2000 XJR with 92k miles

Issue #1
A few weeks ago my car began having a slightly lumpy idle upon start-up. It immediately smoothed out as soon as I drove away. The lumpy idle became more noticeable with each passing week, but still smoothed out as soon as I drove away. The lumpiness was worse the longer it sat (i.e., overnight vs. going to convenience store). No codes or CEL. Last Saturday my neighbor was behind me when I started it up and he noticed a puff of black smoke. Later that day the CEL comes on. I read the codes and got P0306 and P1314. After some research it appeared the #6 cylinder (driver's side (US), second from the front) was misfiring. I opened it up and swapped the coil pack between #6 and #7 to see if that would clear things up. No luck. I figured I probably had an injector at #6 that was stuck open. The next day I took the car in to have the fuel system cleaned to see if that would help. No, it didn't. After the cleaning the car idled terribly and gave me P300, P304, P305, P306, and P1316. I replaced all of the spark plugs yesterday and it has smoothed back out. Still feels slightly lumpy at start-up. Probably an open injector on #6. 3 of the plugs looked fine, 2 looked pretty rough, and 1 had deposits completely across the spark plug gap. After clearing, no new codes.

Issue #2
Over the past few months I would check my coolant level regularly and find that I had to add a bit week to week. I could sometimes smell coolant, but couldn't find any leaks when hunting around with my flashlight and the engine running. Last week I noticed coolant on the garage floor and eventually traced it to a leaking water pump. I replaced the pump last Friday and topped the system up. While driving Saturday I get a "low coolant" warning. I topped it up, figuring air in the system. Same message the next day after driving 10-15 miles. Topped it up and jiggled the coolant level sensor in the header tank. I also notice that the expansion tank is filling with coolant. I had not seen that before, nor can I find any leaks with the engine running or off. I am now getting the "low coolant " warning every day, within 5-10 miles of leaving home. I have test kit to determine if there are exhaust gasses in the coolant. After testing yesterday, it appears that I do. To help confirm this, I tested the compression of each cylinder, which leads me to...

Issue #3
I typically add .5-1 quart of oil every 1k miles. The results of the compression test were (I am referring to the cylinders as #1-4 on passenger side (US) with #1 at the front, and #5-8 on the driver (US) side with #5 at the front):

#1 - 110
#2 - 70
#3 - 108
#4 - 108
#5 - 85
#6 - 103
#7 - 95
#8 - 106

Measurements were with all plugs out, fuel pump/injection relays removed, wide open throttle. I added a bit of oil to #2, 5, and 7, and retested the compression with the following results:

#2 - 137
#5 - 130
#7 - 138

Conclusion
It would appear that I have the following:
1. Blown head gasket
2. Rings for 3 cylinders are shot
3. An injector for #6 is possibly stuck open

The floor is now open for suggestions, ideas, etc. "Let the games begin!"

 

1- definitely
2- not likely- am thinking that the gasket issue is contributing here
3- also not likely, but possible

Leakdown test,followed by head gasket replacement should get you back on the road.