I bought a 99 suburban with a 5.7 Monday and while test driving it it was sluggish if you took off quickly, I figured it was a timing issue coupled with a manifold leak. Tuesday it acted like it was running out of gas after it sat on an incline (driver side higher than passenger side) for a few minutes but fixed itself after 20 seconds or so. While getting lunch Wednesday it did the same thing but fixed itself again after roughly 20 seconds or so, again I thought it was a timing/manifold leak issue. Took it to the shop to have the donut gasket on the manifold fixed and when I picked it up today it acted like it was out of gas again, but didnt fix itself this time. Got it to my uncles to change plug/wires/ and swaybar links and he hooked his reader up to it. It threw a code for bank 1 running lean or something similar so I replaced the cap and button thinking it was maybe the air/gas mixture getting enough spark...still didnt fix it. I checked every vacuum/airline I could find and they were fine, its getting enough fuel. Maybe even a little too much since I can smell gas if I stand by the rear driver side tire. I also discovered you cant time it using the distributor, so with all that being said my best educated guess would be a faulty mass airflow sensor, but im reluctant to spend $110 and that not fix it. Also im not sure if it matters but the exhaust doesnt have cats so the 02 sensors dont have ports to go in. And input would be appreciated

 

Before buying a MAF, get a $12 OBD wireless adapter and the Torque pro app for $5. Then record a data log. Pay close attention to the fuel trims at idle vs. under a load. Here is a reference to other 5.7l operating data.

https://www.pidfusion.net/datalogs/GM57Lpx/500/

The smell of gas by the drivers rear could very well be a small fuel leak or evap system leak and doesn't necessarily mean the engine itself is getting enough fuel. This engine is very fussy about its fuel pressure. You may want to check it with a fuel pressure gauge that you can loan/rent from the local parts store.

 

Fuel pressure was 55 psi when we checked it

 

Fuel smell by back tire?top of tank have a problem?and next time going to start it, disconnect MAF,do that a couple different times,to make sure,if it starts better,yep,and online 60$ for MAF,and I forgot,clean that one first,never hurts

 

I'm thinking there us a small leak on the top of the tank, I'm dropping it Saturday to check it out. I took the maf off but left it plugged in and it started but idled like complete crap, it's also clean and in good shape.

 

Leave MAF in place, but disconnect electrical connection,no input is sometimes better then bad input,if that's the problem

 

Ah okay. I'm gonna try that now

 

I unplugged both connections and it ran fine around the block. It would kind of lunge forward when stopped at a light, but it was much better

 

And reading that again, maybe the check valve at pump is shot,so if you cycle the key a couple times before cranking ,it might start better

 

I would clean it again,hard to see by eye