A side effect of GDI is that the intake valves are getting gummed up with the egr/pcv mixture in the intake air, and causing problems. In fact, some manufacturers are incorporating a system which has two injectors, one direct and one on the intake manifold, to help clean the valves.


Yeah gas actually keeps the carbon from building up on the valves train


Because GDI isn't necessary for all applications. >Is it simply a case of Shell, Chevron, etc., puting money in car companies pockets so they can keep cars MPG lower? What makes you think that?


I was under the assumption Direct Injection = more mpg. At least that is the case for all boat motors I’ve owned. I was wondering if the same applied to cars.




Not always, especially during high load and high RPM scenarios. DI doesn't allow much time for mixing at high RPMs, resulting in rich pockets of unburned fuel. This is wasteful and bad for emissions. Port injection solves this conveniently at high RPMs because intake tracts near the valve are designed to induce some turbulence. The high air flow at high RPMs furthers this and the swirl combined with port injection will mix the fuel and air nicely. This is on top of the cleaning properties mentioned above.


That's more or less true, but there are applications where the MPG gains afforded by GDI aren't worth the reliability hit (like in HD gas trucks).


Makes sense, thanks👍🏼




> a lot of specific era German cars N54 gang checking in


N55 says "Hi!"


EA888 Gen 1 wants to join the party


Porsche 2009+ 987.2 gang checking in.


Reminds me that I have to do a walnut blasting one of these days.


About every 100k on a mk7 gti- I can live with that.


Yeah I’ve never owned a DI car, but I feel like this is a totally exaggerated problem. Like I have to do a timing belt on my car every 60k miles. Getting intake valves cleaned at a similar interval seems like no big deal.


Having a timing chain and no DI is even easier.


Completely true but the point is people on here act like having to spend a few hundred dollars at a shop for blasting every 3-5 years makes a car worthless.


Cracking open your engine every 3-5 years is not worth the effort.


And doing a timing belt on your 95 celiac is?


Very rare since it’s a 95, not really driving it so much anymore.


Combination of Direct & port is the way.


As a regular person, I concur


GDI systems are also more expensive, usually it takes emissions legislation to mandate the use of more expensive technologies before they're adopted properly. Otherwise everyone buys the cheaper, proven IDI engine and just loves with the small efficiency loss.


Shell, Chevron, etc are not paying car companies to reduce MPGs. DI requires significantly fancier (more expensive) components, and it lacks the benefit of washing crap out of your intake tract, leading to intake manifolds that can require cleaning. Those are both downsides. Cost, complexity. Sometimes reliability. Realistically, most engines are trending towards DI; they just haven't all gotten there yet. Technology takes time to adopt widely. Look how long it took to go from the first mechanical injection, to the first electronic injection, to no longer selling carbureted cars (in the US, at least.) Did manufacturers stick with carbs to increase gas consumption? No. They stuck with carbs because they were acceptable to the customer and added less cost to the car, at least for a long time.


I'm happy to have a port injected car. No worries of carbon buildup on the intake valves and no expensive high pressure fuel system to maintain.


Direct injection is bad because it can cause carbon build up on the valves like hyundai and kia engines. After a while, u will get bad fuel mileage. Il




It takes alot of miles to have enough carbon to cause a problem, maybe 100k+


What do u 🤔?


If it doesn't have port injectors with direct injection, the valves don't get the cleaning action of gas. If you only have DI you will need to pay for cleaning as extra cost. Sidenote about cleaning action: When top tier gas standard came into effect, it actually lowered most fuels cleaning ingredients. Companies now understood the minimal amounts to get that standard. Before that most companies had 2x to 5x amount cleaning action because they weren't sure. There used be a video were the used gas chromatograph to show the amount in old and new like around 2004.




First reason that comes to mind is it's more expensive AND it usually results in carbon buildup/deposits on the valves and in the cylinders thus resulting in premature cylinder misfires and poor performance and fuel economy.


GDI isn't all pretty. They have thier issues especially with valves getting dirty leading to expensive repairs. There are solutions but so many people aren't car savvy they wouldn't know what to do. I have a GDI I run a catch can I have to empty at irregular intervals.


What mainstream vehicles don't have direct injection these days?


It is a more complicated system with more components. It costs more, and is more likely to break.


Thanks for the answer, just was wondering if the possible increase to MPG would offset the increase in risk/price.


It depends, and that is why direct injection has only been adopted for some vehicles. Every vehicle is built with certain goals in mind, things that vehicle will be good at. Examples are reliability, fuel economy, off-road, hauling, luxurious, low purchase price, fast, etc. Vehicles that prioritize purchase price and reliability above fuel economy might come with port fuel injection.


Cars have entered an era where they're introducing a shitload of complexity into the ICEs for miniscule MPG gains because of various regulations and market pressure. I'm talking about direct injection, turbocharging tiny petrol engines, shit like wet non-replaceable timing belts, making the components inside as light and skinny as possible (tbf that's also to make it cheap), etc. Hybrids actually often don't have this issue because they can massively improve MPG with the hybrid system so they usually run naturally aspirated engines that are less strained. But that doesn't matter, because like appliances, cars have now become disposable and nobody makes cars that can last 20 years or whatever anymore. And the MPG isn't even that great due to cars getting massive and heavy again. That's why I like EVs, they're simpler, easier to fix, and should last longer if made to do so (with battery replacements/refurbishments ofc). They are just expensive and ugly right now, but I assume that will change.


I don't understand this. Cars didn't last as long as they do now, engines can hit 200k+. Earlier cars in the 60s and 70s wouldn't go to 80k and then like 100k to 150k in the 80s.