1999 4.0 SOHC "Closed Loop"

[merc225]

1999 Ford Explorer Eddie Bauer 4.0 SOHC Vin E

I connected my scanner and found out that the fuel system is going into "closed loop" at ECT temp of 48 degrees. I am thinking of a possible thermostat and ECT sensor replacement, but want to make sure that I am on the right track before I do anything. I would very much appreciate any thoughts from other members.

 

[Turdle]

What are your symptoms you are shooting?

Far as I know, the pcm goes closed loop once o2 sensors heat to temp. I could be wrong .

 

[merc225]

Excessive cranking when cold starting sometimes, Idles a little rough (fluctuates), At low speeds you can feel occasional miss.

 

[Pete Deering]

Its your ECT sensor. The sensor for the PCM.
Your scanner is telling you the engine is cold and the PCM using the engine sensors to make all the adjustment(closed Loop).

 

[merc225]

Its your ECT sensor. The sensor for the PCM.
Your scanner is telling you the engine is cold and the PCM using the engine sensor to make adjustment(closed Loop).

Thanks for the replies, Pete and Turdle

 

[Pete Deering]

Thanks for the replies, Pete and Turdle

Are you talking C of F 48 degrees? Where are you located?

 

[J_C]

I connected my scanner and found out that the fuel system is going into "closed loop" at ECT temp of 48 degrees.

I'm not quite following this, are you thinking that 48 degrees is too cold? Once started, the engine should operate in a rich state in open loop mode, until it senses a certain temperature, then go into closed loop mode where it operates leaner. If 48 degrees is that temperature (which I don't know), what problem would be indicated by this, by going into closed loop at that point?

What is the ECT temp sensor reading when the engine is cold and having trouble starting? I mean does it appear to be roughly what the ambient air temperature is? It's going to be in open loop mode when initially started and idling cold.

Possibly your thermostat needs replaced for other reasons, but that would be if it's stuck open and the engine takes a long time to get to closed loop mode due to that (which means it wastes fuel running rich and the heater takes forever to warm the cabin), or if the t-stat is stuck closed, and the engine overheats, but neither should cause it to run rough. I mean eventually, sure, an overheating engine can cause damage and the result is running rough, but nothing stated so far suggests that cause.

Excessive cranking when cold starting sometimes, Idles a little rough (fluctuates), At low speeds you can feel occasional miss.

Nothing in the original post was necessarily a problem to act on. THIS on the other hand, is.

Did it progressively get worse or all of a sudden? Could it be old or bad gas?

How old are the spark plugs and wires? Battery good and electrical system keeping voltage around 14V running? Does it crank to start at normal speed? Does it start a lot better when ambient air temp isn't very low?

Is the check engine light coming on, any trouble codes set?

You mentioned closed loop, does it get worse once it goes into closed loop? If so then you might have a vac leak. Does your scan tool allow realtime data to look at long term fuel trims while running?

Is there any pattern to when it idles rough, like does it happen when the A/C compressor comes on? If so then your IAC valve may be faulty or dirty/sticking, or A/C compressor failing. However that shouldn't be noticeable once driving, if it still manages to idle. Just wondering if it could be an accumulation of factors.

 

[donalds]

My 99 goes into closed loop after about 5 seconds and it's always been this way as soon as the O2 sensors Are up to temperature then the computer starts to use them to adjust AKA closed loop

 

[J_C]

^ I could be wrong then, thought it can only go closed loop that fast, if the engine was already warmed up a bit, like potentially the 48 degree temp reported.

 

[merc225]

I apologize for any confusion on this issue. Like this morning, outside temp was 45 degrees F, connected my scanner before I started the car and checked the ECT temp and it was at 46 degrees F, started the vehicle and the Fuel system1 indicated OL (open loop) which is normal, but when the ECT temp reached 48 degrees F the Fuel system1 went into CL (closed loop). I know that is not correct because Closed Loop should not take place until at lease 140 degrees F or higher, so the question I have is the ECT most likely causing the issue? I just thought maybe other members have experienced this same issue and could provide their input and fix. Something is telling the PCM to switch to CL at such a low ECT temp, and I am thinking the culprit is the ECT.

Yes, the engine does start up better (quicker) when the outside temp is above 50 or so.

Thanks to all for your thoughts and knowledge.

 

[Turdle]

Closed loop occurs when 02s warm up. That's the confusion.

 

[Turdle]

I'll try to verify this with 2 cold fords and scangauge tonight.

 

[Pete Deering]

I'll try to verify this with 2 cold fords and scangauge tonight.

Its the ECT. Open loop the PCM uses default settings. Engine is up to operating temp it goes into closed loop. after closed loop, the PCM uses the engine sensors values as PCM inputs.
then the 02 sensors adjust the fuel trim and report back too the PCM.

 

[J_C]

The thing is, for it to shortly go from 46F to 48F, that seems like your ECT is reporting correctly. Even so, if you just want to replace it to rule that out, then they aren't expensive but I don't think that is going to help. If while doing that, you were to take the intake manifold off and put it back on with a new gasket(s), that seems more likely to help if it's not fuel or spark issue.

I'm still not clear on what is going on. You stated it cranks a long time till started, but are you also meaning that it seems to run okay UNTIL it gets to the 48F and the scan tool indicates closed loop? If that is not the situation, then I am wondering why you are focusing on these details.

If that IS the situation, then it would seem like it is running too lean and I'd look at fuel trims on a scan tool, or a single or pair of cylinders misfiring. I might also consider checking to see if it might be a single cylinder (or pair since it's a shared spark ignition system), just not misfiring enough to set a code yet. Can your scan tool show that live data?

 

[Turdle]

Ok, I found that eec4 goes to closed loop at engine warm up.
Eec5 uses heated O2 sensors, goes to closed loop when O2 sensors heat. 5-30 seconds.
That is how eec5 uses temp more accurately. It is constantly monitoring the sensor. During open loop, the ECT is ignored.

 

[410Fortune]

1999 is eec-4 so why is this one switching so quickly?

I agree the misfire is more important thing to address

 

[allmyEXes]

My 1997 4.0 SOHC is OBD2/EEC-V(5)...

 

[Turdle]

1999 is eec-4 so why is this one switching so quickly?

I agree the misfire is more important thing to address

96 up is eec 5

 

[410Fortune]

Dang I should go back to bed
We are flooding here a bit, yes that’s right December 6 river is flooded, I was told fall winter is flood seasons and now I can see how. The river is up over its bank which is normal when we get lots of rain… this time it’s caused by a foot of snow followed by warm temps and 3 days rain. The water noises had me up early… too early to think straight! Thanks dudes… stay dry

So in the old days with my old 4.0 and a 93 pcm we used to have to keep a 198 degree thermostat in there to ensure the engine saw 205 water temp and switched to closed loop… this thread has me thinking with the 96+ pcm and eec-v I can run a 180 stat and not worry about it because the pcm with switch when the hegos warm up!

 

[allmyEXes]

@410Fortune I saw that on the Weather Channel. Keep your Jon boats close and your waders nearby too.