Questions and Answers
Rebuilt 4A-LC
Q. I rebuilt my Toyota 4A-LC engine and set the timing. (Aligned the crankshaft at 0°, aligned the camshaft with the arrow or crossbow, I then aligned the timing marks on the distributor and put it in. At this time I took the timing light and started the engine, the timing marks were off about 20°.
As I turned the distributor and drew the marks together the engine began to bog down. When setting the timing the manual also mentioned disconnecting two vacuum lines. The marks were lined up when the vacuum lines were removed, but when I connected them the marks were off.
I turned the distributor to align the marks but it continues to bog down. I have it running now but the marks are not aligned. It is also doing several other things:
1. When it is turned on the idle is very high.
The engine runs great while operating, I getting about 31 mpg, but it just isn't right somewhere in the tune-up. I appreciate your expertise on this issue.
2. At stops or idle the engine lurches up and down.
3. While driving on acceleration the engine has a metallic rattle, that the dealers say is normal.Thanks and God bless,
AlanA. When you set the base timing on an engine, there is a specific procedure to follow. In this case there are two vacuum lines that need to be disconnected. On some engines you have to jump test connectors or put the computer into a diagnostic mode. Whatever the procedure, you must follow it to get the base timing correct. It is alright that the timing changes when the lines are reconnected. This is the powertrain management system taking over and doing its job.
As far as the high idle goes, I would recheck the vacuum lines and make sure they are correct and that there are no vacuum leaks. Sometimes, and too often, when an engine is rebuilt, other components are disturbed and will not operate correctly. This is due to dirt or carbon getting banged loose and blocking a passage or device somewhere. If everything is okay, then you should try setting the base idle speed as per the procedure for your year car.
Surging such as you describe is often the result of a bad O2 sensor. When you work on an engine you have to be careful about what types of sealers you use. Some sealers will damage O2 sensors and cause them to stop working. It is also possible the O2 sensor is covered with carbon from the initial start up after the rebuild.
I don't know what model Toyota you have and I can't hear the noise so I can't say with any high degree of accuracy what the cause of the noise is. However a common noise on acceleration in a Toyota are the heat shields around the catalytic converter and exhaust pipes. These make a metallic, tinny rattling sound. Easy enough to fix by just tightening or replacing the heat shields.
Additional Information provided courtesy of ALLDATA
