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96 GMC Sierra 5.7 upper intake removal
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HKman
Novice
Dec 5, 2011, 3:45 PM
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96 GMC Sierra 5.7 upper intake removal
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Tried to remove upper intake plenum on 96 GMC Sierra 5.7 to resolve OBD2 codes P0300 and P0175. Secondary spark test completed (passed). Fuel pressure test shows a rapid drop from 60 psi to 15 psi after turning off ignition. Need to get a look at the fuel pressure regulator, injectors, poppets, etc. The upper intake bolts are all removed. Intake plenum will shift from side to side and back and forth but hangs up (underneath?).
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Hammer Time
Ultimate Carjunky
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Dec 5, 2011, 3:55 PM
Post #2 of 16
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Re: 96 GMC Sierra 5.7 upper intake removal
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Have you removed the wire harness and fuel lines?
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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HKman
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Dec 5, 2011, 3:58 PM
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Re: 96 GMC Sierra 5.7 upper intake removal
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Yes, along with other misc. parts (throttle linkage, coil, pcv valve, etc.).
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Hammer Time
Ultimate Carjunky
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Dec 5, 2011, 4:01 PM
Post #4 of 16
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Re: 96 GMC Sierra 5.7 upper intake removal
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You're just missing a bolt somewhere.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
Ultimate Carjunky
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Dec 5, 2011, 4:07 PM
Post #5 of 16
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Re: 96 GMC Sierra 5.7 upper intake removal
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If you have the fuel pipes to the injector off and the bolts around the upper intake including the ones in the rear of the upper, then it is probably hanging onto the top of the injector assembly. There is an oval shaped o ring that the top of the injector slides through that likes to stick. Put your thumbs on top of the injector while pushing it down and lift up on the bottom of the intake manifold.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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HKman
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Dec 5, 2011, 4:10 PM
Post #6 of 16
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Re: 96 GMC Sierra 5.7 upper intake removal
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I'm able to move it around about 1/4" or so in all directions. It raises up maybe about 1/8".
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Discretesignals
Ultimate Carjunky
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Dec 5, 2011, 4:12 PM
Post #7 of 16
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Re: 96 GMC Sierra 5.7 upper intake removal
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Then it is sticking to the injector assembly o ring. Hold the top of the injector down and pull up on the intake. It should pop off.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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HKman
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Dec 5, 2011, 5:22 PM
Post #8 of 16
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Re: 96 GMC Sierra 5.7 upper intake removal
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Upper intake removal issue - status: RESOLVED.
Thanks, you nailed it.
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Hammer Time
Ultimate Carjunky
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Dec 5, 2011, 5:24 PM
Post #9 of 16
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Re: 96 GMC Sierra 5.7 upper intake removal
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How do to plan on identifying a problem now that you have it apart? I think you should have done a little more testing before disassembly.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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HKman
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Dec 5, 2011, 6:01 PM
Post #10 of 16
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Re: 96 GMC Sierra 5.7 upper intake removal
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After I hook the fuel lines back up I'll have someone put the ignition switch in the on position to return pressure to the fuel system while I monitor the injector assembly for any signs of fuel leaking. Upon performing a fuel pressure drop test I observed a rapid psi reduction after turning off the ignition. (from 60 psi to around 15 psi within about 15 seconds). Am I chasing a ghost?
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Hammer Time
Ultimate Carjunky
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Dec 5, 2011, 6:06 PM
Post #11 of 16
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Re: 96 GMC Sierra 5.7 upper intake removal
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No, you're probably on the right track but there are other explanations for a fuel pressure drop and if you had looked at scan tool data first, you would have a much better idea what is happening. You would have looked at the short and long term adaptives and watched for them to immediately start trying to correct for the leaking fuel. It would also be a good idea to examine the 2 center plugs on the drivers side for excess fouling because that is where most of the fuel flows.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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HKman
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Dec 5, 2011, 6:22 PM
Post #12 of 16
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Re: 96 GMC Sierra 5.7 upper intake removal
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Sorry, I left that part out. My scan data reading for the long term fuel trim was stagnant at minus 18 at both banks. In my mind that was hinting to a possible continuous extreme rich fuel condition. That falls in line with my p0175 diagnostic code that keeps showing up.
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Hammer Time
Ultimate Carjunky
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Dec 5, 2011, 6:25 PM
Post #13 of 16
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Re: 96 GMC Sierra 5.7 upper intake removal
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Let us know what you find.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
Ultimate Carjunky
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Dec 5, 2011, 6:29 PM
Post #14 of 16
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Re: 96 GMC Sierra 5.7 upper intake removal
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Another thing is if regulator is leaking, you'll see a nice clean spot on the floor of the intake. The gas will clean the carbon off.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Dec 5, 2011, 6:30 PM)
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Discretesignals
Ultimate Carjunky
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Dec 7, 2011, 7:46 PM
Post #15 of 16
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Re: 96 GMC Sierra 5.7 upper intake removal
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Just another thing that I remembered. Sometimes a regulator with a leaky diaphragm may not leak unless there is vacuum on it. You may have to hook up a clear hose to the regulator's nipple and use a hand held vacuum pump while the fuel pump is running.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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HKman
Novice
Dec 7, 2011, 8:12 PM
Post #16 of 16
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Re: 96 GMC Sierra 5.7 upper intake removal
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Replaced fuel pressure regulator. Bottom of intake was gunk free underneath FPR vacuum tube just like you said it would be if it was leaking. Fuel pressure test verified this was the case.
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