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Battery Drain - Noise within Intake

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Old 01-26-2016 | 02:42 PM
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Default Battery Drain - Noise within Intake

My son has a 1995 Blazer 4.3L. After 8 or so hours the battery will drain dead. Just now realize that w/o any key and not running, there is a noise coming from within the Intake Manifold. I removed that central round divert from top of the manifold and sure enough the sound is coming from down inside the intake. Sounds like a hissing noise of something running? When battery is charged it starts immediately so can't be gas pumping through the spider injectors? If I remove fuse # 9 (ECM Batt. - ABS Battery, Fuel Pump), The noise stops... same if I disconnect the battery. Does not stio if I remove fuse # 10 which is the ECM IGN. - Injectors, Engine Sensors). ANY IDEAS WHAT IS WRONG AND WHAT FIX WOULD BE.
 
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Old 01-26-2016 | 03:34 PM
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just a guess here - pop your fuel cap, can you hear the fuel pump running with the key off - if so maybe the fuel pump relay is bad and shorted out - I would think the fuel pressure regulator should send the excess fuel back to the tank making the sound you hear
 
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Old 01-26-2016 | 05:36 PM
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Not that odat. Removed gas cap and sounds like fuel pump is running (key out). So I pulled 2 relays in the glove compartment (1 of which I thought was fuel pump and horn relay. The fuel pump was still running, noise still within the intake, car started but horn didn't honk. So does that mean the other relay in glove compartment is not for the fuel pump since the Blazer started? Any other ideas?? Stumped here?
 
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Old 01-26-2016 | 06:50 PM
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One of the three relays is the fuel pump relay. One of them will have a grey wire, that would be the fuel pump relay, disconnect it. If the pump shuts off with the relay disconnected, we can help you find the problem, (could be bad relay, could be a shorted wire somewhere).
 
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Old 01-26-2016 | 06:57 PM
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I'm sorry but on a 95 I'm not sure where the fuel pump relay is I'll have to do a little looking - my toy in my avatar was made with parts out of a 92 and the relay was under hood by the brake booster - maybe look under hood?
edit captain beat me too it while I was typing - and I was wrong with my reply anyways
 
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Old 01-26-2016 | 07:11 PM
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odat, you are exactly correct in post #2.
 
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Old 01-26-2016 | 07:41 PM
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So this blazer only has 2 relays in the glove compartment. From what I've seen the third relay is for day time lights. Another thing I see mentioned... if the oil pressure switch is bad, that can cause the Fuel Pump to run since it's in the FP circuit?? Well, with the car started the oil pressure is pegged at 80 psi. Maybe this is the problem? With hope it's that easy, I'll buy a new Oil Pressure Switch tomorrow and try it. Sure I can't be that lucky but easier than tracing a short. Will also look for other relays elsewhere. Being I pulled the two relays in glove box and pump still ran with no key, seems something s supplying power to the pump by passing the relay??
 
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Old 01-26-2016 | 08:02 PM
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With the ignition in the off position, if the fuel pump stops when you unplug the oil pressure sending unit, the sending unit is faulty. 1995 was the last year GM used that circuitry, (through OPSU). The circuit supplies an additional path for current to flow to the fuel pump, only when the oil pressure is above ~7psi. They finally figured out it wasn't necessary. If the oil gauge is pegged at 80psi, the contacts in the OPSU are closed which is supplying the fuel pump with current. You can either replace the OPSU, or snip the grey wire at the OPSU connector.
 
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Old 01-27-2016 | 11:00 AM
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PROBLEM SOLVED! Replaced the oil pressure switch and the fuel pump 'IS NOT' running! Who ever designed that circuit whereas the OPS bypasses the Relay and Ignition, is probably the same designer that put the OPS at back of engine behind and down from the distributor. WOW! Thanks for the help!
 
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Old 01-27-2016 | 03:10 PM
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Glad you figured it out, and thanks for posting back.
 
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