Surging/Poor Mileage in town

[roswell998]

Mileage in town was about 14-18mph but is now very poor @ about 10mph (no, foot is not heavy). Can feel surging at lower speeds (about 30mph or so) and also if parked in neutral and held steady at about 2000rpm.

Here are the items that should be able to be eliminated as the cause plus other info such as codes etc.

1. No codes
2. Cylinder balance test passes
3. Walbro 155lpm fuel pump almost new with 40-42psi static, 31psi at idle and 41 with vacuum line removed and plugged. Leakdown is only about 1-2psi maximum per hour with none detected after 10 minutes.
4. Very low mileage on Delco plug wires.
5. New plugs (Autolite APP3924 double platinum) with no oil in wells.
6. New OEM MAF
7. New Throttle Position Sensor
8. New Crank Position Sensor
9. Almost new Cam Position Sensor
10. Almost new DPFE Sensor
11. Intake Manifold "Nostrils" are spotless
12. New Intake Manifold Gaskets

None of the above items replaced have solved the surging. The Cam Position Sensor and the Crank Position Sensors were replaced due to hard failures. The fuel pump, MAF, and Throttle Position Sensor were replaced as preventative maintenance (original MAF & TPS kept as spares). The plugs and wires were replaced as 60K maintenance items.

About the only original items left that I assume could possibly cause this are the coil and the ignition module. Any other input or suggestions will be appreciated.

While the surging is a bit subtle and not violent it appears to be getting worse as time goes by.

Thanks

 

[roswell998]

Bump and I forgot to mention that the O2 sensors replaced and have only about 5K miles on them.

 

[Brook24v]

I"ve been keeping an eye on this thread because my 94 serges too, and gets ****** gas mileage.

 

[zak]

T-stat stuck open, which leter on NORMAL does yours indicate when warm?

 

[greenteagod]

Any word on if it's the t-stat. Mine reads at the A when warm. A bit of surging every now and again, but it gets poor poor mileage. I just recently had an engine swap done and this engine gets about 5mpg less than the old one.

 

[roswell998]

Any word on if it's the t-stat. Mine reads at the A when warm. A bit of surging every now and again, but it gets poor poor mileage. I just recently had an engine swap done and this engine gets about 5mpg less than the old one.

No, it was not my thermostat. Mine reads between the M & A and with an infrared thermometer it's running about 195F which is also the same value given by a scanner.

Turns out that the problem was a bad DPFE. I had gotten a CEL and code 332 about a year ago and replaced the DPFE with a Wells from Autozone. The CEL went out and the code 332 went away. Problem solved? NO!!!!! The new DPFE did not throw codes but was way out of calibration and dumping way too much exhaust gas in the intake. All of it got through because the nostrils had been spotlessly cleaned. I assumed the DPFE was good and spent a lots of time (and gas) trying to solve this. Finally after getting a scanner which gives much more info than just codes, along with some great suggestions from forum members, the problem was finally solved. FYI, this time I got the Motorcraft DPFE.

Bottom line............Engine running smooth as silk and even though the car is still on the first tank of gas since replacing the DPFE, it's obvious from the gauge and mileage driven so far that MPG is significantly improved.

The thread which led to the DPFE replacement is:

http://www.shoforum.com/showthread.php?t=81516

After running a couple of tanks I'm going to update the above thread with gas mileage figures.