1999 S70 T5 - LTFT high Topic is solved

Post by **kallekula** » 02 Feb 2015, 21:26

So, my T5 shows a long term fuel trim of about 20%. When I hit the throttle it dives to 18% but still. Got it smoked with a professional smoke machine and it's not leaking. CEL is not on and all monitors passed except Catalytic Converter which is not ready yet.
Also sprayed starter fluid around the injectors and no noticeable difference.

Someone has any ideas what's going on?

Post by **erikv11** » 02 Feb 2015, 22:58

I wonder if the O2 sensor is bad. They don't always throw a code when they go. Do you know how old it is? They have a date code on the plug. And/or can you watch the O2 sensor cycling, does the voltage cycle pretty consistently between 2 and 8 mV?

Post by **Atis** » 03 Feb 2015, 08:05

I had a leak after a check valve. Smoke did not show that as that had a slight overpressure, causing the valve to close. Although I did not had that high LTFT.

Post by **kallekula** » 03 Feb 2015, 11:09

erikv11 wrote:I wonder if the O2 sensor is bad. They don't always throw a code when they go. Do you know how old it is? They have a date code on the plug. And/or can you watch the O2 sensor cycling, does the voltage cycle pretty consistently between 2 and 8 mV?

Yeah haven't checked the upstream O2. For some reason my stupid code reader can't read that one, just the downstream one which holds steady at around 0.45.

Post by **kallekula** » 03 Feb 2015, 11:10

Atis wrote:I had a leak after a check valve. Smoke did not show that as that had a slight overpressure, causing the valve to close. Although I did not had that high LTFT.

What "check valve" are you talking about?

Post by **misha** » 03 Feb 2015, 15:10

kallekula wrote:... just the downstream one which holds steady at around 0.45.

If cat is ok it should not read anything.It should be at 0v,but i'm not 100% sure on this.

Post by **misha** » 03 Feb 2015, 15:20

erikv11 wrote:I wonder if the O2 sensor is bad. They don't always throw a code when they go. Do you know how old it is? They have a date code on the plug...

They have a date code but that's date of manufacture,not indication on how long they have been used.

I installed once OEM Volvo O2 sensor back in 2002 and date of manufacture was 1994.Rear one was installed in 2004 and production date was 01.

Post by **erikv11** » 03 Feb 2015, 23:42

misha wrote:
kallekula wrote:... just the downstream one which holds steady at around 0.45.
If cat is ok it should not read anything.It should be at 0v,but i'm not 100% sure on this.

The voltage on the rear O2 should be steady, but definitely not zero, that would indicate a dead sensor or bad connection etc. Actually, 0.45 V is about perfect, the cat is doing its job.

Post by **kallekula** » 04 Feb 2015, 11:51

erikv11 wrote:
misha wrote:
kallekula wrote:... just the downstream one which holds steady at around 0.45.
If cat is ok it should not read anything.It should be at 0v,but i'm not 100% sure on this.
The voltage on the rear O2 should be steady, but definitely not zero, that would indicate a dead sensor or bad connection etc. Actually, 0.45 V is about perfect, the cat is doing its job.

Been thinking/reading and this is my plan:

1) Borrow an instrument that can display upstream O2 operation in graph mode
2) Smoke test the exhaust
3) Compression test

Something I forgot?

Post by **kallekula** » 05 Feb 2015, 19:00

Did a compression test today and it showed excellent numbers.
Went to a friend that has Vida and it showed totally different numbers than my POS reader does. O2 sensors work fine. Everything pointing to a shot cat. Now I know that my reader is only good for reading trouble codes...
Just gotta save up for a $500 cat gahh!