f100 question

[camron84]

Hi Guys,

I am having an issue with a 1999 f100 that I recently purchased. It seems to have a dead miss on cylinder number 4 at idle however it will run up to 5600 rpm with no problem. right around the 22-2300 rpm mark the miss is very noticeable and then goes away. I swapped plugs, and coils. and the miss still persists on the same cylinder. I pulled the plug out of the bottom cylinder and it looks to be very clean in comparison to the others. I am wondering if water might be getting into that cylinder causing the low rpm miss? I did a compression test on it and the readings seem to be even. also cleaned out the carbs on it. I ordered a carb vacuum gauge but that has not arrived yet.

Any input on this would be appreciated

Thanks
Camron

[rodbolt17]

my guess would be carbs.

that system fires 1&4 and 2&3 at the same time.

if you suspect water then carefully inspect the plug electrodes and do a leak down test.