98 5.7 chevy suburban k1500 weird hissing from intake area and fuel pump runs constantly

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james28909

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cross posted on ls1tech

this is a first for me so i hope someone here knows what is going on. i recent bent a valve in my suburban and i just got it all put back together. new head gaskets, intake gaskets (felpro premium intake gaskets) etc. after trying to prime the motor with spark plugs out and fuel injector harness unplugged, i noticed that oil was coming from the tops of the rocker arms BUT it said i had zero oil pressure on the dash. so i continued to prime it and prime it, having to recharge the battery a few times and it never built pressure, but i obviously had pressure because the juices were flowing good!

so i installed spark plugs and reconnected the FI harness and put the breather assembly back on. while i was putting the breather assembly back on, i check to make sure i plugged the oil sender back in and i did remember to do it BUT the housing is slightly wobbly so i am sure this is the problem of why the dash is saying there is no oil pressure.

BUT HERE IS THE WEIRD PROBLEM
when i slightly press the oil sending unit housing/connector towards the fitting thats screwed into the engine, i hear this hissing sound. i cannot understand what could be making a hissing sound ONLY when i press/wiggle the housing. it sounds as if water is spewing out and sure enough there is droplets of water running along with the oil to the oil returns on the head (i still have the valve covers off) and i can see it pretty clearly that a few drops of water are running along with the oil while it is running.

my question is, is there somehow that water can infiltrate the oil sending unit? if it was a leaking intake gasket wouldnt it make the hissing noise from intake area all the time and not just when i press/wiggle to oil sending unit? i torqued the intake down to 8 ft lbs then 10 ft lbs then 12 ft lbs per the spec i pulled up, then found another one that said 40 ft lbs so i may go back and tighten them more.

when i open the throttle body, i can hear the hissing a little better but do not see anything spraying or no steam or anything. so i think the noise is coming from an intake gasket, but why would it only make that noise when i wiggle the oil sending unit housing?

if anybody has any idea what it could be, please let me know because i am lost and cannot find anything on google. if i need to supply any more information please let me know. i have not ran the engine since i seen the water running with the oil at the bottom of the head/valve cover area. thanks in advance

EDIT: for clarification, i originally noticed the hissing sound after i ran the motor to temp the first time and then removed breather assembly to make sure oil sender was hooked up because i didnt have any pressure on the dash. its like once pressure built up in the cooling system, and after i turn the engine off, i wiggle the oil sender unit on the back of the motor behind the intake and when i wiggle it to a certain spot i hear this hissing/sprewing/spraying sound from the intake area and i have water in the oil
 
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james28909

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ok, i have narrowed down the hissing noise and know what it is. when i wiggle the oil sending unit housing, it makes the fuel pump kick on. and the hissing noise i think i gas recirculating back to the gas tank. but why? how is this possible? it only does it when i wiggle the oil sending unit housing.

thoughts anyone?
 

james28909

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ok it seems i have solved the issue. looks like the oil pressure sending unit itself is bad. the oil pressure sending unit sends power to the fuel pump when there is oil pressure. so it looks like the sensor has failed in "has oil pressure" position and is causing the fuel pump to run constantly even with the fuel pump relay out and key not in the ignition.
 

Schurkey

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The oil pressure switch is a "failsafe" bypass for the fuel pump relay. If the relay, or the circuitry in the ECM that turns the relay on and off, or the associated wire harness fails, the engine will still run if it has oil pressure.

Failed fuel pump relays are a cause of "hard starting/long cranking time before starting" complaints--the engine has to build oil pressure on the starter motor before the fuel pump engages.

What surprises me is that the system has power with the key off. I thought that fuse was switched with the ignition. But it does explain another problem in another thread on this site, where a guy connected an aftermarket heated O2 sensor to a vehicle that didn't come with one, powered the heater from the fuel pump wire harness, and then discharged his battery overnight--the O2 heater must be powered 24/7/365.

Yes, of course your oil pressure switch is broken. When it was me, I had to buy a "new" oil-pressure-switch socket, because the one I've owned for thirty years wasn't long enough.

www.amazon.com/Lisle-13250-Pressure-Switch-Socket/dp/B0002SR2RY?pd_rd_w=1BJcG&pf_rd_p=5bc65336-a8b0-4888-9e70-4d4ce2f6bd59&pf_rd_r=B2H7P0Z9329C910CCH8Z&pd_rd_r=f7d28da7-5894-4eac-ac96-7e4098e4886e&pd_rd_wg=uQ6H3&pd_rd_i=B0002SR2RY&psc=1&ref_=pd_bap_d_rp_1_t

xc_hide_links_from_guests_guests_error_hide_media
 

james28909

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yeah the oil pressure switch socket. i must have bumped it when putting the intake back on. the oil pressure sensor worked great before this overhaul and i just barely bumped it so i had to disconnect it resulting in no oil pressure.

but luckly.... i had another problem this evening lol. i got a intake off a junk truck in the junk yard. once i got everything hooked up with valve covers off, i crunk up the engine. after it got to running temp, i noticed the was a little few drops of water going down with the oil at the bottom of the passenger side (bank 2) head. i thought the intake didnt seat right on the gaskets, and water was going to the crank/oil pump and back up the lifters etc. but turns out it was the heater hose fitting on the front passenger side of the intake. i took the quick connect loose and looked down in there and it didnt look pretty, so i decided to use the one off my original intake. well i got the socket on it and went to turn it and it broke flush off with the intake. i tried to get it out with a flat head screw driver which resulted in damaged threads on the intake. but luckly i have the other intake :D so i just got to take this intake back off, put the upper intake manifold back on my original intake and reinstall it. hopefully tomorrow i will be done with this thing. what was originally a bent exhaust valve on #4 cylinder has turned into a massive overhaul and i shouuld have just rebuilt the entire motor. but anyway, hopefully i will be done tomorrow.

thanks for the info btw
 

Schurkey

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The GM quick-connect is a known problem. EVERYONE has trouble with it.

The Dorman replacement is--or at least used to be--a long-term fix. Mine was twenty years old when I removed it from one manifold to install on another. Perfect condition even after all that time.
 

Steve A

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hopefully tomorrow i will be done with this thing. what was originally a bent exhaust valve on #4 cylinder has turned into a massive overhaul and i shouuld have just rebuilt the entire motor. but anyway, hopefully i will be done tomorrow.

Did you find what caused the original exhaust valve to bend?
 

james28909

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Did you find what caused the original exhaust valve to bend?
the timing chain had a good bit of slop in it. with how the engine ran, and me being pissed because of how ****** it was running, i think the stars aligned so that when the exhaust valve bent it fulfilled the prophecy. it misfired bad and would bog real bad almost as if it was almost completely cutting fuel off while backfiring and jerking/shaking real bad.

i got it back running though and everything is in great working order. i had a hesitation problem but i cleaned the maf and it seemed to help but we will see in the next few days if it hesitation is resolved. also need to change motor mounts very badly but dont have the extra cash right now so guess it will have to wait a few weeks
 
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