cmcar08

Car has since been fixed and tested, there was a combonation of clogged Cat and worn piston rings. I changed to a 2nd hand cat and the pretty much fixed the fuel trims but the car still failed emissions, im guessing thisnl was also caused by the worn piston rings. Fixed the piston rings and emissions are now almost 0.01% vol. Fyi, a tip to diagnose worn piston rings was to start measuring emissions at a low engine temp, and if the figures start out ok, and worsen as the temp rises thats a sign that increasing volumes of oil is innthe exhaust as the oil temp increase. Mine was passing NCT limits below 75degC but above got worse, at 90degC it was well beyond the test limits.

I did a a couple of flight recordings while driving to work; intake temperature was 8degC at turn on so that would be the ambient outside air temp. during driving it reaches 20degC Intake air temp. With ETC at 84degC (stationary idle) LTFT was 39%, MAP was 24kPa. O2 was oscillating similar to the previous graph upload. Does the above look correct apart from the LTFT figure itself? Are these the only factors that affect fuel trim possibly resulting in overfuelling/ high CO at idle or am I missing something? You are correct NCT emissions test takes the ETC reading and can only be carried out at above 80degc. regarding the 60ish degC running temp at higher speeds, I assume the additional airflow is what’s cooling the engine rather than the coolant being sent through the radiator by the stat? Again assuming the gear ratios are higher than programmed to the ECU. I’m not overly concerned with this for now as it’s not at factor while stationary testing during NCT. Not sure if it helps troubleshoot this but increasing revs at stationary through to 2600rpm , the MAP only drops to a low of 21kPa, however fuel trims reduce down to acceptable levels by this point so I assume Map pressure isn’t actually much of a factor until driving the car on under load with respect to LTFT? I am aware that the map also takes the IAT reading, but if the above looks reasonable for IAT + Map at idle can I rule that out as a potential remedy?

Just getting the motivation to get back to this now over the next few days. The car is warming up fine at idle/low gears, but drops off to 60-75degC in 4-5th gear driving (I think the gearbox is not the original and may have a higher gear ratio, as speed cameras always clock a higher speed the the dash gauge, so there must be more air cooling of the engine than it anticipates). Engine Coolant temp will reach 90degC as seen on the scanner, and as reported by the NCT test sheet also. I do notice however the dash gauge will reach 90degC faster though (ETC may be around 60-70degC while the gauge shows 90degC, but ETC will continue to rise to 90degC and start the fan when needed. The is oil over spilling small amounts into the air filter from the top pipe off the engine, this was noticed when the pipe was off and the engine reved up, not sure if that's normal. Will need to check sparks again, but I would expect its wet with petrol as the LTFT is +38%, I will check later. I attach some live data of the O2 readings. So O2S1 is alternating as expected approx 0.1-0.85V which seems fine and looks to be well centered around the 0.45V mark, so I cant see this requesting +37.5% Long term fuel trim (LTFT). There's a separate "Lambda Control" figure that I suspect is the lambda instruction to fuel trim, and at idle doesn't go above +/-4%, which if true would suggest the O2S1 is doing its job. (Just as an overall update, the LTFT is approx 37-39% at idle, and drops to 9% at 1600rpm, down to 0% at 2500rpm currently, theirs no fault codes present, which is surprising as I though 25% is the limit for LTFM, in terms of driving, its going 100% with no signs of an fault apart from the obvious volume of smoke from the exhaust, the PCV to Oil separator broke over the holidays is now blanked of temporarily, new battery installed also) What could alter the LTFM at idle apart from the O2S1 itself on a MAP only engine? I've read that a MAP only engine's LTFM doesn't get affected by air leak on the intake side, besides a high idle (which isn't occurring as the idle is at it usual level), Fuel pressure is checked to be within normal range. I can check the MAP readings which is returning 25kPA at idle, but I don't know what the target would be for 1500rpm/2500rpm? 02S2 is between 0.55-0.75V approx, average is likely 0.68V. Its zig-zagging a bit but that probably due to the sample rate of the scanner? Not sure what the Skoda spec for this is? Would anyone know if this indicates a good or bad CC1 or CC2? For CC1/CC2 I can see 2no temp readings of ranging from 484-750degC (ish) depending on the RPM and run time (PDF attached). The second CC seems to be around 200degC less at any given time, I assume the higher temp is the CC closest the engine, its not well labelled. Would this be an indicator of CC condition? CC Temp.pdf

Hi, the cars supposedly at 230,000km (I recently Realised Even cheap scanners can alter the mileage though). Im trying my best to avoid going to a specialist as my mechanic is a relative and will get in for if I go elsewhere at this point (prefer not to have an earful over the next 20 years or so, 🙄), not many locally with a great rep either that won’t charge an arm and a leg. hopefully I’ll get access to a higher grade scanner that I can share on the thread and see if anyone can make sense of it. one question if someone can clarify, what is the voltage readings of the preCat O2 sensor compared to post CAT supposed to be? If PreCAT is supposed to cycle 0.1-0.9v which it is, but my postCat O2 appears to be mirroring it with the same range, would this not indicate the Cats doing noting to the emissions? But again no warning or error code present? I’ve recently blocked of the PCV pipe to see if it was leaking air, but doesn’t appear to have changed anything regarding the smoke emissions.

You are correct maybe less than 1.5 lites (I just finished the 5litre can, 3.2 of which was used during oil change, I also used some topping up other cars too over the year.

Can anyone confirm what voltage the lambda sensor is supposed to be? Is it be be really steady or slightly oscillating? My understanding is that the postCAT 02 sensor (lambda) is a warning only to the dash of an ineffective CAT, but no warnings so far, and that this has no bearing on the ECU operation so something else is causing the high fuel trim? I did visually inspect both CATs and no clogging or oil residue on either of them.

This was my initial thoughts when in the shed, it just appeared to be excessive white smoke, but during the NCT when reved, it looks a bit dark alright. Maybe it’s the difference in lighting. id say I need to top up oil 4-5 times a year, so maybe 200ml over 10,000km maybe. Top up amounts are small volumes The engine itself has only an oil capacity of 3.2l

Hi all, I’m hoping to gain some knowledge from you guys! My 2007 1.4 (Bud) petrol octavia failed 3 emissions tests the latest being CO at both idle and high revs. Lambda is just about in range at 0.98. HC reading well within limits now with the fuel cleaner through the system. Here’s the annoying bit, it’s driving 100% and no fault codes present. It is smoking quite noticeablely when up to temperature though especially in this cold weather. Fuel consumption appears normal. service done, sparks, air filter , oil filter, oil, fuel filter too. I have a small diagnostic tool and it shows preCAT O2 sensor at oscillating between 0.085-0.85V so I think that’s normal? Not sure what the average voltage though, I don’t have means to see it in graph form. MAP sensor is showing around 28 hg in. With engine off and around 8-9hg in at idle, which I also think is normal? Not sure what it’s supposed to be at higher revs? LTFT% is high at mostly at +33%idle but it intermittently changes , might be 26% today, 30 tomorrow. Then increasing revs it does usually reduce to less than 10%. Im sure whatever is causing the high idle % is a big part of the overall fault. hard to Judge the STFT% as the values change so quickly. Anywhere between +\-25% at anytime at idle. ETC reading appear fine and sensor was Checked with multimeter. Fuel rail pressure is 4 bar so I think that’s normal and injectors are working fine also Something I’m struggling to confirm, what is the normal range of the post CAT sensor supposed to be? Currently it generally limits around 0.55-0.77V. I would say 0.66V would be the average. sometimes it did oscillate, from 0.1-0.8V, but that may be to me messing with other parts trying to find an issue elsewhere. I tried my best to check for air leaks ( but I wouldn’t have the best tools to 100% confirm), we didn’t cure a very small leak between exhaust and CAT but didn’t make any difference for the last test. Plenty of fuel cleaner in the tank also now, so I’d say that’s as good as that going to be. We took off both CATs and both appears to be as clean as any second hand car would be. Both O2 sensors and MAP sensors were removed and cleaned. I have advise that it may be the ECU, but I find it hard to believe the ECU can resist throwing a fault code and keep the engine running well, while also sabotaging the fuel/ air ratio and emissions? Surely something one of the above with be off. My personal thinking is it’s something wrong with the engine such as an air leak, oil or oil vapours getting back into the engine through a faulty PCB or Oil separator, burning oil or coolant (does need occasional topping up, just discovered a small radiator leak though also), that the sensors aren’t picking up properly, the ECU is just trying to compensate the problem by changing the fuel trim, is this possible?Problem is I don’t know how to test this without expensive and possibly needless trial and error part replacing?