GS4_Fiend

iTrader: (22)

Right thats true. If it was fuel pump it should be lean both banks... Interesting

AZGS4

My 1998 GS400 just had the P0171 code. My car was bogging down under acceleration up until about 3200 RPM and then it wouldn't bog as much as I got into the higher RPMs. Under hard acceleration from a stop the car would bog heavily and the CATs would pop a little bit.

After diagnosis and testing, the MAF, O2 sensors and Vacuum lines all were good. Fuel pressure was testing out at about 21 PSI versus the 44-50 PSI specified in the repair manual. Replaced fuel pump assembly (pump,filters, pressure regulator etc.) and fuel pressure is now at 50 PSI. CEL is out and (more importantly) the car runs great. MY car has 153,178 on the odometer.

wise2k

Hey, thanks for posting. I forgot to come back and update but I replaced my fuel pump too and that took care of the problem

cschroder

the bank that shows lean would be the furthest from the fuel line from the tank...on a gs400 that would the be left bank if you are standing in front of the car looking in the engine compartment. On a gs300 that would be the "front" bank.

wise2k

Interesting thought. Wonder how it didn't trigger both banks, could be the fact that engine is InLine 6, and I'm assuming the fuel 'squirts' into the cylinders from the back towards the front, hence bank 2 (3 cylinders towards the firewall) get almost good fuel pressure but the front 3 cylinders/bank 1 doesn't get much due to the weak pump. Just a thought.

I didn't have the equipment to test for fuel pressure but those symptoms are identical to what mine was doing. Hopefully this pattern will save people time, effort and money as they seem typical of a weak fuel pump. thanks for your contribution to the thread!

wise2k

I second that.

ThomasGS4

iTrader: (19)

Just ordered myself a new Denso fuel pump off RockAuto. As these are the same symptoms as I am experiencing to a tee, I hope this will be the end-all be-all.

burny

Same here. Ordered a denso that will be here tomorrow.