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| | | | Joined: Oct 2003 Posts: 36 Junior Member | | Junior Member Joined: Oct 2003 Posts: 36 | OK guys, I have some symtoms and wanted to ask your opinion/s on what you think could be the problem.
I have a recently rebuilt 1976 Chevey 350 engine. It starts and runs great UNTIL it runs for 5 minutes or so. It begins to idle poorly. I noticed that the output pressure of the mechanical fuel pump drops from 7 PSI to 3.5 PSI after 5 minutes. I can rev the engine OK but the idle is poor. When I first start the engine, I can shift into reverse or drive, and it won't die. Once I have run it 5 minutes or so, when I shift it into reverse or drive it dies.
Now, I was thinking maybe a vacuum leak but how could that cause the fuel pressure to drop? I thought maybe a clogged fuel filter, but wouldn't the engine not rev?
Any ideas?
Richie West
| | | | | Joined: May 2001 Posts: 61 Member | | Member Joined: May 2001 Posts: 61 | By the way, I do not think this problem is due to vapor lock. Not only is the fuel line relatively cool, it is very well insulated. | | | | | Joined: Mar 2001 Posts: 259 Member | | Member Joined: Mar 2001 Posts: 259 | What type of carburetor? Is the choke opening up fully after the 5 minutes of running? After the 5 minutes of running time and the engine is off the high idle step and at the idle step if a Rochester or Q-Jet, have you adjusted the mixtures screws with a vacuum gauge or tach. Any type of a cam on the motor?
Joe
| | | | | Joined: May 2001 Posts: 61 Member | | Member Joined: May 2001 Posts: 61 | All new parts in the engine. I have a Holley mechanical fuel pump, Edelbrock 4 bbl, and slightly higher performance cam.
The choke works fine and after warming it goes off. Its a few minutes after the carb completes its choke cycle that it begines to run rough.
Could this be a heat-related fuel pump problem? | | | | | | Anonymous Unregistered | | Anonymous Unregistered | Sounds similar to an EGR valve problem I had in the past. If the engine is old or if the EGR was not replaced with the rebuild that may be the problem. It is a cheap part to replace and if it does not fix it you can always return it. | | | | | Joined: Oct 2003 Posts: 36 Junior Member | | Junior Member Joined: Oct 2003 Posts: 36 | I found the answer to my question. I post this so it goes into the history file and people can search for it later.
I replaced the fuel filter and it solved the problem. I started the engine and idled it until it warmed up to 210 degrees (electric fan start point). The Fuel pressure started at 7.5 PSI and went down to 7.0 after warm.
Thanks for help.
Richie West
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