71 Mav w/ 250. Started missing a bad beat and barely got me home. I say barely for the fact I drive 26 miles mostly redlight highways and interstate. Nothing like a flat friendly country road. First thing I did was check out the electrical. I swapped the cap and checked points - no luck. Then I pulled the plugs and found my #1 electrode was smashed flat. Could not even straighten it. I'm sure something caused this for she drove fine for weeks after I bought it. Although I feel 95% certain it's going to do it again, I'm going to replace the plug since it's relatively cheap and try to prove myself wrong. Engine, odometer, pedals, even the car appear to be on the front 100k at 74k +/- working towards my second oil change. First oil change was initial before running it not knowing the history. I think it was 72k when I got it, maybe put 2k on it myself at most. Going to inspect down in the hole best I can but any other ideas? Guess if it does it again, next thing is to pull the head and start checking everything out. We just went to 5 - 10's so probably be this weekend before I can get to it. Thought maybe someone that knows the 250 could give me better insight. I'm pretty knowledge of other engines but not in this I-6 family. Drove my last Mav with 200 I-6 for about 3 months with no issues before someone wanted it more than I did and I sold it last year.
Sounds like either something found its way into the cylinder like a broken valve or you have as rod bearing that has gone bad or the bolts on the rod cap came loose and piston smacked the spark plug in which case you should have heard the noise. Sounds like a visual inspection and a compression test is in order. Is the plug the correct one for the engine if it is a hot plug it would be longer in the electrode area. Let us know how it turns out
As mentioned probably a chunk of carbon, if it had any real defect something would have happened as soon as you started driving it... Of course this doesn't mean a chunk didn't fall out of the piston but if it isn't making a noise it'll probably be fine with a new plug...
It still runs, just has the plug miss. I like the carbon idea. Got a new 302 waiting but sure did like the idea of milking this 250. The compression test will be a must as well. Stay tuned...
Changed the plugs and it's all good??? Drove it to town and back, rechecked and still good to go. Have NO idea what happened to it. Going to start driving it to work this week.
Update: Drove 2 weeks and spark plug is fine. Checked compression last weekend and running 125-135 from front to back. Changed plugs 2 weeks ago and had oil foul on #4 but it still holds compression soooooo. Runnin it! And just going to clean #4 every couple of weeks or so if it starts missing. Yesterday coming home it started shimmying at the steering wheel that prompted a thorough check up. Had to put a big washer (under the existing washer) on the linkage body mount doo-hickey on passenger side to take up slack and was a fix. Only thing giving me crap is that the temp goes up slooooooowly as it sits. Put on an electric fan last weekend and went with a brand new 302 radiator (after having old one cleaned) and it holds the temp down longer. Up to about 20-30 minutes sitting on a 80-90 degree day and it starts to reach 210 then I would have to pull over. Not into sitting in a hot car anyways. LOL Haven't hit any jams that bad yet but I'm sure time it will eventually happen. Just glad I'm on the road!!!!
Assumin' it isn't 9/10 ready to spit a head gasket, 210* ain't nothin, once to goes past 230* start being concerned...
Thanks. I really had no idea what was the norm. It's on it's original 74k heading to 75k. Looking forward to dropping a 302 I have reserved into it but right now with the 250 purring, I just enjoy the thumbs up going down the interstate right now, compared to my F-100 that I've been driving that you see everywhere. I've only seen two other mav's in my neck of the woods. Where as there's an F-100 on every corner. I really need to take some pictures to share...
