The problems with GDI

From my research:

  • Clearly some GDI engines are worse than others
  • Driving type must make some difference, because with the same car some have problems and others don't.
  • PM definately matters. If I ever own one I will just gear up for the walnut shell clean.
  • Catch can may help but doesn't get everything and you still have valve overlap pushing combustion byproducts into the back sides
  • DI + MPI seems to be the utopia for both mileage and power, so here's hoping it fixes the carbon problem also and more companies go that way.
 
SC Maintenance said:
From my research:

  • Clearly some GDI engines are worse than others
  • Driving type must make some difference, because with the same car some have problems and others don't.
  • PM definately matters. If I ever own one I will just gear up for the walnut shell clean.
  • Catch can may help but doesn't get everything and you still have valve overlap pushing combustion byproducts into the back sides
  • DI + MPI seems to be the utopia for both mileage and power, so here's hoping it fixes the carbon problem also and more companies go that way.
Click to expand...
Didnt Toyotas in some models add a fuel injector above the valves, to wash the valves?
 
burbguy82 said:
Didnt Toyotas in some models add a fuel injector above the valves, to wash the valves?
Click to expand...
Yes, thats the MPI + GDI. Its not just for that however. MPI is more efficient at idle and low RPM. It also allows them to size the GDI injectors better for load. I have a Toyota Dynamic Force 2.5l Rav4, and the gas mileage for a vehicle its size is very good IMHO - 29 overall mixed use city and highway, 35 ish on highway if I keep it under 75 - my calculations, not a computer.
 
nascarnation said:
My 2004 GM 3.6 had 260hp and averaged about 18 mpg. My 2023 with DI has 310hp and averages 23 mpg. I realize there have been other improvements but the DI along with added compression it allows is the big one.
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It is interesting that the Civic has gone back to port injection for the 2.0l and it has higher compression than their 1.5T, and the same combined mileage ratings.... The turbo has more torque and hp, but if you don't care, then the more complex engine has really done nothing for you?
 
The long oci people are going to have a hard time with this info. I remember when 10k oci's were fought tooth and nail on here. Now you are wasting oil if changing before 10k+. Is the pendulum swing the other way again??
 
buster said:
“You’re not seeing this carbon buildup on race engines as much because they’re essentially wide open all the time,” Dickmeyer says. “The port velocity through the engine through the intake port and through the exhaust port is so fast that a lot of this stuff just doesn’t have the time to occur. It’s really the worst on a production vehicle where it sees a lot of throttle and idle time.”

Hmm so driving it harder helps?



"These valves are running hot, so when oil droplets come through the intake port and pass through the cylinder head they’ll stick to the backside of the intake valve. That starts to build up layers and it’s not just a layer of ash or goo, it almost turns into something like a lava rock and it will be surrounded with a greasy slime, which makes it worse and traps dirt.”

These droplets of oil and small amounts of dust and dirt make their way through the intake ports, which are coated with sticky oil and creates a plaque layer that builds up thicker and thicker and thicker."

GM 3.6 V6 with 42k

View attachment 214479
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nice observation, while we didn't "race" ours, it did get lots of long highway runs with M1 or RL and well as Fuel System Cleanings, Throttle Body/Valve Spray and some oil flushes. When GDI first came out,the public just like a cvt wasn't aware of the additional maintenance needed; they only saw the better mpg but didn't realize that came at a price. Any car will run well if it's driven mostly highway miles, not all cars run well just driven to the liquor store and church. I think that motto "blowing the crud out" was the motto of people conscious of what happens to a.car that doesnt get out much.
 
IndyIan said:
It is interesting that the Civic has gone back to port injection for the 2.0l and it has higher compression than their 1.5T, and the same combined mileage ratings.... The turbo has more torque and hp, but if you don't care, then the more complex engine has really done nothing for you?
Click to expand...
Lower trim only correct - and much less horsepower or torque. I am not complaining - that is what I would buy - but I think that is your answer. People seem to want to drive like Mario Andretti and get 40mpg doing it.
 
demarpaint said:
As you mentioned there were other improvements along the way. My bet is the numbers might be a little closer with those improvements minus the DI. The 3.6L Pentastar makes HP 305 HP in the RAM 1500 w/o DI. My bet is similar HP and mpg for your 2023 example.
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Excellent point! I own a 2008 Cadillac CTS 3.6DI that I have owed since new. I also own TWO vehicle with the 3.6L Pentastar (JGC and Gladiator) and I 100% get better mileage and power from the Pentastart vs the Cadillac - all I get with the Cadillac is more maintenance to minimize the carbon and it gets nasty. The Jeeps - nothing extra needed and more power. There is just no benefit to DI that cannot be obtained with PFI with less hassles. Long live PFI!
 
Revving2Redline said:
nice observation, while we didn't "race" ours, it did get lots of long highway runs with M1 or RL and well as Fuel System Cleanings, Throttle Body/Valve Spray and some oil flushes. When GDI first came out,the public just like a cvt wasn't aware of the additional maintenance needed; they only saw the better mpg but didn't realize that came at a price. Any car will run well if it's driven mostly highway miles, not all cars run well just driven to the liquor store and church. I think that motto "blowing the crud out" was the motto of people conscious of what happens to a.car that doesnt get out much.
Click to expand...
Interestingly Engineering Explained did a segment on the Italian tune up for GDI. The test was whether this "tune-up" would get the intake valves hot enough to burn off the crud. Apparently it was an utter failure. Shame because when I had my BMW diesel I thought this tune-up would keep intake deposits at bay (335d's were sooting up horribly) and boy was I wrong.
 
‘12 GM 3.6 DI

1713288027334.jpeg


Don’t know what the intake valves looked liked but never cleaned them and things other than engine (trans, suspension, etc) made us get rid of it. 🤷‍♂️
 
I'm intrigued by the Valvoline claim that the Restore & Protect will help clean intake valves.

Do intake valves get hot? I'm assuming they do hence the carbon coking. If not I'm not sure the chemistry would work.
 
VW even recommends an "Italian" tune up (15 to 20 minutes) at 3000 RPM (have to use a gear or 2 lower than the highest) to burn away deposits.
 
240k on mine, 10k OCIs, no catch can, and I don't run top-tier fuel. Weird how I don't have any of the problems that anti-DI proponents constantly crow about. Weird. Idle is dead solid stable, oil analysis comes back great at 10k, doesn't burn oil, 31mpg on long interstate trips. It even has a horrible, terrible turbo to make things even worse.

I guess I must be the exception to the rule. According to the Youtube experts, my engine should be so full of carbon right now that it shouldn't even be able to physically turn over, let alone run.
 
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