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Discussion Starter · #1 ·
I've replaced almost every component that has to do with fuel/exhaust system to try and fix this problem. Mass air flow sensor. Oxygen sensors. Fuel pressure regulator. Fuel pump. Fuel filter. Spark plugs and wires. Cap and rotor. IAC valve. MAP sensor. Ignition coil. Still had codes and running lean. Spend a 1000 bucks to a mechanic to fix it. He replaced the multiport fuel injection assembly and intake manifold and valve cover gaskets. I pick it up and everything is good. Next day I'm running lean again. And now sometimes I have codes but light on. I've had light come on then when I go to check it the light is off and no codes. The only other possible culprit maybe could be my brake booster. I changed the one way check valve but my brakes are spongy. Bad. I can hear air coming from it when I depress the pedal. Even after bleeding my brakes 2 times I still barely get resistance. Anyways I gotta know if an air leak in my booster can cause my engine to run lean. I find it odd that the booster connects to my manifold but seems to me that it cause lean problem by allowing too much air into the intake. Idk. If anyone knows about this please let me know. I've spent almost 3000 dollars trying to figure it out. Truck runs ok actually. A little rough. Could I have issues with wiring? I do have other wiring problems. But I can smell that it is running lean. Idk. I'm so confused. HEEELLPP
 

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so you have a distributor on your engine . what is your engine ?
post the PCM codes . the PCV probably is worn and the hose on the PCV is old leaks .
check the fuel pressure when running . some did not use the correct fuel regulator .
forum will give good info on what motor you have .
 

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yes a leaky vacume brake booster will cause a vacume leak when you press the brakes unless it is really bad. there is a rubber grommet like diaphram around the plunger that runs through the firewall. it's usually fine at rest but will still be leaking then it leaks really bad when you press it. with an obd2 scanner you can press the brakes and watch the short term and long term fuel trims rise all the way up to 100% and then when you let off the brakes the truck will fall on its face.

man you fired the parts cannon. never change a part unless it is diagnosed as bad. a new brake booster can be had for $100-$300 and although it's a PITA to install it's not too bad.

yup it failed on my burb, massive air leak into the cab or I guess it's from the cab just only heard when you press the brakes. and at the same time I blew the front brake line that runs from the MC down to the passanger front wheel while coming up to a stop sign with my entire family in the truck. PHEW! nothing happened but I had to terminate that brake line on the side of the road and fill up the MC which thankfully didnt go dry. It failed before the intersection so I had lots of time to react and threw on the 4 way emergency lights and turned around the corner while shitting my pants. man if you have never seen this brake line it probably needs to be replaced because it sits on top of the frame where dirt, mud n saltwater land and stays. I rerouted it ever so slightly. all fixed with new lines and a couple new tools for under $100 plus the brake booster that I bought off ebay. it's made in china but so is most of delcos stuff nowadays and I couldnt find a difference.

Al
 
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I watched a bunch of videos but this guy here explains how to diagnose a leaky brake booster and then removal and replace.

 

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Discussion Starter · #6 ·
so you have a distributor on your engine . what is your engine ?
post the PCM codes . the PCV probably is worn and the hose on the PCV is old leaks .
check the fuel pressure when running . some did not use the correct fuel regulator .
forum will give good info on what motor you have .
its a 5.7liter 350 vortec with multiport fuel injection
 
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