Hi, so to begin with, i have a 2011 Volkswagen Gol G5, 1.6L 4 cylinder 8 valves with a relatively new engine (just about to get 6000km), manual 5 speed transmission.
So I got the car second handed (car had pretty long story, was stolen, found without engine and written off as stolen and bought by my uncle who got it back to street). Engine core parts were brand new, some external components like the ignition coil or battery were bought second hand too. To have a starting point, when I got the car, it was in great shape, besides just one code, P0441 but at the time didn't hinder performance and as my first car, I went by his conclusion and kinda neglected it, looked for the code online and first pages deemed that code not as much as an annoyance, but might be worth mentioning that besides not appearing all the time, it did from time to time.
To explain the issue from the title, about a month ago I noticed the car a bit sluggish to accelerate over 100 KM/h, didn't payed to much attention since I don't usually drive fast and the speed limit of my daily commute is 90KM/h. But it did concern me a bit since I have records of this car in my hands at 135km/h, not only I gone that "fast" but the car reached that speed with ease, not like now.
A few weeks ago I tried stretching 2nd gear to see how punchy the car was and that time was when I noticed that the car over 4000rpm would struggle to accelerate and it hit a kind of rev limiter at 4500rpm. After that I went full into gathering information and what could be the cause of it (if you can't tell yet, i'm still looking for it). It did concern me but I just followed as I do everyday, cruising around 2500RPM which I find the range between 1500 and 2500rpm the car still has some punch, just after 3000rpm now it would do nothing. Some days after that stretch to 4500, the "rev limiter" felt down to 4000.
Last week's monday morning the car failed on me and started misfiring, rev's would be stable if I didn't move but I moved a few meters and stopped and revs got so low the car stalled. As I stated earlier, ignition coil was bought second hand and has had a repair done by my uncle, so I did a ignition coil replace and it's keeping up till now.
At the moment of writing, engine sounds good, doesn't shake; car idle doesn't seems rough, it doesn't transmit any different feeling to the steering wheel or the cabin as it did the first day; rev's are stable. Besides P0441, no other code shows on the computer. When the car misfired for the ignition coil it didn't even registered a pending fault. I'm getting the worst gas milleage since I got the car.
Used to average around 17km/l on my work-home commute, I'm getting 10ish km/l doing similar speed.
Car just has a MAP sensor, not a MAF. Readings with a scanner (generic one) seems quite fine, reads 14.5 psi when engines off, around 4.2 and 5.5psi when idle, it reaches 14.5psi under load (one concern about this).
O2 sensor seems to read something, I don't know if its ok. It oscilates around low and high voltage, recorded as low as 0.08v and 0.78v. I had to do further checks since my scanner doesn't pull sensors quite fast to tell if it's oscilating as expected or not.
Spark plugs looks good, no carbon build up but there are indications of a rich mixture in the engine.
Did an error code clean last saturday since I replaced air filter and tried cleaning MAP sensor and LTFT is reading -15.4%, ~85km since error codes were clean.
Fuel pressure seems OK and no injectors are clogged nor stuck.
Didn't have the time yet to take off the cat and check for it being clogged and cars in this side of the continent don't usually have a downstream O2 sensor to corroborate.
Didn't tackled the EVAP system yet if there is any relation with it.
What do you guys think about this?
Just to add one more thing, I still have my concerns about O2 sensor reading as lowest, under 0.1v and the highest wont go over .78v
Also my concern about the MAP sensor is that it got to around 14.5 psi with just over half throttle and with engine load around 60%. I just had a peek to that the other day and I'm seriously doubting if that sensor is actually good. Also Engine Load no matter how I drive, the highest peak I witnessed these days was 75%.
Sorry for the letter, hope you can help me on doing finding the error since throwing parts at the problem is quite expensive here
Well many things can do that but start by first pressure testing a fuel system that's got low fuel pressure to do that. And two remove the oxygen sensor in front of the catalytic converter and have it pressure tested with the gauge there to see if the catalytic converter is clogged up, that will do it too
It ended up being a clogged catalytic converter. Took a while to look into it properly due to lack of tools and also engine bay space but finally found the culprit. Thanks for the help, much appreciated!
That would definitely do it. Thanks for following up and letting us know!
Thanks for the answer Scotty but sadly the issue wasn't fuel related and gracefully catalytic converter wasn't clogged. Car couldn't be operated since last sunday, it started misfiring a lot and couldn't even hold steady revs, it would even stall after some seconds, spark plugs were full of carbon and quite humid with fuel, but both fuel pressure and fuel injectors are fine. We had spark in every plug and even replaced plugs just in case the carbon build up would disrupt combustion. So it had to be and air related issue. The whole week we were trying things and ended up replacing the MAP sensor today. It made the car hold itself a bit better but it's still stalling, but indeed was air related.
Throttle body just with ignition on would open fully when the accelerator pedal was floored and would close when off pedal, wouldn't have issues with just ignition on. But when we cranked the engine, while struggling to hold itself, my father noticed that the throttle body was almost closed and even asked me to step on the gas pedal a bit, but it didn't open even when I floored the pedal. We finally have a clear sign of something actually working unproperly.
We still have to find out if it's actually the electronic throttle body or something to do with it's communication with the ECU. But we got something now (though we probably could have found this earlier if looked for a bit harder I guess)
Car still not running but I'll keep this updated