94miataM

Help, I'm a noob who recently bought a 94 monster w a 331 stroker. This was originally owned by GT420hp. With the weather in Chicago I haven't been able to drive it but I took it out for the first time this weekend for a short drive. When it first starts it doesn't like to idle and will stall but once I was driving it seemed to run fine. There was some strange noises that sounded like they were right under me. Sounded like something loose but it was only when moving and in gear (need to investigate more). When I got back i let it idle so I could look under and see if something was out of sorts. It idled great, then I realized there was smoke getting into the cabin and the cats were cherry read. I shut it off immediately and am fearing the worse. After seeing that color, I'm sure they are fried and plugged now. The previous owner said he was having blow by issues and low compression on one cylinder. Maybe oil got into exhaust? Was thinking a rebuild was in order but not sure if that would fix this issue?

SVTwins

Is this a carb or FI set-up? When cats get really hot its because youre running to rich and dumping fuel into the exhaust so the cat is trying to clean up even more gasses. If you have a carb, its pretty normal that it doesnt like cold starts(a lot of FI vehicles dont even like to idle well when cold). The carb could also be jetted improperly (did the car drastically change climates or elevation from the PO?) which could definately cause your cats to get hot. As for oil in the exhaust, that shouldn't cause a cat to get much hotter.

My suggestion, check your fueling and make sure you are aren't restricting intake airflow.

As for your noises under the car, possibly a bad universal joint. You can also listen to the transmission through the shifter with a screwdriver to see if any bearings are bad, the noise in this case would occur with clutch in and out. Having a friend drive the car while you listen is advised.

Keep us updated!

-Jordan

94miataM

Jordan-

Thanks man, it's a 95 5.0 FI. It was shipped to Chicago when it was in the teens from Arkansas so there would have been a major climate change.
The noise wasn't consistent and popped up when I was going about 25-30+. I'll check the joint since it was intermitten. The transmission was supposedly rebuilt but it ground a bit going into reverse. I'll see what I can find.

Thanks again.

SVTwins

One more thing: To check blowby quickly you can start the engine and remove the oil fill cap, put your hand on the hole, if it pushes your hand outward then you have blowby.

Basically the combustion pressure pushes past the rings into the crankcase and that pressure will push your hand outward. If your hand gets sucked inward thats good, its supposed to.

5.0MX5

94miata said; was supposedly rebuilt but it ground a bit going into reverse.

That's not that unusual, a lot of us (and Mustang drivers) when needing to hit reverse will go to 4th or 5th, then reverse. No grinding and it's much easier to engage.

On the engine problems, I'd do a compression test first thing. If one or possibly two cylinders (two indicates blown head gasket) have low compression I'd at a minimum pull that head and see what's up. My opinion is the engine had a quality build a few thousand miles ago, the big unknown is what's it been exposed to since then.

Good Luck
Ron