fredfelcher 0 Posted December 23, 2011 Need some reassurance here please fellas... My setup: OBD2 VR6, Rotrex with 6psi pulley, Bosch red top injectors (315cc/min at 3 bar), Malpassi RRFPR, Dubsport 6 branch and decat. This thing is brilliant and drives really well but the Torque app on my phone is telling me that LTFT is between -10% and -12%. I expected this a bit with the bigger injectors and obviously the lambda sensor is trimming back but would prefer to have this less extreme. Also, a couple of faults keep coming up in VAGCOM - MAF short to B+ and idle adaptation limit exceeeded. It seems to me that these are also related to the MAF - it's clipping at WOT I suspect and I see the STFT at the limit (-25%) when slowing to a stop sometimes and then it idles badly for a few secs before it returns to normal STFT. Other times it goes open loop on decel and idles fine - not worked out the different conditions yet. I wonder whether it's because the air filter is stuck directly on the end of the MAF, which is directly on the elbow from the charger and I'm getting some reverse flow over the element. Anyway, I was thinking that wiring in the potentiometer mod would help sort some of these problems, but can't find any exact details on it from searching. Am I right in thinking I can simply wire in 2 poles of a standard pot to create a variable resistor in the blue (signal) wire and then adjust to get fuel trim back to around zero? Or do I NEED to have all three terminals on the pot wired up, one to ground? The MAF wiring came from the original car, which had the charger fitted at Storm. It has 2 resistors in series already giving a resistance of (from memory) 1.2kOhm. I was going to wire in series with this rather than undo all the loom tape. I do have a wideband, chip burner and spare ECU's, so will get round to tuning it myself one day (a la VR6Joni), but am too scared to desolder the tiny legs on the PLCC chip at the mo... Cheers for any thoughts - I get cars and I get computers but electronics just don't seem to click properly in my brain... Quote Share this post Link to post Share on other sites
VR6Joni 0 Posted December 23, 2011 Hi mate. My tips would be: You'll need about 24" between charger and MAF or you will get noise on the MAF, most noticeably when changing gear at full throttle quite an unpleasant jerk if I remember correctly. You'll need to carry out the pot trick to prevent adaptation limits being exceeded. Measure the pot resistance, the 2 pins that stay the same resistance go to ground and MAF output respectively, the pin that changes resistance goes to the ECU. Therefore all 3 wires are used. Unplug your ECU lambda and tweek the pot to get 14.7 on AFR. I'd bin the resistors and just use a pot to maintain simplicity. As for remapping, all my experience is with OBD1 so can't really help I'm afraid. Good luck Joni Quote Share this post Link to post Share on other sites
fredfelcher 0 Posted December 23, 2011 Still very helpful info though Joni, will wire up as you suggest. Will have to find somewhere to run extension tubing along the front - it's currently inside the front wing, so no more room. Your guide on remapping was my inspiration for buying up all the parts I'll need so I'd say you've already done more than enough in sharing that info. Just need the courage to desolder the EEPROM now - can't find anyone else prepared to do it for me! Many thanks for your reply Quote Share this post Link to post Share on other sites
VR6Joni 0 Posted December 23, 2011 One other thing, OBD1 ignores the MAF at WOT so clipping is not an issue, however it can still be present at say 80% throttle but the pot trick generally cures this. And keep an eye on AFR's as the fuel pressure needs to gets quite high with RR Regs and nobody really knows the standard fuel pump limits. Quote Share this post Link to post Share on other sites
