Flooding tendences, large sound of air sucked in, wont run

CROBERTS

MEMBER
2002 CHEVROLET AVALANCHE
5.3L
V8
4WD
AUTOMATIC
170,000 MILES

I have a 2002 avalanche 1500 4x4 5.3L
I was driving one day and got gas, the truck had no power for take of or go above 15mph. About 3 mins driving the truck started to operate normal, this was 3wks ago. Now the truck will idle for 5-10mins, then stall or act as if flooding out. After turn key off then try to start again 2mins of sitting the truck wont start as if no gas, it has gas and pressure is fine it seems. If the truck sits for 1-2hrs then try to start it starts normal then repeats the stall phase. I removed the air box, leaving the MAF sensor connected in place as normal operation. I start the truck and you hear a large constant air being pulled in through the internal ports of the throttle body. This is where the IAC (Idle Air Control Valve) connects to. I have replaced the PCV valve and hose, throttle position sensor, cleaned the throttle body, replaced the throttle body gasket, replaced vacuum lines that I have found and still same problem. The air constant sound is coming from the throttle body, the truck never had this loud sound of air being pulled in before the initial problems.
I have x2 codes pulled and they are P0171 and P0174.

3 Replies

HMAC300

MECHANIC
48,601 POSTS

Fuel pressure should 55-62 psi check with a gauge autopart rent it. The codes ar running lean, could be a vacuum leak as well

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Monday, June 9th, 2014 AT 6:55 AM

CROBERTS

MEMBER
6 POSTS

I checked the fuel pressure with my tester and found the following:
1) While running it was at 40-45psi
2) Turned off then started truck after sitting 5mins, the fuel pressure was 10-13psi and truck stalled.
3) I turned key on, without starting, and pressure went to 30psi and held. This was performed x4 with same results.

Sounds of leaking are faintly noticed around fuel injector at rail side, so I'll do a o-ring kit for those. When turn key on then off the IAC (Idle air control valve) makes a buzzing sound when turn key off (i don't know if this is normal). Anyway would it be possible the the pressure regulator is bad by releasing more pressure through the return line as it should while running over time. I have no idea of what I can use to test the regulator. Also, if I need to test the check valve in pump would I need to drop the tank or is there a access point in floor board in back. You hear a slight exhaust leak so I am going to do a manifold and flange gasket job on it. I'm telling you all this so it may help you knowing everything I have found so far.

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Saturday, June 14th, 2014 AT 2:45 PM

HMAC300

MECHANIC
48,601 POSTS

Your fuel pump pressure is low it should be 55-62 psi unless it's a vin Z then should be 48-54 psi. So don't bother with exhaust leak the proper pressure should take the care of the 171 and 74 codes. The tank h as to be dropped however. As for iac, clean throttle plate on both sides an diac hole and see if it still does it it may not. Also her eis atip although ti may be your pump for the pressure drop as it shold hold a 5 psi drop for 10 inutes. Here is something form our tips apage. Tip. I just came across this today.

Concern : Fuel pressure does not hold steady, regulator tests okay, injectors test okay

Cause : Plastic fuel rail has small pit not allowing regulator seal to function

Correction : Replace fuel rail, transfer injectors and install new regulator.

Concern addressed and corrected.

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Saturday, June 14th, 2014 AT 3:48 PM