Catalytic Converter

[Mike Floutier]

I've been trying to sort out a mis-fire P0301 and flashing CEL for about 15,000 miles but getting nowhere - you may have read the thread.

Anyway, I now lose power if I open the throttle too much AND whenever I start the engine it usually stops unless I catch it with the throttle pedal.

At first there were no extra codes BUT today I got a P0430 and a P0174 (yesterday I got a 171 AND a 174 - BUT no 430).

I have read a few threads suggesting that not every 420/430 is a failed Cat BUT I'm assuming that with: 1) the drive-ability problems, and 2) the longish mis-fire history, the Cat has probably failed - although which one I'm not sure.

I guess that all I'm asking is for confirmation of this theory so that I don't spend money needlessly.

[billydpowell]

I have read your other post also... and this just came to me??

how long since you changed your fuel filter? plus you might want to check your fuel pump pressure... you could be running LEAN on fuel keeping your combustion from being full power (reading misfire) and that is being picked up by your cats...

just a thought....

[curiousB]

I had P0430 problem last summer. After changing a catalytic converter with no success I learned the problem was only leaks in the pipe. See below for more detail...

http://us.lexusownersclub.com/forums/index.php?showtopic=70886&st=0

[Mike Floutier]

Thanks Guys,

Firstly Billy I have dual fuel and the problem is the same on both so that's ruled out.

Curious, I have looked at your thread regarding CATs and was wondering whether your investigations were brought on due to a drive-ability issue OR whether it was the P0430.

I have a severe drive-ability issue which is: 1) Intermittant - toggles between "hero and zero" fairly often but only when the car is switched off and on again??? and 2. Usually NOT accompanied by the aforementioned codes.

I have a question: Does the LS430 have a "Limp-Home" mode? And, if yes, 1. What does it feel like, and 2. What initiates it?

[Mike Floutier]

Hey Billy,

I just read your comment in 2010 about you replacing your cat converters. How did you know they needed replacing??

My car has got steadily worse over the last couple of days and finally today, at the Lexus technician fortunately, it failed even to start.

The Tech guy thinks it may be a vacuum hose or something and is going to look it over. He doesn't want to remove the front O2 sensors to see if this helps as he's had a lot of experience of them cross-threading.

As I said, I'm very interested to know how you diagnosed your bad cats.

Many thanks.

[Mike Floutier]

Ok just had a thought, Torque Converter!!

If the problem was one of the cats then only one bank would be affected, on the other hand the Torque Converter affects the whole shebang.

What do you think? (before I get down another rabbit trail)

[Mike Floutier]

Just to keep you up to date, we got both CATs off the car tonight and it made absolutely no difference.

HELP!!!

[mshaw]

Good evening, and, sorry to intrude, but, maybe I might be of assistance. I have not had the pleasure of reading the background information, only the info posted on this thread. But to retrace those steps, you had a P0301, which created a flashing CEL (not usual unless the misfire is beyond a 10% rate), but you had after that, if I understood correctly, simulutaneous P0171/174, but, somewhere prior to this, a P0430. I may have gottenthe orders a little off, but I think I have the gist of it. Firstly, the torque converter has nothing to do with this - that would create a 700 or 1700 series code, also you would have either (a) shudder issues at or about 50-60 mph, and/or, (B) lock-up issues creating dying when coming to a stop after extended travel. I did not see either of those concerns nor complaints of those codes. Fuel issues, regardless of dual fuel or not, will not create only a 301 - you would have a 300 code, as well as 301- 306, randomly, as well as possibly 1500 series codes. The place to be looking is toward the Mass Air Flow sensor, at a vacuum leak, or, more specifically, something particular to the number one cylinder having a vac leak or fuel shortage - intake gasket leak, fuel injector seal leak, fuel injector failure, etc... The P0430 is likely due to a confusion on the part of the ECU being unable to justify the imbalance of fuel/air mix it sees coming in at the MAF, compared to what it sees as a burn ratio based upon the TPS position and load range, contrasted to the oxygen levels remaining in the pipe as seen by the O2 sensors. Of course, this is just a guess on my part...

M.S.

[landar]

The epic misfire and lean mixture may or may not be related. Perhaps whatever is causing the misfire is now deteriorating so badly that you have the P0171/74 codes.

From what I understand, a lean mixture can also cause misfires and increased NOX output. If you have a scanner, you might see Long Term Fuel trim levels that are elevated.

Causes of lean mixture could be:

MAF sensor reporting less air flow than is actually there. The O2 sensors are correctly reporting a lean mixture(too much air) and this 'confuses' the computer and sets the lean codes.

Vacuum leaks AFTER the MAF sensor such as intake manifold leaks, PCV leak, vacuum hoses.

Weak fuel pump or restricted fuel filter.

Plugged or dirty fuel injectors.

Malfunctioning ECM/PCM.

I believe you have already looked for vacuum leaks but you may have another go at it. Also, since you are running both petrol and gas, the weak fuel pump/restricted fuel filter are probably ruled out. Ditto for fuel injectors if the problem persists with petrol and gas.

I cannot remember...did you look at the MAF?

[mshaw]

Landar: I don't think the gentleman has a scanner, but I agree with your trim analysis, to a degree. I went back and re-read his description, and he stated he had a 301, then the 171/174, then the 430 with a 174. This will not be a general fuel system failure, as he has been battling a 301 ONLY for the past 15k miles. If he had a 300, or had random 300-series codes, such as a 301 today, a 303 yesterday, a 305 three days ago, etc, I might go along with a fuel pump, filter, etc. But that is not the case. A failed PCV system would likewise create either multiple cylinder misfires or an 'out-of-balance' condition for the engine to one bank. A failed or malfunctioning ECU in a vehicle that new would certainly create an internal error code or RAM failure code.

I will go along with anything from a dirty/faulty MAF, to a vacuum leak, but I am strongly leaning toward something pertaining to cyl #1, such as a failed intake gasket or injector seal at that cylinder, allowing excess air, which would also create the high misfire rate (above the 10% threshhold, triggering the flashing CEL) at #1 cylinder.

[landar]

Landar: I don't think the gentleman has a scanner, but I agree with your trim analysis, to a degree. I went back and re-read his description, and he stated he had a 301, then the 171/174, then the 430 with a 174. This will not be a general fuel system failure, as he has been battling a 301 ONLY for the past 15k miles. If he had a 300, or had random 300-series codes, such as a 301 today, a 303 yesterday, a 305 three days ago, etc, I might go along with a fuel pump, filter, etc. But that is not the case. A failed PCV system would likewise create either multiple cylinder misfires or an 'out-of-balance' condition for the engine to one bank. A failed or malfunctioning ECU in a vehicle that new would certainly create an internal error code or RAM failure code.

I will go along with anything from a dirty/faulty MAF, to a vacuum leak, but I am strongly leaning toward something pertaining to cyl #1, such as a failed intake gasket or injector seal at that cylinder, allowing excess air, which would also create the high misfire rate (above the 10% threshhold, triggering the flashing CEL) at #1 cylinder.

Mitchell, in my post, I mention that I do NOT believe the problem to be fuel filter or pump although these can be the culprit in certain situations. The OP can run either petrol or natural gas and reports the misfire on either which is why I generally dismiss the fuel. The OP has also tried 'sniffing' for leaks with a propane touch but has found none. Nonetheless, it might be a good idea to go over it again very carefully. I agree that the MAF sensor is highly suspect. As for the ECU, it is possible for a peripheral component or driver, even a connection, to be going intermittent. The firmware might not catch that type of failure. BTW, even though the vehicle is relatively new (2002) it has close to 300k miles.

[jaswood]

Just to keep you up to date, we got both CATs off the car tonight and it made absolutely no difference.

HELP!!!

What did you do with the oxygen sensors mounted downstream of the cats, open circuit or left connected ???.

Leaving them connected, and exposed to atmospheric oxygen levels the idle and low engine loading mixture would probably run extremely RICH.

Leave them disconnected....GUESS.

[mshaw]

Landar: My apologies for reading your post too quickly. Upon a slower perusal, we seem to be much closer in agreement. I understand it is 300k on the vehicle, but my experience has been that the ECU would still have significant self-diagnostic capacity. There may be weakened circuits and connections, because of vibration and/or simple corrosion occurring because of time mixed with the passage of current, but the circuits are operating well enough within design parameter to both identify external issues, but also to allow for the sensors to have the 'freedom', shall we say, to create confusion in which code to set. It is situations such as these that it would be so much easier to have the vehicle in one of my bays rather than to try and diagnose based upon symptomologies.

M.S.

[Mike Floutier]

Thanks for all this input guys.

My friendly independent Lexus tech subsequently took the car off me for 5 days and wasn't able to find any fault with the engine - personally I agree with idea that the continual P0301 without any other mis-fire codes relates to that particular cylinder and, having ruled out fuelling (due to dual-fuel) and ignition (changing spark plugs and swapping igniters) I believe that the underlying slight mis-fire is probably an exhaust valve seat recession issue on Cyl. 1. I'm now looking for a local diagnostic tech with access to a pressure transducer/scope setup to confirm this - although this is only really so I can stop searching for a solution as I don't see myself paying what it would take to redo all the valve seats.

This mis-firing however was a much longer term issue. The problem that was crippling the car and meaning that I couldn't use it in my car service business was, what I thought was, the Catalytic Converters. My Lexus tech, having exhausted all other possibilities, went along with my idea about an exhaust blockage (the only thing bothering me about this was the fact that the whole of the engine seemed to be affected by this extreme lack of power WHEREAS surely only one CAT would fail at one time thereby only affecting one bank).

Anyway he agreed to remove both upstream CATs as a diagnostic device - he then called me at 9:30pm to tell me it made no difference!! This is where I start to think about the Torque Converter again.

Anyway I get this inspiration and remember that I changed the MAF for a new one a couple of weeks before this severe problem occurred. My tech guy had asked me about recent work on the car and I had told him about this but for some reason it seemed to test ok when when I took it to him.

I still had the original Toyota/Denso MAF (300,000 miles service!!) in a box in my garage so we re-fitted this AND, guess what?.......

The morals of this story, for me anyway - I'm sure I don't need to tell you guys, are listen to inspiration and DON'T use cheap after-market parts. Clearly the cheap MAF sensor worked when I fitted it BUT failed after only two weeks.

Thanks again guys, both of you strongly suspected the MAF and if I hadn't tried it already your comments would certainly have led me to it next. It's amazing to think that such a small component can make such a difference.

Thanks for your input also Jaswood.

Will let you know how I get on with chasing down the residual P0301 & flashing CEL, although the weather is warming up now which helps as the problem is almost entirely limited to the warm-up phase of engine operation.