Vortec 454 Revs up high then dies HELP!!

[cool_as_crap]

Bad o2 sensors would give you a check engine code.

 

[Tom P]

Completely bad O2 sensors, yes. Failing O2 sensors that work just enough to screw with your trims the wrong way wont necessarily throw a code.

 

[Brice Edwards]

Completely bad O2 sensors, yes. Failing O2 sensors that work just enough to screw with your trims the wrong way wont necessarily throw a code.

I unplugged them both, still no code thrown but it runs slightly better. still definitely rich though

 

[Brice Edwards]

I take that back now it runs even worse and has no power, it almost acts like the timing is way off

 

[Christian Steffen]

That is because it is running lean, the o2 sensors are probably correct in how much fuel they're adding. When you unplug them the computer has no idea that it needs more fuel. If it is truly running 25% lean like the o2s are saying that would mean its running at ~18:1 afr, which will make it feel terrible.

You need to get that fuel pressure right, then we can look into other issues.

 

[Christian Steffen]

Do the trims stay that negative while driving too?

 

[Brice Edwards]

Do the trims stay that negative while driving too?

no, they're only like that at idle

 

[Christian Steffen]

So they get close to zero while cruising then?

Did you swap back to the stock maf?

 

[Brice Edwards]

So they get close to zero while cruising then?

Did you swap back to the stock maf?

I sure did, didn't change anything

 

[Christian Steffen]

I sure did, didn't change anything

A vacuum leak seems most likely then. They're usually more pronounced at idle than cruising. The unmetered air makes up a larger percentage of the total airflow at idle than cruising.