V6 interchangeability
 

I will be starting to work on a '95 Cutlass Ciera, which in all likelihood will either need a replacement engine or a rebuild of it's existing one. I have not opened up the engine yet to determine the exact problem- the previous owner thinks it has a rod or piston problem. However, cars like this show up pretty regularly in our local classifieds, and it is not uncommon to find good running cars with not so great bodies for a couple hundred bucks. What usually ends up happening is that the potential parts vehicle has a different engine than the one I am working on. What I am wondering is, which (if any) of the GM V6's are interchangeable with the 3.1L? I have heard that the 3.3's and 2.8's are essentially the same engine. Knowing this would allow me to pounce on a good deal on an engine if one came along.

Well, I discovered why it pays to investigate before I speak! As it turns out, I may be lucky. When I got the car, the spark plugs had been removed and were laying on top of the engine, presumably from a compression test. The plugs and wires were in terrible shape, and the engine was low on oil. Just for grins, I got some other plugs and wires and put them in, and topped off the oil, and lo and behold- the thing started.:D However, it is not running smoothly. It does not knock or tick in the least, it does not smoke at idle, and it smokes a dark color (definitely not blue smoke) at higher rpm's. It runs smooth at higher rpm's, but varies at idle. Sometimes it will idle roughly at normal speed, then it will drop down so low that it barely continues to run (or quits), or rev itself up a bit like it is hunting for the right speed or fuel mix. My dad stopped by and said that he thought it was running rich. There is no service engine light on when it is running, and I was not able to do anything with the old paper-clip-in-the-ECM-port trick (does that still work in '95?). I also tried hooking a vacuum pump to what I think is the MAP sensor and varying the vacuum but no change. Also tried disconnecting the battery for a few minutes in case I bothered the computer but that didn't help either. Any ideas what I should try next? I am kind of excited at the possibility of not having to pull the engine after all!

I would clean the MAF sensor with MAF cleaner, then clean the throttle body out, and make sure the idle air passage is clean.
After that, search for a vacuum leak.
Sounds like things aren't as bad as you thought at the beginning, that's always good!

I did as you suggested (except the MAF sensor- I take it that is a specific type of cleaner?), also cleaned out the PCV valve and what I think is called the air motor. The car now tends to idle more smoothly- though not perfectly. A friend helped me do what I call a "load test", by putting the car in gear and running the engine up a bit. On some cars I've worked on, it made other symptoms come to light. In this case, I got a blast of smoke in the face that came from the area of what I think is the EGR valve (I can't believe how much I've forgotten since I left the mechanic shop). For some reason, this suggests to me a plugged catalytic converter. I'm still blowing a lot of smoke in general- not white like water in the cylinders or blue like burning oil. But it doesn't burn the eyes like unburned fuel either. Still a puzzle!

Yes, MAF cleaner is special. It comes in a spray can like brake parts cleaner, and can be found at most auto parts stores.
You may have a bad/plugged egr valve.
A plugged cat will result in increasingly rough running as rpm increases, and the cat will be very hot after a few miles, maybe even glowing. You can remove the upstream O2 sensor and see if the symptoms go away. If they do, you might have a plugged cat, since the exhaust can now escape from the o2 sensor hole. I wouldn't drive with it out for more than a mile though.

I removed the EGR today and saw that it was pretty oily inside. I didn't have a replacement or the means to test it at the moment, so I just put it back. I looked inside the throttle body again today and saw oil in it again. When I opened the butterfly, more oil ran out. I cleaned it out again and started trying to find the source of the oil. As best as I can tell, the only way oil could be getting in there is through the PCV valve. I started the car with the PCV out and did not observe any oil coming out of the hole, even when I revved it up. There was some air blowing out of the hole though, I don't know if that is normal. I suppose I should bite the bullet and do a compression test before I go too much further, but I still don't think it is acting like it has burnt rings.

Some air is okay, a lot means you might have a broken/stuck ring. Compression test is next, I think.

Sounds like blow by need to do compression test.

your avatar in another diminution?