Expert: Skip Bollinger - 4/7/2007

Question
A friend of mine has a 1984 gmc jimmy with a 4 cyl engine.
she said it was getting hot ( not near redline she swears ) but she went to a gas station took the cap off ( I told her never do this again on a hot engine! ) and added water as it seemed low, and she did this while it was running.

anyway shortly afterward it died and hasnt started since.
i have checked the spark on all cylinders.. nice and bright, checked the timing and its dead on tdc,used a tester and checked the computer for error codes.. all ok,also this is a throttle body injection system and it is working fine, but tried starting fluid and pouring gas in just to be sure.. nothing, just cranks and cranks but doesn't even attempt to start.. by now your probably thinking compression, and i did too, and tested it on all cylinders with and without plugs in the others and get an even 55 psi on each cyl. this seems a little low to me but i cant find the specifications anywhere to what it should be, also cant see how it could have blown the head gasket or cracked the head to where every single cylinder loses the same amount of compression. ( also no water in the oil or vice/versa) all spark plugs look good with no signs of oil fouling or heat damage.
I am stumped.. this young lady needs her vehicle very badly ( she was about to lose her job without it so i loaned her my car and am now driving my project car, a big block 1966 galaxie which gets 6 mpg but i cant keep doing this for long) she doesnt have enough money to take it to a shop, and im willing to work on it but dont know what else to do.. any help would be greatly appreciated.

oh and a happy easter!

Answer
David,
  A few things I need to say. First, I'm a Parts Professional, NOT a tech but I will continue with some thoughts that may help you.
  I looked in A/C Delco catalogs and ALL 1984 Jimmys had a carburetor so you might double check the year. I say this because if you need parts, you will need the correct year. I'm guessing '85, the first year for fuel injection OR the engine has been changed.
  I agree with all the test you have performed and agree 55psi is WAY too low for the compression. It should be around 130. I know you said the timing mark is at TDC when the piston is up but remember, the timing mark is "up" twice during a 4 stroke engine cycle, once for "compression" and once for "exhaust". I think the timing has jumped and it is just a rare circumstance that the timing mark is up when the piston is up. You didn't tell me how you checked the timing.  
  Not knowing which engine it has, 1.9, 2.0 or 2.5 (or sure of the year), it could have a belt drive, chain drive or a gear drive, respectively. Here is what I want you to do:
  Remove the distributor cap and have someone watch the ignition rotor.
  Get a socket that fits on the bolt in the crankshaft. With a ratchet, rotate the crankshaft either direction until the rotor begins to move. Next, reverse the rachet and turn the crankshaft in the opposite direction and see how long it takes for the rotor to begin to move. If it takes any more than a couple degrees of crankshaft rotation before the rotor begins to move, I'd say the timing has jumped.
  It seems you have covered all the other bases like fuel & spark. The low compression is what leads me to think crank/cam phasing. Let me know what you find..
  Happy Easter to you also. NOW tell me more about this 6 mpg. Galaxie. Have you got a Cammer motor in it or just a built to the hilt FE? Remember, FE doesn't stand for Factory Experimental, it stands for Fat Engine!! Jeeze those suckers were massive!!
Skip