I rebuilt an engine bottom up. Run it and after the lifters pump up, you hear a chirp like when the battery is dying in your smoke detector. It is not cyclical and occurs at low idle. You can't tell where it is coming from at all. We have it running out of the bus and can stand on left and it sounds like the right side, if on right it sounds like the left side.
We finally figured out that if you disconnect the number 1 spark plug wire, it stops but as soon as you touch the plug wire back the spark plug, it chirps. We replaced the plug and the wire and still the same issue.
Any ideas?
