Rough running engine

Phil66Mustang

New member
Hey,

i have a problem with my engine, it's running rough in idle mode and when im trying to maintain the same speed.

The car is a 66 Mustang with a 200cui engine with an Autolite 1100, 3-Speed manual transmission, Pertronix ignitor and coil.
I importet the car to Germany a couple years ago.

For now i rebuild the Carburetor, changed the spark plug wires, tried to adjust the timming with a timing light and a vacuum gauge and adjustet the idle mixture screw. Installed a relay to give the coil full 12V. Spark plug gap is set to 0.04. Non of that really helped.

Compression test results are 130-145psi.

When the engine is cold it runs better, ones it's hot it's getting worse.

The sparkplugs 1 and 2 look good - lean, plug 3-6 are oil fouled. Plug Cylinder 1, Plug Cylinder 5

when hooking up the vacuum gauge the needle is flipping around 18Hg. I cant get it to maintain steady. Vacuum video

I appreciate any idea on how to get the engine runnig smooth.
 
Run, a compression test.
Check spark pug wires for resistance.
Make sure coil wiring has correct polarity, + 12V - to distributor.
 
Thanks for the reply.

have done a compression test. Results waere: 1: 130psi, 2: 145psi, 3: 147psi, 4: 140psi, 5: 139psi, 6: 137psi
Spark plug wires are brand new, not much different to the old ones.
Coil wiring is set up correctly and 12V to distributor.
 
It sounds like an ignition issue. Bad or failing coil most likely being it get's worse as it heats up, or maybe the pertronix unit or both. Have you double checked that the firing order is correct on the plug wires? That the gap on the pertronix unit is set right? What is the timing set to? If you still have the resistor wire available to use you could swap back in the points and condenser and a new oem 1.5 ohm coil, that would rule out the coil and pertronix module. If it turns out they are fine and it doesn't fix the problem you could keep them in the car as emergency back up parts. I've had a coil test fine with an ohm meter and still be faulty and make the car run like crap. If the resistor wire has been removed I would swap the coil with a 3 ohm coil and see if your problem goes away.
 
I'm thinking the rough idle might have something to do with the low compression numbers you are getting. The shop manual states that compression should be between 155-195 psi. Perhaps addressing this issue might smooth things out.
 
Ok I'll try a new coil to see if that's the problem. The firing order is correct, checked that over and over. The gap in the pertronix is set up as the instruction said. Since the car came with it already installed I don't know if it did run better without the pertronix module.

On thing that irritates me is that the einginge runs smooth once I hit the gas. It runs great until I reach a certain speed and try to maintain it

The low compression is concerning me too. I can't see any blue smoke though. Any thoughts on the plug Pictures i posted on the first post?
 
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