10-30 Mobile 1 full synthetic and a wix filter. I use the same stuff in all of my turbo sr20 cars.

 

Just finished a 600 mile trip in the tC. Got 29.18 MPG with lots of hills and curvy roads, also doing 80 most of the way Started popping P0171 and P0420 codes.
Thinking about getting a OEM MAF and front O2 since they are originals and probably needed to be changed a long time ago.

Also have almost 6k miles on the new engine rebuild and it isn't using oil like it was through the initial break in. Going to change it once more in the next week or two and see how it looks.

 

Do you think the P0420 is a bad cat? I started getting this after 200mi on the new engine, and now I'm getting it consistently that the temperature is down. I am getting 26mpg in city driving, but with my short trip to work, I've only got 600mi on the new motor.
I'm not using oil either, but I didn't do any internal work. The car runs great and no typical dead cat smells....

156k on the original cat is probably enough, and I've read that a lot of people have this issue and they're touchy. I replaced the rear O2 and it was off, but my monitor for cat wouldn't set and when the temp dropped to 15f outside, it started popping the code again.

I'm ordering one of the CNT 90deg "fixes" for the second O2 for now. I might stick a header on it anyway.

I've never heard of anyone having to change a MAF for this. Isn't that kind of an expensive part?

 

MR_LUV, you sure are a stickler for grammatical errors!

 

I'm not sure about the cat, but I have seen them get over 250k miles before. Using Torque pro and a bluetooth adapter the O2's seem ok but STFT and LTFT are way off. I'm going to build a smoke machine and check for intake and hose leaks before I get too deep. I have a feeling the lean error and fuel trim corrections may be popping other codes.

Things I have learned about MAF's: The ECU fueling is matched to the OEM MAF, I have found aftermarkets are usually out of spec somewhere across the 5v spectrum and that's why you should always use a OEM replacement. They also get dirty and degrade over time. I chased tuning problems on my boosted G20 for months until I used a factory replacement that cleared everything up. On these cars they only cost $80 at Rockauto for a Denso OEM replacement.

 

Out of curiosity, what are your long and short term trims?

 

I got to drive the car to work today so I monitored the fuel trims this morning.

Short Term Fuel Trim
-.08 / 0 / + .08 at Idle and while driving varied loads never went above 4.7

Long Term Fuel Trim
+27.6 at Idle and while parked throttle to 2500 RPM goes to +9.4. While driving it goes down to 3%-5% under load but jumps up every time I let off of the pedal.

O2 AFR - stays at 14.7 within .5 volts in any situation

Catalyst temp bank 1 and bank 2 is about 200 degrees apart under load while driving.

I'm starting to think there is a intake manifold leak and am going to smoke it to see if that is the problem. Everything but the fuel trim seems alright so far but it's also hard to diagnose from one trip to work trying to watch the scanner and drive

 

What do you monitor this with?

and why do you think there is an intake leak?

 

I use a bluetooth OBD2 adapter and torque pro on my phone to monitor the ECU.

I'm guessing that the ECU is commanding almost maximum fuel allowed to compensate for too much air. At idle (closed throttle plate) it's almost maxed out, when the throttlebody plate opens it gets better (+9%) which is usually a sign of a leak, sucking air from a source not metered by the MAF.

Does anyone know the max compensation % for these ECU's?

 

I use torque pro as well. Technically speaking wouldn't you expect STFT to lead a change in trim with the LTFT then moving in response? e.g. drive at 3500rpm for 10 min, STFT goes to 0, LTFT stays where it think it needs to be based on sensor inputs. Then pull over and idle: if it is a non-metered air leak you expect STFT to increase dramatically followed by a delayed change (increase) in LTFT while STFT trends back to 0.

Air incursion after combustion and before an O2 sensor will also give a lean condition.

What surprises me is that STFT isn't changing significantly at all. I would also assume that at +27%FT you are approaching or at max positive trim. Maybe if LT is maxed the ECU doesn't bother with a ST trim at all...

 

The STFT constantly watches the O2 value and updates the LTFT table. The LTFT on most cars can only compensate 23% or so (These obviously more) before having to add STFT to fuel correctly. That's why I believe the LTFT isn't maxed out yet but is probably real close. (If LTFT is maxed then STFT starts adding) If I disconnected the ECU and reset it so it would have to retrain I'm sure the STFT would go high until it updates the LTFT table for correct AFR.

Actually I may try to disconnect the battery in the morning and let the car retrain just to watch the STFT. To be honest I haven't done anything to the car since it was back together almost 6k miles ago because my girl snatched it up as soon as it was finished. The only reason I have been scanning it was because the CEL was on while traveling to TN and bugged me the whole drive. Runs awesome like there isn't any problem at all.

 

Finally had a 57 degree day to check for leaks. Spent about $15 and used some random junk in the garage to build a smoke can to fill the intake. Took about an hour to build it and find the leak.


Youtube vid of the smoke leak
https://www.youtube.com/watch?v=HzWc...ature=youtu.be

 

Is it the IAC or the intake manifold connection thats leaking. I couldn't tell.

 

The intake manifold gasket is not sealing. Grabbing one at O'reilly today. Idle air control on these are controlled by the electronic throttle body and ECU I believe, at least that's how all of our Nissan stuff works.

 

I thought that motor on the left corner of the valve cover is the IAC device. The intake gasket is supposedly problematic. I was worried that mine was having problems sealing when I replaced the intake because it seems to take a lot of turns to torque it down properly....on that plastic.

 

It was a leak on the left. Just fixed it today. I couldn't tell if it was the intake gasket or lower fuel injector oring so I replaced all injector orings and smoked it again. It leaked on the left corner again right at the #1 cylinder area by the Variable cam solenoid. I changed the intake seal and smoke tested it and it fixed the leak. The intake seal was a cheap brand that came in the engine kit from the guy that I bought the car from. The seal was brand new but when I held it up to the Felpro that I bought this morning I saw that it was 1/3 the thickness. Started the car and it instantly ran differently and started retraining. Fuel trims are approaching normal / acceptable % numbers. I'll cross my fingers and see if any codes pop this week.

Edit: The seal kit brand was "CAP" Certified Automotive Parts

 

The difference between the seals is shocking. Glad you got this sorted out.

 

why does o2 1x1 show a "-" in the reading? I set this up also (I got a Veepak adapter) and show the same thing. I do keep seeing a warning saying that something about rich to lean current max threashold reaching 133 (where 12 is the max.

 

Probably was setup for my other cars and was only monitoring the fuel trims for the Scion. I am working on 3 different vehicles right now and keep going back and forth checking them.

The car did pop the P0420 again so it's going to need an O2 or cat to get it codeless. I'll probably wait until I decide to either weld up a T25 turbo setup or just longtube header and put a stainless spun cat down the line. At least the lean condition was solved!

Edit - I was thinking about the catalytic last night.. Since this car had the oil consumption problem until death maybe the cat did take some damage. I can't imagine how many gallons of oil was going through the exhaust.

 

I think yours is going to need a new cat. Mine is doing the same thing and I bought a CNT 90deg spacer, but havent installed it yet. I think the ECU is picky and a lot of people have this problem for some reason. It might be the consumption because the motor this cat came from had one of those failures. If I were going to keep the car, I'd probably do an entire exhaust and relocate that sensor down stream, but I am going to put this one back up for sale after I can get it a bath and take some more pics.