4500 rpm miss

[306lx]

looking for some suggestions as to what my problem might be. my car started intermittenly missing above 4500rpm's about a month ago and now it seems to do it all the time. whenever the motor revs to about 4500, not necessarily under WOT either, it feels like an ignition miss. i have tried changing the mass air with a known working unit and that did not help. plugs and wires are good and i replaced the cap and rotor. i thought maybe it was floating valves but sometimes after it pulls a check engine light, i can shut the car off then back on and it will pull to 6000 rpm no problem, but only once or twice. the codes just read left and right bank lean condition. so i am not really sure where else to check, TFI maybe, coil, injectors? thanks in advance. oh by the way, the car runs perfect other wise.

 

[HISSIN50]

Could be a weak coil. Intermittant issues like that suck for diagnosing though.

Good luck.

 

[331 stang91]

how about your fuel pump is it old could be going I had a similar problem and it ended up being the fuel pump. GOOD LUCK

 

[HISSIN50]

how about your fuel pump is it old could be going I had a similar problem and it ended up being the fuel pump. GOOD LUCK

good thinking! I dismissed that possibility with the WOT info, but given the situation, codes and re-reading the post, that is entirely possible.

 

[5.0fox]

i also think you should check the fuel pump. my car was gutless up top and when i switched to a bigger fuel pumpit fixed that. i also gained 8 tenths and 7 mph.

 

[Bottomlesspit]

From a previous experience I had your miss leads me to think it might be your TFI module. I had the exact same thing happening...my car would only start missing above a certain rpm. Ford told me that they had seen this several times where a TFI would develop a "soft" spot and only miss at or near certain rpms. I replaced the TFI and sure enough the miss went away. I even got in on a class action suite where I got a full refund for the module. Seems Ford settled and all members of the suite got a refund. There was a defect in the modules ....at least at that time about 4 yrs ago.
If you do get a TFI module I recommend you get a stock one...not a Auto Zone type module. You don't want to play with those electronic parts.
Ken

 

[306lx]

thanks for all the replies guys, i will replace both one at a time and see what happens. any ideas what a new TFI mudule cost, and do i need to go straight to ford to get a OEM? thanks again!