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Well, I'm about at my wit's end right now. I've been battling wonky fuel trims for the past few weeks, replaced/checked nearly everything I can think of and my car runs much better but still keeps throwing lean codes. Also getting evap codes but those /should/ go away after tonight.

So far I have:
- Cleaned air filter
- Cleaned throttle body
- Replaced MAF
- Replaced spark plugs and wires (Not coil packs)
- Cleaned spark plug valley
- Replaced B1S1, B2S1 and B2S2 o2 sensors (B1S2 is next for consistency but unimportant relating to fuel trims)
- Replaced every single vacuum line under the hood with silicone lines and new spring steel clamps set very snug (2 exceptions to replacement, the 2 very small vacuum lines under the upper intake Y but I checked them and they looked in fine condition)
- Replaced gas cap seal

Fuel trims are normal while idling, but spike on what seems like a set pattern while simultaneously the revs drop to 500-600 and the car shakes. I believe the radiator fans kick on at this time, and this occurs much less frequently while the A/C is off. I was running the gas tank evap on the drivers side of the car venting to the open air for a few days and finally replaced that last vacuum hose today - I reset the ECU by disconnecting the battery for 10-15 mins tonight so no codes right now. Previously it took a few days for the ECU to actually throw lean codes and I'll update this post when/if I get codes again. I honestly have no idea why the long term fuel trims are changing so drastically, if my understanding is correct they should have much less variance than the short term trims.

If you need more information I'll do my best to answer, currently I have an OBD2 sensor connected through Torque so can log things if need be. You can hover over the pics below to see what I was doing during each graph.
 

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Next to vacuum leaks, Fuel pressure is probably the next thing I'd want to check. I've had a pump get tired and give me erratic fuel pressure. The filter is in the tank with the pump. It's not that easy to check the fuel pressure but it's pretty critical to know if it's correct.
 

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Discussion Starter #3
Update:

Today I pulled codes and got:

P0440 Evap emission control system
P0441 Evap emission control system incorrect purge flow
P0446 Evap emission control system control circuit

I definitely smell gas when I turn my A/C on after my car has been sitting for a while, since I replaced all the vacuum lines already the last place to look would be injector O rings right? It might even make sense since my fuel trims look to return to normal when under WOT where fuel pressure could be seating the injectors better so there's less vacuum leak?

Since I'm getting evap codes it would make more sense than a failing pump but it's one of the things I considered along with clogged injectors. Just ordered some re-manufactured injectors - if old injectors are coming out might as well clean them and at the end of the day buying new seals + getting injectors cleaned is around the same price as getting flow tested re-manufactured injectors that come with all new seals.
 

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The possibility that all the injectors clogged at once seems pretty low.

The evap codes have specific trouble-shooting instructions in the manual. There's a bunch of vacuum lines at the tank end of the evap system. The evap system is essentially a calibrated vacuum leak which uses engine vacuum to pull fumes out of the top of the tank. I might plug the vacuum line from the tank to the intake (it goes through a commonly broken plastic L shaped thing on the driver's side of the engine, near the back side of the intake manifold).

I'd probably pull and plug it on the manifold instead of trying to pinch the line.
 

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Have you tried spraying starter fluid around the intake for any leaks? It sounds like an intake leak. At idle the intake has positive pressure and under load the intake is under vacuum. Which could explain why the Long term trim is so dramatic when driving.

Fuel injectors can fail intermittently so changing them might be a good idea. I bought GB OEM reman injectors from rockauto and they came with new seals. If you clean yours, the cost will be the same but if one or more are defective, now you need to buy new injectors. On my car, I had bent the TB metal gasket previously and created a leak. Its cheap and easy to replace the TB gasket.

Also I had spilled some coolant above the intake runners where they mate to the head. While finishing up the injector install, I saw small bubbles coming from number 3 intake runner. The right thing was to replace the gasket. What I did was clean it and pack it with black FIPG and its been sealed ever since. What I saw was bubbles at idle and then they diasappeared under accleration.

Keep looking. Its probably some cheap hose or gasket leak.
 

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Discussion Starter #6
Have you tried spraying starter fluid around the intake for any leaks? It sounds like an intake leak. At idle the intake has positive pressure and under load the intake is under vacuum. Which could explain why the Long term trim is so dramatic when driving.

Fuel injectors can fail intermittently so changing them might be a good idea. I bought GB OEM reman injectors from rockauto and they came with new seals. If you clean yours, the cost will be the same but if one or more are defective, now you need to buy new injectors. On my car, I had bent the TB metal gasket previously and created a leak. Its cheap and easy to replace the TB gasket.

Also I had spilled some coolant above the intake runners where they mate to the head. While finishing up the injector install, I saw small bubbles coming from number 3 intake runner. The right thing was to replace the gasket. What I did was clean it and pack it with black FIPG and its been sealed ever since. What I saw was bubbles at idle and then they diasappeared under accleration.

Keep looking. Its probably some cheap hose or gasket leak.
Last night I replaced injectors with re manufactured Denso, new seals etc. Also replaced small vacuum lines coming off the intake and that go to the secondary throttle body inside the plenum (Actually ended up deleting the actuation and have it stuck open, just took off the C clip that holds the part that actually levers the throttle body - the valve actuates but doesn't move the shaft basically). Oh, also found a small blue connector going to the intake unplugged so I plugged that guy back in.

Drove around for a bit, sure enough running lean and P0440 Evap code. Intake gasket might be the answer, but I'm kind of lost if that still doesn't fix it. I threw a little bit of oil on all the mating surfaces to try and get it to seal up better but I guess that didn't help.
 

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Did anyone monkey with the o2 sensor wiring? Maybe both banks are merged and its freaking out the ECU in the stock configuration. The same thing happened to me.
 
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