Subject: 91 Talon with Mitsubishi 2.4L w/16vOHcam
Question: Engine just started making a loud clacking sound. Believe it is under the valve cover and not deep in the engine but not sure. Also started to bog down on acceleration at the same time. Does run, but clacks really loud.
Any advice on what it is and how to fix it? Would appreciate the help.
Don't have the funds to take it somewhere and can do most minor repairs myself. Engine overhaul I can't. Hope its just the lifters or something.
Car is a 5speed with 110m miles. No major problems till now
Answer: Rich, That's pretty unique set up if you actually have a 2.4L engine in a '91 Eclipse. The only Eclipses I know of that you could get stock with a 2.4L engine were the convertible models that didn't evens started to come out until '96.

But regardless, the clacking noise your most likely hearing are your lifters (Mitsu refers to them as hydralic lash adjusters). The lifters they put in the Eclipse from '89-'99 had very small oil passages in them.
With small passages, the oil would be restricted and it is common to hear your valves clacking. Some people have resolved this by using a thicker engine oil (10W-30 in warmer climates) and swtiching to a full synthetic oil (Mobil 1 is a good commercially available oil). For other folks, the clacking has become such a bother that they install all new lifters in the head (16 valves means there is 16 lifters). Depending on where you buy them and if you put them in yourself, that can be expensive.

But rest assured that if the clacking is just noise lifters, nothing bad will happen to your engine. Now some models of Eclipse come with knock sensors. If the clacking gets bad enough, that noise will trip the knock sensor into thinking there is a problem inside the block of the engine.
In that case, the knock sensor would retard the timing, and your acceleration would drop.

I'd recommend a full synthetic oil change next time you change you oil, and get a full tank of high octane fuel. See if that helps.
Good luck!