Missing and Surging

[MustangPaul]

Hi all---Probably in response to the thread where I was singing the praises of the Mustang as a daily driver, my GT started to give me problems today on the way home. It drove fine to work, but on the way home, it was surging and missing as you tried to accelerate. Push the pedal down and a slow, surging acceleration. I could only get to 35 mph by the end of the on ramp, although I was eventually able to make it to 70. Just took awhile.

Nursed it home and at idle, there isn't a miss I can detect, although it did give me problems all the way home.

The Tach wasn't showing any drop off in RPM's.

This would suggest to me, possibly, some sort of fuel problem as the car only seems to misbehave at speed or getting to speed.

What do you think? Fouled plug? Fuel Filter? Fuel pump? Bad Gas? Gremlins? Evil spirits? It is using oil (quart every 1000 miles or so), so a fouled plug may be the culprit. Suggestions? I'm stumped.

I'll start checking things this evening after it cools off.

Well, at least when it is home sick, the front end doesn't squeak!



--Paul

PS Damn new Corvette drove by my sputtering car on the highway and laughed. Bastard!

 

[65fastback2+2]

Either timing, points, or your carb is a lil messed up, those things can change at anypoint in driving...

 

[krash kendall]

If your car isn't backfiring violently, then it probably isn't spark (read - no raw fuel filling the mufflers).

I'd check the fuel filter. If it is a transparent one be sure to check for water in it as well before draining it. Other problems may be debris in the tank or a loose screw on your points plate (if applicable)

I've had this problem in a couple of different vehicles, it's usually easy to sort out.

 

[MustangPaul]

If your car isn't backfiring violently, then it probably isn't spark (read - no raw fuel filling the mufflers).

I'd check the fuel filter. If it is a transparent one be sure to check for water in it as well before draining it. Other problems may be debris in the tank or a loose screw on your points plate (if applicable)

I've had this problem in a couple of different vehicles, it's usually easy to sort out.

No points. Got one of the Petronix modules. No backfiring, either. I'll swap the filter as I have an extra one. I'll add some HEET to get rid of any water in the tank. The tank is about 1 year old, so I dodn't think it is full of garbage.

I replaced the vac advance last year, so that should be ok, too. I'll check timing, too, and see what I have.

What gets me is that at idle, it behaves. Sitting still, but revving the engine, no sign of problem. However, when you move, it is like driving a two-door slug.

--Paul

 

[krash kendall]

When you demand power it will drain the float bowl faster than the pump can refill it because the filter acts like an inline resistor. At idle it requires less fuel so the pump can easily keep up.

The car would probably idle up a hill, but if you floored it it would probably die instantly.

As for water - on my sixty five it was pooring straight into the filler neck off the trunk lid because of a bad gas cap gasket. I drained 3/4 OF A GALLON of water out of it that day!

 

[Pbum5]

No points. Got one of the Petronix modules. No backfiring, either. I'll swap the filter as I have an extra one. I'll add some HEET to get rid of any water in the tank. The tank is about 1 year old, so I dodn't think it is full of garbage.

I replaced the vac advance last year, so that should be ok, too. I'll check timing, too, and see what I have.

--Paul

I had a similar problem and I racked my brain thinking it was a fuel problem or water in the tank. Turned out to be the distribitor. I had a Mallory Unilite (alomost new at the time) electronic dist. What was happening was the gel that insulated the firing inside the ditributor was worn away and heating up causing a misfire. I'm not saying that is what is happening with your Petronix but I wouldnt be surpriised.

 

[Max Power]

Classic fuel filter symptoms.....

 

[MustangPaul]

Classic fuel filter symptoms.....

I added two bottles of HEET to the tank to get rid of any water in there and since, at least in SE Louisiana terms, it is going to be damn cold for the next two days (highs of 48, lows of 25 ). While I was at it, I replaced the fuel filter since I had an extra. Car is running like a top, and, although it may be my imagination, doesn't seem to be cold-blooded (starts easier when cold.) The last gas I put in was off-brand, so I won't do that again. Probably half water.


How often should you swap out the fuel filter?

 

[krash kendall]

If you use a clear one you can usually see any particulate buildup, but for the low cost of them every 3K miles or every oil change is a good schedule.

 

[jshcobra]

Wow. While driving my 68 Cougar (J code 302) to work this morning, it did the exact same thing as your GT. It bogged and lost power at speed or on accelleration, but idled great. Tach didn't bounce or anything. Checked the points, cap, wires, etc and all looks fine. After the car cooled down, drove it back home 25 miles without any problem.

I had just put a new fuel filter on it about a month ago.

 

[MustangPaul]

Wow. While driving my 68 Cougar (J code 302) to work this morning, it did the exact same thing as your GT. It bogged and lost power at speed or on accelleration, but idled great. Tach didn't bounce or anything. Checked the points, cap, wires, etc and all looks fine. After the car cooled down, drove it back home 25 miles without any problem.

I had just put a new fuel filter on it about a month ago.

JSH--I'd swap it out. Any chance you have water in your gas? I think that is was started the problem.

As others pointed out, you might want to add a clear filter (inline) ahead of the one on your carb. That way, you could see what is going on. That's going to be my action as soon as I ditch this cold.

--P

 

[jshcobra]

Considering that I just got this car, who knows what's actually in the tank. I'll swap filters and report back.