I have a 1994 toyota tercel, and the water pump went out. Till now it was running great. I changed the water pump and also oil seals around the oil pump cause of a big oil leak. I had to take off the timing belt and then put it back on. After I put everything back together, the engine was running terrible. I isolated the problem to the the 4th cylinder, cause when you unplug the 4th cylinder spark wire, you do not see a difference in the sound and running of the engine. I thought this meant that it was the fuel injector. I ordered a refurbished one for 30 dollars, and installed it. Then engine did not change. I asked a friend about it who works in an auto shop, and he said change the spark plug wires and check the timing belt marks and the distributor timing. I did both of those. the timing marks were fine, and the distributor timing did not change anything. I also installed a new coil, cause the original coil went out while I was checking the car, after the water pump was replaced. At one point the car lost spark, however the new coil fixed that, all the wires have spark, Also while the engine is running like this, it will die on idle if the AC is off, when the AC is on, the idle speed increases and it is able to stay on. After changing the spark plug wires, I did the 4th cylinder test, where I unplug the 4th cylinder while it is idling, Now I notice a very slight change in the sound and rhythm of the engine, but not a very big difference, making me think the 4th cylinder is the problem. I did a screw driver check on the fuel injector, to see if it was running and could hear it clicking. I also did a compression test on the 4th cylinder, and it came out as 120 which I am told is acceptable. I have no idea what to do to fix this problem.
Please help, I really need this car for commuting. Thank yoiu.