DMPesso

I figured that would remove the code as it usually does. So now my nightmare. Is it the cats? When I bought the car it had a bad valve cover gasket leak and you can see the oil everywhere. The guy claims he changed the gasket and I don’t see oil on the floor. Could the cats have been damaged from the oil leak? Not sure what else to look for on the P0420 after changing o2 sensors. It’s usually the cats if not the oxygen sensors I heard.

Arsenii

Hello,

The cat dies on the inside, the oil leaking on it from the outside won't cause that much harm, unless if it got a uniform coat of crust on top as a result, worsening heat dissipation. Here is a thread that goes in details on how to check catalysts, in short, look at the Live Data for Fuel Trims and Downstream O2 sensors, Fuel Trims should be as close to 0 as possible, O2 sensors should show about 0.5-ish volts, but not stuck on that value, if the values are going from like 0.3V to 0.7V, then the catalyst does have issues. What you can also try doing is going for a confirmation drive, which may reset the CEL you have, here you can find a manual describing the steps required for that.

Hope this helps and best of luck!

DMPesso

thank you. For this I need one of those large fancy scanners right? I have a small orange one I don’t think the cheap ones can read this right ? I guess I have to bring to mechanic then. I’m not sure what else it could be besides the cat at this point. The hesitation is really bad

Arsenii

You do need a more or less advanced scanner to read Engine Live Data, and you have a couple of options for that. First option is to visit Advance Auto parts store, they do have good scanners, but not all employees are too keen on you going beyond just code reading for one reason or another, so you will have to find the right shop. Next you can get a simple ELM327 device, which should provide the data, but it has a set of its own limitations, so I would only use it as a cheap alternative, nothing more.

One of the better all-around alternatives would be to get something like Launch scanner, which are pretty capable not only as OBD2 compatible, they are also designed to diagnose some of the manufacturer-specific systems, like Airbags and ABS systems. Though the best option specifically for Toyota vehicles is Techstream software and Mini-VCI cable, it is the most capable, but can be tricky to make work, since what you see on eBay is not the most legit way of obtaining that software..

If the car hesitates as a result of the code you have, it may indicate that the catalyst is clogged. If so, you will be able to see it with the temperature gauge - if the catalyst is hotter at the outlet than at the inlet, there is a good chance the catalyst is clogged.

Hope this helps and best of luck!

01LEXPL

iTrader: (10)

This is a tricky one. It's been mentioned on here a few times.

I refuse to replace a cat on something this old. So I run a spark-plug spacer
It still brought the issue back temporarily as the sensor wasn't getting enough exhaust... so I ran it on premium++ for a couple of tanks, and kept clearing the code (with a basic scanner).

Now all is well. This car has done it sporadically over the years. Some people on CL swear it being **** gas.

DMPesso

spark plug spacer? What does that do? I think my problem was there was a bad valve cover gasket leak when I got the car so I don’t think bad gas is the issue I always use 93.

01LEXPL

iTrader: (10)

It's a cheap & ghetto way of fixing a cat without doing so.

Basically it spaces the sensor "out" from inside the exhaust by 1/2" or whatever fits, so that the sensor reads less... so when your cat is bad, the (sensitive) o2 sensor won't constant trigger a CEL.

DMPesso

if that would stop the hesitation I would do that but I rather just keep resetting the CEL. This sucks. Just after I fixed the car up.

Margate330

Hi dmpresso, maybe you like to post up your live fuel trim data since a misfire will sent unburnt fuel to the exhaust and in theory can mess up the cats- can possible retore with Cat cleaning products if problem is from misfire.

Fuel trim test:
1) With car fully warmed up at idle, report fuel trims.

Twice my fuel trims were running +8-10 both banks and couldn't figure out why.
Fixed it first time by replacing fuel injectors with some flow matched injectors from trusted seller on ebay.
Fixed it 2nd time when I had weak spark from my ebay fake denso coils and replaced them

DMPesso

I was actually going to try those cleaner products out of desperation just didn’t think they work.

now you got me thinking. This all started some time after changing the spark plugs. But I used NGK from AutoZone so I don’t see how that could be it. I noticed only one coil pack was changed when doing the plugs. Since previous owner repaired the gaskets and changed only the one coil that was affected by the leak. He was being cheap he should’ve did them all while in there it’s a big job. Now I can’t decide if it’s worth changing plugs and coils since I just did the plugs.

Margate330

Like Arseni says above we need to see live data and that will tell everything.

If you have a bad vibration at idle you have a misfire I can promise. New engine mounts will soften it up but only disguises a problem from my own personal testimony and witness.

Fixing any possible misfires and fuel trim issues and O2 & AF isues as seen in live data is what make the car's exhaust run clean.

PS- some members on here swear by cataclean, but again you are not handling the problem if one exists in the form of a misfire and poorly running engine.

Felix

I'd be figuring out what cylinder & checking that coil....

DMPesso

AutoZone only had the dura lube cat cleaner but he said it works. Going to try it first.

I thought misfiring wouldn’t cause only a 420 code to pop up, but your right the vibrating at idle is reminding me of when my coil went bad on my GS. So reading this live data would be able to tell me if it’s my cat or the coils and exactly which coil it is? Or should I highly consider changing the coils?

I have to go to a mechanic and get this data read. Thank you all for your help.

Arsenii

It frankly sounds like a wild goose chase, replacing coils without prior diagnostics. Catalysts do have a tendency to fail over time, especially if the car wasn't very well taken care of in the past, which I can't be certain about. The fact is that you have a solid code that indicates a problem with the catalyst, so you need to start by fixing a known issue, what caused it to occur in the first place is an entirely different matter that must be investigated separately.

Failed coil will definitely find a way to manifest itself, it will either fire or not, which the ECU is pretty good at picking up, triggering a Misfire code if a certain threshold is exceeded, scan tools that are capable of reading Engine Live Data should provide a misfire count for each cylinder as well. Good quality coils are expensive, one can go up to $150, and you need 6, it makes almost no sense to just come in and replace them all on a whim. If you are really not sure about their condition, here is a spark tester tool that will help you check them, a good coil should be able to fire through about 5-8mm gap consistently, if so, there is no point in replacing it.

It is true that rich mixture will wreck the catalyst, but you need to verify that you do have a Rich condition in the first place before going out replacing stuff. Check Engine Live Data, look for Fuel Trims and A/F sensor readings, if those look fine, then the engine is working as intended and a failed catalyst is just a result of it being almost 20 years old by now. Hesitation that you are experiencing is not necessarily caused by a failed coil or any other component, it can be a result of the catalyst being clogged, not allowing enough flow to evacuate all the exhaust gasses, which can and will drop the performance by a noticeable margin. As I wrote before, the only way to check if it is clogged without actually taking it off is to compare its temperature at the Inlet and the Outlet. Other way to test this theory may be to take the catalyst off and go for a pretty loud ride without it to see if the performance will return.

Hope this helps and best of luck!

Margate330

You are correct, misfire does not cause P0420 "catalytic efficiency below threshold" code.
What I'm trying to hint is that a poorly running engine will destroy your cats..., and your new cats too if that sounds like fun. lol

You need live data and if you take it to an exhaist shop he can unhook the O2 sensors and put a pressure gauge on the bung and find out really fast if there is a restriction- thats how I checked mine.

Ps- can always do the down and dirty way and unhook them yourself like posted above- nothing wrong with that either. Yeah so what it's noisy but can answer the question if you have a restriction causing your engine hesitation.