99 Explorer 4.0L OHV - Stuck open loop, rough idle, hesitation

[remzej]

I bought a 2nd hand 1999 Ex 4.0L OHV and it was running fine for atleast 4 months when i purchased it. But now my truck in in bad performance and unknown problem. I bought an ELM327 Bluetooth Scanner and used FORScan software to check for errors/faults in my truck. I observed that the truck is stuck at open loop system even the ECT reaches it's operating temperature. And upon checking the real-time values of LONGFT1, LONGFT2 SHRTFT1 and SHRTFT2 only SHRTFT's generates percentage values and LONGFT's stuck at zero and no voltages. I manually inspect for oxygen sensors of my truck but what I found was these







Anyone had these kind of sensor installed on your truck? It doesn't look like sensor at all but just a jumper type. I removed those from my truck and tested running engine and check again for errors/faults using the scanner and to my surprise even without those jumpers the SHRTFT's still generates percentage values the LONGFTs remain at zero.

I have no other idea what causes the truck to remain in open loop system.

 

[ThreeJs]

are those some type of O2 simulators that plug into the harness?

 

[lobo411]

Definitely not stock...Looks like o2 sensor dummy plugs. Did they leave the actual o2 sensors threaded in the exhaust line?

 

[remzej]

Definitely not stock...Looks like o2 sensor dummy plugs. Did they leave the actual o2 sensors threaded in the exhaust line?

I checked the locations where the O2 sensor plugs should be installed it was covered and no actual plugs installed. What surprised me was the scanner still generated variable values for SHRTFT1 and SHRTFT2. The LONGFT1 and LONGFT2 is fixed at zero.

 

[remzej]

are those some type of O2 simulators that plug into the harness?

It doesn't look like O2 simulator and its just jumper and nothing special on it. I checked for resistance and its fully shorted.

 

[RandomNerd2000]

Your truck still have it's catalytic convertors on it? I'd bet they clogged and were bypassed.

 

[lobo411]

I checked the locations where the O2 sensor plugs should be installed it was covered and no actual plugs installed. What surprised me was the scanner still generated variable values for SHRTFT1 and SHRTFT2. The LONGFT1 and LONGFT2 is fixed at zero.

Well I don't know too much about it, beyond the fact that those aren't o2 sensors. Here's a primer on o2 sensor simulators. Apparently, they're designed to generate a waveform so the computer doesn't illuminate the CEL. Anyway, the endgame is the same. If you want the truck to run right, you'll need to restore it to stock. Hopefully they didn't permanently seal up the o2 ports in the exhaust line. If necessary, you can weld in a new bung. I had to have that done once...I brought in the Y-pipe and paid a welder $20 to do the job since I don't know how to weld.

Primer on o2 simulators:
http://www.ebay.com/gds/Truth-about-O2-simulators-/10000000002812356/g.html

 

[lobo411]

It doesn't look like O2 simulator and its just jumper and nothing special on it. I checked for resistance and its fully shorted.

I'm not an electronics person at all, but is it possible that a multimeter isn't capable of generating enough power to cause the simulator to activate? IE, it would have to behave like an o2 sensor, which means it wouldn't do its thing until it was fully powered.

 

[remzej]

I'm not an electronics person at all, but is it possible that a multimeter isn't capable of generating enough power to cause the simulator to activate? IE, it would have to behave like an o2 sensor, which means it wouldn't do its thing until it was fully powered.

But what surprises me was with or without those dummy plugs the SHRTFT's generates the same values. How come the ECU generates values from no sensor at all.

Yes the truck still has the catalytic converter installed.

 

[lobo411]

But what surprises me was with or without those dummy plugs the SHRTFT's generates the same values. How come the ECU generates values from no sensor at all.

Me too, but the endgame is the same--install real o2 sensors. What did they use to plug the bung?

 

[remzej]

I checked the exhaust manifold and it was plugged with bolt. Like in this photo. And also there is no CAT converter installed on my truck.

 

[koda2000]

You'll probably need to take your truck to an exhaust shop and have everything returned to stock (install cats and O2 sensors). It wont be cheap. O2 sensors aren't that expensive, but cats are and then there's the labor required.

If you can't enter closed loop mode, your truck will run like crap and your already poor fuel economy will suck that much worse. I had a thermostat problem in a 2000 V8, which prevented it from entering closed loop mode, and my fuel economy went from 21 MPG hwy to around 13 MPG.