The Gdi Engine -
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post #1 of 6 (permalink) Old 07-17-2010, 05:14 PM Thread Starter
Join Date: May 2010
Posts: 30
I am the happy owner of a Mitsubishi Carisma 1.8 GDI LX from 1999.

During my ownership I have been acquainted with the GDI engine, and it's few, but fatal flaws.

I was able to get my engine running smooth, with high mileage, and no ticking/tappets from the valves.

When I first got my car, it was running odd. Pretty stable idle, but many judders, shakes, and just NOT smooth. The mileage was poor, and it didn't pass emission test.

The cause of these problems I wound, was carbon deposits in the inlet, and on the valves. My first view down the throttlebody:

I've read my valves looked quite like this (called an elephantfoot):

I have gone through the procedure of cleaning the crap off the inlet and valves, and got interested in why It was even there in the first place.

I can explain the cleaning process if anyone likes, but for now, I'll explain what is the cause of the problem, and how to correct the design flaw.

There are two systems on the engine, that are the combined cause:
PCV System:
On the inlet manifold, there are connected two pipes from the valve covers. It dumps blowby pressure, to the inlet... if it weren't there, the pressure would build up in the valvecover,
and oil system, and push out oil of all the seals. It's on all cars. The problem with that, is that it leaves oil fumes through the pipes, which seat in the inlet like a tiny film of stickyness.

EGR System:
To decrease NOx emissions, a small amount of exhaust gas is recirculated through the inlet. That keeps the burn temperature and NOx emissions down. The problem with that, is,
that small unburned particles enter the inlet through this system, and it really like to settle in the oil film the PCV system is responsible for.

In short, the PCV system deposits oil to the inlet and EGR deposits carbon in that oil. Oil, carbon, oil, carbon, oil, carbon.... through the years, that's allot of gunk.

It's actually a problem on most cars... the problem was just solved by accident. In normal MPI car's the injectors are seated in the inletmanifold,
spraying it with disolving/cleaning gasoline... keeping it neat and clean longer, and because the injectors in a GDI is seated directly in the combustion chamber,
it doesn't clean the valves and inlet.

Get the gunk cleaned out.
Put universal gasolinefilters on the pipes on the PCV system. There are two. I can provide images... That'll catch the oil.. and then the EGR cant deposit crap.
On the -1999 cars... not the facelifted ones, you can remove the seal from the EGR valve, and put in one that pugs the hole completely... the computer won't find out...
it's a different case with the facelifted version though. And it'll pollute more, so I would suggest the first solution.
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post #2 of 6 (permalink) Old 07-18-2010, 06:05 PM
Join Date: Jul 2010
Posts: 31
Yeah, good info right there. Btw here`s some info on how to clean out a clogged EGR :

Simple 10 min job. Clean it out with brake cleaner or diesel. And a toothbrush!

This is how it looks like on a 90s Mitsu engine

It`s placed beneath the throttle body. In general on the intake manifold.

As stated, full of carbon deposit..


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post #3 of 6 (permalink) Old 07-22-2010, 06:26 AM
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Good info, please post the valve cleaning procedure.
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post #4 of 6 (permalink) Old 07-31-2010, 11:31 AM Thread Starter
Join Date: May 2010
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Don't have time to write a thorough guide.
You need a new gasket for the throttlebody, and you need some stuff to clean off soot.

I tried to burn it off, but that wasn't very effective. Most effective was some BellAdd PartikelFilter Rens. It foams up, and removes soot. It was hugely expensive though.
I'm told brake-disc cleaner, and carburettor cleaner also works very good. Don't know what you are able to get in your respective Countries.

The cheapest way to get the soot of the intake, I'd say is gasoline bath for a night. And 120 bar high-pressure water cleaner, but you can't use that down the cylinderhead.

I chose to go for the open intake valves, so I could get the valve ports, and the entire valve cleaned, but that meant getting the cleaning agent down in the cylinder. I'm not sure it's a good thing to do, but my car have run absolutely brilliantly for 8.000 km now, without any odd noises, and as told. The tappets are gone.

Be sure to plug off the holes for the sparkplugs. And remember to clean up the crap you get down the cylinder head.

I had to have someone pull me up to speed. It couldn't start, but once it got going it was running perfect, except for the fuel filter had to be changed also.

Feel free to ask questions.
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post #5 of 6 (permalink) Old 08-03-2010, 03:14 AM
Join Date: May 2010
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Martin, many thanks for a most interesting post. Perhaps I will try the same on my Carisma. How long did the work take?

And excuse my ignorance, but what does PCV stand for?
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post #6 of 6 (permalink) Old 08-03-2010, 03:37 AM Thread Starter
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<div class='quotetop'>QUOTE (Charles Liddell @ Aug 3 2010, 09:14 AM) <{POST_SNAPBACK}></div>
Martin, many thanks for a most interesting post. Perhaps I will try the same on my Carisma. How long did the work take?

And excuse my ignorance, but what does PCV stand for?[/b]
10-12 Hours for me the first time. Saturday and Sunday.
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