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Old 10-27-2004, 08:54 PM
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TBI Starting problems

i have a tbi 350 truck that i just put together when i go to start it the ecm delays the fuel from the motor for about 20 secs. it wont prime the fuel it wont fire the injectors and turn the fuel pump on till about 20 secs in on cranking it over. even when i crank it for few secs like i normaly would it still wont start untill it cranks over for around 20 secs basicly 3 trys to get it started. i dont know why ecm wont even prime the pump ive replaced the relay ive tryed differant ecm all of them do the same thing. anyone know anything else i could try?

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Old 10-27-2004, 09:15 PM
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Old 10-27-2004, 10:03 PM
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Fuel Pump Relay

If you look at a wiring diagram for a TBI truck, the fuel pump is also powered through the oil pressure switch located at the back of the intake. (At least my 94' Suburban is wired this way).

Sounds like your fuel pump relay is bad. Not priming and starting after 20 seconds of cranking. Cranking the engine, oil pressure eventually comes up, closes the switch and activates the pump. There is also a fuel pump fuse (20 amps) in the same area as the relay.

Good luck, Ed www.edgesz28.com

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Old 10-28-2004, 06:21 PM
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nope still doesnt work and power wire is good in both run and start ill keep working with it but i still dont know
thank you anyway that was the first reply ive hard that wasnt really dumb i was waiting for someone to tell me that my tire pressure is low (it has happend before)
if you have any other thoughts let me know
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Old 10-28-2004, 09:52 PM
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If possible tryin 'hotwiring' the fuel pump to see if it makes a difference. That way you could check if it or something else is at fault.
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Old 10-29-2004, 06:17 AM
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Oil pressure is the suspect. Most ECM's require oil pressure to allow fuel and ignition. The purpose was to shut the engine down when oil pressure drops below a certain level in the 15-20 PSI range. If your oil pressure is slow coming up on start, then the feature prevents fuel and ignition. If you look closely, you will have two oil pressure sensors: one for the guage/light and one for the fuel injection. They are not the same sensor and are not interchangeable

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Old 10-29-2004, 06:20 PM
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sorry i was worng you were right about the oil pump sensor. the fuel pump relay was good and coming on as it should but the socket its in was bad there was a brake in the wire from the relay to the fuel pump and i found it the socket to be bad. pulled the relay out and the truck still started as it did before so i repaired the relay and now it starts the first try. Thanks for giveing me something to look for and getting me thinking
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