Proton Persona 1.6GLi, 1994. And going strong until this. Failed MoT emissions at low speed idle with very high HC. I replaced the Cat, the Oxygen sensor and the front exhaust pipe (suspect tiny leaks). Recently serviced, oil and all filters, plugs, etc. As it comes in to the test station after a good run, the HC is immediately tested and initially ok, but then just slowly creeps up and up to 300+ppm on slow idle and 230+ on fast idle. Local experts think that something is telling the ECU something wrong and causes it to richen the mixture, ie widen the pulse width, so its runs far too rich. Given the parts replaced, is it reasonable to suppose the ECU has a fault? The only thing I can think of to explain the behaviour is that the ADC has a fault on the low order bits (probably 10 bit ADC) which are insignificant at high air flows, but critical when idling. Any thoughts? Philip ***********
When last on the diagnostic, with this problem, there were no fault codes. The injectors have been cleaned on an ASNU system and do not appear to be leaking when de-energised and fuel pressure seems to be about 40psi when the reg is connected to the inlet manifold and about 50psi when not, spray patterns appear to be ok.
If by fuel trims you mean the emission results, I have those, after a few minutes at idle, they are:
Fast Idle Test
CO 0.58%vol Fail against 0.30
HC 296ppm Fail against 200
Lambda 1.054 Fail against 0.980 to 1.020
Second Fast Idle Test
CO 0.75% Fail against 0.30
HC 308ppm Failed against 200
Lambda1.030 Failed against 0.980 to 1.020
Natural Idle Test
CO 0.020% Pass Against 0.75
HC 123 ppm Pass Against 200
Lamba 1.022 Fail against 1.020 to 0.980
If fuel trims means something else, please explain and I'll try to get them.
OK. I'll try and find someone who can do this without breaking the bank. Meantime, do we just suspend this conversation until I can get back to you?
Proton cars (UK) tell me that this car does not produce the STFT1 and STFT2 information, they came in later models.