1990 F250 5.8L automatic 2wd. Engine light comes on occasionally and doesn't leave codes. So bought a scanner and noticed that the DCL data shows the truck running in open loop mode all the time and the O2 sensor at .86 to .91 all the time. (engine light still a mystery). Investigating, I found that open loop is for cold start (runs rich) but ECTv at 0.6 and ECT temp at 186-187F. So engine shows normal temp. when in open loop. I also saw open loop used for full throttle. But here again, DCL data shows 1.1 to 1.8 volts TPv and calls this P/T or partial throttle. So the engine should be in closed loop, but its not unless there is another "if" for open loop operation.

Testing the TP, I see it range from .9 to about 4.5 volts. THe O2 shows 0.01 at engine off. So I am assuming the high O2 results from the engine in open loop ignoring the sensor feedback and running rich. Therefore I assume at least one of my gas hogging issues is something other than the temperature and throttle position keeping the engine in open loop. Any ideas?

Also is Fuel PW1 on the DCL data the actual fuel pressure or the vapor pressure in the tank as the aftermarket manual suggested? This fuel pressure varies from 1.9 to 4.4 and showed 15.4 at engine off.

 

The O2 sensor output is correct if the motor is running rich, and as you say all the other inputs look normal.. so it seems the computer is not reacting correctly to the input from it's sensors. My quick and dirty conclusion after 1 minute looking at this.. bad computer.
Have you seen this page? www.fordfuelinjection.com.

 

Fuel PW should be the injector pulse width, most likely measured in milliseconds. Is the data logger showing open loop explicitly? I would check the fuel pressure to make sure nothing funny is going on there. If it is actually getting into closed loop and an incorrect fuel pressure or fuel leak through a faulty fuel pressure regulator is dumping unmetered fuel into the system, the O2 will read rich, but the computer will trim the mixture lean up to its maximum adjustment. If there is still too much fuel, the O2 sensor will constantly read rich and the computer cannot correct the condition. Do you have a readout of the fuel trim percentage?

 

Paul, thanks the injection site was exceptional, and brought up plausable answer. If the computer evaluates ECT temperature of 185 as the open/closed loop decision factor, why is my engine running at 186-187? I know this is a thermostat function, and being mechanical at best, it would seem to me that more "tolerance" would be needed when selecting a thermostat. Is the wrong thermostat in the engine? Maybe it should be higher? Maybe the computer is still seeing 186 or 187 as closed loop or maybe the ECT sensor is a few degrees low. But I did catch it at 192 today and still closed loop. The injector sight also mentined RPM of 672 for warm idle. More like 475 to 600 max, the alternator disingages charging while idling. Maybe I have multiple problems.

Eric: Thanks for clearing up the pulse width, I guess I assumed.... Yes, I see open loop all the time, cold through normal temp (if 186/187F is normal). Fuel Trim is always 5% positive and I see 4% at warm idle, the only time I have seen different is on cold start which was around 27%. I did notice the 02 sensor at cold start showing .62, but that may be a heat up delay issue.

I've never checked fuel pressure, but picked up a gauge the other day. I'll see if I can figure the location, connection and procedure.

 

Is there a way that you can separate individual fuel trims? There's obviously one for cold engine temperature, probably one for air temp, and one for O2. Can you tell if the O2 trim is doing anything? I thought open loop temp was around 165-175 or so, but I don't remember. You might be on to something with that low idle...

What hardware/software are you using to give you all this information? It seems like it is pretty cool stuff.

 

The info and where I found the code reader is below.
http://www.autorepairmanuals.biz/sit.../CP9110-CP9112
CP9110-CP9112
Actron ScanTool Diagnostic Analyzer with Ford, Lincoln & Mercury OBD 1 Scan Cartridge $89.95

As I understand it, only the 1990 models and later had the DCL (real time information recording data stream), I know it wont record on my 1988 F150, but the other code reading functions work. When it works... pressing the button downloads the last 8 seconds of data in the computer and then continues to record about another 26 seconds. These are recorded basically as slices in time for about 5 pre button and 16 post button data points. This is displayed spreadsheet fashion but rather clunky since you can only see one time slice and about 3 data items at a time. Of course navigation arrows get you around to all the data.

Actually its pretty cool, and for the money hard to beat, but... this one does have a glitch and hangs up quite offen.

Set up is by vehicle, selections process and then all the available menus are offered for that model. Multiple trims are not available for my truck.


As for the open/closed loop issue I have been questioning, on the interstate I did let off the throttle and coast 70-50 and the spead back up to 70 while recording and did see the truck go into closed loop and then back out but nothing jumped out at me to say why it decided to do that.