RTEC / 3000GT Engine problems due to overboost

Here you'll find the information about the problems (and headaches) I had (have) with the engine :( The rebuild was done and since then a new dyno session showed that the engine is back to good again. Please follow this section and do not ignore my warnings !

After getting the Blitz DSBC I started with testing the thing out and was amazed about its features as well as the power my car made at more than 1.34bars !! I then runned in some fuel cuts as well as hesitation problems until I decided to set the max boost to about 1.2bars where the car runned great. This was purely ignorance of me as I expected that the things are going well and the engine has a lot over stock potential. Before I went to the first dyno session, I runned the car several times on the german autobahn with high boost settings over 1.2bars and when shifting up to fifth I noticed a white steam coming out the right side front of the hood (at the popup light). Also on the dyno the steam was very visible as it came out of the HKS BOV (blow off valve) during shifting.

The output of the BOV was then very oily and the steam was a typically oil-steam blown out of the valve. The dyno guy told me that a small amount of oil in the IC and intake piping is normal but this could be too much. This was the first sign of something going really bad.

I always listen to any knock sound but haven't heard anything during the test period. Even on the dyno I was not able to hear anything. We then used the old poor mans technique and put a garden hose close to the knock sensor under the intake manifold. The other end was put into a sealed headphone with a hole for the hose. With this the dyno guy was able to hear the "high speed knock" appearing around 5600rpm. We held the car under fully load at 5600 and I increased the boost Ratio of the Blitz until knock was heard. Finally this lead us to the knock starting at 1.05bars ! Now my face turned white and I remembered how many times I ran boost up to 1.25bars / 18psi (gulp).

Finally I set the boost limit to 1.05bars with a short overboost to 1.1bars what sounded healthy. Also I was happy to see 397hp (DIN) at this level. This lead me to the conclusion that the car is running pretty well and is very healthy .... I was wrong !

After driving a lot with the car I noticed that the oil steam became noticeable even under somewhat low boost. Definitely a sign that something was going wrong. I then took the y-pipe off and this is what I found :

	This is the front view of the y-pipe after taking the IC pipes off. No, this amount of oil in the intake path is not a sign for good things. Immediately, the thoughts went to bad bearings or seals in the turbos. But I never did bad things to them and also I never heard any grinding sound from them.
	This is the y-pipe where it connects to the throttle body. Again, too much oil where it not belongs to ! Now, this describes the oil-steam coming out the BOV and I just can imagine how all the vacuum lines look like :((
	Also the TB showed some signs of oil. But it flew into every gap and opening ! People who know how the TB is built know what the oil can cause : Yes, the idle stepper motor below the TB got totally clogged by the oil ! Fortunately the mechanic was able to clean it and it looks better than new now. This really saved up some money :)

Point one could not be investigated without taking the turbos off. The second point was checked during the 60k service and everything was fine. During driving the car the weeks before, I noticed the oil-lamp coming on. But I always checked the oil and never had a lower level than normal. Also the oil-pressure was ok. Even Mitsubishi was not able to explain the oil-light is coming on, especially under very high load.

I never had this problem before (others say that their oil-cap is leaking frequently). Once I wanted to check the level I found a lot oil spilled allover the front row. But then within hundreds of miles nothing happened. Finally I felt that power became something less than before and I decided to go to the dyno again to see what's going on.

On the dyno we plugged a oil-temp sensor into the dip stick tube. A the first time measuring the drivetrain loss everything felt good. But then the first run and high load caused this sensor to pop out like crazy as well a the oil cap leaked heavily. This then where the clear sign for my problem : The pressure in the crankcase was too high and caused the oil to be pressed into everything, especially through the crankcase ventilation back into the intake. Also I saw a loss in power of about 50hp and over 100Nm tourque !

Please note: This is DIN70020 corrected hp. To get SAE corrected hp add about 2-3%

On the dyno sheet the red engine power curve indicated that at around 4700rpm the problem started and the timing got retarded. This was with only 1.02bars.... and a bad engine. After 5500 the power then came back slowly. BTW, the lower green line shows the drivetrain loss. To get the engine curve (red), the wheel hp (blue) curve will be added to the loss (green). Interestingly the drivetrain loss was about 30kW bigger than on the other dyno ... dyno is not equal dyno !

For me, only one reason could cause this high pressure : broken pistons or at least bad rings.

An easy compression test on the front cylinders showed 120,112,105psi (dry) and 145,155,130psi (leak down). The leak down test is done by putting a small amount of engine oil into the cylinder and then do the check again. If no or only a little increase could be found, the valves are leaking. The front ones showed that the valvetrain seemed to be ok. The rear ones showed 115,71,130psi (dry) and 155,92,145psi (leak down)

Well, #4 showed really bad numbers that definitely indicated a piston problem. The Mitsu dealer made the compression test by applying some pressure to the cylinders and found out that the air is blown out through the front valvetrain. The mechanic then attached a special tool to the injector lines and inserted some cleaner fluid (smelled horrible). After this I runned the car for a few days and then we did the compression test again. The figures on the front ones then became better and the mechanic was not able to hear any leaking from the valves anymore. But #4 was still bad. They then used a special tool, like a stethoscope, and looked into the cylinder. They were able to inspect the cylinder walls and haven't found any signs. Also from the top, the piston looked good. We finally decided to take the head of the rear bank off and found a 100% perfect head and valvetrain. Therefore we had to take the block apart. Fortunately, Mitsubishi found a way to do all the work with the engine in the car by removing the transaxle and oil pan.

As the block came off, some parts just fell down almost any lower ring was broken and on #4 a big part of the landring fell off.

Here you can see the broken landring of piston #4. Interestingly, on the other 2 pistons of the rear bank (left), the lower rings where broken into 3 to 4 pieces but not on this one. For sure this piston will release some pressure into the crankcase !

As the mechanic took off the oil pan, some strange parts appeared and he then thought that these are parts from the rear #4 piston fell down. But they came off from other pistons :

We aren't 100% sure but I think the pistons are #1 & #3. You can easily see where they are broken, both on the same outer side of the cylinder. The braking sign points to a really heavy knock they have gone through. The parts didn't looked like old or that they where under heavy stress for a long time. Comment of the mechanic : "This must have been a real big bang !" My comment : I swear, I've never put Nitro or TNT into the tank.

I just forgot to mention that only the #5 had intact rings. On the other pistons at least one ring was broken.

I was on holidays when I got the call on my cell phone that the pistons are broken and I decided pretty quick to get new ones. Especially as they gave me them for $86 per piston, balanced and reworked. This is a very decent price and I decided to go this way. Also Mitsu will not give me 1 year warranty on their rebuild if the pistons are not original. I thought about forged pistons and I got a quote on around $900 (add shipping and taxes) for a set. Luckily, the cylinder walls were absolutely undamaged as well as other parts. Even the mechanic said that the walls are looking like a car with 20k miles and not over 70k it has now. Therefore the job was pretty simple, especially as the heads where absolutely plain and in perfect condition.

This is the engine with the left head already mounted and the right row of new pistons. I will present some more close-ups soon. Also note the rusty part in the middle between the banks. This is the knock sensor with its plate. I definitely will replace this rusty part too, but Mitsu said that it only comes with the knock sensor and is pretty expensive. I just hope that this does not harm the sensitivity of the sensor !

I hoped that we don't have to rebuild the engine but fact is fact. The good in the bad is that I will not have the trouble of adding the performance parts lying on the floor (or I'm still waiting for). The new headers and turbos that usually cause the biggest headache for an aftermarket install will go in for free as it makes no difference for the mechanic to put them on instead the stock parts :) Also there is now plenty of space to work on the car.

Furthermore, I'll be able to check the work very often and also will take pictures whenever possible. The whole rebuild/upgrade was quoted for about $2600 and now with some more parts (I wanted to have all pistons made at once) it will be around $2850 but not more. This is not that bad at all but still an unplanned rebuild.

The signs show that the rings where gone due to too much boost causing lean conditions as the fuel sdystem was not able to deliver the porper amount ! The broken pistons are caused by an extremely heavy knock situtation. I still think that the early test-situations with the many fuel-cuts I runned in did not a good thing to the car ! Also the long high-speed runs on the German Autobahn with high boosts over 1.15bars where responsible for the problems too.

Finally I'd like to tell everybody to listen to your car and watch the signs. For the future I'll do this with :

Last but not least, don't run more than 14-15psi with stock parts and any Boost Controller (manual or electronic). Don't overboost too much for a long time as this could slap your pistons. Also a good knock sensor monitor would help a lot but there are not many around if any !

I hope the information on the page helps you to avoid the situation I runned in. I must admit that I learned very much now. Especially how to throw out my money out of the window.