97 Ford Explorer - cylinder misfire/O2 sensor issue?

[Cap067]

I have a 97 Ford Explorer, 6 cylinder, push rod, automatic with 197k miles. A few days ago I noticed several things happened at once.

1. Very rough starting (will turn over, but a lot of vibration, and takes 10-15 seconds)
2. Can smell of gasoline from the cabin. Is at its worst during the start, but persistent throughout ride
3. High vibration while operating
4. Slow acceleration - does not respond to accelerator very quickly
5. Gas mileage is about 1/2 of what I am used to. Currently I have gone only 150 miles on over 3/4 tank since last fill-up, which was shortly after the symptoms first showed.

I have seen no obvious signs of a gross fuel leak.

The check engine light has never come on.

I went to Advanced Auto Parts today and had them run a code check. The following 7 codes came up:

P0153 - Oxygen Circuit slow response, Bank 2, Sensor 1
P1152 - Lack of HO2S bank 2 sensor 1 switched - indicates rich
P0302 - cylinder 2 misfire
P0304 - cylinder 4 misfire
P0305 - cylinder 5 misfire
P0174 - bank 2 system too lean
P1151 - Lack of HO2S bank 2, sensor 1 switched, indicates lean

Any ideas on what is going on?

 

[budwich]

first idea... your check engine light is burnt out....
second idea ... you need vehicle maintenance...

depending on how long the codes have existed, you may have damaged your cats with excess fuel. You probably need wires, plugs, sensor (MAF) cleaning along with possibly a o2 or two.

 

[Cap067]

So I replaced the check engine light, and installed new wires, plugs, coil, and reset the codes. The car sounded the same, with the same issues. After driving around for a few miles the check engine light came on and there were 3 codes, one regarding the Bank 2, Sensor 1, another regarding a cylinder 4 misfire, and a third regarding running too rich.

I took it to a shop and they replaced the upstream O2 sensor. After running further diagnostics they recommended the following:

1. replace 3 fuel injectors. I was told #4 is bad, but while in there, might as well replace the other two on the same side.
2. replace the catalytic converters. They are shot.
3. replace the downstream O2 sensor.

The cost of doing so is worth more than the vehicle, but the mechanic spoke with me and gave some encouragement that it was not difficult to tackle these myself. He noted the FI had to be replaced before the cats replaced or I might burn out the cats again.

Out of the shop the car ran a bit better -
1. Gas mileage up from ~ 8/gal to 12/gal, but not normal yet
2. Start-ups less rough
3. gasoline smell less pronounced.

So I took the following steps
1. Removed the upper intake manifold to access the FI's. At this point I was unclear why the mechanic thought I might as well replace the other two since with the V6 pushrod there is a fuel rail where all 6 FI's are exposed. Perhaps he was thinking of the SOHC where the manifolds are separate and 3 from one side would be exposed.
2. Looking at the lower manifold holes air intake to cylinders 1, 2, 3, and 6 were black. 4 and 5 were clean
3. I tested the resistance for each FI. They all read about 16 ohms, which is normal according to the Haynes book I have.
4. I took the FI's to Advanced auto parts. They had no FI's available. I could have ordered, but after speaking with the folks there I was not confident that FI 4 was necessarily bad. I purchased a new set of gaskets for the upper portion of the upper manifold (the o-ring style), the FI's, and the lower portion of the upper manifold (large green and blue).
5. I reinstalled the upper manifold replacing all the gaskets with the new ones except the lower portion of the upper manifold (it looked OK, the replacement was expensive, and I expect I will have to get back in there soon).
6. I used an automotive stethoscope to see if the FI's were working. 1 and 2 were easy to access with the probe and I heard clear, load clicking sounds. 3 was blind, but I was able to feel for it and listen at the same time. I also heard clear loud clicking sounds. 4 was easy to access with the probe. I head faint clicking sounds. Hard to tell if it was from one of the others in the engine, or 4 was operating OK. I could not access 5, and 6 was a two person job. I found the FI, while my wife listened. She told me it sounded more like #1 than #4 (was louder and clearer).

So here are my questions

1. Is there any other way to confirm if a FI is operating OK? Haynes mentions a noid light, but in this engine how would you get to the FI electronic connection while still having the control system send the proper signals to the FI? To get access to the FI's, I have so many things disconnected it is unclear to me the signals would be sent to the FIs.
2. I am convinced the cats are bad. They have creaked and hissed loudly after the car is turned off since this problem arose. Should I wait until the upstream problem is definitively fixed before considering changing them? Is is possible to know the upstream problem is fixed without new cats?

 

[budwich]

well, now that you are experienced at "intake removal", perhaps you can just swap fi4 with another easy to reach / hear fi that you know works. Put everything back together and see what happens. That would just cost you your time. Ultimately cats issues are going to be a problem cause they effect the intake because of excessive "back pressure" (assuming they are clogged). Since you are expecting to replacing them, cut them off and replace "temporarily" with straight pipe "inserts" and see what happens there after.

 

[Cap067]

Thanks for the advice, it was very helpful.

1. I switched FI 1 and 4. The original #4 was still very faint in position 1, while the original #1 had a loud distinctive clicking sound in position 4. I intepreted this as a the original FI 4 was bad.

2. While in there, I arranged the harness cables and other obstructions to allow for access to FI's 5 and 6 after putting everything back together. I found FI 6 clicking loudly while #5 sounded alot like the FI originally in #4. I interpreted this as FI 5 was also bad.

3. I purchased two new FI's and replaced the two bad ones. After reassembling all 6 FI's were accessible with a stethoscope and I confirmed them all clicking loudly, thus presumably working well.

4. The 4 of the 5 original symptoms dissipated.
a. start is smooth
b. no noticeable gas smell
c. vibration gone
d. acceleration/power is back
It is too early to check the gas mileage, the 5th symptom.

5. The check engine light is not on, but I checked the codes to see what was still carried by the computer. There is 1. P0420 - Catalyst System Efficiency Below Threshold (Bank 1). I cleared it, and will see what codes show up after driving around for a while.

6. I still think it is likely my cats are bad and need replacing, but I will drive a few miles to see if anything else shows up.

I do have one question. Is there a definitive way to determine if the cats are causing excessive back pressure?

 

[budwich]

You might be able to compare temperatures with another vehicle run the same "course" (ie. time / highway speed / load etc)... using a hand held temp gage.... that might tell you something about the cats functioning. I suspect that if you were "burning" a lot of fuel, your cats were likely running hot which I think will cause them to "bond" eventually.

check your exhaust system for leaks.