little deuce overfueling issue resolved.... i think???

[frog_eyed_mk1]

As the new owner of little deuce discovered a slight fueling issue which was found by a strong smell of fuel and sooty plugs, the fuel pressure was marginally high so the gauge was replaced and the recommended pressure set but still the issue was apparent.

looking at the live data readings the MAF readings at idle were over 6g/s and was slow to react when revving, so this was removed, cleaned and refitted bringing the readings down to 3.2-3.3g/s and increasing with engine revs as expected. which I think is within tolerances.

the smell of fuel and puffs of black smoke have disappeared completely and the car comes alive even more than before on the road:laugh2:

now the reason I'm confused is the fuel trims are way off, at idle they read,

stftb1;19.5%
ltftb1; 30.5%
stftb1; 19.5%
ltftb1; 30.5%

now these figers do not change at all until revving when both short term fuel trim come down to zero but the long terms stay at 30.5%

now I was under the impression that the short and long terms should be within 10% of zero??? please correct me if I'm wrong :icon_redface:

also the bank 1 O2 sensors are sat at 0.66v, should these not be switching?

also got 4 codes, 3 of which relate to auto gearbox the other is; [P1130 A/F sense circuit range/performance malfunction (bank 1 sensor 1); OK]

should I just replace the sensor or is there more chance that something else is causing it?

loving the car and the smiles it puts on my face, back in the garage keeping dry now

[rainen]

Not sure what engine you have but two years ago I had exactly the same problem as yours on my 1MZ-FE. You are right at idle both LT and ST should be close to zero. If your are on the same engine as me the MAF reading you have is about right. Now my problem in the end was traced to both of the AFR sensors not having any power and therefore not working. My trims mirrored yours as they are now. So you could have both senors out which would cause this. Mine did not have O2 sensors so not sure what voltage they should show. The other main advice I got at the time was a big air leak will also cause this as the MAF says one thing to the ECU but the sensors report something else as extra air would be getting in after the MAF. Net result is weaker mix at the exhaust so the ECU throws in more fuel. Hope this helps??

[gavsdavs]

When in closed loop, the ECU will try and keep short term trims around zero, but they'll move a lot.
The long term trims will tend to a particular value which gives you a better view of whether the engine is rich or lean but those aren't a problem unless it's at the full value - the edge of what adjustments it can perform to the defaults

Ideally you want the engine to be in the middle of it's dynamic range as opposed to at the extremes.
If it's showing full positive fuel trims it thinks the engine is running lean and will keep trying to add fuel until it can get zero short term fuel trims
If it's showing full negative fuel trims it thinks the engine is running rich and will keep trying to REMOVE fuel until it can get zero short term fuel trims.

Hope my explanation makes sense.

[frog_eyed_mk1]

Hi guys, thanks for replys, firstly its the 1mz vvti engine.

Well looking at how the fuel trims are sitting so still at what totals exactly 50% i think its like there not doing anything in a "default" mode maybe?

Now, forgive my ignorance if im wrong but are the o2 sensors not the same as the afr sensors just a different name used????

I have checked for an air leak and theres no leaks, not sure if I should be worrying about this problem and changing o2 sensors or just leave it be as it runs absolutely sweet.....

Im sure the o2 sensors should be switching when in closed loop though, but i may be wrong....

Thanks in advance

[rainen]

Yes O2 sensors are different to AFR ones which I think are an improved version. The VVTi engine has the AFR (Paul will correct me if I’m wrong). Your trims are maxed out and need addressing. They should be running close to zero. The sensors should be switching which you will see on the graph depending on the type of analyser you have. Now the voltage on my AFR sensors on my non VVTi engine run at close to 3.3v. If need be I can send you some screen shots of what they should look like on my analyser. The fact that both banks are showing the same problem would point to the sensors. They are usually supplied by power which has a 25amp fuse in the original Lexus cars. Not sure how yours are wired but I would check that you have 12v on one of your four pins. Also when you sorted the MAF did you reset the ECU? That would clear the trims and the engine will learn again. Hope that helps.

When you check for power to the AFR ignition usually needs to be on. So of the four wires one is Power, the other three go to the ECU. Of course I really don't know anything about your car, whether its a new problem or always been there? Is it home build and self wired? Any background always helpful.

[frog_eyed_mk1]

Hey,

Well they are definitely not switching the voltage just sits the same at 0.65v so maybe I should look at fitting 2 new sensors.

I have cleared codes and disconnected battery for a couple of minutes to reset ECU but maybe thats not long enough so il try disconnect it for longer tomorrow to be sure everything is reset....

I haven't owned the car for long so not sure how long issue has been there and its a paul woods conversion, so yes, im lucky enough to have a shiny intake pipe :icon_gayfight:

A pair of AFR sensors are not cheap so I'd rather not buy any until im sure its them at fault, but with one throwing a code up i think im going to have to...

Thanks again for your help

[frog_eyed_mk1]

Yes well after a think and a little research they are different with a clean engine running how it should a o2 sensor shows 0.45v where as a AFR sensor shows 3.3v (like you say) , if these are AFR sensors showing 0.65v the ecu will be thinking the engine is way too lean and try to richen the mixture by increasing fuel trims like it has done right up to the top of its range.... Hopefully im correct in what im saying... If so do you know where is the best place to get quality sensors at a reasonable price is? I noticed you have changed them on your vvti build :)

Ashley

[rainen]

If Woodsports did the conversion them I’m sure when it left Paul it would have been in perfect working order. Have you spoken to Paul on this one? Also Paul puts new AFR sensors on his conversions so for the issue to affect both banks both new sensors would have to have gone faulty. Yes they are very expensive. I’ve bought two new ones for my conversion. Now I have the old ones from the Lexus that were both working, one being a bit sluggish getting going. I’m happy to lend them to you if you want to try them rather than buying news ones in the first instance. You would have to extend the wires though. I would still check that you have 12v at each sensor plug just to rule out any power feed issue. Not sure how Paul wires the power feed for the AFR and whether he runs it through a fuse. Can check mine when I get the car back tomorrow.

[rainen]

I got my new sensors from Woodsports.

[frog_eyed_mk1]

yes I definitely agree it would have left woodsport running perfectly I forgot to say that the conversion was done 4 years 4,000 miles ago, im wondering if the overfueling caused by the MAF could have dirtyed the AFR sensors and caused them to fail maybe?

When i next get chance i shall test for 12v at the sensors.

Thank you for the offer of the used sensor loan i shall bare that in mind :)