Malaysia
Boleh Side Notes from Engine Tuning page
This side notes made the Engine Tuning page too long, therefore it is placed here as a reference to Engine Tuning page.
AFM & ISC Valve
Sometimes when something is wrong, perhaps some setting(s) is / are OUT, or whatever, therefore some people would blame / suggest that the AFM is broken / damage. This is un-likely, as the construction design is extremely mature.
Sometimes there are occasion where the engine cannot idle properly and keeps dying, especially on choking / coughing / in-consistent breathing conditions. Where the engine want to die but regain idle and repeat the die live die live sequence.
It is due to the FLAP closing, which shorts the fuel pump engage and switch the fuel pump off, hence no fuel, hence engine stop. But as the engine choke for the final breath, the flap opens again, now the fuel pump re-engages and the engine lives..... but due to other technical faults, causing the breathing to be weak / in-consistent hence the AFM flap opens and closes, causing the fuel pump engage pin to engage and disengage. This does not mean the AFM is broken. !!!
The choking / coughing MAY be caused by the ISC Valve trying it's best to compensate for constant idle or something else altogether.
Also, the ISC Valve does not appear to be something easily broken, as it is a DIGITAL switch device. It has a maximum digital on/off frequency of 125Hz. It simply work on the theory of higher frequency - pumps more air - to maintain constant idle. It is principally made of magnet and coil and these items do not get damage easily or at all.
For this case when it idles high, it is suspected that the ISC Valve is in constant OFF mode, because the TPS setting was wrong (although accelerator is zero, but TPS setting angle is at a position where it thinks the throttle is open and hence tells the ECU to shoot more fuel???
Mr.S.K.Leow once told me that during idling the AFM is ignored by the ECU and only read TPS [in this case NOT zero] therefore causing the ECU to think there is accelerator motion / action, then reads TPS in-conjunction with AFM and hence causing the idle to be higher than normal.
In short the ECU did not have a chance to really read a condition of true idle???
Side Notes Ends
Side
Notes - added around 13th June 2003 morning
Suddenly out of no reason, figured out why it has sudden power burst. This is because the intake surge tank is too small. Causing the AFM's Flap to be extremely sensitive on motion from road vibrations / air movement.
The conclusion is that for AFM L-Jetronic EFI Systems, the surge tank is required to stabilize the air and let the flap to be less sensitive.
To worsen the situation, the AFM is installed not flat, where the flap may be affected by gravity more to close easily than stock, which may affect it's behavior??? Found out by Mr. Wong Yee Yong.
Side Notes Ends
ACOUSTICS SECTION AUDIO SECTION CAR SECTION
HOME - Technical Website for Acoustics, Audio and Car