I have a '96 Jeep Grand Cherokee and mine was recalled for a faulty O2 sensor and catalytic convertor. That might be the problem, because after getting those fixed, i get 15 mpg instead of 13.
The diagnostic code 12 51 55 is actually not a code for the 1994 Jeep Grand Cherokee Laredo. The 12 means that it has started searching for codes. The 51 is oxygen sensor stuck lean. The 55 means it is finished searching for codes. Getting this means nothing is wrong.
if its the 5.2 liter model thats your answer right there
the reverse switch in the transmission
Fuel pump going out maybe?
It could be the timing is not set correctly. Possibly one or more of the spark plug wires have been put on the wrong plug.
Check the crank sensor, i had the same problem with my 94 Grand Cherokee
If the jumper cables were hooked up the wrong way by mistake on a 1997 Grand Cherokee Laredo 5.2L, it might be necessary to check the alternator to make sure it is turning in the right direction. If the battery is still being charged, the vehicle should be fine. A high idle could be a problem with the EFI or Electronic Fuel Injectors.
Check the starter relay that is just behind the battery. The positive wire from the battery goes to it.
Short circuit in your vehicle alarm system. In most alarms, some lights will flash on and off as an indicator of an attempted break in.
You may have gotten the valve timing wrong. If a valve is open when the piston is at TDC it may hit it, doing considerable damage.
He felt the he was forced in his action and that the removal of the Cherokee's was wrong.
Not even close, wrong region.