I recently bought a 2003 honda civic with a blown motor. It had a hole in the block but i had it start up for 10 sec or so before it dumped all the oil. It came with a replacement 1.7l out of a 2002.

i put a new timing belt and water pump in the replacement enegine, plus made sure the valve were set properly too. I did the swap all went smooth.

now it is all together and rolls over strong but will not start. I checked the fuel pump, it hums. There is no spark. So i got a code reader to see if that can help point me to the problem. There are no codes but with the reader plugged it fired right up. It runs smooth with the reader plugged in but as soon as it is unplugged it dies. I even took the car for a drive to see if that would clear it up.

I checked the ground from the battory and the one from the rad because of other posts i read said that is usaly the problem. They both are secured and dont look bad. I am not sure if there is one i am missing or what next step to take.

any ideas or pointers are very appreciated.

 

The code reader is obviously doing something to help the engine run.
So, first check all fuses and relays
Then look up schematics for ECU and DLC
Then check voltages, i.e. 5 volt reference etc.

 

Check the ground at the thermostat housing. Make sure all surfaces are clean and shiny.

 

In most cases, if the car starts and runs with an OBD-II reader/scanner, it is due to a ground issue with the ECM/PCM. The ground would be G101. The OBD reader is probably supplying ground to the ECM, enabling it to start.

 

Thank you very much everyone it was the ground behind that pile of wires on the thermostat. It runs by it self now

 

I just had my neighbor help me with installing a new thermostat, and he lost the bolt. I asked if that was a possible ground wire, and he said it was more likely to keep the wiring harness from shifting around. If I didn't have my HUD plugged into the OBDII port at the time, it would have resulted in an "Oops!" moment when the engine wouldn't start. Glad I looked into the problem and found so many similar situations! I'll see if he can put in a new bolt as I have a ton of metric and SAE bolts on hand.