Exhaust smell, down on power...

[Sirocco20348]

What about manifold to cylinder head?

Haha possibly. I think I'll do a seafoam smoke test first as this is on the realm of my abilities.

I'm thinking exhaust to cylinder head gasket would require some serious Labour? Turbo removal etc?

Sent from my LG-H870DS using Tapatalk

[Sirocco20348]

......

[h100vw]

Where is the cat in your downpipe? Had a Polo recently that was going well and then wouldn't make boost. Messed around looking for leaks. Last ditch guess and I found the cat had broken down and was blocking the exhaust.

[Sirocco20348]

Where is the cat in your downpipe? Had a Polo recently that was going well and then wouldn't make boost. Messed around looking for leaks. Last ditch guess and I found the cat had broken down and was blocking the exhaust.

Drive SPM | MK4 GTI Downpipe Street Kit

Mine is a separate section that looks like it could be easily inspected.

What other symptoms was the polo showing? Strong exhaust smells when driving?

Sent from my LG-H870DS using Tapatalk

[Sirocco20348]

I had a night to think about this and I think you might be 100% on point.

Gav, so the cat was Broken down but stayed within the cat housing? Our did it flow further down the exhaust?

I also have this insane metallic rattle at like 2800rpm. If I hold out at this rpm, sounds like a hammer drill drilling into concrete. This only started after my exhaust was secured into place.

And snapping those photos, we only have a pre cat 02 sensor, so if the cat was stuffed we wouldn't pull any codes with vagcom, correct?

Damn I'm getting excited


Sent from my LG-H870DS using Tapatalk

[h100vw]

No other symptoms except down on power/boost. Definitely drop that section out.
I actually took out both the probes from the downpipe first. Expecting similar puffing out of each but the front one was markedly stronger. Leading me to look at the cat.

[Sirocco20348]

I had the exhaust inspected today, nothing wrong with it.

I'm going back to fuelling issues now.

I'll do some more testing tomorrow but I'm thinking the fuel filter or the uprated fuel pump I installed a while back.

Sent from my LG-H870DS using Tapatalk

[Sirocco20348]

Installed a new fuel filter.Ran some logs, no timing is getting pulled so I don't think it's fueling.

It must be a leak still even thou smoke tests suggest everything is ok.

I had a dream last night about check valves.... Especially the one on the brake booster line. I wonder if when the car is off, it's sealed, but when it's on its let's boost into the brake booster? Am I crazy?

How do I inspect check valves, I assume just blow into them from either end. I'll report back.

[h100vw]

That check valve is just one way, The arrow tells you which.

[simon k]

I had the exhaust inspected today, nothing wrong with it.

what did they inspect? how did they do it?

[Sirocco20348]

what did they inspect? how did they do it?

He said to to test for restricted cats an infra red heat gun is pointed to the back and front of the cat. If the rear is 10% hotter than the front, then it's in ok condition and operating correctly. Where it's the other way round then the cat has broken down and causing a blockage.

He didn't actually take the cat off and inspect because he said he didn't want to waste my money as it was working fine he said.

He further mentioned that since it's an aftermarket high flow cat, it would be stainless steel, and near impossible to melt, brake down unless raw flames were going down the exhaust.

For leaks he just listened for them. Not exactly rocket science, and doesn't really take into account high boost situations, but he was confident of the mufflers condition.

Sent from my LG-H870DS using Tapatalk

[Sirocco20348]

Just inspected my check valves, operating as per spec... Sigh

Sent from my LG-H870DS using Tapatalk

[simon k]

if he just had the car up on a hoist with the engine idling and shot at the cat with a temperature gun he wouldn't be able to tell anything about what was going on under load & boost - being a high flow cat, it could be 90% blocked and still flow enough at idle for the temperature front to back to be stable

I'd be taking the exhaust system apart and having a good look at it myself - if that cat pipe is removable in one piece, take it off and look down it with a torch, tap the inlet end of it on the ground and see what falls out, go for a (short) drive with it removed...

[jmcc]

I just bought a little usb borescope, for like $15, hasn't come yet but I'll test it out when it does, if it works any good you could just take the 02 sensor off (carefully, don't want a dead ecu) and put in the there to take a peek at the condition of the CAT

[Sirocco20348]

if he just had the car up on a hoist with the engine idling and shot at the cat with a temperature gun he wouldn't be able to tell anything about what was going on under load & boost - being a high flow cat, it could be 90% blocked and still flow enough at idle for the temperature front to back to be stable

I'd be taking the exhaust system apart and having a good look at it myself - if that cat pipe is removable in one piece, take it off and look down it with a torch, tap the inlet end of it on the ground and see what falls out, go for a (short) drive with it removed...

I agree with what your saying and this is definitely on my list of things to further cover off. I have done some hard driving and measured the cat with my own heat gun and is very consistent with what he was saying. Within 10% tolerance.

I have some doubtS thou. The high flow cat is about 30k km old. For that last 30k km the car has been very reliable, and without borrowing an innovate wideband air fuel sensor to confirm, I assume the mixtures have been quite good. I know assumptions are the mother of all ****ups, but I find it hard to believe the cat would be fouled to the point of failure.

There is another test that can be done without removing the exhaust and that is reading values from a vacuum gauge before and after the cat. The values should be very similar but if the pre cat value is higher it indicates some sort of flow restriction. ...I just don't have an accurate vacuum gauge handy.

I did some more driving last night and I noticed some certain situations.

If I do a WOT in 3rd from 1500rpm to 6000rpm, the boost peaks at 15psi and drops to 9psi by 5500rpm.

If I'm cruising at 3000rpm in 3rd and ease the throttle up to full boost, the car will hold 17psi throughout rest of the rev range.

These two scenarios lead me to think it's something unrelated to the exhaust, but maybe fuelling. I would test fuel pressure but I don't know how. Do I test fuel pressure with a manual gauge? I have doubts it is maintaining 4 bar pressure at WOT.

Tonight I might swap in a new high flow fuel pump as it costs me nothing but time (seller sent me two by mistake) and is easier for me to achieve than the exhaust removal as I don't have accessible space to raise it up on jack stands.