Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - TBI fuel delivery problem when starting
View Single Post
  #20 (permalink)  
Old 04-19-2013, 10:54 AM
joe_padavano joe_padavano is offline
Registered User
 
Last wiki edit: Wheelbase database Last photo:
Join Date: Jan 2007
Location: Virginia
Posts: 3,644
Wiki Edits: 1

Thanks: 6
Thanked 172 Times in 157 Posts
Quote:
Originally Posted by fleetsidebob View Post
When I turn the key to the run position, the fuel pump runs for a couple of seconds and shuts off. I was assuming it stopped running because it was pressured up.
This is normal. In a factory TBI system, there are two separate methods for operating the fuel pump. When you turn the key to START, the ECU closes the fuel pump relay for two seconds to build pressure in the system. This is the only time that the fuel pump relay is used. Once the engine is cranking and builds fuel pressure, a separate circuit closes through the oil pressure switch. This bypasses the relay and keeps the pump running whenever there is oil pressure.

Quote:
How can I test to see if there is actually pressure at the injectors during start up? I hate to disconnect fuel lines and have gas shooting all over the place.
The only way to test this is to temporarily attach a fuel pressure gauge to the test port on the fuel line to the throttle body. You should see ~15 psi when you turn the key to START. The pressure should remain there the whole time you are cranking the engine. If it drops, you have a problem someplace, like a bad check valve in the pump or a bad pressure regulator.

Quote:
The pump itself is not very accessable, but I'm wondering if I could use a clamp meter around the power wire to the fuel pump and see if we have current while the starter is turning. Would that make sense?
No. See above. If the problem is a check valve the pump will run but you won't maintain pressure in the system, so an ammeter won't help.
Reply With Quote
The Following User Says Thank You to joe_padavano For This Useful Post:
fleetsidebob (04-19-2013)