I have a '97 with a 4.6 engine that isn't original. I bought it with what appeared to be a loose timing chain so it wen to the mechanic's for a new one. I got it back and hit the highway and rattled real loud, slowed and died on my. Inspection showed the valves were bad so those got done. Went back on the highway and it started rattling again, slowed and then died. Back to the shop to learn it burnt out the plugs and damged the intake valves in the # 7 & 8 cylinders. The truck has the following new:
Timing chains, water pump, valves, plugs, coil packs, plug wires, oil screen and a couple of main bearings (the oil pan was pulled to inspect under the engine to play it safe).
Now it is back together and runs but the mechanic said when they speed up the engine past idle the TIMING SLOWS DOWN!
The computer checks out fine with no problems or errors showing.
So, has anyone come across this and does anyone have a solution? Thanks.

 

did you replace the crankshaft position sensor?

 

No, the 97's doesnt have one according to chiltons.

 

Which motor do you have? The 4.6 has one