1996 Monte Carlo seems to be missing

Hello and thank you for the amazing web page. I never looked for anything like this until I had a problem, but now that I know it's hear, I'll certainly be checking in.

Okay, here's my problem. My Monte Carlo is 255,000 miles young, and other than an alternator at about 50,000, and a new upper ball joint last week, the car has NEVER given me any mechanical problems. I just change the oil with Valvoline max-life and a K&N oil filter, and a bottle of Restore every 2,800 miles, and it just keeps on running strong. It’s got the Goodwrench 3.1L v-6, and a 4speed auto tranny with lock-out.

Well, a good part of the way through this winter, while going 75 on the freeway, twice in one trip the engine seemed to “miss”. That is, it felt like one of the plugs fired before the piston had reached the apex of its circular motion, since it really jarred the car. I let off the gas and popped it in neutral thinking something bad had just happened. It returned to it’s idle at about 900 rpm, and after revving it a couple times up to about 3,500 rpm and having it act fine, I put it back into OverDrive, and kept driving. Then it happened again about 10 minutes later.

But that was it- until about two months ago. The “missing” came back with a vengeance. At first when it happened, I would put it in neutral and rev it up a few times, then keep going. Probably just coincidence, but it seemed to help. It would do it a couple time a day at that point. No biggie.

Well it gradually got worse, and now I’m to the point where it occurs solidly regardless of how far I’m driving. It does seem to act better if I’m on the highway doing a solid 62mph, but the minute you have to kick it down to go up a hill, or stop for a stop sign, BOOM BO-BOOM. It starts again.

The “misses” do not feel as harsh if I drive in “Drive”, which runs my engine at almost exactly 3,000rpm at 60mph. I have always driven in OverDrive though, which takes the rpm’s to 2,000 at 60mph- giving me a remarkable 31 miles per gallon- even at 255,000 miles. Running in Drive is really tearing down my gas mileage, but more importantly, I’m worried that I’m going to blow a head gasket or snap a rod or crankshaft if I don’t do something about this.

Here’s some relevant information:

-I just put new spark plugs in it 4 nights ago, hoping that would fix it.
-I put new wires on a year and a half ago. Was going to do the plugs then but I couldn’t even see the back 3.
-The last “tune up” was at 158,000 miles.
-My K&N Air filter is spotless and moist.
-The “Service Engine Soon” light is on (and has been on since about 200,000 miles), and when I had AutoZone check it out, the car said that it’s “Crank Shaft Position Sensor” and its “Cam Shaft Position Sensor” were both bad. That was tonight.

I’m not afraid to work on the car myself. I hope it IS something that I can do, because we really can’t afford to take it in right now. I’m a computer technician by trade, but I’ve wrenched on cars longer than I’ve replaced RAM modules and motherboards.

THANK YOU FOR YOUR HELP!


Pat