So my engine was running rough ('96 f150, straight 6, 4x4) and sure enough, I had codes P0301 and P0302. I pulled those two plugs to take a look, and there is a lot of carbon buildup (see pics below). I'm asking on here to find out what are the most common problems I should look at first. I should note that about a year ago, I removed the catalytic converter. It was bad and I couldn't afford a new one, so i just welded a straight pipe in. Wondering if that would affect the O2 sensor, and thereby affect air to fuel ratio? The truck has 190,000 miles and the injectors have never been touched (cleaned or replaced) since I have had it (I got it when it had 90,000 miles) so maybe the injectors need to go? Any tips would be helpful.

Cylinder 1 plug

Cylinder 2 plug

 

I would guess blow by. Compression test those cylinders. I'd also pull the other plugs and see how they looked and compare those two to the remaining plugs, and compression test the whole thing.

 

the insulator looks pretty good down in. looks like it might be pulling in some oil from the guides. not too bad though.

 

[QUOTE=joegeds;18211609]So my engine was running rough ('96 f150, straight 6, 4x4) and sure enough, I had codes P0301 and P0302. I pulled those two plugs to take a look, and there is a lot of carbon buildup (see pics below). I'm asking on here to find out what are the most common problems I should look at first. I should note that about a year ago, I removed the catalytic converter. It was bad and I couldn't afford a new one, so i just welded a straight pipe in. Wondering if that would affect the O2 sensor, and thereby affect air to fuel ratio? The truck has 190,000 miles and the injectors have never been touched (cleaned or replaced) since I have had it (I got it when it had 90,000 miles) so maybe the injectors need to go? Any tips would be helpful.

I would replace your PCV also. If you don't have an O2 sensor you can weld a bung in which I would do. Your computer is making your truck run rich if you do not have the O2. . You can also put #2 and #3 plugs their place with a swap and check codes again. This would also take care of checking the other plugs as was mentioned above.. Not having an O2 is probably the issue and would show fouling long term. Sandy

 

What does weld a bung mean? I assume this means to weld some type of port so that I can connect the O2 sensor? If so, does it matter where I weld this port?

 

What heat range are those plugs?

 

Their website says they have a heat range of 5. they are Autolite 5125 plugs.

 

FYI removing the catalyst typically triggers a code for non-functioning cat (I'm surprised you don't have them), but it will not effect the PCM strategy for fueling. The third oxygen sensor, often called a "cat checker" has no bearing on A:F determinations. The upstream sensors are critical though (bank 1 sensor 1, bank 2 sensor 1).

 

[QUOTE=joegeds;18213765]What does weld a bung mean? I assume this means to weld some type of port so that I can connect the O2 sensor? If so, does it matter where I weld this port?[/QUOTE

Your assumption is correct and yes it does matter where it is. I would locate your old wiring and it should be located where it will reach IMO. Sandy

 

Sandy, are you under the impression he has removed the oxygen sensors? I didn't see that in his text; only that the catalyst itself was removed.

 

Well I reread it and he didn't say that directly but, his answers indicate he did. He has not denied it, so yes I am under the impression, but you raise an area that I apparently assumed also.

So, Joegeds did you remove the O2 sensor when you went to the straight pipe? If not, do you have one in your exhaust system? Sandy

 

Yes, the furthest downstream O2 sensor is not connected to anything - it's just hanging there. Also, the air inlet tube that connects to the exhaust between the first and second cats on the 4.9L was also just cut off and is hanging there.

 

I don't weld, so I would take it to a muffler shop and they should be able to fix you up with a bung quickly. That should eliminate your rich condition. Your gas mileage has probably suffered also if that matters. The air inlet tube is not something I am knowledgeable about but someone will know and chime in. Sandy

 

No, it doesn't matter what you do with the cat checker (downstream HEGO sensor). No effect on fuel, timing, etc, you'll only get a CEL for the emissions issue. Upstream sensors matter, a lot, but not the downstream.

I wouldn't waste the time or money on the downstream sensor unless you're reinstalling a catalyst.

This is a half ton, EEC-V, OBD-II vehicle with three HEGO sensors. Not the single sensor EEC-IV.

The two codes you've mentioned, are those the only codes in the PCM? With no third oxygen sensor (edit, with no cat and the sensor not in the exhaust), there should be more than just the misfire codes.. I would be suspicious of the PCM if it doesn't see that you've removed the downstream sensor.

 

I replaced the two sparkplugs and erased the codes to see if P0301 and P0302 would reappear. No emission codes have popped up, but I haven't driven it since I started this. Guess I should've checked for other codes before I erased them.......