Back in the summer, I blew a coil pack on the #8 cylinder on my 01 cobra which shattered the spark plug. Part of the ceramic portion of the spark plug chipped and fell into the cylinder. Took it into ford and they indicated that the cylinder wall appeared to be damaged...and they voided my warrenty due to "modifications" (that's another story I won't touch right now). Since I didn't have the funds to tear down the engine at the time, I replaced the coil pack, vaccumed out the cylinder and replaced all the spark plugs. I've been driving it since that time and of course it's been burning oil. Usually a light grey smoke starting off in 1st and 2nd gear, and lots of smoke at WOT. I'm getting ready to rebuild, but decided to do a compression test first, and here are the results: 1 - 210 lbs per sq in 2 - 209 3 - 210 4 - 201 5 - 195 6 - 192 7 - 205 8 - 190 I was told that a 10% variance is acceptable, so I'm right on the line, which doesn't add up. I was expecting to see #8 a lot lower. I put a few squirts of oil in #8, ran the test again, and it did jump slightly to 201. So I'm looking for some input from anyone with experience in this area. I was preparing myself for a rebuild as I was sure the piston ring was shoot, but now I'm not sue what to think...is it possible the problem is with the valves instead?
When running a compression test on my car the results varied from 190-215. Anything in that range is considered normal. I puff a little oil after letting it run for a while and shutting it down. Starting it up belches out a little blue smoke (oil). I believe some oil is dripping past the valve seals. Not too concerned. I burn about a quart of oil every 3000 miles. The only reason i can think of for causing the above symptoms is going lean on nitrous while dynoing. I'm gonna put a NOVI on it now, so we'll see what happens. Matt
RE: your compression test #'s Those look pretty healthy overall, but I would keep a close eye on the oil level from now on in order to prevent any problems from ocurring in the future. If you are burning a quart every 3K miles like isdnmatt is, it's not a *major* problem IMHO. For example, my snake will roughly consume 3/4 of a quart of oil every 3K miles and I can attribute that to the way I drive the car & the PCV system (I've noticed a handful of other 99/01 owners having this problem). I would monitor the situation for awhile before you choose to go through the rebuild process, then make your decision. Hope this helped...
if i was u i would do a leak down test. this would give more information as to what could be causing the problem, valves or rings(cylinder wall scratches in your case maybe). Make sure you are doing all these tests with the engine warmed up.
I'm burning about a quart every 1000 miles, and the amount of smoke on WOT is rediculous...I'm talking about enough smoke that the drivers behind me have to close their eyes, drive throught the cloud and pray nothing is on the other side. I think I will try the leak down test as suggested. I'm also going to check out some of the race shops in the area and see if they have a cylinder scope that I can use to inspect the cylinder wall condition. Also, I may try running with the diablo chip off for a while to see if I notice a difference in oil consumption.
