Doing the compression test should technically involve have no plugs in the holes (as not to interfere with results on any other cylinder), but the key is to not actually START the engine, just crank it...

Also, another part to this is to do the 1st compression test, then squirt some gear oil (like 80w90) into the cylinder and retest. The idea is that if you have leaky rings, the oil will temporarily improve sealing in that cylinder. The only downside is don't use TOO MUCH oil...and that you will have to burn it off at startup...

If it ran the same at startup with one plug gone...you may have more problems...replace the plug wires and see if it improves...otherwise you may have a dead cylinder...hopefully not though.

To be fair, I have accidently tasted coolant too, like when draining a rad...but you didn't specify...so I made my own conclusions.

HTH,

 

may want to check that your gas tank doesn't have a leak

when i noticed my mpg plumted to 10-12, i found out why.... IT WAS POURING ON THE GROUND. and no it was not fun to drop the rear end to change the tank.... (after 2 trys at patching it)

tj

 

After spending 20 minutes reading this whole thread, one thing comes to mind. First, spend the $20 and change the damn O2 sensor if you haven't already.

#2: Do a compression test NOW. From the looks of those pics (ie. the sludge and the fact that the overflow has NO coolant in it) , you have a water/oil problem there. Just my guess, but I've dealt with my fair share of head gasket failures to know what one looks like and my friend, those are two really nice signs... Not to mention the mileage. Does your exhaust smell sweet at all? Does the car stumble when you turn it on in the morning or after its been sitting for a while?

Does you oil dipstick have sludge on it? Does the oil look milky? If there is coolant in the engine your engine will compensate for the poor performance by dumping more fuel into the engine.

 

dante thanks for reading....i think tomorrow ill go ahead and spend 20 for the 02 sensor. i just ordered my headers today from jegs so ill install it when i get those installed (so i dont risk damaging it when i install, take out, then install again)

car doesnt stumble, starts up fine, and exhaust has no sweet smell (actualy smells like an old carbed car since i have no cat, come to think of it, it does kinda smell and run a little rich.) however as i stated earlier (dont know if anyone read it) my timing it at about 7*. that shouldnt make a huge diference would it?

and the oil looks fine. nothing milky. however, ive got to get my compression tester to work before i can test the car.

well i thin thats about all the ideas i can think of......if you guys have anymore keep them coming PLEASE!!!

 

The stuff in the tank picture looks like some kind of "Stop Leak" stuff. Mine had that when I got it. Though the strand in the coolant looks kinda like oil.

No, the 1 deg increase in timing isn't causeing your bad mileage.