Hello all,
Been reading here for a long time but can't recall the last time I posted.
1995 Taurus 3.8, 80k miles since new.
Items replaced:
- Heater hose
- Bypass hose
- VSS
- Both EX gaskets
- Fac/A.C./Fuel Pump relay box assy
- Trans speed sensor (the one on driver side outboard)
- EGR gasket
- DPFE
- MAF
- TPS
Into it for $130.00 in parts (with spares to boot)
Thanks to the clunkers program a local yard has a fistful of very nice, clean Taurus'. Some of the parts are new (TPS, VSS) but otherwise were pulled from same-year donors with the 3.8. Overall the car runs great, no overheating, no leaks, trans is shifting fine and the A/C is so cold it'd give an eskimo frostbite and hallucinations.
QUESTION IS: What causes a mid-range flat spot while driving?
While driving it will occasionally have a flat spot about mid throttle. There are times when it's fine, with no issues, but there are others when it's just flat. No pinging or other signs of a vacuum leak or timing issue. However, if you press the pedal to say 80% of travel, it makes good power and runs great all the way to WOT. To me that sounded like a bad TPS since it acts like a potentiometer; and wouldn't a bad potentiometer not be linear in response? Kind of like a dirty dimmer switch for the ceiling fan. So I swapped it out for new TPS and tested the old one. Both are within resistance spec, so I don't think it's that.
I also replaced the Fuel Pump relay, especially since the problem was pronounced with the A/C on. No change. I then focused on the fuel pump; replaced the in-line filter and drove around with the FP gauge hooked up to the Schrader and wedged under the wiper. Results were 35 PSI at idle, 45 under throttle. Disco'd the fuel pressure regulator and at idle the fuel pressure jumps up to 45, just like it's supposed to. Hooked up my vacuum pump to the EGR and pumped it up; engine started to idle down and die again, just like it's supposed to. To me if the FP is going bad it'll just go. Haven't seen too many immerse FP's be intermittent but I'm keeping that in my mind as a consideration.
So I think what I have is potentially a sticking EGR. I'm guessing it closes ok (which results in the good idle behavior) but under power it's maybe not opening all the way? The mileage is erratic too. Last tank was 17 MPG, this one looks more like 22 MPG. Conditions are about the same (% of FWY and surface street driving). These conditions tend to indicate more toward EGR than a servo/sensor or ECU/M controlled device. I have disco'd the EGR hose and can feel the vacuum pulses from the solenoid if I hit the throttle so I think that's a good functional test.
So far no codes and no CEL.
Any ideas would be appreciated.
Thanks!
Been reading here for a long time but can't recall the last time I posted.
1995 Taurus 3.8, 80k miles since new.
Items replaced:
- Heater hose
- Bypass hose
- VSS
- Both EX gaskets
- Fac/A.C./Fuel Pump relay box assy
- Trans speed sensor (the one on driver side outboard)
- EGR gasket
- DPFE
- MAF
- TPS
Into it for $130.00 in parts (with spares to boot)
Thanks to the clunkers program a local yard has a fistful of very nice, clean Taurus'. Some of the parts are new (TPS, VSS) but otherwise were pulled from same-year donors with the 3.8. Overall the car runs great, no overheating, no leaks, trans is shifting fine and the A/C is so cold it'd give an eskimo frostbite and hallucinations.
QUESTION IS: What causes a mid-range flat spot while driving?
While driving it will occasionally have a flat spot about mid throttle. There are times when it's fine, with no issues, but there are others when it's just flat. No pinging or other signs of a vacuum leak or timing issue. However, if you press the pedal to say 80% of travel, it makes good power and runs great all the way to WOT. To me that sounded like a bad TPS since it acts like a potentiometer; and wouldn't a bad potentiometer not be linear in response? Kind of like a dirty dimmer switch for the ceiling fan. So I swapped it out for new TPS and tested the old one. Both are within resistance spec, so I don't think it's that.
I also replaced the Fuel Pump relay, especially since the problem was pronounced with the A/C on. No change. I then focused on the fuel pump; replaced the in-line filter and drove around with the FP gauge hooked up to the Schrader and wedged under the wiper. Results were 35 PSI at idle, 45 under throttle. Disco'd the fuel pressure regulator and at idle the fuel pressure jumps up to 45, just like it's supposed to. Hooked up my vacuum pump to the EGR and pumped it up; engine started to idle down and die again, just like it's supposed to. To me if the FP is going bad it'll just go. Haven't seen too many immerse FP's be intermittent but I'm keeping that in my mind as a consideration.
So I think what I have is potentially a sticking EGR. I'm guessing it closes ok (which results in the good idle behavior) but under power it's maybe not opening all the way? The mileage is erratic too. Last tank was 17 MPG, this one looks more like 22 MPG. Conditions are about the same (% of FWY and surface street driving). These conditions tend to indicate more toward EGR than a servo/sensor or ECU/M controlled device. I have disco'd the EGR hose and can feel the vacuum pulses from the solenoid if I hit the throttle so I think that's a good functional test.
So far no codes and no CEL.
Any ideas would be appreciated.
Thanks!
