Hey everyone. So Idid a rebuild on my 4.0 and the only thing that was changed was the bore size. Everything else is stock components. When i got the engine running and dialed in, I took it for a test drive and about halfway through the engine overheated and shut the engine down. Found out that the frost plug on the back of the head had come loose and fallen out causing the overheating cause all the coolant was dumped out. After replacing the plug and head gasket after checking all components (none were damaged) got it running and now it does not idle correctly. It will bounce between 800-450rpm and eventually die. Have to keep it at 1000+ rpm to keep it running. Along with that issue. 1st-2nd gear is fine but when in 3rd and up, I cannot let the rpm’s drop below 1000 rpm or else the engine will die. Also had random bouts of the engine shutting down while driving and having to bump start while going down the road (not fun).
Any help on what the issue could be would help immensely. TIA
Given that the overheating issue was caused by the frost plug and the subsequent problems with idling, here are a few things to check:
Vacuum Leaks: After a rebuild, vacuum leaks can occur if any lines were disconnected or missed during reassembly. Check all vacuum hoses and connections for cracks or disconnections.
IAC Valve (Idle Air Control): The IAC might be malfunctioning or dirty. A stuck IAC can cause erratic idle behavior. Consider cleaning it or testing for proper operation.
Throttle Position Sensor (TPS): If the TPS is out of adjustment or failing, it can lead to poor idle stability and can affect performance in higher gears. Make sure it’s set up correctly.
Fuel System: Ensure that the fuel pump is working properly and that you have good fuel pressure. A clogged fuel filter or an issue with the fuel injectors could lead to low fuel delivery, especially at low RPMs.
PCM/Timing: If the engine has been overheated, it may have affected the timing. Double-check the timing settings and make sure the PCM is properly calibrated for any changes that were made during the rebuild.
Compression Test: Since the engine overheated, it’s worth doing a compression test to ensure that all cylinders are operating properly.
