Seems like a decent bunch of blokes here. It not common to get this many replies in an introduction thread
4 fatal letters that when combined together spell 'pay day' for mechanics & auto electricians. Please share your stories, I owned one for 6 bankrupting years. 
The was a 2006 (maybe2005) wrangler, 60 000km old, check engine light was on and wouldn't rev past 3000rpm, the ECU was limiting the engine due to the fault code that was logged.
The code was a CKP-CMP correlation error code. (CKP CranK Position sensor, CMP CaM Postion sensor)
Being so few KM it was a strange code to get, Live data from the ECU the CKP/CMP out by 11.5 degrees.
The code can be set be either the correlation being wrong OR a corrupt signal from either sensor.
I scoped both sensors and the signal from each senor looked good, So that rules out a corrupt signal.
Checked for timing chain stretch and found none. What I did find was spanner marks on the CMP retaining bolt.
Called the owner back and asked a few leading questions, the info I got back was the cam had been replaced and the light had been on ever since. (why he didn't tell me this at the start I don't know)
We correctly installed the CMP and got the correlation back to 0.5 degrees. Checking the actual cam timing would mean tearing into the engine, As the engine made plenty of power and had no other running or starting issues we decided the cost of tearing it down wasn't going to be good value for money.
Like I said man made problem.
The other stuff wrong with this jeep was a jeep made problem. A 60 000km old 4x4 that has never been off road should not need every suspension bush replaced due to cracking/tearing of the original stuff.
