08_Impala

I'm checking fuel pressure on a 2008 Impala 3.5L Flex fuel.

What value should I expect when:
1. Ignition ON engine OFF? [I'm getting 60 psi]
2. Switching from the above state to Ignition OFF? [I see an immediate drop to 57 psi, then down to about 52-54 psi after 5 minutes]
3. The engine is ON and idling? [Not yet measured]

I'm doing these checks to follow up on a P0172 (Fuel Trim Rich) condition. I expect to post more on that later.

Thanks for any feedback!

oilcanhenry

60 PSI is normal for gasoline or 10/90 gas/ethanol as most fuel is normal for traditional intake port injection. Cant say about Flex Fuel as I know little about it. 55 is minimal for port injected gasoline engines, but should operate normally, particularly in a GDI motor which boosts the fuel pressures much more, so the fuel injection works in a compressed cylinder as high as 2,250 psi,

08_Impala

Thanks, oilcanhenry! The 2008 Impala 3.5L has port injection, so it looks like it's capable of the correct pressure. Any idea about the specification on holding pressure?

oilcanhenry

As long as you are getting enough proper FP during operation, it shouldn't be an issue. Over time things tend to wear down,, and ethanol is slightly corrosive, but not like
methanol would be.

tech2

have the flex fuel sensor trim data reset...if its askew it will cause a rich condition.

08_Impala

tech2, thanks for the suggestion!

My fuel composition reading is incorrect. I monitored it after the last fill-up (from near empty) and saw it changing (in the 70%-85% range), but it still settled at a very high number. I have confirmed MAF, MAP, IAT, ECT, HO2 sensors and my STFT is generally in the 5 to -10 range. LTFT is generally -15 to -30. Compression tests are in the 170-190 psi range. Spark plugs are consistent and look ok.

I have seen more than a couple of car owners follow the path of a fuel composition value reset (including in the Uplander forum) only to have the value to return to a high value days later. So, I'm a little skeptical of resetting the values, when (if all is working properly), the fuel trims and fuel composition values should correct themselves. If hypothetically, I have the fuel trims and composition reset and then the P0172 reappears, what would be the likely causes?

I have no other fault codes and have checked everything else I can think of, including the purge solenoid and vacuum lines.

Looking forward to any feedback you might have.

08_Impala

Reset the Alcohol composition and fuel trims. There was an immediate improvement.

Alcohol content went from 75% to 1.2 %.

LT fuel trim went from the 25-30% range to 9-12% range. So, there is still a problem to be addressed. I expect with a low LT fuel trim, the alcohol content will be incorrectly calculated at the next fill.