[alexandru96]

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[alexandru96]

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[alexandru96]

As for OBDII codes, regarding the engine, it had 2 historical codes and one active
The historical ones were one regarding the oxygen sensor that comes after the cat, on the exhaust pipe underneath the car and the other (which for me was expected) was a cylinder 1 misfire, I mean expected because I've experienced engine intrerruptions both during idling and driving and I've changed the ignition coil and that fixed the issue right away.
The oxygen sensor does not seem to have been changed, it is old and rusty just like the rest of the exhaust piping.
The active code was about an uncalibrated clutch pedal sensor (I never knew cars these days have sensors even for the clutch pedal) which was fixed by calibrating it.
Unfortunately the guy which checked them for me deleted them afterwards but instructed me to have the exhaust and intake systems checked by a mechanic.
Also the engine runs at 102 degrees celsius (215,6 degrees fahrenheit) and that seems to be its normal temperature (as it said on the expected column of the parameter table 102 celsius).
After driving for a while I've noticed the exhaust gas flow was very small, the gas was extremely hot (i was not able to keep my hand on the exhaust flow) and it was smelly, it smell like rotten eggs or something which makes me think there is some sort of a restriction somewhere on the exhaust, between the engine outlet and the tail pipe, this issue becomes worse as the engine heats up.
I think I could check that myself by unscrewing the joint between the cat and the rest of the exhaust to see if the mufflers are clogged and if that doesn't make a difference then the oxygen sensor which is mounted right on the cat itself but that would get me fined(in the best case, in the worst case that would get my car's registration suspended until i "fix" the issue) as within the EU the laws on noise pollution are extremely harsh especially in densely populated areas.

 

[alexandru96]

I've sent the car to a local professional service station, they've pulled out the oxygen sensor in order to pour a cleaner into the cat but found out the honeycomb was collapsed inside and the cat needs to be changed. I've went for the aftermarket option for US $600 since the oem version was US $3700 and was not economically viable as I bought the car for US $4000.

 

[alexandru96]

The culprit was the catalytic converter, the guys at the service changed it and the issue disapeared
Most probably tomorrow I'll get my car back from the service and if i don't forget to take the old cat back I will post some pictures in case anyone's interested.
So, for people who are experiencing a exhaust leak type sound that comes with a loss of power while accelerating and a aberant fuel consumption, they'd better check the tail pipe, if the exhaust flow is very low and extremely hot (in my case i was not able to hold my hand in the way of the exhaust for more than a second without getting burned) there's a clog somewhere in the exhaust and most probably that is the cat
As a reference, I will post a video I found online

it is a honda but the humming is exactly the one I've experienced on my chevy, but without the whooshing.

UPDATE:
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Problem solved, the cat was changed and now the car runs and drives normally.
I've picked it up and shaked it and sure enough it rattles, fun fact: the cat's honeycomb wasn't broken at the bottom as I've expected, it was broken on the other side, the one with the oxygen sensor and the engine's exhaust ports

In total the repair was around 800 euros with aftermarket cat, oxygen sensor & labour.
I've got the old cat back since I'm curious how much I'll get for it as scrap, I've heard these things are quite valuable as scrap and some people steal them for that reason

 

[alexandru96]

For anyone interested or experiencing the same stuff here are some symptoms I've experienced (also i have not had any check engine light or any ECU alarm(code) on):

• lack of power, your car will struggle to reach 80 km/h
• humming sound, something like a exhaust leak combined with some sort of a race car, when you begin to hear that sound the power of the car will instantly drop
• when flooring the car it'll begin to jerk back and forth under normal circumstances it should not do that, let's say you're at 2k rpm and floor it, it should begin to slowly pick up speed and pick it up faster as the engine rpm raises but not jerk
• very little, very smelly (like rotten eggs) exhaust, also extremely hot (so hot that i was not able to keep my hand near the tailpipe output without getting 3rd degree burns)
• very bad fuel economy, my car was guzzling around 17 liters per 100 km, after the cat change it dropped back to 14L/100 km in city and 10L/100 km outside the city (this is to be expected as my car is dual-fuel, LPG and gasoline and I run it on LPG as it is way cheaper, the LPG consumption is around 1 to 2 liters higher than the gas consumption, also fuel consumption in bucharest will be always way higher due to traffic jams)
• the engine won't rev up over a certain number of rpm's, mine was not going past 5000 rpm i noticed this as, with its reduced engine power i have tried to overtake...an e-scooter, this under load, in neutral it was behaving normally, after the cat change it goes to 6500 rpm (only did it once after the cat was changed, as a test, i usually do not go over 4k rpm) without any problems, mine it's manual and i can rev it up as much as i wish but not sure about the automatics, never owned a automatic, i don't know how it behaves

other symptoms for which you need a OBD scanner, I've used a cheap $5 ELM327 bluetooth one with the torque lite app on my phone, not much but enough to get a general idea of what is happening:

• the engine runs very hot mine stood at around 102 celsius (I ain't a specialist but as far as i know these things should run at 90-95 celsius, the cat change solved another issue, a mysterious coolant loss, there were no leaks, the head gasket is good so it did not ended up either combusted either in the oil sump, yet the level was decreasing a few milimeters from where I've marked the level with a sharpie every 100 kilometers, looks like it was lost in the thin air, literally, by evaporating and getting released by the safety valve as the pressure built up) after the cat change it stays at around 88 to a maximum of 93 celsius, usually it sits at 90 this with 35-40 celsius outside, as it is summer
• with the vacuum&boost gauge in the app you can check the vacuum, there are videos online on how to check your engine with a vacuum gauge, but this test should be done with AC and any other higher load on the engine like headlights and other high-consumption electrical stuff turned off as any higher load on the engine will affect the reading
• the O2 sensors, (bank = row of cylinders), the upstream sensor (bank 1 sensor 1, the one before the cat) should jump up and down making some sort of a sine wave, the less oxygen the higher the voltage that the sensor produces, the downstream sensor(bank 1 sensor 2 that which is after the cat) should not jump like the upstream one, it should be generally stable without very high variations at idle (this test have to be done with the catalytic converter hot, at its operating temperature) of course when revving the engine up or when driving around it will react but it should not make the same fast sine wave like the upstream one

from my perspective it was bad as this was a little annoying and costly but also good as I've learned things I had never knew before

 

[alexandru96]

Hello Will,

My advise: forget about the plugs, mine were replaced by the previous owner god knows when and they're fine, you can measure the gap if you want, it should be around 0.7mm or som' like that but don't worry about them, you'd better replace the ignition module as these things get bad as they get old, replace it before it'll send your cat to its early grave and end up like me (well, I've tried different sets of plugs before replacing the coil, the last set misfired so violently that I've literally ended up driving on only one working cylinder out of 4, that's how bad it was, it jerked back and forth so violently that i've felt like the whole car was collapsing under me, which most probably murdered the poor catalytic converter in the most gruesome way possible, thanks God I've had the tools in the trunk with me and ended up replacing the spark plugs in public, people were looking at me but that helped me to get home driving and not pushing you know what I mean)

My car's on LPG, which makes any misfire way more noticeable, I will share my experience with this: at idle on LPG the misfires were pretty violent (engine like it's about to stall and the misfires felt like a kick) on gasoline not so much but still noticeable => after my sparkplug-related experiment (which most probably destroyed the cat) I've changed the ignition coil and the issue was instantly gone

The simplest way you check to confirm if your cat is bad is to basically cruise at 2000 rpm and push the gas pedal to the floor, under normal circumstances nothing should happen other than the speed beginning to slowly increase and increase faster as the rpm gets higher, if the car jerks back and forth (like it has chain of misfires) it means that something's clogging the exhaust most likely the cat, other way to check this is with a vacuum gauge (using the OBD2 tester, the live data, no need for a physical one) if the place where you are has a max 1000ft elevation at idle you should have between 18 and 22 inch mercury of vacuum pressure, from idle (in neutral) rev it up to around 2000 rpm the needle on the vacuum gauge should decrease then increase to a higher value than the one you've been reading at idle, for example mine at idle stays stable at 20 inch mercury and if i rev it up at around 2k rpm it will be at around 21 inch at 2.5-3k around 22 which means it pulls in vacuum but turn off the AC and headlights when you do that

Other thing you can do is, when the car is still cold and the choke is on go to the tail pipe and check how much exhaust is coming out, also after you've been driving through town for some time park it in a enclosed parking lot and let the AC on so it has some load (like the underground lot of a shopping centre) and check how much exhaust is coming out it should be a decent flow, mine has a decent flow that way(after the cat change, before it was very little and extremely hot under all circumstances), after a minute or so if i turn the AC off it will decrease but that's due to the VVT as it closes the intake early or something like that to pollute less i belive

Also using the live data on your OBD2 tester (if you have a cheap 10 eur tester it won't read the codes or only read some of them) you can put 2 graphs of your oxygen sensors, bank 1 sensor 1 = upstream bank 1 sensor 2 = downstream, the upstream should jump up and down, that's okay as that's how the engine tunes its mixture, by jumping between rich and lean very fast however the downstream sensor should be more or less stable, it will react to acceleration of course but it should stay somewhere in the middle between rich and lean, my sensor unfortunately is working intermittently but the cat is good, when I accelerate it goes up to around 0.7V and stabilizes there, but only when the engine is under load and the exhaust pressure is higher then on coasting or cruising it drops to 0.1 and below, in my case I have a P0141 alarm on it which in delphi software states:
P0141

• HO2S 2 Heater
• Faulty function
• Malfunction
• Intermittent

I've suspected the heater that as it takes around 5 mins to begin to read something while the upstream o2 sensor which is brand new changed together with the cat begin to read data right away

so the sensor's bad in my case but since I have a small exhaust leak after the cat was replaced and I have to go back to the service station to have that fixed under warranty I'll pay for the sensor and labour for it to have that replaced as well

"I'd assumed 66k miles would be relatively low to need a new cat " I assumed as well, mine had 84 000 km (51K miles) when it failed, but in my case most probably the chain misfires that I've mentioned killed it, because the car was fine when I've bought it

And for the coil, don't get a oem one, get the cheapest aftermarket coil you can find, I've bought the cheapest aftermarket coil and it works okay, if it lasts for 2 years I'm satisfied, as soon as it misfires again I'll just buy another one, I paid 60 eur for it while the oem one was at least 200

I hope you find this helpful.