Power loss when engine is warm

[Destynx]

I have this problem with my 2000 1.7 Puma:
When the car is cold, it accalerates fine, no issues there.
But as soon as it reaches normal operating temperature, there is a significant power loss.
It accelerates slower, and i have to give it more gas to pull away or it will stall.
Also, when it's at normal temperature it sort of stutters when it exceeds 5000 rpm.
When the engine is just under normal temp i have no issues whatsoever.
It idles just fine when the engine is cold or warm.

The problem started after the cam belt was changed, but because this only happens when the engine is warm, I don't think they did it wrong. I can also feel the VCT kick in at around 3700 rpm, so that's fine as well.

I already tried disconnecting the oxygen sensor, when the engine is warmed up, but that doesn't make a difference at all. It drives exactly the same with or without the oxygen sensor, in both cases there is a loss of power.
I thought that if the oxygen sensor is working the car would at least drive different, so is it the oxygen sensor that is gone?

Also when I disconnect the maf the problem already exists when the engine is cold.

Oxygen sensor? Or something else?

 

[MaxSparta]

No expert by any stretch but I would go with upstream o2 sensor, maybe fuel pump?

 

[evilrob]

From a cold start, the ECU uses predetermined settings until everything is up to temperature (i.e. it is not taking readings from the oxygen sensor) aka Open Loop.

Once warmed up, normal operation will commence (Closed Loop) where the ECU monitors the fuel-air mixture and makes adjustments as necessary. In your case, it sounds like the sensor is providing duff information, causing the engine to make the wrong adjustments resulting in your engine not running properly.

So yeah, it sounds like your oxygen sensor is bollocksed basically.

 

[Destynx]

Fuel pump is relatively new, so I'm going to the garage net tuesday and try a new oxygen sensor.
Thanks for the confirmation :grin: . Ill update this once it's replaced..

*edit: Would a bad oxygen sensor also explain dtc code 9359 that comes up on the digital dash?
This code came back after resetting the ECU 2 days ago.

 

[MaxSparta]

9359 in your case probably means a bad fuse or connection. Could be related to the sensor.

 

[Destynx]

Update:

I went to the garage today. He hooked up an obd 2 scanner, which resulted in 3 error codes:
1 was with the o2 sensor, 1 was the MAF and 1 was a problem with the camshaft timing.
He cleared them, I took it for a drive to see which ones came back.
Eventually he scanned it again, and it turns out the camshaft timing is incorrect. Because I encountered this problem right after a timing belt switch, I'm pretty sure the garage I went to for the timing belt (another one then the one that scanned my car) did it wrong. Also, apparently my check engine light is manually disabled, so no light came on to indicate that there was something wrong.