Running rich?

[99BB3500]

Ok so for a little bit now my K3500 7.4 exhaust has been smelling like it’s running pretty rich. And by pretty rich I wouldn’t be surprised that you could light the exhaust fumes on fire at the tip . Anyways. This has now become out of my realm of knowledge. So far I’ve replaced the fuel pump, fuel filter, distributor, distributor cap, rotor, spark plugs and wires, coil and ignition module. I’ve also cleaned the IAC and MAF. I’ll post some pictures of the scan tool data display and hopefully someone can give me a good idea. I know the fuel trims are way off but I don’t know where to begin.

 

[99BB3500]

Other pictures that wouldn’t fit

 

[Schurkey]

Shows lean on both banks.

If the exhaust is "rich" smelling, you probably have misfire. What is the cylinder-by-cylinder misfire counter showing?

No misfire? Failed catalyst?

How old are the O2 sensors? Are the crosscounts reasonable?

 

[RichLo]

Everything there is pointing to O2 sensors...

Can you data log what those are doing with your scan tool?

It thinks that its running lean so its giving it more fuel to compensate. How long have you had the truck and do you know if the PO did any work to it?

 

[99BB3500]

I love only had the truck for a couple months now. I don’t know what’s all been done to the truck. I know It’s had a lot of timing pulled because both knock sensors were broke. It’s been running better than it did when I got it. The engine light isn’t on, buts it’s throwing a code for one of the downstream o2 sensor heater circuit. The cats have also been removed. I have one high flow cat and I’m more than likely gonna pick up another one either today or tomorrow and weld them in.

 

[99BB3500]

I can data log it when I get home.

 

[RichLo]

Is the knock sensor repaired now?

The downstream O2's dont control the fuel trim but the upstreams do so data log those.

The lack of cats can account for both the gas smell and obviously the downstream O2 codes. But since everything else shows that its calling for more fuel there is something more than the lack of cats going on there.

EDIT, also since the PO tried to bypass the knock sensor he could have done some weird things like adding a resistor to the O2 sensor wiring... check for any hillbilly-ed work on those too.

 

[99BB3500]

Both knock sensors are brand new and one pigtail is also. It looked like the passenger side burnt off somehow. I’ll double check the wiring tonite. The guy I got it off of put 83 miles on it, he got it from an undercoating shop about 50-60 miles from my house so I know absolutely nothing about the truck

 

[Schurkey]

The lack of cats can account for both the gas smell and obviously the downstream O2 codes.

Yup.

 

[Supercharged111]

Lean exhaust reeks too. Are the O2 voltages p e g g e d (******* seriously?!) at 0 or 1V? If one pegs and sticks that usually means a failed sensor. If you give it enough gas to enter PE mode you'll instantly see a change. Sadly, with a stock tune, this doesn't work as there's a 60 second delay for PE mode.