1995 caravan won't crank

It is a 1995 caravan with the 4 cylinder. When trying to crank it the engine vibrates very badly then cuts off after a couple of seconds. The engine will stay on for around 20 seconds if the gas pedal is kept on the floor and shakes considerably less than when the pedal is not pressed but even then it seems to be hitting only about 1000rpm( no tachometer). It is my sister's work car and it has previously had a rebuilt motor installed so I have no clue as to true mileage.

Any thoughts as to the problem? Is it something relatively cheap and easy or would it be better to get another car since this is a commuting vehicle used only for work? Thanks for any suggestions.

Tim

Is check engine light on?? Do the key dance for codes.

Has fuel pressure been checked??

Any idea when timing belt was replaced?

I have not checked the fuel pressure, but I just replaced the fuel pump and filter for her back in February. I can smell fuel under the hood and there is a bit of unburnt fuel coming out of the exhaust for the couple of seconds that I can get it to stay cranked.

The check engine light does not stay on after the initial cranking. Is the key sequence the same for the caravans as it is for my old eclipse- off,acc,off,acc,off,crank?

I ran the key trick and got a 12 (which I think is from unhooking the battery) and a 55. Does anyone know what the 55 diagnoses?

edit: I found out in another thread that 55 is for the end of codes.