Catalyst Efficiency Fuel Trim And The Escan
I currently have a 2007 Toyota Hilux with a 1GR-FE in it and 192031 km on the clock. (Pretty sure you call it a 4Runner in the US).
Anyway, vehicle came to my workshop with codes p0420,p0430 catalyst efficiency on both banks. Knowing this, I Questioned the customer for possible causes without success, customer had just bought the vehicle, on inspection it was noted that the spark plugs were worn so we replaced them and carried out our test with the escan. What a great tool! Now I have only had this tool for about 2 months so I am still learning how to use it. My question is in regards to the fuel trim table and the ve comparison table, Could this cause premature failure of the Cat? I can obviously see some squares that maybe shouldn't be there so I am looking for some input on what sorts of things I should be looking at based on these tables? I have tried a bg induction and onboard injector clean without success. I still have the vehicle here so I can run more tests if required.
The first image is the after test once the cats were replaced, ( I only printed the before test sorry but readings were down at the 40% mark on both banks and on a visual we could see half the cats missing.
Note this vehicle has wideband AFR fitted but the cat test worked both before and after replacement.
Hi Chad. Do you have just the VE results? And while you're at it, do you have the idle MAF value in grams/second?
Hi Tim, thanks for the reply.
Here you go.
Looks great. OK, no breathing faults. Love that tool by the way. We're ruling out whole categories of faults here. How about all O2/AFS sensors at idle, and then snap-throttle and deceleration using the 'graphs' tab? A steady test drive would be nice too, but if it's any hassle we can save that for later if needed. Fuel pressure and quality faults aren't too common on these, so I'm trying to rule out sensor calibration, and a very confusing Toyota fault - exhaust leaks causing downstream sensor lean-shift.
Ok, So I think I did this correct. I used lambda for the AFR readings. Hopefully I have what you need.
Yup, that's what I needed. Before answering, I have to ask if there are any symptoms or codes?
Now, assuming that there aren't and you're just being thorough, yes Fuel Trim is high all the time, and jumps higher at higher RPM, indicating that fuel pressure/volume should be at the top of the possible cause list. Fuel quality is also a possibility, although I don't what they add to your fuel down there and if it affects average Fuel Trim. Sometimes in the States our vehicles underestimate or cannot learn the Ethanol content of the fuel (yes we burn our food) and the results are similar.
Now to actually answer the original question: Any time Lambda average is outside of a 0.98-1.02 range, the catalytic converter cannot work properly, and over time this causes a coating (that won't burn off because they are too cold). I can't prove it with your captures because they are just a snapshot, but it looks like your Lambda spends a lot of time in this range, indicating that the vehicle is in good fuel control (Fuel Trim did its job). So the answer is that even with this severe Fuel Trim correction, average Lambda is preserved and the converters should be fine. Still, it looks like you are right to chase this one further, since the vehicle may degrade further and Fuel Trim may run out of adjustment range. This can harm the converters over time, but it's very likely to set lean mixture codes long before then. Again, I think that fuel pressure and volume tests are appropriate. The only other variables I can think of are:
- The O2/AFS sensors are lying. But they behave the same on each bank, so that is unlikely.
- There's an exhaust leak shifting the rear sensors lean, which richens the mixture through 'Rear Fuel Trim', which is very active on Toyotas. Again, unlikely unless both banks are leaking the same amount. A smoke test will find this leak with some patience (and a smoke machine!).
Ill check the fuel pressure dynamically and see what happens. Also I will ask my customer what fuel he has been using. Again, thank you.
You are welcome. Please let me know if it helps or if other information comes up. Now off to bed for us Californians!
Tim I would just like to tell you that I am pretty sure you were on the money, with 30 psi and no flow on a return type system, I am going after the fuel system. Absolutely awesome. Can you tell me what the key points were that you concentrated on in the captures I uploaded? I had my suspicions in the fuel system but because at full load the AFR was staying rich and the fuel trim table was in the green I didn't really go further with it.
Ah I think I see it, on the snap throttle the lambda readings go lean not rich ( opposite to narrow band ) and based on all of the other tests, this indicates a fuel delivery problem. Am I on the right track?
Glad to hear! Rather than testing 'everything', our diagnostic thought process is to rule out as much as we can with as little effort as possible. The good VE rules out clogged exhaust, clogged intake, and timing faults. The good idle MAF rules out vacuum leaks (we like to see at least 1 g/s per liter at idle, or even up to 1.2 if the idle is a little faster). So that's at least 4.0 g/s on this 4.0 liter engine, which you had. Therefore, the problem is not 'air', so it must be fuel.
Fuel: Your Lambda values (as I read them w/out cursors) actually show small dips on snap-throttle, and the tall spikes are from closed-throttle fuel cut. This proves that the vehicle can run rich at least for short bursts, but mostly that the upstream sensors are reacting nicely. The higher average downstream sensor voltage proves that the converters are lit off and the vehicle is in fuel control.
Knowing these two things, we look at how hard the vehicle is working to be in fuel control, which is the short term and long term fuel trim. Your values were mostly high and showed some very high values at higher RPM. With good VE and MAF and reactive O2 and AFS sensors, this could only be lying sensors (often due to an exhaust leak), low fuel pressure/volume, or bad fuel (or additives). We can't rule out lying sensors, but we can put it at the bottom of the list because both banks behave the same, so we would need multiple leaks or sensor faults to get your results. That leaves fuel pressure/volume or quality, and quality is harder to test. The next step, by elimination, is fuel pressure.
NOTE: Yes, there was lots of green in your Fuel Trim tables, but remember that while the EScan is awesome, it can only display data that it sees from the Scan Tool, and with ST and LT combined, if it hits a cell on a lean sensor cycle AND that load/speed condition hasn't learned a LT value, you'll see green. The longer you drive the vehicle, the more accurate those tables become. In any case, we look for an overall feel rather than individual cell values unless there's a symptom that specifically occurs under those conditions. So based on a lot of red and orange cells and the steady high Fuel Trim during cruise and acceleration from your later test drive, it 'felt' like a fuel pressure fault despite the many green cells in the Fuel Trim tables.
This diagnostic ideology prevents us from testing a lot of things that we can rule out instead. For example, the good MAF reading means that vacuum won't be low, so we don't test it. Good VE means that compression will be good, so we don't test it. The list goes on, and of course this thought process covers faults that affect the whole engine or one bank - for misfiring or any form of uneven running, it's a whole different process.
Chad, I initially responded just because I love the idea of this site and the diagnostic process, not to sell anything. But yesterday I remembered that Jeff Digance is launching some training in Australia through mechanic.com.au The subject advertised in this link is actually our drivability seminar and it comes with our 280 page manual describing this exact thought process (and some EScan captures).
Check out the link and register interest if appropriate, as Jeff and the site are trying to offer this kind of training throughout Australia and need the support of anyone interested.
Thank you Tim, in actual fact today I fly out to Melbourne for an automotive aftermarket expo. Mechanic .com will be there with a booth. I will definitely go past and get some info on training. Thanks again.
Hey Tim. Thought you would appreciate these pics. Spoke to Jeff, sounds like we will be learning from your books in no time. Thanks for the tip.
I think you'll really enjoy the material Chad. I happen to have a few ATG books I keep with me on the road. Kris Lewis is an excellent trainer if you ever get the chance to take a class with him.
My first ATG class was the 6.7 powerstroke in Warminster, PA and I was lucky enough to make it to TST where Kris put on a 3.5 hr or so class on GDI. Both excellent classes with great material.
Hi Jeff! And thanks Chad for the pix.
Did you save the log files? If so, please Consider sharing those here as well.
No I didn't but I can redo the test and save the log files, will upload tomorrow.