onespiritbrain Posted February 21, 2017 Share Posted February 21, 2017 Khrrrmm... so I have been seeing poor gas mileage since acquiring my QX4 and my only check engine code has been for misfires. I replaced my spark plugs, wires, dist cap, and rotor which sent the misfire code packing. Now I have a catalytic converter system too lean code. Naturally I ripped off everything from the pre cats back. So after inspecting the main cats it appears they are okay. I couldn't figure out a way to inspect the engine side of the pre cats so I went for a spin and got them nice and hot. Here are pictures of the glow pattern: Driver side Passenger side I am running with both o2 bank 1&2 sensor 2's disconnected. With just pre cats I am no longer experiencing an issue where the vehicle hesitates between 2-3k rpm, opening up beyond 3k rpm. I now have smooth power thru the upper rpm, smooth and loud as crap. I have been reading that gutting the pre cats is fine as long as the main cats are not gutted; the nox is still taken care of and emissions won't be a problem. Nissan, along with many other manufacturers, sought to obtain ULEV status by using pre cats but for the most part they are unnecessary and cause problems being so close to the exhaust manifold. I am sort of at a loss here. I don't know what to do.. I am wondering, can a failing o2 sensor 2 give a false lean code? Has anyone gutted the pre cats? Has anyone replaced the pre cats? Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
onespiritbrain Posted February 22, 2017 Author Share Posted February 22, 2017 I thought this might be a lonely road.. So I am in the process of repairing all the broken bolts before I reinstall everything. I just don't know what to do.. the pre cats are glowing about the same on both the driver and passenger.. I would like to just replace them but the pre cats are 3-4 times more expensive and I just don't have the money.. plus they appear to be in OK condition. I want to remove them to have a look see at the engine side since that would be where the clogging would be, but the bolts are impossible to get to with the heat shield on and I'm afraid I won't be able to get the heat shield back on once I get it off and that will leave me in a worse condition than when I started. Today I noticed that the top of my MAF sensor is cracked. If turbulent air is making its way in to the MAF from the road or radiator fan then maybe this was the source of all my woes. Anyone ever see Catalytic System Too Lean because of a MAF? Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Cuong Nguyen Posted February 22, 2017 Share Posted February 22, 2017 The maf is a heated wire. More air flow cools the wire and tells the computer to spew more fuel. Less airflow less gas. Link to comment Share on other sites More sharing options...
fleurys Posted February 22, 2017 Share Posted February 22, 2017 I thought this might be a lonely road.. So I am in the process of repairing all the broken bolts before I reinstall everything. I just don't know what to do.. the pre cats are glowing about the same on both the driver and passenger.. I would like to just replace them but the pre cats are 3-4 times more expensive and I just don't have the money.. plus they appear to be in OK condition. I want to remove them to have a look see at the engine side since that would be where the clogging would be, but the bolts are impossible to get to with the heat shield on and I'm afraid I won't be able to get the heat shield back on once I get it off and that will leave me in a worse condition than when I started. Today I noticed that the top of my MAF sensor is cracked. If turbulent air is making its way in to the MAF from the road or radiator fan then maybe this was the source of all my woes. Anyone ever see Catalytic System Too Lean because of a MAF? Sent from my iPhone using Tapatalk Getting air in AFTER your maf could definitely cause a too lean mixture and even misfire..... Do you have any reading of your O2 sensors (via obd2) ? Link to comment Share on other sites More sharing options...
onespiritbrain Posted February 22, 2017 Author Share Posted February 22, 2017 So I found this collapsed hose.. I believe it's the EGR?? Might this be the cause of my lean code? Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
onespiritbrain Posted February 22, 2017 Author Share Posted February 22, 2017 Getting air in AFTER your maf could definitely cause a too lean mixture and even misfire..... Do you have any reading of your O2 sensors (via obd2) ? I don't have access to an obd2 reader. I have just about decided to buy one of the Bluetooth ones from Amazon... The maf is a heated wire. More air flow cools the wire and tells the computer to spew more fuel. Less airflow less gas.But wouldn't a rich condition cause the cats to disintegrate, ultimately causing a clog in the exhaust and a lean code at o2 sensor 2? I don't think air can get to the actual wire from the top of it being cracked. I'm going to silicone it lightly for now. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Snowboarder12345 Posted February 23, 2017 Share Posted February 23, 2017 I chipped out my cats years ago and have never noticed a difference in how mine ran. Link to comment Share on other sites More sharing options...
onespiritbrain Posted February 23, 2017 Author Share Posted February 23, 2017 I chipped out my cats years ago and have never noticed a difference in how mine ran.Pre cats too? Or only the main cats? Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Citron Posted February 23, 2017 Share Posted February 23, 2017 That hose looks like part of the PCV system. Looks like it is coming off of the valve cover? It would not cause a lean condition. On a side note, your tranny dipstick is not bolted to the back of the head. Careful when checking tranny fluid, they are usually pretty easy to pull out when unbolted. I think it is just an oring holding it in now, if it's like other vehicles. There should be a procedure in the FSM for checking the O2 sensor. If it fails the test, then you know it is bad. Just takes a multimeter. Injector not firing would cause lean condition on only one side, but you should get a code for that. Link to comment Share on other sites More sharing options...
onespiritbrain Posted February 24, 2017 Author Share Posted February 24, 2017 So that hose is going directly into the back side of the intake manifold and the hose, in addition to being sucked flat, has a big hole where air may be pulled in to the intake. Sooooo might this hose have gotten way too hot from poor timing? The timing belt was so loose when I changed it that I could pull it off without adjusting the tensioner. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Snowboarder12345 Posted February 24, 2017 Share Posted February 24, 2017 Main cats. Mine were melted up and starting to clog so they had to go. Pre cats too? Or only the main cats?Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Citron Posted February 24, 2017 Share Posted February 24, 2017 So that hose is going directly into the back side of the intake manifold and the hose, in addition to being sucked flat, has a big hole where air may be pulled in to the intake. Sooooo might this hose have gotten way too hot from poor timing? The timing belt was so loose when I changed it that I could pull it off without adjusting the tensioner. Sent from my iPhone using Tapatalk On the vg30 that hose doesn't go into the intake, it runs under the intake. It changes to the metal pipe, which is attached to the underside of the upper intake, and runs toward the front of the engine. It ties in to the vent on the other valve cover and to the PCV valve on the intake. Are you sure that is not what it is doing? You may need a mirror to see what is going on back there. Link to comment Share on other sites More sharing options...
Slartibartfast Posted February 25, 2017 Share Posted February 25, 2017 A hole in the PCV system would be a vacuum leak, which would cause a lean condition. Retarded ignition timing will make the exhaust manifold hot as hell, which I guess might've softened the hose--if you suspect that's what happened, check the other plastic and rubber components in that area for similar damage. Link to comment Share on other sites More sharing options...
onespiritbrain Posted February 25, 2017 Author Share Posted February 25, 2017 (edited) Thank you guys. I am going to make repairs tomorrow afternoon. This is a great forum, thanks again. Just to gloat.. I mean note, just to note, I am getting 19- yes, you read that right, 19 miles to the gallon!!! My wife's vehicle stays on full 100 years after a fill up and when comparing usages through the week I always feel like mine gets terrible gas mileage but I'm actually getting 4 miles a gallon better! Haha Sent from my iPhone using Tapatalk Edited February 25, 2017 by onespiritbrain Link to comment Share on other sites More sharing options...
onespiritbrain Posted February 25, 2017 Author Share Posted February 25, 2017 No more cel and she is quiet as a mouse again! Initial impression regarding mpg is that I am not getting great mileage now that I've got everything back together.. I am at 44 miles of 100 and the needle is in the same position it was at 60-65 miles yesterday. Is it possible that a vacuum leak was causing me to have better gas mileage?!? Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
onespiritbrain Posted February 26, 2017 Author Share Posted February 26, 2017 So it is possible... as I am researching the subject it looks like, to a point, running lean can dramatically increase engine efficiency. Combustion temperature does increase quite a bit and more nox is created but efficiency is definitely increased. I am not going to do this but I won't lie, I am tempted to take it all back out, gut the pre and main cats, delete bank 1&2 o2 sensor 2's(replace with resistor), and install a fine adjustment globe valve to purposely get it running lean... 19 miles per gallon is tempting. It really is.. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Slartibartfast Posted February 26, 2017 Share Posted February 26, 2017 The computer should try to tune out a lean condition by adding more fuel. Running lean also tends to make the mixture predetonate, which the knock sensor reports to the ECU, which adds fuel and pulls timing to compensate. Predetonation and the heat associated with it are hard on the engine. Apparently some rigs will intentionally run lean under certain conditions, but there's more to that than just introducing a constant vacuum leak. It is possible that the leak was offsetting something else being wrong. I'd go through the standard tuneup stuff, clean the MAF, clean the throttle body, make sure the EGR valve's not jammed up, and see if that changes your mileage any. 1 Link to comment Share on other sites More sharing options...
onespiritbrain Posted February 26, 2017 Author Share Posted February 26, 2017 I'm getting 14.5 mpg now... and my "lean condition" code came back right at the 100 mile mark.. Okay so now I am going to repeat the mileage test using cruise control. I think I may be laying on the gas heavier since the exhaust isn't blaring loud. The loud exhaust may have been an aid in operator control since I was doing everything possible to drive as quietly as possible, and cruise control was by far better than me at giving it the least amount of gas possible per mph. Also I had a full size floor jack, two big jack stands, and my 100# toolbox in the back for the last 100 miles. After that, if I still have junk mpg, I am going to unplug the bank 1&2 o2 sensor 2's. If my 19mpg returns then I may leave it in this condition. Before I leave it with bank 1&2 o2 sensor 2's deleted, I am going to find the source of the lean code and fix it.. Maybe I'll try to find the source of the lean code first... I don't know. My wife's vehicle has it's power steering high pressure hose leaking like a sieve. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
RIPB.88 Posted February 27, 2017 Share Posted February 27, 2017 My TBI VG30 gets 17 in town and 19-20 on the highway I'm careful with the gas pedal and not traveling against high winds. I run Ethanol free 89 Octane fuel. I would think yours should do better. Link to comment Share on other sites More sharing options...
onespiritbrain Posted February 27, 2017 Author Share Posted February 27, 2017 As soon as I leave work I will stop by a station and we'll see what I get using cruise control and being light on the pedal. It looks like around 18mpg.. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
onespiritbrain Posted February 28, 2017 Author Share Posted February 28, 2017 17.1 not too shabby Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Slartibartfast Posted February 28, 2017 Share Posted February 28, 2017 Not bad, especially for winter. Leave the O2 sensors in, the computer needs them to set the fuel mixture. The secondaries, not so much, but you'll still have a code all the time. Link to comment Share on other sites More sharing options...
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