Fix a Toyota

[El Andrew]

Alright lads, anyone feel like turning your collective brainpower to a different make?  (I'm sure many of you do this already.)  The Toyota forums are pretty quiet!

 

Got a 2010 Toyota Kluger (3.5L V6) throwing an engine warning light and disabling stability control.  Is giving me codes of P0171 and P0174 which is lean bank 1 and lean bank 2.  Basically means that the O2 sensors are detecting more oxygen than expected and the car is adding fuel to compensate.  Long term fuel trims are sitting around 15%, fluctuating up to 30%.  I'm pretty sure these should sit on zero, which I've confirmed by logging the same data on the XR6T.

 

So far the car has been checked out twice by an independent mechanic.  They thought they got some improvement by cleaning the MAF sensor, and I then put in a brand new one because it wasn't that expensive but didn't help.  They thought it was likely that O2 sensors were the cause, which I doubt as it is both banks.  Quotes were $800 x2, so I ended up fitting genuine Densos myself for a $200 each, figuring they were well into their useful life anyway.  I seemed to get a noticeable bump in economy from this, but no improvement in fuel trims.

 

Ended up taking it to Toyota twice - first time they just cleared the code and said yep fixed, second time (today) I made a bit of a song and dance and they got a diagnostic tech to go over it.  He agreed the long terms fuel trims were out of spec but couldn't find anything to cause it.  Thinks it is either gummed up injectors and suggested a couple of tanks of 98 plus some injector cleaner (unlikely I think, as no misfires or loss of power and it is equally affecting both cylinder banks) or a leak in the intake manifold gasket, on the basis that the service where the spark plugs are changed (requiring removal of manifold for access) was not done by Toyota and therefore was probably stuffed up.  Ridiculous reason, but could be.  I asked him to smoke test the intake system, but they didn't have a machine.  Fuel pressure is good.  He also said that most of their mechanics wouldn't have the experience or training to dig into the data to explain a code, and that they didn't have another Kluger handy to compare the data with.  Geez, the new ones have the same engine and I find it hard to believe they couldn't find a V6 Camry or Aurion handy!

 

I'm still thinking it must be an intake leak between the MAF and the individual banks.  I tried smoke testing it myself with a cigar a few weeks back with no effect, although you'd have to be lucky to catch it with that I reckon.  An exhaust manifold leak (pre-O2 sensor) is also unlikely as again, it is affecting both banks.

 

Along with the injector cleaner, I also grabbed a couple of metres of vacuum hose.  Will cost me almost nothing to go through and replace all of those.  After that, I might pull the intake manifold apart and replace the gaskets.  That's a big job to do on a hunch though.

 

Anyone got any other thoughts?  Given the car drives fine and nothing major has been detected in the diagnosis, I'm pretty keen to do some troubleshooting at home before chucking more money at it. The plan was to focus my attention on the BA and house stuff, and leave the family daily to the pros but I'm not having much luck with that so far.

 

Cheers!

[k31th]

is it actually a MAF or a MAP on that motor?

 

If it's a MAP, I'd say you're on the right track with smoke testing the intake manifold and replacing vacuum lines, as it sounds like a leak after the air is measured and the fuel trim is compensating based on the readings in the HEGO sensors.

The engine isn't idling/running rough in general?

 

MAF changes things significantly.

[El Andrew]

Yeah MAF. Should be same concept though as it measures the air going in, adds appropriate fuel and expects a certain amount of oxygen left on the way out.

Nah runs like a treat - perfect idle and power is fine.

[k31th]

cheap is cheap, I guess...

if it's idling OK and doesn't feel like it's falling over under power, the only explanation I can guess at is a specific sensor is not reading the right information to the ECU for the actual physical/mechanical conditions.

 

if it's a MAF, where's it getting the temperature information?

[El Andrew]

Has a air flow wire and a temp wire. Effectively uses the two to calculate air density and volume.

[Puffwagon]

Does the fuel you're using have any amount of ethanol in it? That would do it.

 

Have a read up on O2 sensors and their need for reference air and suitable connection methods. Maybe some of that info applies here as you recently swapped them. 

 

An intake leak seems the most likely culprit but you never know.

 

It's a pity it's not leaning the other way cos you could just chuck a resistor in the circuits provided it was just a sensor issue. 

[k31th]

and you said you've replaced both the MAF itself and both of the HEGO's?

 

I'd be looking into the the fuel/air calculation system on this particular engine configuration to see if there's any other sensors that can affect it. Maybe it's the ECU itself (or the wiring from the sensors to the ECU)?

[El Andrew]

Nup, no ethanol.

Yeah two new genuine oxygen sensors and MAF. Same symptoms before and after.

Time to get cracking with the new vacuum hose I think and then maybe find somewhere to smoke test it properly.

Or Barra conversion.

[k31th]

barra conversion FTW! haha it'd have a big enough engine bay

[OZYWALKER]

This ^^^^