5.7 vortec troubleshooting

what kind of meter do you have?
 
From the off position you have voltage positions to the left and the right.
(the white numbers on either side)
The left side of off from apprx 9 o'clock to 12 o'clock is the DC voltage positions. The right siode is the AC voltage positions.
For your car you will (always) use the DC. The number represents the top end of the scale you expect to measure. Use the smallest number possible that is GREATER than what you epexect to measure. In this case 20.
 
Im using this pic for reference
81kXPNs6LRL._SL1500_.jpg
 
Did you ever check the fuel psi? I wouldn't think it's the pump unless you have low fuel psi at the intake/injectors.

A relay is just a remote activated switch. It either works or it doesn't. When you turn on a relay, it energizes an electromagnet and closes the contacts to close the circuit and perform whatever is desired.

You can test whether the cat is clogged by using a back pressure gauge.

My guess is it's geared high, with a relatively loose converter, and a partially stuck open egr valve.

No way of confirming any of that without testing. Block off egr and see if it runs better. Keep a code reader nearby as it will throw codes and then probably run worse.

Make sure the timing is set correctly, and that the balancer hasn't spun on the crank pulley. This would throw off the timing mark and the base timing. Not sure if this applies to you specific model or not.

Fuel filter.

Make sure return line for fuel isn't pinched somewhere. This would cause fuel psi to increase and potentially run rich.

A good scanner will show and graph the data stream for all sensors and can confirm or rule out many things.
 
Have you changed the fuel filter?
 
Fuel pressure key on engine off is 60 then drops to 55
At idle it's 49 psi
While driving it sits at 42 psi and highest it goes is 55 uphill wot

fuel filter is good also
 
C.Berry said:
Fuel pressure key on engine off is 60 then drops to 55
At idle it's 49 psi
While driving it sits at 42 psi and highest it goes is 55 uphill wot

fuel filter is good also
Click to expand...

That looks like pump is fine. Maybe time for a regulator though.

Actually looks like vacuum leak though.

Should have same psi idling as driving around low load as vacuum is at highest.
 
I do have a rather loud fuel pump and the jumping fuel gauge just made me think the whole unit was going bad, carb cleaner around the manifold will tell me if I have a vac leak on manifold gasket won't it? I figured with 42psi driving that means no pump pressure!? Pressure should be 60-66 driving the lowest I've heard on this engine is 55 driving 52 at idle!?? I'm starting to question everything I've read on this engine! Lol
 
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Yes, 60-62 at WOT. Look back at my post with the specs. It should never be at 42 psi driving. If the injector assy was replaced and the pump was not, it likely is the pump at fault. the volume test would tell you for certain. if it lacks power when you slam the throttle at speed and the pressure doesnt jump to 62-65, ita not got enough volume. if you plug the return and check the pressure running, it should jump to at least 80-90psi. vacuum leaks will nearly always set a code, because its a mass air motor. speed density systems get away with a lot more without tripping a code, but the mass airflow systems are pretty sensitive to leaks. Yes I have seen the fuel gauge bouncing around with a failing pump. restricted fuel filter would do it as well but normally ive not seen that cure such problems, although filter replacement is necessary to validate pump warranty in most cases.
 
Gonna try volume test Tom first thing and I'll post back! Y'all need a award on this one lol... :beer:
 
So I have no soft lines to block return off to test volume any ideas on this?
 
Just use hose for what and where? Lol Sorry not sure I'm grasping how that will measure volume!? I have to have the gauge to see if it goes over 65 psi don't since it will be testing max without the regulator so t I have to get reading on that?
 
You may be confusing volume with maximum pressure. Testing volume is done by having an open pressure side line discharging in a container. Without starting motor turn key on and observe amount of gas flow while pump cycles on. Pressure test is done to determine pressure the pump will produce without regulator. Regulator lowers pressure from pump by bleeding off excess via return line to tank. I usually check pump pressure on my Suburbans by disconnecting return line just in front of driver side rear tire at connection fitting. I have short piece of factory line that the open end is blocked that I tighten into connector fitting. This stops flow back to tank allowing to check maximum pressure of pump without regulator
 
Yep I was def confusing the two by thinking they were the same thing!! Lol I found a ground strap up front that I'm guessing goes from frame to engine since the other one goes to cab from frame I hooked it to the bolt in back on engine thought it may be a cause for shit performance since it was unbolted but no change! Got a acdelco pump and another new filter on the way tho! Gonna try these test before installing new pump just to be safe!
 
Well fellas the old pump had slow volume coming out of it started poring fast and slowed down quick I got truck to operating temp bc pump seemed to run good when old then worse as it heated up!! Replaced the pump today and viola got all power back dash gauge still jumps on startup but I can live with that!! I greatly appreciate the help troubleshooting this fuel issue hope this thread helps someone one else on down the road! Feel free to use this as a info thread on vortecs if anyone needs help!!
 
Yeah it has a lot more pep in its step now for sure! Still have a roughing idle sorta surges but I'm chalking that up to bad 02 sensor going to invest in a tach2 scanner for my personal use to find issues! Also the 4.10 gears may it slower on takeoff like said above...
 
Back to this shit again... burb stayed running decent after fuel pump but now slowly seems to be dying replaced torque converter no change cut cats off no change, it’s gettin air not sure what the hell it is has new maf,tps,Delphi pump,Delco filter, it won’t even turn over rear tires in gravel now after converter replaced fluid in pan was perfect red color no big shavings in trans own new trans filter, I’m truly stumped! I loaned fuel pressure gauge to a guy so now I need a new one he lost it. This has the newer spider injectors in it also dizzy all looked great, timing was set good, sprayed carb cleaner around engine no idle changes I noticed... fml I need my truck back in action anyone have a idea to get this thing figured out or do I need to find a actual mechanic with computer skills to diagnose this problem?
 
Just coming on the last page of this, but I had a 98 5.7. After, a fuel pump change, It Stumped great mechanics, Scanners, & a Dealership! I kept getting emission codes. Everything related was changed out, & even a smoke test run. On a Trail ride, Jason Lackey heard me talking about it. I had bought & installed an Autozone fuel pump. Nothing wrong with the Pump, B U T, the dang tank pressure switch, was Not compatible with the GM computer. GM/Chevy, had a Bulletin on this, but I guess the Dealership Didn't read it. ONLY the AC/Delco sensor, can be used. That Fixed the problem, that had everyone Stumped. Sounds like you got another "Stumper"! Good Luck!
 
rodney eppes said:
Just coming on the last page of this, but I had a 98 5.7. After, a fuel pump change, It Stumped great mechanics, Scanners, & a Dealership! I kept getting emission codes. Everything related was changed out, & even a smoke test run. On a Trail ride, Jason Lackey heard me talking about it. I had bought & installed an Autozone fuel pump. Nothing wrong with the Pump, B U T, the dang tank pressure switch, was Not compatible with the GM computer. GM/Chevy, had a Bulletin on this, but I guess the Dealership Didn't read it. ONLY the AC/Delco sensor, can be used. That Fixed the problem, that had everyone Stumped. Sounds like you got another "Stumper"! Good Luck!
Click to expand...
We’ll ordering delco pump tomorrow! I’m sick of this sluggish burb engine has 189k and seems to Be awesome shape trans seals and in pan was surprisingly perfect filter wasn’t even that bad! Pump it is again lol luckily I can do pump in like 30mins with section cut out in back now! I’ll def post up results
 
You said the dizzy looked great, have you pulled it out and checked the gear? I seem to remember there being some bad dizzy (soft gears) out there a few years back. Might also be a worn gear on the cam side.....I can't remember if it was overly hard gears eating cams, or overly soft gears.
 
Don't mis-understand. The Autozone pump was fine, & no power problems. It was the china tank pressure sensor, on top of the pump, that had the wrong Ohms. The sensor is separate & interchangeable. Just plugs into a hole. After I put the AC Delco sensor on, it stopped throwing emission codes.
 
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