O2 sensor fault?

ex-Chinese Dave

ClioSport Club Member

• Nov 28, 2024

• #1

Yesterday my 172 Cup started to feel rough under 2k rpm, almost like a misfire, but no lights came on the dash. The car was tuned at EFI a few months ago and has run perfectly since then, until yesterday morning (1am). I drove the car to Birchdown yesterday (to have a gearbox fitted) at 6am and it ran fine but I asked them to have a look at this problem. They plugged it in and it showed no fault codes at all. When Steve did the road test he said one time under 2k rpm he felt something that he thought was the engine being cut. He suggested that it could be an O2 sensor on the way out. The engine is standard on 128k and the exhaust is standard. Any ideas as to what it could be, and if it is an O2 sensor which do I get etc?

 

JamesBryan

ClioSport Club Member

  OG Megane 265

• Nov 28, 2024

• #2

The Birchdown lads will be able to sort it, if it's still with them.

Would need to graph the pre-cat sensor to see if it's switching fast enough.

 

ex-Chinese Dave

ClioSport Club Member

• Nov 28, 2024

• #3

I've got the car back now as it was just a day trip to Birchdown.

 

JamesBryan

ClioSport Club Member

  OG Megane 265

• Nov 28, 2024

• #4

Ahh, in that case you'll need to get it logged.

I can do it if you're ever near Warrington for a while.

Does it do it from cold and hot?

 

ex-Chinese Dave

ClioSport Club Member

• Nov 28, 2024

• #5

Thanks for the offer.
From hot but it only did it from yesterday. The drive back was fine and when I left the car to cool down last night it was fine again.

 

ex-Chinese Dave

ClioSport Club Member

• Saturday at 12:01 AM

• #6

This has been getting worse over the past week. It’s really hard to pin down but it seems that hot or cold if you are below 1500rpm in any gear and put your foot down to accelerate quickly (not necessarily to break the sound barrier) the car will jolt until the revs are up. If you do the same but gently apply power it’s fine. You can be at 1200rpm in 4th and it will gather speed, but put your foot down and it jolts. It’ll even pull in 4th uphill if you’re gentle. To give an example, tonight I was in 2nd gear, about 1300rpm, and wanted to get past an idiot quickly. I pressed the loud pedal hard and the jolt was as if the engine mounts were shagged. Once above 1500rpm it was fine.

Could it be a fuel pump issue? (Car on 130k)
If it is the O2 sensor how does that affect it?

 

N

npt

  BMW 320d- 172 cup

• Saturday at 8:04 AM

• #7

I'd check the plugs first

 

ex-Chinese Dave

ClioSport Club Member

• Saturday at 10:06 AM

• #8

It had a full service a few months ago.. plugs, belts etc.

 

Mr Underhill

ClioSport Club Member

  182 FF RB

• Saturday at 10:33 AM

• #9

Could be fuel pressure. Dirty fuel pump? On its way out?

A faulty O2 sensor would send the ECU incorrect fuel mixture information.

Might also be carbon build up in the throttle body - sticking slightly. Won’t take long to check. Give it a clean up. Worth a try.

My old 182 used to be terrible on cold starts. Bounced all over the place until it warmed up. That turned out to be a missing acoustic valve which people take off to lighten the car by 00000000000000000.1111 grams for track days init 😆

Good luck!

 

Matt Cup

ClioSport Club Member

  Leon Cupra

• Saturday at 10:42 AM

• #10

Has the fuel filter been replaced?

 

Brigsy

ClioSport Club Member

  T.Turbo

• Saturday at 11:25 AM

• #11

Injector on its way maybe. Had similar on my old 172 kangoo just before one failed.

I would also get fuel pressure checked, if its original fuel pump it might be tired.

 

ex-Chinese Dave

ClioSport Club Member

• Saturday at 11:36 AM

• #12

Matt Cup said:

Has the fuel filter been replaced?

Click to expand...

It hasn’t. This will be the first thing to do as it’ll be the cheapest. I’ll find a guide and see if I can do that next week.

 

ex-Chinese Dave

ClioSport Club Member

• Saturday at 11:37 AM

• #13

Mr Underhill said:

Could be fuel pressure. Dirty fuel pump? On its way out?

A faulty O2 sensor would send the ECU incorrect fuel mixture information.

Might also be carbon build up in the throttle body - sticking slightly. Won’t take long to check. Give it a clean up. Worth a try.

My old 182 used to be terrible on cold starts. Bounced all over the place until it warmed up. That turned out to be a missing acoustic valve which people take off to lighten the car by 00000000000000000.1111 grams for track days init 😆

Good luck!

Click to expand...

Also I’ll clean the throttle body as again it’s the easiest thing to begin with.

 

ex-Chinese Dave

ClioSport Club Member

• Saturday at 11:58 AM

• #14

Ahh... just remembered that the fuel filter on a 172 Cup is part of the fuel pump

Throttle body clean first it is then!

 

Mr Underhill

ClioSport Club Member

  182 FF RB

• Saturday at 1:57 PM

• #15

 

Advikaz

ClioSport Club Member

• Saturday at 3:30 PM

• #16

Mr Underhill said:

View attachment 1725820

Click to expand...

I felt this