Fuel additives

LuckyBenski · 18 May 2019 at 11:25

Hi all, first post in Motors as I drive a clown car inherited from work...

I'm looking for recommendations on a good fuel additive for reducing carbon deposits... I think. I've recently had a couple of fault codes stating a misfire. No obvious bangs or lurches though, but I'm now a bit paranoid my engine's running rough.

It's a Smart, 1L 3-cylinder engine. I live in London so do loads of low speed/stop-start driving and very rarely get to high revs. Doesn't help that I try to drive the car in a fuel efficient way

. Other Smart users have suggested the engines are prone to carbon/general buildup at low speeds.

If the engine light comes on a third time I'll take it to the garage for some tests but in the meantime, it's been suggested to use a fuel additive to try and clean things up a bit.

What do you lot like to use?

smilertoo · 18 May 2019 at 12:00

Petrol or diesel?

LuckyBenski · 18 May 2019 at 12:09

smilertoo said:
Petrol or diesel?

Petrol.

smilertoo · 18 May 2019 at 12:27

I use a couple of bottles of reddex then hit the motorway, once im warmed up i change to the wrong gear and push up the revs to increase heat. I was told it needed heat to clean the bits and pieces...so i'm either cleaning it a bit or being misled and making a lot of noise for no reason.

Orionaut · 18 May 2019 at 12:32

Though I haven't been able to find anything conclusive, but since the Smart engine is actually a Mitsubishi unit, I would guess that it might well be a GDI setup.

GDI engines are a bit prone to developing coking issues, particularly behind the inlet valves (Ask anybody who has a BMW Mini!)

Unfortunately, while an additive might help keep the injectors a bit cleaner (Or might not!

) It wont do anything for the backs of the inlet valves (Assuming it is a GDI engine)

The only way to stop that from happening is to modify the PCV system so it vents to the road (Illegal) or fit an aftermarket catch can system.

Orionaut · 18 May 2019 at 13:09

Oh, And another thing.

If the engine light is coming on, do you have a fault code?

Stephanie Peterson · 18 May 2019 at 13:11

Fill car with good fuel, take car to motorway or backroads, hash the xxxx out of it at high reves for a while.

Repeat once a month, car will be happy.

LuckyBenski · 18 May 2019 at 13:13

Orionaut said:
Oh, And another thing.

If the engine light is coming on, do you have a fault code?

Misfire on cylinder 3. Apparently Smart don't always use the standard codes though - but this code did lead me to other threads on forums . They mainly had loss of compression issues.

Orionaut · 18 May 2019 at 15:42

LuckyBenski said:
Misfire on cylinder 3. Apparently Smart don't always use the standard codes though - but this code did lead me to other threads on forums . They mainly had loss of compression issues.

Do you have the actual Pxxxx code?

LuckyBenski · 18 May 2019 at 15:52

Orionaut said:
Do you have the actual Pxxxx code?

P0303:

BUDFORCE · 18 May 2019 at 16:12

Have you checked the spark plugs and HT lead etc?

Orionaut · 18 May 2019 at 16:46

Yeah, That is totally generic.

The ECU can detect uneven running, and generate this code as a consequence, but that gives no clue as to what is causing it.

BUDFORCE said:
Have you checked the spark plugs and HT lead etc?

Indeed, This fault code can be caused by a faulty HT system/plugs since this is not something that is normally directly monitored by the ECU and so wouldn't generate more specific fault codes.

It can also be generated by mechanical issues such as faulty injectors, mechanical wear and severe coking.

But Plugs/Coils etc is actually a good starting point if not already checked. This is the same group of fault codes that are generated when the Ford 4 terminal coil/Plug leads packs fail (Which anybody who has ever owned a Ford with a zetec petrol engine will almost certainly have experienced at some point

)

LuckyBenski · 18 May 2019 at 17:22

Thanks, that makes sense. Someone suggested swapping coil packs around to see if one is starting to fail - as the error has always been cylinder 3. Does that make sense?

Annoyingly they're not easy to get to as the engine is tucked in under the boot. Have to take a panel off. But a set of Torx bits should work out cheaper than a garage trip!

Simon · 18 May 2019 at 18:03

Use a decent branded high octane fuel. More than enough additive

BUDFORCE · 18 May 2019 at 18:43

Orionaut said:
But Plugs

hehehehehheheheheh

Nasher · 18 May 2019 at 20:40

If it is being caused by carbon buildup, additives won't help now nor will premium fuel. These things are to prevent it getting bad. Once it's clogged it won't clear it.

An Italian tuneup once in a while is a good idea though. Find a stretch of road and rev the crap out of it for a bit

LuckyBenski · 18 May 2019 at 20:47

Nasher said:
An Italian tuneup once in a while is a good idea though. Find a stretch of road and rev the crap out of it for a bit

Indeed, I used to rag it pretty hard as it's small and light. Loads of fun until you hit 40+, I just started being "sensible" at some point

Simon · 18 May 2019 at 20:58

Nasher said:
If it is being caused by carbon buildup, additives won't help now nor will premium fuel. These things are to prevent it getting bad. Once it's clogged it won't clear it.

Rubbish. High detergent fuels will clean up existing deposits

~Dockie · 19 May 2019 at 00:22

Cataclean

Orionaut · 19 May 2019 at 05:01

Simon said:
Rubbish. High detergent fuels will clean up existing deposits

Not coked up inlet systems on a GDI engine. (I still dont know off hand if the Smart is a GDI, so I am just saying...)

This is the big problem with GDI. Conventional injection systems keep the backs of the inlet valves clean by spraying fuel onto them. This doesn't happen with GDI and the oil/muck from the closed PCV and EGR system will eventually fill the inlet tract with hard black crud. Once the inlet system on a GDI gets coked up it has to be mechanically cleaned. Either by dismantling or by using one of the "soft" grit blasting processes as is common with Minis. (See http://www.germanautohaus.co.uk/r56-walnut-blasting/ )

Of course, this sort of thing is also common with diesel engines too thanks to EGR and PCV systems. though the crud on diesels tends to be softer and is more amenable to cleaning by spraying fluids into the air intake (See https://www.forteuk.co.uk/product-detail/35/Diesel-Intake-Cleaner and even https://www.revivecleaner.com/ ) though to be effective, products like this need to be used regularly rather than waiting for a serious problem to occurs first.

Like I said elsewhere, Like most "Green Initiatives", GDI (Along with EGR and closed PCV) looks like a good idea on paper but out in the real world it can be a complete PITA.