High Rpm Miss 1991 5.0

[sphugh1967]

I have an occasional high rpm miss. I have performed all of the normal tune up stuff (cap, wires, rotor, plugs,) and the other day I purchased a code scanner and the scanner pulled two codes. from the 02 sensors. But bothe say the same thing. o2 sensor out of range always lean. they are continuous codes. I replaced both 02 sensors and disconnected the battery to clear the codes. I still have a high rpm4-5000 miss. Does anybody out there have any suggestions? Thanks all help is greatly appreciated.

 

[jadedinpa]

replace the TFI module on the distributor.

 

[jrichker]

replace the TFI module on the distributor.

Another vote for replacing the TFI module.

 

[HISSIN50]

I like the advice from the wise men above. I would toss out one more thing. You dont by chance run platinum plugs do you? Seems to me that a weak coil can also cause a high speed miss.

Just tossing out other things for the sake of doing so.

Good luck.

 

[90mustangGT]

Both O2's reading lean and doing the same with new O2's and the codes cleared. I would suspect a fuel problem first. If you had a weak fuel pump or a restricted fuel system, it would supply the fuel at low throttle and/or low rpm but as the fuel demands became higher, the fuel system not able to keep up would make it run lean until it would actually miss. Check the fuel pressure and see what it is doing while the engine is missing. How old is the fuel filter? Have you ever cleaned the injectors (at a minimum the in tank cleaners) and is the fuel pump stock. A weak fuel pump can have the pressure, but not the flow.

 

[txstang84]

Both O2's reading lean and doing the same with new O2's and the codes cleared. I would suspect a fuel problem first. If you had a weak fuel pump or a restricted fuel system, it would supply the fuel at low throttle and/or low rpm but as the fuel demands became higher, the fuel system not able to keep up would make it run lean until it would actually miss. Check the fuel pressure and see what it is doing while the engine is missing. How old is the fuel filter? Have you ever cleaned the injectors (at a minimum the in tank cleaners) and is the fuel pump stock. A weak fuel pump can have the pressure, but not the flow.

x2...ck fuel system

 

[sphugh1967]

Both O2's reading lean and doing the same with new O2's and the codes cleared. I would suspect a fuel problem first. If you had a weak fuel pump or a restricted fuel system, it would supply the fuel at low throttle and/or low rpm but as the fuel demands became higher, the fuel system not able to keep up would make it run lean until it would actually miss. Check the fuel pressure and see what it is doing while the engine is missing. How old is the fuel filter? Have you ever cleaned the injectors (at a minimum the in tank cleaners) and is the fuel pump stock. A weak fuel pump can have the pressure, but not the flow.

I replaced the fuel pump recently with a FRPP 190 lph unit. I replaced the fuel filter when I replaced the pump. I have ran 44k in the tank but I have never had the injectors cleaned professionally.

 

[SamSnyder]

Could you be hitting the factory rev limiter?

 

[jadedinpa]

Could you be hitting the factory rev limiter?

6250 is the stock rev limiter.i doubt it, unless his tach is that far off.....

 

[sphugh1967]

6250 is the stock rev limiter.i doubt it, unless his tach is that far off.....

The tach does jump a bit when the car misses. but the miss is much lower than 6250.

 

[HISSIN50]

With a bouncing tach, have you pulled trouble codes? You might get an IDM, etc code from that.

Good luck.

 

[JerryDaugherty]

I had a similar problem. I also think it is fuel related. I had a severe one with 19lbs and a stock fp. I uped to my spare 24lbs and it cut in half the cutting at high rpms. But it was still there. Then the fuel pump gave out. At the initial slam of the gas, I would get close to ****ting myself, but as the r's rose the power dropped. Fuel pump 255 is wut im going with at least a 190 and 24's. If not the fuel i would suspect an easy fix. New plags all around and make sure the wires didnt get disconnected inside the boot... Good luck man

 

[sjhm9102]

valve springs ? my 2 cents

 

[sphugh1967]

With a bouncing tach, have you pulled trouble codes? You might get an IDM, etc code from that. Good luck.

The only codes I have been able to pull have been 41 and 91 both engine running and both say sensor signal low voltage lean. But nothing specific as far as ignition is concerned