Fuel economy problems...any suggestions appreciated

[notflyingscot]

Go for a drive - 20-30m at a minimum (constant) 4000rpm. You've got to keep the revs (and heat) up above 4k). If the economy improves for a few weeks after that then it's probably inlet gunk.

You might try a chemical clean after that but generally the inlet removal & manual clean is the best solution.

It won't help the inlets but try a bottle of Wynns Complete Fuel System Cleaner - it might just help the injectors a fraction.

Are there no 21st century equivalents to the 1950's Redex which I still recall my father and his contemporaries either adding to the tank or squirting into the carburettors? Was a pretty instant partial de coke as I recall. Never quite the same as lifting the head and cleaning manually so suppose in many ways nothing has changed. Maybe these 'old' solutions have no place with modern EFI and ECU controlled engines?

[Gerrycan]

Are there no 21st century equivalents to the 1950's Redex which I still recall my father and his contemporaries either adding to the tank or squirting into the carburettors? Was a pretty instant partial de coke as I recall. Never quite the same as lifting the head and cleaning manually so suppose in many ways nothing has changed. Maybe these 'old' solutions have no place with modern EFI and ECU controlled engines?

Anything you add to the fuel tank gets injected with the petrol directly into the cylinder (direct injection) bypassing the inlet manifold and valve stem where the carbon accumulates. All the petrol mk2 models were DI as are the mk3 except for the 1.8 and vRS which have both direct and port injection systems. The latter system has at least a chance of 'wetting' the inlet valve stem and doing something to remove the carbon build up there which is the main issue.

There are chemical (including the Subaru ) products that you spray into the inlet manifold after warming up the engine leaving it a while and then revving the loosened gunk and material through the exhaust. Worries me a bit what it would do to the catalyst on the way through
I remember GTR27 related a story where he used something similar on his totally gunked up motorbike and expelling a whole load of black soot and chemicals onto his driveway. Ran better after though.

[Mi16 Man]

8500 kms seems very low to be getting these problems. What engine does your Polo GTI have?

G'day Gerry,

I've got the new 1.8T engine.

My suspicions were correct. It does NOT like Shell V-Power. I've filled up on Ultimate 98 and it's fine again. Usually run Mobil 98, again, without fault.



MY13 Kluger KX-S AWD / MY16 Polo GTI

[GTR27]

Anything you add to the fuel tank gets injected with the petrol directly into the cylinder (direct injection) bypassing the inlet manifold and valve stem where the carbon accumulates. All the petrol mk2 models were DI as are the mk3 except for the 1.8 and vRS which have both direct and port injection systems. The latter system has at least a chance of 'wetting' the inlet valve stem and doing something to remove the carbon build up there which is the main issue.

There are chemical (including the Subaru ) products that you spray into the inlet manifold after warming up the engine leaving it a while and then revving the loosened gunk and material through the exhaust. Worries me a bit what it would do to the catalyst on the way through
I remember GTR27 related a story where he used something similar on his totally gunked up motorbike and expelling a whole load of black soot and chemicals onto his driveway. Ran better after though.

Indeed! Nulon Foaming intake cleaner.

It was on a gsxr750 that had valves SEVERELY coked up. Basically, you do it same as subaru upper engine cleaner - run the engine, then empty half the can in squirts directly into the manifold while running, then shut off and hose the rest into the manifold. let it sit overnight, then hose them again! When mine started (after LOTS of cranking) it blew literally a cup of soot out the exhaust!


Walnut blasting of the valves is the only real sure fire way, but after that experience (and hearing others using seafoam or subaru upper engine cleaner) I think some of those items can actually help!

[Martin]

There are chemical (including the Subaru ) products that you spray into the inlet manifold after warming up the engine leaving it a while and then revving the loosened gunk and material through the exhaust.

Worries me a bit what it would do to the catalyst on the way through

Fully agree - especially with a stock 800 cell CAT (small holes)

[brad]

Are there no 21st century equivalents to the 1950's Redex which I still recall my father and his contemporaries either adding to the tank or squirting into the carburettors? Was a pretty instant partial de coke as I recall. Never quite the same as lifting the head and cleaning manually so suppose in many ways nothing has changed. Maybe these 'old' solutions have no place with modern EFI and ECU controlled engines?

yes, you can still buy equivalents.

No point adding to the tank though as it's direct injection.

I've posted the various methods many times on this forum.

There was no sign of any gunk on the cat when I had the DP off (twice). It's right on the outlet of the turbo - any gunk turns to ash due to the heat and passes through.

[Gerrycan]

G'day Gerry,

I've got the new 1.8T engine.

My suspicions were correct. It does NOT like Shell V-Power. I've filled up on Ultimate 98 and it's fine again. Usually run Mobil 98, again, without fault.



MY13 Kluger KX-S AWD / MY16 Polo GTI

I'm really surprised the type of petrol made so much difference on your 1.8tsi.
In relative terms your engine is in a low state of tune compared to say my 1.4tsi and the 2.0tsi in the RS so I would have thought it would be more tolerant.
My engine shows no obvious performance difference between 95 or 98 Octane so I tend to use the 95 Octane but others swear by and would not consider using anything but the best.
You could also have got a bad batch of fuel, it does happen. A friend's brand new Discovery 4 diesel engine was ruined by contaminated fuel in one Darwin service station as were at least 30 others by his account.
Pleased for you that it is resolved so easily though.

When I say your 1.8 in a relatively low tune state that is because it (officially) produces the same torque as the 1.4, albeit over a larger rev range, yet it has the same sophisticated manifold/direct injection fitted to the 2.0 engine. Scares me to think what your 1.8 would do if were chipped.

[Martin]

There was no sign of any gunk on the cat when I had the DP off (twice). It's right on the outlet of the turbo - any gunk turns to ash due to the heat and passes through.

Good to know, thanking you

[brad]

Good to know, thanking you

You've got an APR DP. The cat is further back near where the #2 (600cell) cat is on the OEM DP & 200 cells.

Gerry
The torque is artificially limited but I get your point. What's the kw/cc & Nm/cc ratios for those 3 engine sizes?

[Lucas_R]

Good to know, thanking you

I second this - removed the stock DP off my Mk6 GTI at approx 60,000km and the cats looked good as new....very restrictive in their design but not blocked etc