Engine Running on after shutoff

[McChalium]

I just bought a fairly nice 2000 Explorer. My daughter has just informed me that when she turns it off it sounds like it is revving up. I believe it is EFI equipped so I wonder how a run-on can occur as I thought that problem went away with carburetors. Am I misinformed? Any history of something like run on occurring in this model? I don't even have a service manual yet so I am flying blind. Any help appreciated. Regards, Don.

 

[koda2000]

another poster recently had a problem where he could not turn his truck off. it turned to to be a relay back-feeding power through the electrical system. he found the problem by switching relays around under the hood, but couldn't determine which one was bad, so he said he was going to replace them all.

 

[2000StreetRod]

Which engine?

Does it have the OHV V6 or the SOHC V6? An engine needs three things to run: fuel, ignition, compression. The fuel and ignition are PCM controlled. If the engine continues to run after turning the key to off then the PCM still has power. Does the vehicle have an aftermarket remote start capability?

 

[McChalium]

The explorer has a 4L SOHC engine. This morning it threw a CEL at me but I was unable to read the code before I had to go to work. Car is sitting until I can figure out the code. Observable symptoms seem limited to a slight roughness at idle, otherwise it seems to run ok, no weird noises. I have no history of maintenance performed, but I plan to read the code tonight, possibly pull the plugs and check compression. This weekend I planned an oil and filter change (oil, gas, and air) just so I know the date they were last changed, but that's all I know at the moment. In general the car seems well cared for, but it does have 167000 miles on it.

 

[koda2000]

167k is a lot of miles on a SOHC 4.0L. Especially if it's never had its timing chain parts replaced. Another common problem with this engine is lean codes. This is usually contributed to intake O-ring/gasket leaks, or other vacuum leaks, and can even sometimes be caused by a clogged fuel filter. Do you hear any engine rattle at start-up or when warm?

if by "running-on" you mean dieseling after turning off the key, this is also indicative of running lean, because running lean really heats up the combustion chamber, however, there shouldn't be any additional fuel being injected once the key is turned-off.

 

[McChalium]

New Timing Chain..

I've had no chance to delve further into this due to work schedule, but I was told by the previous owner that he had replaced the timing chain. He also said something about not installing the full kit as he was trying to address what he thought was a noisy chain. I am not sure what he meant by that. Apparently I can get the rest of the kit. This weekend I plan to change all filters, change the oil and check the spark plugs and compression of all 6 cylinders. For all I know the plugs have been in there since it was first built. Anyway I appreciate the suggestions and the experience you have brought to bear on my problem. I will check in again after I know more. I tried to read the code but my shop computer acted up and wouldn't read my scanner. I have another one that'll work but haven't tried it yet. Yes I did mean dieseling but couldn't remember the correct term as I hadn't encountered it in a long time. I'll check the long and short term fuel trim for evidence of air leaks into the intake system, otherwise I understand that one can spray unburned propane from a propane torch while watching the O2 sensor outputs for an indication of the mix being enriched. I don't miss carburetors, but sometimes all this error code business gets to be a bit much....

 

[2000StreetRod]

complete timing chain kit

The complete timing chain kit includes left and right hydraulic tensioners, left and right cassettes (guides, chains, sprockets), primary (crankshaft to jackshaft) chain tensioner and guide, and if 4WD balance shaft chain tensioner and guide. Either the engine or the transmission must be pulled to install the right cassette. The block girdle (upper oil pan) must be removed to install the balance shaft tensioner. The previous owner probably installed the left and right hydraulic tensioners, the primary chain tensioner and maybe the left cassette.

 

[McChalium]

Wow! It sounds like this engine has a complicated timing chain design. I just obtained a manual this weekend but haven't had a chance to peruse it yet. I did change the oil and oil air and fuel filters and pulled the plugs and ran a compression check. Plugs looked like new and compression check looked pretty good to me being uniform across the 6 cylinders at about 165 PSI.
I was able to get one reading from my scanner before it started misbehaving but that one reading showed a P0174 code (system too lean bank 2 O2 sensor)
and all the fuel trims set way too high. When I went to start the engine so I could monitor these things as the engine was running the Auto Tap crapped out on me. A simpler scanner confirmed the P0174 code but did not provide real time monitoring of the O2 sensors or the fuel trims so I was in the dark again. I reset the DTC and test drove it without any symptoms. Engine does not seem to present any drivabiliity issues. I am not sure how only one bank is running lean unless I have an air leak in the intake manifold common to only the left side or a bad O2 sensor. It seems to me that a vacuum leak upstream in the manifold would make the whole engine run lean. The plot thickens...

 

[McChalium]

Here is a recap of things I've seen, heard, or done so far. I reviewed the codes with my new scanner and the P0174 code was confirmed. Watching the PIDs as the engine warmed up from a cold start I noticed that the bank 2 O2 sensor 2 output never climbed over .18 volts while the bank 1 O2 sensor 2 output climbed to about .48 volts which I think is about normal. So I suspect the bank 2 sensor 2 is bad. All 4 O2 sensors have the look of being there a long time, possibly since it left the Ford plant, and I understand they should be replaced every 100K or so (please correct me if that's wrong), so I am planning on replacing them all next weekend. Also, the long term fuel trim was up to about 25% positive while the short terms were down below about 8%. I recorded the Freeze frames and DTCs but have no way, other than manually transcribing them, to get them into the forum.
The engine does have a rattle when it starts, for maybe a second, then it quiets down. I suspect that, due to its mileage and unknown maintenance history, that the oil passage(s) to the various hydraulic chain tensioner(s) may be partially blocked. Has anyone here tried a product named Auto RX which is added to the engine oil and run 2000 miles as a way to clean up the engine? It claims to gradually dissolve built up deposits. I have always been very skeptical of such claims about automotive additives, but I recently saw a really gummed up engine and it really freaked me out. Black crud built up over a quarter inch thick under the valve covers. I ran a FIAT SOHC 1.5l engine over 350K miles and when I popped the valve covers to adjust the valve shims (only way to adjust valve lash on that engine) there was only a faint light brown film on the insides. Maybe that came from only running a premium oil (non synthetic) in it but I have no way to prove that hypothesis. Well, all for now...

 

[2000StreetRod]

engine flush

I would never drive a vehicle with any type of engine flush in the oil. If the flush is strong enough to break down and loosen sludge then it also reduces bearing surface protection. If it doesn't reduce bearing surface protection then its too weak to remove sludge. When I pulled my valve covers after purchasing my Sport I found excessive sludge. I suspect the previous owner had an overheating problem (he lived in Texas) and had removed the thermostat. I purchased a 195 degree thermostat (to prevent sludge buildup), replaced the single row core radiator (1 inch thick) with a double row core radiator (2 inch thick), and flushed the engine. I have used Gunk engine flush for decades and follow the instructions on the container: Do not drive the vehicle with the flush in the oil.

P0174 System too Lean (Bank 2)
The first O2 sensor on each bank is upstream of the catalytic converter and the second O2 sensor on each bank is after the catalytic converter. The first sensors are used to sense the AFR and the second sensors check the efficiency of the catalytic converter. The PCM adjusts the long term fuel trims in an attempt to achieve the correct AFR. When pre-established limits are exceeded the PCM sets the associated diagnostic trouble code.

Replacing your second O2 sensors will not correct your incorrect AFR. Unmetered (didn't pass thru the MAF sensor) air is entering your intake manifold causing a lean condition. You need to plug your leaks.

If your LTFT bank 1 is also at 20% or 25% positive then you probably have leaking upper and/or lower intake manifold gaskets. It is very common with the SOHC V6. The gaskets dry out with age, shrink, and then leak - especially when cold. There are other possibilities: Lean condition procedure

 

[McChalium]

Replacement interval for O2 sensors?

Any thoughts on replacing the O2 sensors at 100K intervals?

 

[koda2000]

Any thoughts on replacing the O2 sensors at 100K intervals?

they're about due to be changed. the old unheated ones lasted about 50-60k and the newer heated ones last around 100-120k.

 

[2000StreetRod]

O2 sensors in closed loop

When in closed loop the PCM continuously cycles the AFR between slightly rich and slightly lean. According to my Bosch Fuel Injection & Engine Management manual a new O2 sensor typically outputs 0.93 volts at 0.98 Lambda and 0.07 volts at 1.02 Lambda. As the O2 sensor ages the values change to 0.84 and 0.09 respectively. Since the PCM is measuring the voltage readings the Lambda variation will increase as the O2 sensor ages. Since the max voltage output decreases more than the min voltage increases the AFR spends more time slightly rich than slightly lean and fuel consumption increases. Most members report a slight increase in fuel economy after replacing their pre-cat O2 sensors. Since you don't know the maintenace history of your vehicle and have the capability to read the sensor output voltage I suggest you do so before replacement.

 

[McChalium]

Further plans.

My best one is at about .75 volts on the high side reading. I have received my new sensors and between replacing those and chasing vacuum leaks my Sunday schedule is full. Is there a special cleaner for the MAF sensor?

 

[koda2000]

My best one is at about .75 volts on the high side reading. I have received my new sensors and between replacing those and chasing vacuum leaks my Sunday schedule is full. Is there a special cleaner for the MAF sensor?

yes, there is a special cleaner for the MAF. CRC Mass Airflow cleaner and don't touch it with your fingers.

 

[2000StreetRod]

Fuel trims?

My best one is at about .75 volts on the high side reading. . .

If the long and short term fuel trims were not at their limits for the .75 volt reading then a new O2 sensor might improve your fuel economy.