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GSXDNA

15+ Year Contributor
256
14
Nov 19, 2007
Los Angeles, California
My profile is up to date, but for a summary:
  • 7-blade HX40, .70 a/r, T3
  • Brian Crower 272/272 cams (otherwise stock 1G head)
  • Stock valve springs
  • 2.0L 6-bolt bottom end w/ (newer) oem 2g pistons, 1g rods
  • Stock IM
Due to (accidentally) fixing an unknown boost leak, I recently did a pull with a bit more boost than I like to run (~36psi). It pulled very hard, but at the top of the pull, my knock light started flashing - which never happens. After the pull, it sounds like the car is running on 2 or 3 cylinders. Kind of sounds like a subaru wrx. There's a slight ticking/knocking sound, but it doesn't seem correlated to RPMs. For example, if I'm coasting along at 3-4k rpm under light load, it sounds about normal. But, as soon as I try applying some boost, it shakes/stutters, and can't even get out of it's own way.

Things I've checked:
  • Intake/Intercooler piping leaks
  • Spark plugs (one had completely black right with pure white tip - replaced that)
  • Plug gaps
  • Plug wires are all new(ish)
  • Turbo shaft still looks good and has no play
  • Reset the ecu (with the hopes I put it in some type of limp mode)
  • Rocker arms are all still in tact and look good

Any other ideas on what it could be?
 
Last edited:
Do a leakdown test. Concentrate on the single cylinder with the odd plug. Broken piston perhaps.
 
Sounds like a compression blown HG, just swapping compression back and forth between cyls 2 and 3
 
Sounds like a compression blown HG, just swapping compression back and forth between cyls 2 and 3

Interesting...

Sounds like that could be my best case scenario. I should find out today or tomorrow, hopefully. If it is the HG, and if it did blow from excessive compression, what's the best way to avoid that in the future?
 
Last edited:
Head surface finish, block finish.

What is your measured and calculated CR?

Look for "washer bite" in the head casting.
 
Out of curiosity, did you have the block and/or head milled the previous build? What HG did you use? What was your average boost range previous to the spike, and were you experiencing any cooling/overheating issues?
 
Thanks so much to everyone for all the help - the dsm community is one of the best benefits to owning one of these things.

Head surface finish, block finish.

What is your measured and calculated CR?

Look for "washer bite" in the head casting.


Are you referring to the compression ratio? If so, it's basically a stock 1g long block, so should be 7.8:1. Thanks for the heads up on the "washer bite."


Out of curiosity, did you have the block and/or head milled the previous build? What HG did you use? What was your average boost range previous to the spike, and were you experiencing any cooling/overheating issues?


It was so long ago, and my memory is terrible. I'm pretty sure the block was milled, and I used a Felpro HG. My average boost really stayed the same (I misrepresented that in my original post). I've basically been at around 30-33psi for years. What changed is a fixed leaky exhaust manifold. Even though the measured boost level didn't change, the car felt significantly faster after fixing the leak in the exhaust manifold. That's when the issue occurred.

Great question/thought on cooling/overheating issues. No overheating issues - when the car had coolant. About once a month (I only drive it maybe 1-2 times a week), I could put about 1/2 - 3/4 a gallon of coolant in. I wasn't sure if that was b/c I was running a higher distilled water / coolant ratio, or because the coolant was leaking somewhere. But, it kind of seemed like the coolant was just evaporating ever few weeks.
 
Ok so you have not taken the measurements and figured your true CR.

Not many do.
 
The coolant drinking issue seems kinda sketchy...I ran high amounts of water top coolant and never had to do that...maybe your headgasket was bad and the extra pressure just toasted it....
 
Got the head off today. The head itself cracked between cylinders 2&3. the HG must have gone bad in that area, then the metal eventually wore out from the heat. Have a new head, springs, valves, etc on the way. With any luck she'll be up and running end of next week.

Thanks again for all the help in diagnosing.
 
I'd get the block resurfaced as well. The same pressurized heated gasses that melted your head, torched the block in the same area. While the iron didn't melt away like the aluminum head, I doubt it's flat anymore.

Yeah, I was thinking about that. Unfortunately, this is actually a DD right now, and all the decent machine shops in the area are on 1-2 month waits. I really don't want the car to be in the shop another 2 months if at all possible.

Right up until the very second the head cracked, the engine felt very strong. So, even if the block is slightly worn there, it certainly didn't result in any noticeable compression loss. The thing that most concerns me is if the block is warped in that region it may cause the new gasket to fail prematurely, then in turn, risk cracking the head again.

Is there any reliable way to tell if the block needs resurfacing, or are the increments so small that the best way is to just resurface it?
 
Its best just to surface the block.

Take a new razor and scrape the area well and check with a straight edge.

Being that its a DD, run another composite HG.

BTW the old head can be saved too with a bit of grinding, some welding and a surface.
 
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