would be there all of the time not just now and then. So I guess I would have to say it feels and sounds like an electrical problem. That is why I am looking at the coil. Everything thing else is new on there except it and the igination module. It doesn't seem to be a fuel problem, but the reason we got a new carb (rebuilt of course) was because the old one was dried out and was leaking around the gasket near the bowl. It was old and it was easy to just put the new one on. BUT, we had the same problem before the new carb.
So far it nothing we have done has made it worse or better, and it does it when it is hot, and when it is cold. That is why none of it makes much sence. THat is what brings me to the coil and/or the module, but I guess I have never seem either of those cause that type of problem (but I guess they can).
Thank you for your thoughts, and ideas. I will take all of them and hope one of them will fix the problem.
Thanks,
Randy

 

[SteveMelchiorre]

Hey there,

I know you mentioned that the carb was new but I had all those symptoms with my '69 Mustang - 250 running a Carter RBS carb. When I dropped the bowl on the carb I found a fingernail size piece of the float had come free and was intermittently blocking my fuel flow.
Might be worth taking it off and having a look.

All best,

Steve...

 

[Ronbo]

Like Steve said, its going to be something wierd. You haven't changed the gas cap by chance? I finally got my car dialed in and it was running fantastic. Parked it Tuesday night, came out Weds morning and it was dropping cylinders. Still havent figured that one out Point being, the problem won't always be obvious. Good luck and keep the faith! They ARE good running engines when you get the bugs worked out.

Ron

 

[fordconvert]

Do you have a hand vacuum pump? Im thinking unhook the harness between the dizzy and module then put an ohm meter on the orange and purple on the dizzy side. Wiggle the wires around. Reading should not change. Run the vacuum advance through its range again reading should not change. I am wondering if there is an internal crack in those wires. That was a fairly common problem with GM's. They used a smaller wire. They would usually idle just fine but as you accelerated the would start to stutter. The only way you could get going was to feather the gas till you got to speed and then you were alright till you needed more power. You loose that connection you loose the spark which changes the vacuum state of the engine which moves the advance plate and flexes those wires again so you can imagine the death spiral. If thats it on yours the reason it may be intermittent is that something is controlling the vacuum to the distributor so at times its not trying to move. By 76 if its still all in place there are likely multiple sensors that will alter the vacuum signal to the dizzy and other things based on things like coolant temp. That could also explain why messing with vacuum lines seems to temporarily correct it.

 

[69.5Mav]

One day it will run great, then later that day, or the next day it will run rough, die at a stop light, or in general be a pain.

BLPONY

Next time it acts up try spraying a small amount of starter fluid in the carb. If this clears it up for a short time them your problem is fuel related. Check "ALL" the fuel filters including the one in the tank. My 170 1972 Mav would drive for a few blocks then starve out. When I removed the tank it had a ton of solid chunkies 3/8 " thick in it. This problem snuck up on me over the years getting worse and worse. Yours may be at the beginning of the cycle. The starter fluid in the carb should point the way if you do have a cruded up tank. A trip to the radiator shop cured my ails.

Good luck

 

[69.5Mav]

Any Progress?

 

[BLPONY]

I want to thank everyone for the ideas and help.
We changed the coil about a week ago now and it starts, and runs great. It always started pretty good, but now it starts really good. Cold or hot it doesn't matter, and everything seems to be fine now on that front.
But it is an older car, so I am sure we will have another issue at another time. We will just keep having fun working on it.
THANKS again for all of the help.
Randy (BLPONY)