2001 Infiniti QX4 Air/Fuel Alpha values 110-140%, low power at high rpm.
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First a bit of background. I am a nearly 40 year veteran tech working in a multi-franchise dealer (Infiniti, Maserati, Alfa Romeo, Rolls-Royce), ASE Master, L1, Infiniti Master, Rolls Master, Porsche Gold Tech. I own a PicoScope 4423. Now on to my questions. I just installed a JDM engine pull in a 2001 Infiniti QX4. As far as I was able to research, the core engine (Pistons, crank, cams) are the same as the original. I did have to swap over the intake cam sprockets, front timing cover, upper oil pan, crank pulley, and flex plate to accommodate the different cam/crank sensing setup as the original engine. Using E3 spark plugs. Shortly after I had it running, I noted it would not rev freely into the upper RPM's (4-5K). The original engine had a head gasket issue on bank 1. There was a very steamy exhaust stream for the first several minutes after new engine start-up. Have driven it several days so far, with no codes set yet. Looking at O2 waveforms (Using my own Consult II in line graph mode), it is apparent that the bank 1 cat is not functional (rear O2 mirroring front). Rear O2 on bank 2 staying low/lean. Air/Fuel Alpha readings 110-115% both banks at idle, climbing to the 140% range on moderate to hard accel., then falling to 120-130% at cruise. Have cleaned air flow meter and new air filter. I have a home made in cylinder transducer available. New fuel filter and fuel pressure test are next steps planned. Looking for suggestions as to least invasive/simplest/best bang for the buck diagnostic steps. OE cats are $400 each my cost, not too keen on aftermarket ones unless you have a known QUALITY suggestion. I do have an exhaust back pressure gauge available as well. Through the years have seen cats "survive" a coolant bath and keep on trucking, hoping to hear your thoughts.....
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- Andy.MacFadyen
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Because of your high Alpha readings on both banks, I'd suggest staying on the fuel path. A fuel pressure reading would be nice, but it's work on this vehicle. I've also never seen a bad fuel pump in one of these.
What's the highest Engine Load reading you can get at WOT in 1st gear? If it's lower than 85%, then you may still have a skewed MAF sensor, despite cleaning it. If both upstream O2's are stuck lean doing the same WOT run, then that's just more evidence for a fuel problem.
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"Common sense ain't so common is it?"
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SHIMHEAD wrote: It set P0171 and P0174 codes yesterday morning finally, and would reset them pretty quickly if erased
I was wondering why it wasn't coding. :lol:
Hoping a previous employer can get hold of some MagnaFlow replacements for me to look over before I commit to them if that turns out to be my issue.
I'd suggest holding off on the cats for now? If you truly had a B1 cat that was plugged or otherwise not flowing, you'd have negative trims on that bank. Equal trims on both banks suggests equal flow across both banks. If you get a P0420 after solving the P0171/P0174 issue, then that's a different story.
I think the WOT test through 1st gear will get you the most maximum diagnostic bank-for-your-buck. If Load is low, you know there's either a volumetric efficiency issue or an airflow measurement issue. Lean suggests an airflow issue, not VE. Alternately, you can record your highest airflow rate and put it into a VE calculator . Again, if it's low, I'd suspect a MAF.
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You're probably aware that Nissan/Infiniti sometimes won't run the downstream heaters when just sitting there? Might explain some of the O2 sensor behavior you're seeing.
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Any suggestions for verifying the secondary Cats functionality? Thermal imaging?
Without a five gas analyzer, that's about the best option you have. Or just a infrared thermometer. If the outlet is hotter than the inlet (after a test drive), I'd call it good.
Are you in an area that still does tailpipe emissions testing?
Nope, Bank 2 rear pretty much sitting at .28 volts ALL the time, barely a ripple in Line Graph mode. Using Fuel Injection active test to richen/lean mixture +/- 25% does not phase it. It may very well be the original 242,000 mile sensor.
Ah yeah, it's probably dead. :silly: I gotta say, I really wish other manufacturers had that Fuel Injection Active Test available. Toyota has a similar test, but that's about it. It's a very powerful test in the right hands.
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Thanks for your input so far, very helpful! I will post up my final results when I am done.
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