syzygy

I also WOT my IS350 virtually every chance I get. It's too fun not to.

I've heard that going WOT every once in a while will help to prevent this issue. With 25k miles on my car, I don't have a single symptom of carbon build up. Take that n=1 correlation anecdote for what it's worth.

Gas-wise, I switch it up between Chevron premium and Shell premium.

IS-SV

"4) IS350 engines with dual injection apparently have issues with carbon buildup as well."

Have not heard that. Any evidence of that is becoming a known issue?

Clay Easto

Honestly, I don't see how WOT would help this issue.

quick123

iTrader: (2)

EXCESSIVE CARBON BUILDUP

Some late-model engines can develop carbon problems in less than 10,000 miles, as now seen in the 250 motors. There are 2 kinds of deposits, so lets try and not get them confused.

Oil-based carbon deposits - these are the traditional gummy, black one like those sometimes found on intake valves (like the pictures above). They are caused when oil and heat come together.

Carbonaceous deposits - are from fuel. They are also called "cauliflower deposits" because of their resemblence. These deposits are not as thick as oil deposits and are hard, dry, and tougher to remove. Driveability problems can result from them.

The carbon deposits that are causing driveability issues in our engines are from fuel and not oil. A malfunctioning PCV valve will cause oil-based deposits, which is not our problem. An apparent design flaw has caused the 250 motor to have excessive fuel-based carbon deposits, which I do not know yet. All of our motors will have some sort of fuel-based carbon deposits eventually, and will need to be serviced.

Carbon deposits cause driveability problems because fuel vapors can be absorbed into them. That means some of the fuel never reaches the combustion chamber. This results in rough idling when cold, as well as loss of power, surging, and high emissions. Carbon deposits on valves sometimes cause problems in as little as 5,000 miles.

These carbon deposits can be removed by using an additive such as Top Engine Cleaner, but be aware that carbon removers can damage catalytic converters if used too often.

Hopefully that helps

hades281

I agree that our carbon buildup problems are from fuel, not oil. I also agree that the deposits shouldn't look like the RS4 valves a few posts up.

Though carbon may absorb fuel vapors, it is not true that it could prevent any amount of fuel from entering the combustion chamber in our particular engines -- direct injection takes care of that. If bad enough, the only thing the carbon can do is prevent the valves from closing completely - causing a loss of compression and power, or cause an airflow restriction.

I cannot believe there would be so much carbon in the intake port that the airflow could be restricted enough in 10,000 - 20,000 miles, where some people are reporting the problem. Secondly, I would think the force (impact) of the valve against the valve seal would prevent accumulations of carbon on these surfaces. If both of these assumptions are true, the valve should be operating just fine in the presence of carbon, and the real cause of the issue is elsewhere. Comments?

syzygy

I have no idea how these things work. The WOT comment was made by lobuxracer in a previous thread, I believe. He said something along the lines of "just go WOT every once in a while" and there should be no problems.

I'd ask him about it.

Pnuge88

iTrader: (1)

can't be the gas? i use shells 93.. have you seen their advertisements? lol can't be oil. i use mobile 1 synthetic every 3k and i floor my car everyime i'm in it. 68k miles. have had the rpm drop multiple times coming to a stop. do i have a problem? NO.. runs fine. drives fine. NO ONE has ever had any problems cause of this.. what's the big deal. lol just sayinn

quick123

iTrader: (2)

Well, think of the carbon deposits like little pieces of charcoal. The charcoal bits will 100% absorb as much fuel as possible, that is just their nature. Now, they may not absorb much, but enough to cause a stumble at idle when cold. Think of it like this, the ECU sends a set amount of air and gas into the combustion chamber, and if something keeps even just a little from getting there, it could cause a stumbling idle.

Also, everyone shouldn't think that there is something wrong with the gas they are using. It doesn't matter what brand of gas you use, carbon deposits will accumulate over time. Think of it like calcium deposits building up on your shower head, as water travels through the shower head, very small amounts of mineral deposits stick to the metal and will gradually increase over time. You don't really notice it until it causes a reduction in flow, and then you just clean it out. Just about the same thing with carbon build up in engines.

The 350 motor does not build up as quick as the 250 motor due to the way the EFI system is designed. The further the fuel travels from the injector to the combustion chamber, the more metal surface there is for deposits to stick to. Since the direct injection cancels out most of this, the 350 motor will not have build up issue as quick as the 250.

I kind of agree that going WOT every once in a while could help, because the extreme rush of air and fuel could help break loose some deposits that are forming, but not much can really prevent this from happening. When your idle starts to feel low and rough, especially when its cold (and no check engine lights), its just time to do an EFI service.

Koz

There is nowhere near the issues with carbon on the 350 (One that I've seen posted) as there is with the 250. The main difference between the engines is the injection systems used. The 350 uses port and direct, the 250 using just direct. This makes sense because the port injection allows the a/f mix the flow across the intake valves. The additives/detergents that are used in the fuel will help clean and/or prevent carbon build-up. The volume and velocity of the intake mix will also vary the cleaning affect.

The build up will start to affect/disrupt the flow of the a/f mix and compound the problem and eventually cause carbon build-up in the combustion chamber. Now you are raising the compression and further compounding the problem. What has also compounded this problem is the fuel formula itself. Has anybody noticed that small engines (Lawn and snow equip) develop some of the same symptoms? I was having this problem with my lawn mover and my two stroke snow blower for the last couple years that got to the point that I did some research and was advised to add Iso-Heet (isopropanol) to the fuel. After doing so I immediately started to see the problem getting better. Also Amsoil just came out with a new product to help with this exact problem. Attached are links to these products. I suggest adding one of these types of products to the fuel used for small engines. Just make sure the one you use is recommend for that type of engine. Two stroke and four strokes use different isopropanol formulas.

This product can be used in both 2/4 stroke engines and can be found at Walmart - http://www.amazon.com/28202-Iso-HEET...6689926&sr=1-4

This the new product from Amsoil - http://www.amsoil.com/storefront/aqs.aspx

Koz

quick123

iTrader: (2)

^^ AMSOIL ROCKS!!!

On a side note, I use their 100% synthetic oil...yes thats right, 100% synthetic and not FULL synthetic like other petrolium based synthetics like everyone else. Next time you get oil for your car, check out the bottle. Full synthetics are still using carbon based petrolium oil and they can't claim 100% synthetic like AMSOIL.

I also just changed my differential fluid with AMSOIL 75w90, and I could actually feel a difference. If you are really in tune with how your car drives, when using this in you diff you will feel it. It almost feels like a rise in compression when decelerating, like you have the car in sport mode, but it is still in D....I am sold for life...

Koz

Just a little heads up. Yes there is a difference between PURE synthetic and synthetic. The synthetic oil can use petroleum base oil and still be labeled synthetic. What is important to know is these synthetic oils (Castrol Syntec - Mobil 1) have been proven to provide the same protection as a pure synthetics (Amsoil) with a regular (OCI) oil change interval (Up to 1 year or 12K miles). The difference is, the pure synthetics can use an extended OCI (12K+ miles, depending on UOAs (Used Oil Analysis). As far as feeling a difference using the Amsoil Severe Duty 75w90 gear oil, I did not feel any difference and find it hard to believe it would be possible (Could be).

I only use Amsoil products!

Koz

Infra

iTrader: (1)

This doesn't make sense. The IS250 is direct injection only, therefore there is nearly zero travel distance to the combustion chamber.

Koz

Carbon deposits originate from blow-by gases combined with internal and external exhaust gas recirculation, and in this process, the blow-by gasses and the re-circulated exhaust gas come into direct contact with the intake valves.

Koz

quick123

iTrader: (2)

Did you know that you have a cold-start injector located in the intake manifold???

syzygy

There's a diagram and short explanation at this top engine cleaner site:

http://www.barsleaks.net/Refs/TEC_ap...app_notes.html

I don't know if it helps clarify anything, though.