CAT Delete and Smoke

[Keith Browning]

Opinions please... A 2003 6.0L with a straight pipe turbo back with no catalytic converter and no other modifications. Do you think that the absence of a cat will increase visible black smoke?

[Bruce Amacker]

Yes, the cat absolutely will reduce smoke output. Here are some pics of my 6.4 DOC (/DPF) showing clearly that in the first two inches the soot is burned by the DOC and reduced to ash. Most of these photos were already in the archives. The inlet is on the left:

 

 

 

Zoom in of the DOC:

 

 

It is really difficult to photograph carbon due to the fact it reflects almost no light. This picture does not show it well, but there is a huge reduction in carbon present from the inlet to the middle section of the assembly.

 

 

 

The specs are metal shavings from the bandsaw, these were rough photos taken directly after the unit was sawed open. Even today after cleaning, painting, and years of handling, there is a noticeable reduction in carbon present after each component. After the DPF the pipe is white-glove clean.

 

 

Comparison of EGT's: Note how sooty EGT11 is compared with EGT12. Anyone who says the DOC does not reduce soot/carbon/PM is wrong. PM is black smoke, so here is proof that removal of a DOC will increase black smoke dramatically.

 

 

Sidebar: I'm wondering if removal and inspection of the 3 EGTs would help in diagnosing a 6.4 failed emissions complaint.....

 

[Alex Bruene]

Thanks for that. I am having an ongoing battle with somebody that has a smoke issue on a truck with the cat removed. I told him that I can't properly diagnose it without the cat installed. He went to the exhaust shop and told them what I said. They said I don't know what I'm talking about, and the cat doesn't reduce smoke... I know guys working at exhaust shops know WAY more than I ever will... But, come on...

[mchan68]

I actually have one in my bay right now as I post this. An out-of-warranty tow truck with a failed EGT_13 and a cracked EDOC up-pipe. Information from the owner is, the cat has been hollowed out. I guess that might explain the frequent regen when I drove the vehicle home and back to work. Bruce, is it safe to say that hollowing out a cat on a 6.4L will eventually lead to premature DPF failure?

[Bruce Amacker]

I know guys working at exhaust shops know WAY more than I ever will.

Originally Posted By: mchan68

I actually have one in my bay right now as I post this. An out-of-warranty tow truck with a failed EGT_13 and a cracked EDOC up-pipe. Information from the owner is, the cat has been hollowed out. I guess that might explain the frequent regen when I drove the vehicle home and back to work. Bruce, is it safe to say that hollowing out a cat on a 6.4L will eventually lead to premature DPF failure?

This rig has the DOC hollowed out and the DPF still in place? What an ass-backwards way of doing things, I'd think most hillbillies would do the opposite.

 

Think about it- if the DOC reduces the amount of soot by at least half (and probably way more than that) coming into the DPF, of course it will cause frequent plugging of the DPF and excessively frequent regen.

 

When you refer to "failure" I'm not sure just what method of failing you're referring to. If it's by plugging, yes of course, and quickly. I'm actually surprised the tow truck may have been in operation a while like this. If it's by contamination (where it won't "light off" because the catalyst compound in the DPF is poisoned) then I'm not so sure.

 

 

[Aaron]

I know of one particular 6.0 truck with no cat on it, and it doesn't smoke at all.

 

I also know of a couple 6.4 trucks with DPF/DOC deletes with no real horsepower added (0 or 40hp) that don't smoke, either.

 

They have sooty pipes, but no smoke under accel. And then there's a couple trucks I have seen with 210-275hp added and DPF deletes, and smoke is...HEAVY. My buddy's truck has a 210hp tune in it, with a manual trans, and he can't get any mre than 2/3 throttle before the clutch starts to slip. He sees a slight haze behind the truck when he gets on it hard from a stoplight.

 

 

 

I agree 100 percent on the diag by viewing the EGT sensors. I had my EGT13 out to anti-sieze it (I keep one in the glovebox in the event of a roadside EGT sensor failure so I can get back rollin' down the road again) and that thing, at 44,000mi is CLEAN as a whip. You could put it in the bag and sell it as new, had it not been for a little bit of light surface rust on the head of the flare nut.

 

There are TWO trucks that I know of with any significant mileage on them that have no soot in the pipes -- one of them being mine. I had mine chipped for some time, until it started causing idle problems, especially up on the fast idle.

[Jim Warman]

I think your thread got hijacked....

 

My opinion? Yes... a cat can reduce smoke output... It sure as hell works with gas jobs that burn a quart of engine oil every couple hundred miles...

 

Now... if I have a customer that repeats the exhaust shop mantra regarding cats.... all I can tell him is that all of my training and documentation is gear towards a predetermined engine operating condition... If he wants me to vary from things tried and true... "bring your wallet and ask no questions". I'm sure I can fix it... but we need to get past the R&D...

 

FWIW, there are many times when your life will be much better if you "fire" a bad customer.

 

Something too easily forgotten.... pull the manifolds and see if any individual cylinders smoke more than others.

[mchan68]

Something too easily forgotten.... pull the manifolds and see if any individual cylinders smoke more than others.

THAT, is a test that was suggested by Hotline for me to check on one particular truck that I won't soon forget. The gasser tune-down guys in the shop weren't happy with me running that test.