1999 s70 NA fuel trim problem Evita P0172 [ Fixed with oil change] Topic is solved

Post by **abscate** » 22 Sep 2023, 07:49

Evita is coding very 500 miles or so with a P0172, system too Rich.
Fuel pressure checks in at rail at 43 psi, on spec.
STFT is short term fuel trim
LTFT is long term fuel trim

Here is the weird behaviour.

At idle , STFT SITS AT 8% , a bit high for an engine with 175k but , whatever. LTFT settles at -7% so overall trim 1%, quite good

Under load or rpm, the STFT rails at 20% and he long term trim then rails at -20%. Same net fuel trim but trying to figure out why this happens.

Post by **850 LPT** » 22 Sep 2023, 08:49

How old are the oxygen sensors? I would start there.

Post by **abscate** » 22 Sep 2023, 17:34

Front brand new , maybe 12 months 7500miles
On edit - 3 years old, 12,000 miles

But, that’s a good check, added to list

Fuel pressure again
Intake manifold leaks
Exhaustleaks
Leaking fuel injectors
Plugged cat
OXS

Swing test here

One of these should get it

Post by **misha** » 23 Sep 2023, 17:24

43.5psi is correct fuel pressure for up to '99.
ME7 should have more...around 60psi?

Post by **bmdubya1198** » 23 Sep 2023, 23:24

misha wrote: ↑23 Sep 2023, 17:24 43.5psi is correct fuel pressure for up to '99.
ME7 should have more...around 60psi?

'99 NA in the US market uses Denso engine management. I believe 43 PSI is the spec for the Denso cars, and 51ish for ME7.

jsrnsis · Post by **jsrnsis** » 28 Sep 2023, 05:52

We had this same code but on a 98, it turns out the O2 sensor wires were unplugged just enough that it didn't throw codes, but must have been throwing the voltage readings off. Pressing on the connectors clipped them into place, and voltage values read through Torque seemed to go back to normal. Probably something you already checked but sometimes it's the simple things.

Post by **abscate** » 28 Sep 2023, 10:12

Now I’ve got lots of spare parts to try…

Post by **abscate** » 03 Oct 2023, 12:14

Pulled fuel rail and cranked. Nice even pattern, no drips. I could also rule out leaking injector from good fuel pressure holding, too.

Post by **abscate** » 27 Apr 2024, 18:41

Interesting. I never got back to diagnosing this , but when I hit the 180,000 oil change mark, it stopped coding.

I checked fuel trims and both LT and SAt are under 1%

Fuel in oil perhaps?

Post by **scot850** » 28 Apr 2024, 08:13

Maybe bad fuel or possibly a leaking injector that fixed itself. Seems strange that an oil change would fix it otherwise?

Neil