intermittant stumble

[mjm8850]

I am having a problem with my 88 mustang stumbling while cruising down the road. It acts like the power is cut off to the coil for a fraction of a second once every 2-10 minutes of driving. It did this with the stock computer, stock distributor and coil. I changed the tfi module with no help. It still did it with a aem computer, msd coil and new distributor and totally new engine including injectors and 3 different sets of plugs and wires. It has been doing this for a long time and has never gotten worse or totally died. I am about to put a turbo on this and don't want any pre-existing gremlins messing things up. Any ideas?

[85turbocoupe]

Have you run koeo/koer and checked for any codes? Do the cylinder balance test?

[mustangguy289]

When it does this, does your tach go to zero instantly?

[TENGRAM]

Hard to say from the description but it sounds an awful lot like a bad ignition switch. Take a look at that; it's usually pretty easy to tell if it is shorting out or coming apart.

[mjm8850]

The tach drops instantly about 1500rpm(it has never gone all the way to zero) and goes back almost instantly to where it was. It is never long enough to drop speed even 2mph. I got no codes other than the ones you get from removing the smog pump stuff.

[mustangguy289]

I had a 98 that would do this... the main harness had melted against the EGR tube and the crank sensor wire kept shorting out. Took me forever to find the problem. Even paid some shops to try and they couldn't find it because it was sporadic when it did it.

[mjm8850]

Hard to say from the description but it sounds an awful lot like a bad ignition switch. Take a look at that; it's usually pretty easy to tell if it is shorting out or coming apart.

The ignition switch was replaced about 8 years ago, but I haven't taken it apart since to see what it looks like. I guess I can look at that again.

[mjm8850]

I had a 98 that would do this... the main harness had melted against the EGR tube and the crank sensor wire kept shorting out. Took me forever to find the problem. Even paid some shops to try and they couldn't find it because it was sporadic when it did it.

That is exactly why I have let this go on for so long. If it were to go totally dead, it would be easier to figure out.

[donnie90stang]

Most likely the ignition, or a short somewhere... ignitions are cheap, if that dont work... start checking all your wiring looms for hot spots and melted wiring. Also check all your grounds in the engine bay. Im betting its super simple thats driving you nuts!

[Josh.0]

I had the exact same problem and its was the ignition switch....

[5.8foureye]

I would put my money on a loose ground. check all the different little ground screws in the engine bay they dont seem to be but are each very important when you talk fuel injection and sensors

[mjm8850]

I know it has been a while, but I finally got a chance to work on the stang. Thank ya'll for your input. I bought a new ignition switch and cylinder and tore it apart to find that when Ford replaced the ignition switch many years ago under recall, they didn't tighten the screws on the switch. They also left the wire terminal clips spread apart in the slightly melted wire connector housing to where they were not making a tight connection. I crimped the wire terminal clips together and put the new switch and cylinder on. I drove it for 25 miles and not one stumble! Now it is time to pull the engine and upgrade the short block for my turbo.