: Fuel Pump and Erratic idle



joefloyd
10-07-05, 06:24 PM
On my 2001 Deville, the SES light came on and I noticed the idle was erratic (speeding up and slowing down continuously). Otherwise car ran fine. Took it to local dealership and they said I needed a new fuel pump. The new pump was installed and still the same problem. They said that sometimes the new pumps are bad. When I questioned the serv manager about the fuel pump he said that at idle the pressure was fluctuating. Waiting for a 2nd pump to be installed. Anyone with similar problem?
I retrieve the codes and PCM 0171 and PCM 0174 came up. Trim system lean bank 1 and 2.
Sorry if I'm posted in the wrong forum - just registered - still learning.

eldorado1
10-07-05, 06:47 PM
Trim system lean... I have no idea what that means, but it sounds like the pcm has exceeded it's fueling limit, and it's still detecting a lean condition?

Did this just happen suddenly? Surging idle can be a result of an overly lean condition, I would suggest changing the fuel filter before anything else. One bad tank of gas is all it takes to plug one up.

A surging idle with a fluctuating fuel pressure is kind of a catch-22. They both could cause each other.

If after the fuel filter change, it doesn't get better, you can probably suspect the fuel pressure regulator.

mcowden
10-07-05, 08:11 PM
Trim system lean... I have no idea what that means, but it sounds like the pcm has exceeded it's fueling limit, and it's still detecting a lean condition?

Did this just happen suddenly? Surging idle can be a result of an overly lean condition, I would suggest changing the fuel filter before anything else. One bad tank of gas is all it takes to plug one up.

A surging idle with a fluctuating fuel pressure is kind of a catch-22. They both could cause each other.

If after the fuel filter change, it doesn't get better, you can probably suspect the fuel pressure regulator.

Eldorado1, I think the code is telling us that the PCM has leaned out (trimmed) the mix as much as it can. It sounds to me like the $tealer$hip strikes again, replacing expensive parts with expensive labor for absolutely no reason. Bobby the Certified Pinhead Technician might know how to bolt an aftermarket carb on a 350 and balance tires, but it seems like he might have this one wrong. If the idle is weird but you can accelerate just fine, I don't believe it's a fuel pump or a fuel filter. It sounds exactly like a leaking fuel pressure regulator to me.

eldorado1
10-07-05, 08:54 PM
Eldorado1, I think the code is telling us that the PCM has leaned out (trimmed) the mix as much as it can.

Well if that's the case, then yeah, it's definately the fuel pressure regulator. It could also be the vacuum line to the regulator got disconnected. That would send the max pressure to the fuel system.