Bad TBI injectors on 454?

[Mick Je]

Hey Guys,

Normally I'm on the 67-72 page, but I have a question you guys might know. On my 93 dad's dually it seems to idle rough and fumble around leaving from a dead stop. We changed plugs, fuel filter, cap and rotor, checked all the smog stuff and sensors on it and it's fine. 77,000 miles ago we changed the injectors on it. Do you think it's time for new injectors again?

Thanks
Mick

[Cabnchassis]

I wouldn't mess with that yet. Here are the things that typically cause a TBI engine to stumble/cut out. Failed CTS sensors, vacuum leaks at TB, TB gasket, or intake/intake gasket, failing IAC, weak fuel pump, fuel pump transfer hose broken in the tank, or low fuel pressure.

Coolant sensors are cheap and probably need to be changed by now anyway. There are two. One on top near the intake and one on the drivers side head or just below it toward the front of the engine. These engines are programmed to overfuel anyway if they run cold. if you have a failed CTS that says the truck is cold it will just dump fuel down it's throat so as to save the engine.

Spray diesel starting fluid around the base of the throttle body (basically on the tb gasket) and intake with the truck running if you hear it rev at all you've found a vacuum leak that will need sealed.

The intakes can cross over inside as well so you might not necessarily find the problem if it is an intake problem around the outer part of the gasket. Mine was crossed over inside and pulling air from the coolant passage it has crossed to.

The IAC is a large valve screwed into the TB. You can take out and spray with carb cleaner liberally. don't work the piston on it, it can damage it. When you re install it start and kill the engine 3 times in a row. Don't rush it or anything this is just to reset the CPU/IAC connection. Alternately you can leave the truck running for about ten minutes. After you do this the truck will probably run correctly until you leave it parked for a few hours or over night. That's the computer making adjustments trying to fix the problem. After a few days if the problem goes away the IAC was dirty. If it comes back the IAC could be failed. It's about a $75 part so make well sure ahead of time.

As for trouble shooting the fuel pump it can be really hard on some TBI's cause there is no service port to check fuel pressure. In my case I fixed the intake gasket leak and still had a hole in the fuel pump transfer hose. The leaky hose typically only causes stumbling on start up unless it is badly failed.

[Kudzupatch]

Sounds similar to my initial issue with mine and it was a bad EGR vavle. In case you missed it, DO NOT buy aftermarket EGR! Delco or Delphi only.

[Cabnchassis]

I swear I posted this earlier but here goes again.

Good catch on the egr. I knew I was missing some possible stumble causing culprits. I also forgot to add that the oxygen and MAP sensor can cause idle issues.