Everything I have read says that the O2 sensor is not used when the engine is cold and in open loop.
I was having a hesitation when starting off with the engine cold. In the last week the engine just wasn't running right and seemed to have lost power once warmed up to temp and running in 3rd gear up an incline. It has never gotten very good gas mileage since I have owned it.

I have had a new Motorcraft O2 sensor for over a year now and just got around to changing it out this weekend. The hesitation when cold is gone, the power is back when warm, and though I haven't actually calculated the fuel mileage yet but it was only getting 9 or 10 last time i checked. Today I drove around town a good bit and can defiantly say it may have doubled now. Overall it is much better...

BTW this is a heated O2 sensor.

From what I have read the engine coolant temperature sensor has to tell the ECM that the engine is up to temperature before the ECM will go into closed loop and start using readings from the O2 sensor.
SO I am wondering why the hesitation went away when cold?

Can the ECT be bad and falsely tell the ECM that the engine is up to temperature before the O2 sensor is ready or a combination of both cause the problems I was having?

 

Before changing the O2 sensor did you ever try disconnecting the battery for 15min to erase all memory?
All of these ECMs learn and modify fueling based on the current feedback from engine sensors, and it is possible for any of these sensors to drift out of spec but remain functioning and that will sometimes produce strange results.

 

No I didn't. something I forgot to mention was that before the loss of power and stalling, if I was sitting on a slight uphill and just barely gave it some gas to get it rolling, and held it at that point, the engine would serge slightly. You could hear it more then feel it. So I was planning on changing the o2 sensor anyway. That cleared up too.
It's been in the 20's and 40's here and the engine has gone through 3 or 4 cycles now of getting up to temp while driving and cooling all the way back down while sitting during the day and overnight. I have driven over 100 miles now.

Last summer I had to replace the valve cover gaskets and while at it I changed the TPS, EGR, cleaned the inside of the plenum, throttle body, and IAC. The summer before I did a tune up with new plugs, wires, cap, rotor, PCV valve and grommet, FPR, and MAP sensor. It has a new gas tank, pump/sending unit, and fuel filter. I can't remember if I replaced the ECT or not!

Everything was replaced with Motorcraft except for the Napa plug wires and the Napa MAP sensor.


If the o2 sensor goes bad and the ECM goes to limp mode, does it stay in limp mode till the o2 sensor is replaced? If so then how does that affect cold start up?

 

It would stay in open loop mode in that case but maybe your truck wasn't in open loop.

 

one thing I have never done is to open up the 30 year old ECM and check the capacitors I read so much about going bad.

Part of the reason I changed so many parts is that the van had sat for probably 15 years before I bought it. The MAP, EGR, and FPS all have rubber diaphragms in them and I was thinking they might be on the verge of dry rotting. The gas tank, fuel pump, sender, and filter was changed because it was full of rust... The TPS is on the bottom side of the throttle body so it was changed when I had it off for cleaning.

There is not much left but the ECM and a couple of vacuum solenoids..

 

Well sounds like it it is running much better now, are you getting any codes?

 

Just 11,11 on the KOEO. 11-11 means no hard or memory codes. I still have not disconnected the battery.

According to the Actron CP9015 code reader instructions:
11-1-11 = (The single 1 is the separator code between hard and memory codes) System pass. No problem found by computer during KOEO Self-Test. No codes stored in computer memory.
Go to SELF-TEST PART 3: Check Engine Timing.

The directions with the scanner say to check the timing before doing the EOER test but I have not done that yet because I need to clean the timing marks, pointer and mark 10 degrees BTDC with some chalk or something to make it easier to read.

Interesting the directions say when using the scanner, that the timing should be 20 degrees more then the base timing + or- 3 degrees.

Connect the code reader, start the engine, start the test and let it read the codes.
Check Ignition Timing.
• After the last code is sent, the timing will remain fixed for 2 minutes (unless Self-Test is deactivated by moving Test/Hold switch to HOLD position).
• Ignition timing (only during this 2 minute period) should be 20 degrees more than the base timing value (give or take 3 degrees).
EXAMPLE: If base timing is specified at 10°, the measured value in this step should be
10°+20°=30°±3°. That is, the timing should be in the range of 27° to 33° BTDC.
• If measured timing does not meet this specification, refer to vehicle service manual for procedures to check base timing and computer timing advance circuits.
• If measured timing is OK, proceed to SELF-TEST PART 4: Key On Engine Running (KOER) Self-Test.

 

You need a timing light to measure timing during that test anyway so you could just check base timing with the spout removed and verify that it advances above that value some when the spout plug is reinstalled.

 

Yes that would be much simpler then using the code reader and going through its process!

Well if I understand the basics of open and closed loop, I can definable say it is not running in open loop on the highway.
I checked the gas millage several months back and believe it was around 10 mpg with a lot of in-town short trips. Today I filled the tank and went for a 70 mile trip with all but about 5 miles of that interstate... When I got back I filled the tank and it only took 3.6 gallons.. IF my math is correct, that's about 19.4 mpg. I know a short trip is not the best way to check mileage but that's a lot better then the 10mpg!
I also tried to keep my speed around 55 to 60 mph and would let off the gas just a little on uphill grades so the transmission wouldn't kick out of OD.

The temperature finally warmed up a little since I changed the O2 sensor and I found that I still get a slight hesitation or perhaps uneven idle "sometimes" when starting off very slowly. Other then that I am quite happy with the improved fuel mileage.

Getting that high of mileage on the freeway, could the hesitation or uneven idle be caused by a capacitor failing in the ecm? I have been thinking about pulling it just to look at them since it is 30 year sold but if there is no point in pulling it I have plenty of other things I need to do to the van..