Engine problems - break up above 2500 RPM

habiv · Sep 28, 2011

jrichker said:
Have the alternator bench tested. There is definitely a problem with it somewhere.

The alternator is fine. Also, there have been three alternators on the car since this problem started occurring when I acquired the car 10 years ago; the original alternator and then two new ones. The newest one is only a couple of weeks old, as I was thinking the same thing you are, that the alternator was bad. That would be some extremely bad luck if all three were duds

jrichker · Sep 28, 2011

Have you done any of the testing I posted? The voltage drop tests are the best way to find bad connctions in the power and ground wiring for the alternator.

habiv · Sep 29, 2011

jrichker said:
Have you done any of the testing I posted? The voltage drop tests are the best way to find bad connctions in the power and ground wiring for the alternator.

Yes, We have tested everything and there is no voltage drop. The car runs at normal voltage, which is the problem. When there is lower voltage (when using the resistor) the car runs fine. I know it is hard to diagnose things over the computer and I appreciate your help very much. I do have a very knowledgeable friend here helping me but we are both kind of at a loss at this point

mike0227 · Sep 30, 2011

Engine miss

My mustang did this at 4000 RPM, looked all over for the problem and finally found the computer ground wire had way to much resistance. We replaced one of the 2 ground wires (#60 and #?) problem was gone. Good thing my son being an experienced master tech.

Also Jrichter always reiterates to check ground wires as part of diagnostic process.

habiv · Oct 3, 2011

mike0227 said:
My mustang did this at 4000 RPM, looked all over for the problem and finally found the computer ground wire had way to much resistance. We replaced one of the 2 ground wires (#60 and #?) problem was gone. Good thing my son being an experienced master tech.

Also Jrichter always reiterates to check ground wires as part of diagnostic process.

Interesting. I will look into this. Thanks!

habiv · Oct 14, 2011

I decided the computer ground couldn't be the problem, as the car only breaks up when the alternator is connected, so that was a dead end

We have been able to get the voltage up to 12.5 when using a resistor and still have the car run well. I took it out for a ride and everything seems to be okay. I guess I will have to keep it like this for now and just hook it up to a battery charger when it is in the garage. Maybe I will look for an original Ford alternator next time I am down in Carlisle. Who knows, maybe the new repo ones I have been using are just no good Thanks everyone for the help.

Coboose003 · Nov 22, 2011

Ok so I am having this same issue and have had it ever since I have changed my distributor to a pro billett distributor. I since then have changed my coil to an msd coil, changed my alternator to a PA performance 130 amp alternator, and replaced my timing chain while doing it i broke my timing cover and replaced that and noticed a seal was comming out of the back of my harmonic balancer so I replaced that. My car is doing the same thing at 2500 rpms no idea what it is though

Engine problems - break up above 2500 RPM

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