Holed Exhaust Emissions

[Raize]

If my exhaust midpipe has a large hole in it with a major leak of exhaust gases, will the emissions measured from the tailpipe show as having a higher, lower, or the same CO reading than they would do if the exhaust was intact?

[simon1987]

impossible to know really.

Maybe lower because exhaust gas is escaping through the hole or is sucking clean air in.

But the mot tester wont probe it with an obvious leak

[aw51 121565]

They shouldn't test it in that condition, and it will fail with a reason along the lines of "exhaust emissions not tested due to significant leak of exhaust gases from the exhaust system".

[redstu]

It will be the same. Why do you ask?

[Raize]

aw51 121565 said:

They shouldn't test it in that condition, and it will fail with a reason along the lines of "exhaust emissions not tested due to significant leak of exhaust gases from the exhaust system".

The point is that I set the mixture myself using a gas tester and I'd like to know if I'm likely to have it running too lean or too rich because of the misleading readings.

[Dodsy]

The lambda reading will probably be off the scale as it will be sucking air in through the hole. My TVR had a leak in on one of the exhaust gaskets. It was so minor it was hard to find it. That was enough to put the lambda reading out of the MOT range.

Edited by Dodsy on Saturday 23 February 17:52

[Crafty_]

I think it'd show lean.

[clarkey540i]

I always wondered about cars with multiple exhausts running from separate cylinder banks. Are the emissions tested for those cylinders, and then multiplied to give a reading? This is with regards to MOT testing.

[rigga]

Dodsy said:

The lambda reading will probably be off the scale as it will be sucking air in through the hole. My TVR had a leak in on one of the exhaust gaskets. It was so minor it was hard to find it. That was enough to put the lambda reading out of the MOT range.

Edited by Dodsy on Saturday 23 February 17:52

Op leak was mid pipe so after the o2 sensor so wouldn't affect the mixture reading ...... but yes if leaking pre sensor it will cause problems.

[m0isty]

As Dodsy said, a holed exhaust usually puts the lambda readings off the scale.
Note: this has nothing to do with the lambda/oxygen sensor on the vehicle itself! Many people assume that a high lambda reading on an mot emissions test means that the car needs a new lambda sensor, and get very disappointed when the car still fails after its fitted!

[Raize]

Apparently they did do an emissions test which it passed (although it failed MOT for the exhaust hole) with .3% CO and 40 ppm UBHC.

I also found the exhaust holes which were quite badly described... One is a pretty standard hole on the circumference of the silencer, but is the more major leak of the two. It's under the exhaust holder strap. As it's a fairly standard hole location it can be repaired with an exhaust repair kit I am sure.

The other hole is where the back pipe (not the tail pipe, the one at the other end) joins onto the silencer, it's a hole in the weld itself where they join. The difficult location of that hole is going to make it a problem to repair. Can it even be repaired in that location?

[andymk3]

clarkey540i said:

I always wondered about cars with multiple exhausts running from separate cylinder banks. Are the emissions tested for those cylinders, and then multiplied to give a reading? This is with regards to MOT testing.

I'm pretty sure that say if a V8 engine was tested, if the exhaust meets together at any point then only one test is needed, but if each bank of cylinders has a completely separate exhaust pipe then an emissions test on each one is required. I've never seen a car that doesn't have each bank meeting at a silencer from factory yet though

[Raize]

andymk3 said:

clarkey540i said:

I always wondered about cars with multiple exhausts running from separate cylinder banks. Are the emissions tested for those cylinders, and then multiplied to give a reading? This is with regards to MOT testing.

I'm pretty sure that say if a V8 engine was tested, if the exhaust meets together at any point then only one test is needed, but if each bank of cylinders has a completely separate exhaust pipe then an emissions test on each one is required. I've never seen a car that doesn't have each bank meeting at a silencer from factory yet though

Each exhaust exit pipe is seperately tested then an average is taken of the two figures.

[andymk3]

Raize said:

andymk3 said:

clarkey540i said:

I always wondered about cars with multiple exhausts running from separate cylinder banks. Are the emissions tested for those cylinders, and then multiplied to give a reading? This is with regards to MOT testing.

I'm pretty sure that say if a V8 engine was tested, if the exhaust meets together at any point then only one test is needed, but if each bank of cylinders has a completely separate exhaust pipe then an emissions test on each one is required. I've never seen a car that doesn't have each bank meeting at a silencer from factory yet though

Each exhaust exit pipe is seperately tested then an average is taken of the two figures.

Ah that's it! I knew it was something like that

[Raize]

I've been looking into various products. Seems like there's 4 solutions.

1: Exhaust putty that you just smear on and hope it sticks
2: A kind of mat that you wrap round the exhaust and the heat of the engine bonds it on
3: Buy a whole new stainless system for ££££
4: Weld in a patch £££

[hairykrishna]

Raize said:

I've been looking into various products. Seems like there's 4 solutions.

1: Exhaust putty that you just smear on and hope it sticks
2: A kind of mat that you wrap round the exhaust and the heat of the engine bonds it on
3: Buy a whole new stainless system for ££££
4: Weld in a patch £££

Putty works well for little leaks. In my experience 'Gun gum' (or whatever the orange tin name brand is) was far superior to the Halfords generic stuff, i.e. it actually stuck.