My 5.0 carbed motor has a MISS!!!!! WTF, HELP

[Matts89LX5.0]

i have a 1985 mustang GT. Holley carb, weiand intake, full exhaust. Everything else is stock. When during cruising conditions, the car does not miss or anything. While stomping on the gas it starts to miss at about 3500 RPM and up. Not sure what the problem is. Thought it only needed a tuneup. Already did plugs wires, cap, rotor, fuel filter, new ignition coil. Can't figure it out. If anyone can help me out, please do lol. Thanks in advance.

Matt

 

[retro50]

Try seperating the #6 and #5 Plug wires from each other. You may be experiencing ignition crossfire in these two wires. Just don't run them side by side. And check your total timing with a timing light. This may help.

 

[Dark Knight]

are you running the stock horseshoe connector for the coil? mine had one of the wires break inside.. took forever to find the prob..

what about the duraspark box?

check the alt. too, might not be putting out enough to fire the plugs good under load..

 

[blackstangt]

what retro said and check to see that you are getting enough charge from your alternator.

 

[dastang2]

you might be starving for fuel, try replacing the pump. it is pretty cheap. even an aftermarket pump is cheap

 

[Matts89LX5.0]

brand new altenator, brand new battery, and brand new starter as well. The headlights still get dim though for some reason. Wouldn't something like the duraspark ignition going bad effect the entire driving range and not just 3500 and on?

 

[dastang2]

ignition is a tricky subject and ***** like this happens a lot.

 

[hllon4whls]

Ignition is affected by high rpm. If it was fuel, I think you would have more issues.

What does the miss sound like? More like ignition, a poping or poofing from the exhaust? What?

 

[dastang2]

not really, when i only had one electric fuel pump on my carbed stang, when i was racing at high rpm, the car would cut out terribly. now that i put 2 pumps on it, it runs strong throughout the rpm range and no cutting out either. we just put a new fuel pump on a 93 e250. the van would run great at idle and below 2000 rpm but when revved it would not go over that and backfired in the cylinders. it also made the cat glow red. now it is running good again

 

[dastang2]

since your engine has a mechanical fuel pump here is a little check you could do. go and smell the oil on your dipstick. if it smells like gas, replace the fuel pump and change the oil. not saying this is exactly your problem but it is a good idea to keep this in mind. even if it has no gas in the oil, your pump may be going or your pickup screen could be clogged in the tank.

 

[maverick0716]

I had a similar problem last november. It started doing the same thing you described and I couldn't find the problem for the life of me. New cap, rotor, msd wires, new spark plugs.....nothing solved it. It gradually started getting worse and worse until it started doing it in low rpms too. When I got off the throttle the exhaust would make popping sounds. I decided it was probably a vacuum leak and I should pull the manifold (I really didn't want to). Well I'm glad I did that because all the intake manifold gaskets were totally screwed. Both of them were pushed towards the front of the engine and most of the ports were half covered by gaskets. I still don't know how the hell it happened, my only guess is they came untorqued when I put my new performer rpm manifold on (I only torqued them once).

Your's may not be that problem but its a thought

 

[Matts89LX5.0]

it's like a bucking and popping from like 3500-4500 rpms. Usually rite after i pass that the car runs like its trying to make up for the hesitation for that rpm range. I will try smelling the oil lol and see if i can smell gas in it. I've only had EFI mustangs and this is my first carb and I'm trying to learn everything as quick as possible lol. Thanks guys.