High fuel trim on bank 1 causing P0420 code?

Hey Everyone,

This is my first post as a Tacoma World member, and the first real issue with my truck which I bought used recently. It's an 06 with about 175,000 Miles on it.

I'll try to keep this short and sweet without leaving anything out, as I have done a lot of research on this forum and others, and a decent amount of my own work before deciding to make a thread myself, as I am now stumped.

The truck started by throwing both the P0420 and P0430 codes which states that the catalyst system is not performing efficiently enough on either side of the exhaust. (bank 1 & 2)

Naturally, since both codes were showing I began looking at the engine rather than sensors and cats. Cleaned the MAF and Throttle Body butterfly valve. Checked the air filter and felt and listened for any possible exhaust leaks. All to no avail.

After my mechanic suggested that it may be both cats I had it diagnosed by the dealership as well as a THIRD mechanic, who all said I should replace both cats. So I spent a day off replacing both cats with used but re-certified original toyota cats. This solved the problem for the P0430 code (the passenger side) but not the drivers side P0420 code, which comes back on within 20 miles of driving.

After replacing the rear and front O2 sensors on that side, I still have the light coming on without hesitation after reset. So the problem can no longer be in the catalyst system at all.

I've noticed now that the fuel trim is higher on that side than the passenger side, causing the cat on that side to be hotter as well. My hunch is that because the bank 1 side of the engine is running rich, the cat is performing but simply can't take care of all the extra un-burned fuel, resulting in what seems to be an under performing cat, throwing the light. I'm trying to fix this quickly as I'm sure this is doing slow damage to my all new catalyst system. Through some research it seems I could be looking at malfunctioning fuel injectors, or maybe a vacuum leak. But I have no idea where to start troubleshooting an engine that is running rich. The engine purrs like it should and doesn't misfire or anything, however I do think acceleration seems somewhat sluggish. Any help would be greatly appreciated, and feel free to ask for any other relevant information. Thanks a bunch people of Tacoma World!

 

With the engine at idle spray some non flammable brake clean around the intake plenum paying special attention to any vacuum fittings. If you hear the engine RPM bog slightly, you may have found your vacuum leak. Personally, I use flammable carb cleaner and listen for an RPM increase, but I don't know that it's the "right" way to do it. Other than that double check the O2 sensor connections and ensure they are clean. If none of that works do a compression test on a warm motor. I also noticed the FSM says it requires TWO trips to cycle the CEL. http://www.customtacos.com/tech.old...06toyrm/06toypdf/06rmsrc/rm2006ta/0050034.pdf

 

How do the plugs look?

 

Thanks for the quick response folks! I'll definitely try that check for vacuum leaks. And each of you reminded me of something I forgot to mention about my troubleshooting. I have already done a compression test on that side of the engine, and all came out about the same, close to 100 I believe. The spark plugs were changed just a few months ago.

 

Do you have a scanner that reads real time? If so look at the O2 sensor voltages. They should between 0 to 1 volt and be active. 0 volts being lean 1 volt being rich. There is no real reason why one side should be different than the other as the manifolds cross if there is a vacuum leak it would effect the cylinder closest to the leak most likely with a misfire at idle.

 

Leaking fuel injector on the right side ?

 

I have used a real time scanner, I'm gonna do it again so I can post the exact numbers, but the drivers side was reading .9 or so if I remember right. The other side was a few points below that.

 

Ya, I wonder if it is an injector, as I have no misfire symptoms that maineah suggests would be indicative of a vacuum leak. Changing injectors might be a bit out of my league, what's the process and approximate price of doing so?

 

I've never done it on a Tacoma but hopefully someone here can offer some advice. I would change all of them if it was me.

 

Yes an injector could give you problems more so from a bad spray pattern than a leak.

 

Maybe a couple of good squirts of Lucas fuel system cleaner in the tank may free up sticking injectors. I'd be slappin' some new spark plugs in it if you haven't already.

 

Ya, that's what I was thinking. Not atomizing the fuel correctly or something. Any idea about the cost of changing them? Also, do any other possibilities come to mind to try or look into first? Anything before the injector that might cause it to malfunction?

 

Here is what I know from my experience with my passenger side CAT going out:

The ECM performs a test of the CATs whenever certain conditions are met, once during each drive cycle. Once it's done the test, that's it until the next cycle. A CAT must fail the test during two consectutive tests before a code is set. If it later passes three times in a row, the code will be cleared. The test basically consists of deliberately dumping excess fuel on the CATs and watching the result on the O2 sensors. For that reason I don't think the fuel trim is really relevant, since the test isn't done during normal operation, it's done under an artificially created set of conditions.

The sensors normally generate their own fault code if there is a problem. The Toyota dealer I used says they watched the voltages from the sensors with a scanner to see if they were rapidly cross counting or not. They were, an indication of good health.

There is an acceptable efficiency rate for these CATs programmed into the ECM. Toyota actually has a TSB out for the RAV4s to have the ECM reflashed to be less sensitive to a CAT that is less than brand new. I don't know what the numbers are, but let's say Toyota was tired of replacing CATs under warranty that were performing under 95% efficiency. A quick reflash and no more codes until down to, let's say 80% efficiency. That doesn't help Tacoma owners at all, but it's a good example of how an ECM can be programmed to set an inefficiency code when the vehicle will still pass tailpipe emissions tests. My truck had just passed smog less than a month before my check engine light came on.

I've never heard of a used, "recertified" CAT. Are they coming off of wrecked trucks? One has to ask why they ended up off the vehicle they were originally installed on.

My truck is now out of warranty and I know that others have had this problem. I worry that my driver's side CAT my fail. I live in CA, although there is no difference in factory supplied emissions equipment, any replacement must be CA approved. Guess what, no aftermarket company bothers to get their parts CA certified. Not worth the hassle and expense. This leaves us CA Tacoma owners with only one legal option: a $1000 dealership CAT. Knowing that the truck will still pass tailpipe with these codes infuriates me and makes me ask what's the difference between Toyota reprogramming RAV4s and me tricking my ECM to keep the light off so I can pass visual and move on to the tailpipe tests. If I am passing tailpipe, then I am not polluting, right?

Somewhere on here there is a writeup for using a spark plug anti fouler to space the downstream o2 sensor out of the exhaust stream a bit, making it see less o2, and therefore give the impression of a higher efficiency level, and not set a code.

My service advisor told me that once that code comes up the CAT needs to be replaced nearly 100 percent of the time.

Good luck.

 

Thanks for the info Joe! I do think that most re-certified converters would be taken from a totaled vehicle, then tested to ensure they performed above the efficiency requirements of the vehicle. I actually used that term to shorten my story, but in my case this cat was taken off a vehicle where the problem was misdiagnosed. The vehicle was throwing a code for the passenger side cat efficiency but the mechanic replaced the driver side. So I'm quite certain the Cat is okay because it came off a vehicle that was not throwing the code for that side when it was removed. Again, quite certain is still somewhat unsure, but even if it is a bad cat, I have to question why one side is running richer than the other, pretty sure this is abnormal and I'd like to fix that regardless and go from there.

 

I had problems with it myself. I've ran everything from mixed 2 stroke race gas to questionable fuel from a rusty container through my truck and the cats were clogged and o2 sensors were smoked in under 100K miles. I have a wideband gauge and see the AFR live, and it still ran fine, so I tried the sparkplug spacer trick. Helped for a while then the code came back. I then hollowed out the cats and installed an URD 02 simulator. The code went away and the truck runs better than ever. If I lived in an emissions state, I would still have the simulator just not the hollowed out cats. Just tuck the box out of sight above the trans...
http://urdusa.com/store/Electronics...1GR-FE-4.0L-V6-Dual-Channel/product_info.html

 

The O2 sensors have to be hot in order to do any thing at least 600* putting a spacer in would only make it worse. Watch the sensor working with a scan tool they will tell you where your mix is, there is no miss fire or rough idle and you say it runs good so I doubt there is an injector issue. Until the sensors are hot they should not set any code modern sensors have heaters in them to get them hotter sooner it's all about emissions. Look at each O2 sensor and watch it's voltage it should swing a lot if it's lazy it's toes up or if it reads a steady voltage + or - a 10th or 2 of a volt it's toes up. The O2 simulators do what the O2 sensor should they were developed for propane/hydrogen fueled vehicles in the case of a modified exhaust system it maybe the only way out basically they generate random voltage.

 

This was gonna be my last resort. But it seems I'm about to that point. In looking at this it seems it's one part that takes care of both sides. Is that correct? I'll be tempted to hollow the old cats now too! Utah is an emissions state but I'm quite sure they don't use a sniffer, as long as you pass visually and without the light. How did you go about hollowing them out anyway?

 

I actually noticed a box between each rear sensor taped up and already on the truck when I bought it. Now I'm wondering if something like this was already installed! I'll have to take the tape off and see if I can figure out what it is. If it already has these on them I'll be really stumped!

 

I unbolted the Y pipe and used an aircraft drill bit that is about 15" long to poke holes in it, and a long screwdriver to crack chunks out. It breaks apart fairly easy. Make sure to wear a good mask, those fine particles aren't good for your lungs.

The simulator does both sides.

 

Does anyone know if URD or someone else makes or used to make a simulator for one side only? Trying to figure out what these things are. I'll post pics later if I can't figure it out.