I have a 93 3.9L/auto with around 160,000 miles on it. No check engine light is on. seems to run fine as long as you don't go over 3500rpm i.e. passing someone. I checked the plugs all looked good, rotor replaced with cap, pick up coil tried with same results. I would hold it to the floor and it bogs out around that rpm. I sprayed some flammable into the TB while it was bogging with no change, which leads me to think it's a spark issue? Any commonly know problems like this? I can feel all the injectors pulsing, not sure how else to check them. Any ideas would be appreciated.

 

The most likely cause will be timing. Make sure your distributer is correctly positioned and make sure your wires are routed correctly. A new cap+ rotor and plugs and wires will help too.

 

Thanks for the reply. I have newer plugs, wires, less than 10k on them. The cap and rotor are brand new. I switched out a new pick up coil with no change. Could the ignition coil be bad? It started doing this this past winter on it's own, nothing was worked on prior to it running poorly.

 

Yes it could be the coil.