check engine light no codes

[jhonda]

I tried pulling the codes but none show up...I have a 91 mustang that I bought from my dad and it has been doing it for the past 30000miles. The check engine light will come on and go off about every 5-8seconds while in the city below 40mph but the faster you go the more it flashes.....now when I say flashes it stays on for about 5-7seconds.
any ideas
jason

 

[2000xp8]

I had an intermitten engine light problem back a few years. No codes.
Turned out to be the o2 sensors, only reason it was figured out what when removing my x pipe, we broke one. And when i put a new one in, it never happened again.

 

[HISSIN50]

Do you literally get 'no codes' or do you get a system pass (11)?

 

[ninety15.0]

Oh thats a good point. Also what tests have you done?

I would try inducing an obvious code. Unplug the MAF, TPS, or O2 sensor and then do all diagnostic tests.

Then i would pull a plug off and run the cylinder balance test. This should help you verify that the computer is functioning properly. good luck man.

 

[jhonda]

yes I get a system pass but no fault codes

 

[jrichker]

Have you dumped the codes with the engine running? You will often find different things.