far too much air

[skyway]

HI again guys I have had some codes come up on my old ls430  P0171 and P0174 to be exact after much searching on the net the codes point to an air leak post filter I have had a look at the airbox doesnt seem to be leaking from there but I did just look at it maybe there is a better way of checking.

has anyone else had this problem?

thanks for reading and any advice you guys are awesome 

[Ben01]

It is not air leak "post filter" or airbox, this is wrong interpretation. Typically it is "post MAF" (air flow sensor), or even "post throttle body" leak. Check every vacuum/pressue pipe connected to manifold (there is a few of them). Keep in mind the leak could be in distance, on any elbow, pipe, a half meter from manifold. Common weak point is short fat pipe from passenger side cover, from PCV valve to somewhere next to throttle body, this pipe sucks oiled hot air from engine, after years is badly detoriated, cracked etc (it was in my current GS). Next point are gaskets of manifold, throttle body, etc. it is rare, but they could "gone", crack, etc.too and make nice leak into manifold. Unscrewed (a bit) manifold or throttle body etc is very rare, rather human error (somebody forgot to proper screw it), but **** happened.

A bit of lecture now: codes for "lean mixture" typicaly are interpreted as "too much air" leak into engine after MAF, like above. In fact, ECU "watching" the MAF and the O2 probes, and he "knows" how much fuel is feeding every moment, as he alone controls injectors. So, in every cycle ECU calculate from MAF (air flow) and a few more parameters, how much feed the engine with the fuel, open injectors accordingly, and next check if O2 probes confirm expected values in acctual conditions, with proper delay, both ends of cat, etc. If O2 values are out of tolerance (for steady revs and closed control loop = out of steichiometric) up or down, we have "lean" or "rich" codes. Keep in mind, every link in chain above could be "wrong physically". Worse, every ECU input or electronics could be "wrong electronically".

So, typicaly for "lean" codes above is "too much air" and leak after MAF (MAF shows 5, but leak unnoticed gives +1, ECU calculates and injects as for MAF=5, O2 sensors shall be "in tolerance", but they are lean (+1 air, 6 not 5), ECU is "whoa, what the hell, code P0171 please"). But it could be ANY other option, like O2 probes faults (power/input IC broken and both of them shows too much/too low, out of pretty narrow characteristic), fuel pressure (MAF=5, no leaks, ECU injectors 5, but really only 4, because petrol pressure regulator/sensor half broken, O2 probes have seen +1 air and report same "we are too lean, captain"); in case of code for one head only - broken single injector, single O2 probe, etc.

[skyway]

thanks Ben I will check for leaks tomorrow

 

[Ben01]

I forgot to mention most "funny" leak into manifold thru PCV - oil stick not fit properly or without seal or with broken plastic, etc. In fact, I never have seen such a stupidity, and I dont think the "sucking" from stick pipe thru half of engine is enough to fool the MAF/ECU of big engine (the same - small crack on distant vacuum pipe for acctuator, EGR, sensor etc. is not very significant vs. dragonbreath of V8), but some people mentioned this.

Other point - always remeber 90% of vauum pipes around manifold etc. it is not critical for engine "to work". For test you could patch suspected seals with silver tape, remove pipe and plugged hole with anything fit, disconnect PCV valve and close his hole with tape, etc. Next reset codes for lean and try a bit drive or rev up/down engine stationary a few times. And again and again 😉

[Texas]

Also ( at your own risk and you never heard it from me!) one method to find induction 'leaks' is to spray a volitile aerosol ( EasyStart) in and around the inlet manifold and hoses and note if engine revs increase when on idle. Watch out for moving and Hot parts obs!

paul m.

[skyway]

Thanks guys.

I think that I may have found the leak.

The fat rubber pipe that goes from the side airbox thingy to the top of the engine (looks like an L) which was loose and the clips holding it down were baggy to say the least.

I am going for a run soon to check it.