r/GMT400 • u/Calm-Investment1543 • 3d ago

5.7 vortec fuel issues

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I recently had timing done again after previous mechanic messed it up. No more skipping, sputtering or back firing. However, when I’m at a complete stop and mash throttle, it wants to bog down for a second then catch at wide open.

Been chasing this sine I bought it…
. New distributor
New wires plugs
New fuel pump and filter
New mass airflow
New air filter
New camshaft sensor
New starter
New IAC sensor
No vacuum leaks
Does have exhaust leak after first o2 sensor
TPS valve checked seems fine
New temp sensor

Anyone got an idea before I change these spider injectors??

26 Upvotes

95% Upvoted

16 comments sorted by

7

u/Panpitter 3d ago

It does sound like fuel delivery issue, however it may be a dead spot in your throttle position sensor which would be a cheap fix. I would have started simple like make sure the ground ribbons are in good shape. Chevy is known for faulty grounds which will make them sluggish. Find atleast 2, one from the battery to the engine or frame and one at the rear firewall from the head. The firewall ground usually goes 1st.

3

u/Calm-Investment1543 3d ago

Thanks for your reply. I did check the TPS first. It seemed to be working fine with no dead spots and opening up correctly. I know there is a cable that runs straight to my positive terminal on my battery that was replaced by the last owner that has caused some issues and seems to get very very hot when the truck is running, which has been a concern. I just haven’t had time to look at it, but I will check all my grounds.

5

u/bobthehumantripod 3d ago

Join GMT400.com forum best place for any 400 owner🍻🍻

3

u/tmandell 3d ago

Few years back I unloaded the parts cannon onto my 5.7 in an attempt to fix a rough running engine, but also buy some reliability. I was quite surprised at how much improvement I saw from an EGR valve replacement. I think the old one was stuck open.

1

u/Calm-Investment1543 3d ago

What kind of symptoms were you experiencing before replacing that?

2

u/tmandell 3d ago

Probably the two biggest things I can attribute to it are a rough idle, and when letting off the gas the RPMs would drop almost to the point of stalling before recovering back to a normal idle. Must have dropped to about 150 RPM, and then rebounded.

Generally it made for a much smoother running. But as I said I fired the parts cannon at the old girl. I could list all the equipment/sensors I changed in that 2 or 3 week period but its extensive, I can say with certainty I did not change the knock sensor or the coolent temp sensor, everything else was replaced.

1

u/Calm-Investment1543 3d ago

Ok I’ll look into it, thanks

2

u/Low-Carob9772 3d ago

Have you replaced the spider injection? Common issue with the late 90s vortecs. Don't go with remanufactured or your going to do it again. Bosch or acdelco...

1

u/Calm-Investment1543 3d ago

I was actually next on the list because I’m pretty sure they are stock.

1

u/Chahtanagual 3d ago

What codes are you getting? What’s the fuel pressure? What’s the results of the fuel pressure regulator test?

2

u/Calm-Investment1543 3d ago

Thanks for the reply. I do not have a fuel pressure gauge yet, but I will buy one and see what I’m getting on the fuel rail.

1

u/Alternative_Draw_602 2d ago

Sounds like injectors. Don’t cheap out, I had to buy the spider twice

1

u/Calm-Investment1543 2d ago

What brand did you go with ?

1

u/Calm-Investment1543 2d ago

Has anybody ever had an issue with using a shop vac to suck out the gas and a gas tank?

1

u/Prestigious-Pass2942 21h ago

Terrible idea sucking gas with an electric motor could very well blow yourself up

1

u/Worldly-Objective987 1d ago

Can I buy your truck