Hey- first time here, hopefully someone can help me out. I tried browsing the faq's but couldn't figure out what exactly to look for so I figure I would try my luck here. I'm a little knowledgeable when it comes to cars but not terribly. I'm very mechanically inclined and great at figuring out what I need to do when it needs fixing so I hope I can explain this enough to see what I need to do to fix it.

I have a 72, 351 Cleveland V-8 Mustang Coupe, which sat for a long time by my parents (it's my Mom's but for the immediate purpose, I'm to be the main driver once it's back to operating condition) and the engine was recently rebuilt. The car ran into some issues a few months ago when my Mom was driving it while I was away at school and it sat for awhile with this issue.
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The issue:
The car will start okay, and in park it revs normally to high rpms and sounds great. When in drive and idling, however, the car will act normal until the accelerator receives any pressure. Trying to give it gas to gain speed results in strange idling, like the engine is stuttering, and result in the occasional back fire, not gunshot loud most of the time but once or twice it may have. It also exhibits a tendency to want to die.

Any one able to help with what I should trouble shoot? My mom thought it was the fuel pump but to me, it doesn't make sense that it would rev perfectly in park (which unless I'm really wrong, thinks that it means the engine is getting enough fuel...) and it has a new battery, as well as fuel filter. Not too sure what else it could be. It didn't even idle until I siphoned out and replaced the gas after which point I let it run for a good ten to twenty minutes in park where it sounded fine most of the time (some of the time it idled a little low like it was going to cough and die but then it picked up again).

 

Well it almost sounds like a fuel pump...sometimes they wont make volume so you get a small flow of fuel adequate for free rev and idle but under load it cant keep up and falls on its face. It sounds like its doing it the instant you press the gas which makes it sound more like a vacuum leak. If it were a fuel pump you could idle then accelerate hard and it would run great for maybe 5 seconds then fall on its face as the floats run dry.

To check for vac leak spray carb cleaner around the base of the carb with the engine idling if the engine changes tune when you spray the carb cleaner that is the location of the leak

 

Check the fuel filter as well. It is where the fuel line goes from the pump into the carb. If it is backed up you can have this issue. I've had it happen before.

 

Sounds to me like an advance problem with the distributor. Check to see if the vacuum advance diaphram is ruptured or if the plate in the distributor that has the point on it is stuck. It should move back and forth with the diaphram.

 

I recently replaced the fuel filter, however, it may need a new one depending- but it was replaced a few months ago and never really run due to the problems. I also replaced (I think it was) the fuel diaphragm.. I'll look into the fuel pump more and a potential vacuum leak. I wasn't aware it could give enough gas to rev high like a monster but not when I tried to apply gas in drive which you guys are right, it just flops when I try to depress the accelerator.

 

Why aren't you playing tennis?

I vote for the faulty accelerator pump. As the others said, the fuel pump could be at fault too, with a diaphragm that is punctured/damaged.

Welcome to the Forum.

 

I've been lazy which is why I haven't been playing tennis. Trying to get some buddies from high school back into it since we're all totally out of shape, haha.

So... there's an accelerator pump? O.O

Dear me.. Even not knowing there was one- I'd want to bet on that since it seems to only be when the engine is under a load. I'll have to check into both of those as soon as the time becomes available. Thanks!

 

I second the fuel pump. I had a problem where the car would run fine up to a certain point and when i would accelerate the car would actually lose speed, just like yours. there was also a sound of air escaping from somewhere and the pops like you described. 2 days later it was in the shop and it was indeed a fuel pump

 

Does the car have points in the distributor?..If so I would replace the points and condensor..