TahoeInFC
Member
Hi All,
I've done some hunting around out here, and I think that I might have a fuel pressure issue with my Tahoe.
It's been running OK, and hasn't thrown any codes (since recently replacing the catalytic converters), but sometimes has a rougher idle and I can faintly smell gas in the intake plenum. I can shine a light down there through the throttle, and don't see moisture, but can smell the fuel.
Also, not always, but sometimes when driving on the highway, I've heard some popping when letting off the throttle after going at highway speed or downshifting in the mountains. Not huge backfires, but enough to where I'm thinking it's a little rich.
I went and grabbed a fuel pressure test gauge today and did some quick testing.
Key On - Gauge jumps up to 60psi for about 1 second, then drops to 50psi and holds for a few seconds, then slowly sags to 40psi all without the engine running. Sits still at 40psi and doesn't seem to sag any more than that.
Key Off - Gauge holds at wherever it was shut off...doesn't drop out quick (which might be a good sign, indicating no leaking injectors or leaking pressure regulator). If it was shut off at 50psi, it holds there until the pressure relief valve on the gauge itself is pressed and drained.
Engine running - Fuel pressure gauge stands solid at 50psi. If you goose the pedal a little, it jumps to about 55psi, but settles quickly back to 50psi and holds, even if you goose it and hold it around 1500-2000rpm.
These readings all sound too low to me. I've been seeing posts that suggest that 60-65psi should be the holding pressure when running, some of them in this forum.
Not sure if the low pressure readings explain the fuel smell in the intake, but could certainly explain an occasional rough idle.
The background:
- 99 Tahoe, 5.7L
- 135k on the ticker
- Already converted to MPFI spider (guessing around 97,000 miles, according to previous owner records)
- Starts and runs very easily, so doesn't seem to be a spark issue (although I suppose I could have a wearing cap/rotor that are not allowing full combustion of the fuel). No idea how old they are. I think the previous owner did a tune-up with plugs and wires at 110k, but not sure if he did cap and rotor. His scribbles are appreciated, but not the easiest to read.
Sound like a potentially failing fuel pump?
If so, who's got the best pump these days? AC Delco? Someone else?
Am I barking up the wrong tree here?
Thanks in advance!
I've done some hunting around out here, and I think that I might have a fuel pressure issue with my Tahoe.
It's been running OK, and hasn't thrown any codes (since recently replacing the catalytic converters), but sometimes has a rougher idle and I can faintly smell gas in the intake plenum. I can shine a light down there through the throttle, and don't see moisture, but can smell the fuel.
Also, not always, but sometimes when driving on the highway, I've heard some popping when letting off the throttle after going at highway speed or downshifting in the mountains. Not huge backfires, but enough to where I'm thinking it's a little rich.
I went and grabbed a fuel pressure test gauge today and did some quick testing.
Key On - Gauge jumps up to 60psi for about 1 second, then drops to 50psi and holds for a few seconds, then slowly sags to 40psi all without the engine running. Sits still at 40psi and doesn't seem to sag any more than that.
Key Off - Gauge holds at wherever it was shut off...doesn't drop out quick (which might be a good sign, indicating no leaking injectors or leaking pressure regulator). If it was shut off at 50psi, it holds there until the pressure relief valve on the gauge itself is pressed and drained.
Engine running - Fuel pressure gauge stands solid at 50psi. If you goose the pedal a little, it jumps to about 55psi, but settles quickly back to 50psi and holds, even if you goose it and hold it around 1500-2000rpm.
These readings all sound too low to me. I've been seeing posts that suggest that 60-65psi should be the holding pressure when running, some of them in this forum.
Not sure if the low pressure readings explain the fuel smell in the intake, but could certainly explain an occasional rough idle.
The background:
- 99 Tahoe, 5.7L
- 135k on the ticker
- Already converted to MPFI spider (guessing around 97,000 miles, according to previous owner records)
- Starts and runs very easily, so doesn't seem to be a spark issue (although I suppose I could have a wearing cap/rotor that are not allowing full combustion of the fuel). No idea how old they are. I think the previous owner did a tune-up with plugs and wires at 110k, but not sure if he did cap and rotor. His scribbles are appreciated, but not the easiest to read.
Sound like a potentially failing fuel pump?
If so, who's got the best pump these days? AC Delco? Someone else?
Am I barking up the wrong tree here?
Thanks in advance!
