2006 ford five hundred 3.0L 2wd. Replaced a brake caliper yesterday. Went to start the car and it wouldn't turn over. Had a very weak crank. Then the tachometer needle sporadically bounced up and down for a few seconds. It did that a couple times before it finally turned over.

What the hell was that?! I had a non start issue a few months ago that was solved by replacing the fuel rail pressure sensor i think it was? It was similar to that but without the needle jumping. No check engine light, no other problems other then a small exhaust leak that I need a gasket to fix.

Thanks in advance!

 

.The crank sensor will not affect the cranking ability of the starter You said "engine wouldn't turn over and had a very weak crank".. I suggest you start by getting the battery tested and the battery connections cleaned up. If the engine is barely cranking, I wouldn't expect the tach to be displaying properly.

Get the engine's starting system working first and address any other issues thereafter.

 

The battery is fairly new and the terminals are clean. Its happened that two times and never before that. Thos morning it started right up and it had a weak crank but turned right over at lunch.