k31th less WHY; more WOT Site Developer 29,054 Member For: 16y 8m 14d Gender: Male Location: Melbourne Posted 29/03/19 02:22 AM Share Posted 29/03/19 02:22 AM maybe the previous tuner took it into account... from what I've read and seen that the myth is true... hmmm Link to comment Share on other sites More sharing options...
El Andrew Gold Donating Members 2,036 Member For: 9y 8m 2d Gender: Male Location: Canberra ACT Posted 29/03/19 02:35 AM Author Share Posted 29/03/19 02:35 AM Yeah dunno. I guess I could replace the sensor and switch it back on to see what happens in the name of science.An example of one thing I read:https://mechanics.stackexchange.com/questions/37442/is-the-after-catalyst-oxygen-sensor-used-for-engine-mixture-control Link to comment Share on other sites More sharing options...
FiftyOne Bronze Donating Members 1,145 Member For: 11y 5m 23d Gender: Male Posted 30/03/19 04:52 AM Share Posted 30/03/19 04:52 AM Most modern rear sensors are more to check the heat differential across the cat too aren't they? Link to comment Share on other sites More sharing options...
k31th less WHY; more WOT Site Developer 29,054 Member For: 16y 8m 14d Gender: Male Location: Melbourne Posted 30/03/19 04:57 AM Share Posted 30/03/19 04:57 AM yep, basically for emissions... something we don't care so much about as car manufacturers must. Link to comment Share on other sites More sharing options...
El Andrew Gold Donating Members 2,036 Member For: 9y 8m 2d Gender: Male Location: Canberra ACT Posted 05/09/19 11:20 PM Author Share Posted 05/09/19 11:20 PM Unfortunately this issue continues to hang around, even though at times it looks a bit better. I built a tune that basically got rid of any lambda corrections, kept the car in open loop and targeted a flat 0.95 everywhere so I could see easily what was going on. Car could happily hold commanded lambda with a bit of load, but was very rich at idle. Made me suspicious of fuel pressure and also I think eliminated things like an erratic O2 sensor. Had some rose joints replaced in the rear yeaterday so got them to test my fuel pressure while they had it. Had been tested before (reported back as "ok") so asked for the actual value. Good news is that it was 65psi at idle - I think I've found the cause of my negative fuel trims. Reckon step 1 is to disconnect the return line under the car and point it at the mower petrol tin. If the fuel trims settle down while idling, I know I've got an issue somewhere between there and the tank. Hard lines all look good so reckon checking the pump module would come after that. 1 Link to comment Share on other sites More sharing options...
k31th less WHY; more WOT Site Developer 29,054 Member For: 16y 8m 14d Gender: Male Location: Melbourne Posted 06/09/19 02:05 AM Share Posted 06/09/19 02:05 AM sounds like you're on the right path to diagnosing it. Link to comment Share on other sites More sharing options...
El Andrew Gold Donating Members 2,036 Member For: 9y 8m 2d Gender: Male Location: Canberra ACT Posted 30/11/19 03:08 AM Author Share Posted 30/11/19 03:08 AM Finally got around to sorting this. Pulled the fuel module out, as last time I'd had to reuse some fuel hose and wanted to have both lines using the proper flexi stuff.Drilled out the fuel return thing in the bottom of the cradle to 4mmBut I also noticed that the return port in the cradle was blocked. Not sure if there is meant to be something there or not, but either way it wasn't passing any fluid. So drilled that out too. Before and after pics below.I now have positive fuel trims (remembering that I fudged my low slopes to tune around the issue temporarily) so think I have resolved the fuel pressure issue.I'll do a few km to make sure the trims continue like that, then flash the correct low slopes back on. 2 1 Link to comment Share on other sites More sharing options...
BarraT Member 34 Member For: 4y 11m 4d Posted 21/03/24 09:36 PM Share Posted 21/03/24 09:36 PM (edited) Thanks Andrew Any updates to the issue?? I was about the fudge up the low scope trims to resolve as well, though now that you mention pump!!! I am seeing the same problems with mine, after I fitted a complete 255L Walbro drop in unit I suspect the seller never drilled the required holes, Can you kindly pin point the other hole that requires drilling to 4mm? and what size you drilled the return port?, I will pull the pump today and check Many thanks for posting this !! Great Help Edited 21/03/24 09:38 PM by BarraT Link to comment Share on other sites More sharing options...
El Andrew Gold Donating Members 2,036 Member For: 9y 8m 2d Gender: Male Location: Canberra ACT Posted 21/03/24 11:41 PM Author Share Posted 21/03/24 11:41 PM Hey mate. I honestly can't remember exactly where the other hole was, but I remember just visually tracing how fuel flows through the module to identify any restrictions so I suspect it will be obvious once you are in there. Sold the car last Friday so I can't even have a look to confirm.I did also have to adjust the low slope a little to get LTFT spot on. As Puff says this is likely just due to aftermarket dump and cat so nothing unusual. Since the above, car behaved beautifully in the years following. 1 Link to comment Share on other sites More sharing options...
BarraT Member 34 Member For: 4y 11m 4d Posted 23/03/24 12:51 AM Share Posted 23/03/24 12:51 AM Thanks heaps for this, hopefully this can help others that's the difference drilling the hole out to 4mm Could do it neater, Luckly I got spares Link to comment Share on other sites More sharing options...
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