I have a 82 chevy camaro 305 crossfire injection. We rebuilt the motor and had it bored 30 over. Put the rebuilt engine back in and it ran awesome for about 2 weeks. I started it the other day and it started I put it in gear and it died. Cannot get it started, I've got fuel, however the fuel I drained crap floated to the bottom. Ive got spark, I checked compression #1 cylinder had 30 then none then I put oil in cylinder thinking all the gas wiped out the oil and I got a reading of 60 then. I checked the timing gear and it was fine and timing is fine. I checked #2 cylinder and had about 120 and 90 in #4. Checking #3 I had between 60 and 90. I put oil in all cylinders and the compression did come up. Im at a total loss, I really hope someone can help me...

 

Sounds like you took your compression test readings without having the throttle blocked open; in which case they mean nothing and are worthless. But that's not your problem anyway; compression isn't perfectly fine for 2 weeks and then suddenly "goes away" to the point it won't run, so don't worry about that.

First, put a new set of plugs in it. Doesn't mater if the old ones "look" good, or if you just changed them a week ago, or what. Just put in new ones. Stick with nice normal ones, like Delco R45TS. No "gimmicks" like E3 or Splitfire or Bosch "Platinum +4". Just yerbasic ordinary ones. Then charge the battery overnight.

Try starting it. Only try for a few seconds; either it'll start, or it won't. If it starts, .... ,,,, well, it starts. Problem solved. If it doesn't, shoot some starting fluid into each TB and try again. Again, just for a few seconds; either it'll start RIGHT up, IMMEDIATELY, or it won't: whirling it over until the battery is totally drained won't accomplish anything. If it starts this time, then you know you have a fuel problem. In that case, start by changing out the fuel filter; but before you take the old one off, put a gallon of denatured alcohol in the tank first and let it sit for a day or 2, then when you take off the filter let the tank contents siphon out. Then put a gallon or 2 of NEW gas in the tank after you put the new filter on.

 

Why does the throttle have to be open? Never had a crossfire. Is this something particular to a crossfire?

 

No; it's peculiar to motors in general.

THINK about what a "throttle" does.

It BLOCKS the air intake. If the throttle is closed, the engine won't get enough air to fill the cyls completely, and the test will read REAL low. And worse, depending on how fast it turns, the readings can vary ALOT even if the cyls themselves are the same, while all being generally WAY too low. Basically, not having the throttles wide open ruins the test.

 

Did you do a running compression test or a starting compression test? Try just a cranking compression test first and see if the compression is the same between all cylinders.

Although as the person above said compression doesn't just go away like this, well usually I mean you can never say never in automotives. Replace the fuel filter and do a volume test on the fuel pump, make sure it is pumping the right amount of fuel and check your fuel pressure. I always check spark and fuel if a car never starts.

 

It BLOCKS the air intake. If the throttle is closed, the engine won't get enough air to fill the cyls completely, and the test will read REAL low. And worse, depending on how fast it turns, the readings can vary ALOT even if the cyls themselves are the same, while all being generally WAY too low. Basically, not having the throttles wide open ruins the test.[/quote]

The throttle plate isn't air tight - far from it. Otherwise you would have to press the gas to start your car, or press the gas to keep it idling. In fact, I know that when you remove a plug, insert the gauge, spin the engine (coil wire off), your readings can be just fine. There might be small variations in air volume per each cylinder, but the measurement system variation associated with a compression gauge is going to be more than I care to think about.

 

The throttle plate isn't air tight - far from it. Otherwise you would have to press the gas to start your car, or press the gas to keep it idling. In fact, I know that when you remove a plug, insert the gauge, spin the engine (coil wire off), your readings can be just fine. There might be small variations in air volume per each cylinder, but the measurement system variation associated with a compression gauge is going to be more than I care to think about.

 

When you measure your compression, don't just bump the engine. Remove the coil wire and spin it several times. This will give you a maximum psi reading. You are looking for variation across the cylinders. You should have equal readings across all cylinders in the range of 150 psi or so.