Silverado running bad after seafoam

[81_malibuclassic]

Also when I changed the plugs they were covered in straight oil, didn’t smell or feel like anything else, just wet with oil

[db4690]

Here’s something else to think about, on top of all the other good ideas already mentioned . . .

You may very well have flat intake gaskets

This causes rough running . . . and misfires . . . until the engine warms up and the gaskets expand and do a slightly better job of sealing

Next morning it will repeat . . . until you fix the problem

As for that fuel pressure regulator, even if you don’t have a fuel pressure test kit, there’s something you can do

With the engine idling, carefully pull off the vacuum hose going to the fuel pressure regulator

If fuel shoots out or if the hose smells like fuel, the fuel pressure regulator is definitely bad and needs to be replaced

[Rainflurry]

@81_malibuclassic

I ran the marvel then drove it about 2 miles then it died, got it started back up, just couldn’t take my foot off the pedal.

Did you put the Marvel Mystery Oil in the fuel tank or in the oil?

[81_malibuclassic]

Blockquote ran it in oil

[81_malibuclassic]

Blockquote

It only runs rough once it gets up to temp though. When it’s cold it still misses but just barely, once it gets up to temp the whole truck starts shaking and it sits there and surges

[George_San_Jose1]

@81_malibuclassic

It only runs rough once it gets up to temp.

The computer which determines how much gasoline to inject for the driving condition ignores the O2 sensors until the engine warms up. Maybe something to do w/that. A simple fuel trim test would usually identify if that was happening.

[PintoKid]

@81_malibuclassic

I can’t figure out how to quote on here

Select text from the post you are replying to and up pops a menu item to “quote”. That starts a post with the quote.

[81_malibuclassic]

@PintoKid

Select text from the post you are replying to and up pops a menu item to “quote”. That starts a post with the quote.

Thank you.

[Nevada_545]

@81_malibuclassic

the truck was a family member of mine and he started it twice a week but it hasn’t been driven since 2020

Seems like the right thing to do if you want an engine that smokes. All that cold idling pollutes the engine oil, bad for the valve guide seals.

@81_malibuclassic

Just went slow with it and did 1/4 can, when I took it out it started sounding like it had blown up

A mild case of hydro lock. The additive pooled in the bottom of the intake manifold until the throttle open, this moved the fluid to the cylinders.

@81_malibuclassic

When it’s cold it still misses but just barely, once it gets up to temp the whole truck starts shaking and it sits there and surges

Fix the misfiring before driving or operating the engine again.

[keith]

There are two modes of operation for the fuel injection of this truck, open loop and closed loop. When it is cold, it operates in open loop. That means the fuel/air ratio is set by the computer based on preset parameters. Once the engine warms up, the engine goes into closed loop where the air/fuel ratio is determined by data from the O2 sensors. You unplugged the O2 sensors and that is why it runs better when cold.

At least plug in the O2 sensors, they may not be as bad as you think. Without them, this engine will never run right.