pumping tbi

[PeterbiltChrome]

This evening i went to start the truck up after not going anywhere for a few days since it was snowing and I was just working around the apartment...

 

I go to start it like i usually start my truck... no pedal, just crank it over. It fires once without much cranking and dies right away... I try it again, no pedal and same result- fires once and dies. so out of instinct from our carbureted trucks, I slap the pedal once, crank and it runs fine. NEVER BEFORE have I had to do that to any tbi or injected engine.

 

sure the manual calls for pedal play for warm, cold, and hot starts but I only gas a carbureted engine. Did i not let the fuel pump get going long enough, because I went right from off to start... Kinda rushed it because I was freezing and I wanted it to get it warmed up before I headed out... I wonder if cold weather slowed down fuel delivery....

 

it started fine after a warm-up tonite... so i'm baffled about it because it never happened before. No dummy lights so i'm not worried about it, i just have the last question~

 

I'm also curious if you should ever pump the pedal to injected trucks.... every one I've ever driven didn't need it whatsoever.......carbureted are a different story, I know...

[Hecktorx]

With a TBI motor, if you hold the gas pedal down to the floor while starting, it's like manually setting the choke to help it start. Just make sure you let off as the engine fires up.

[PeterbiltChrome]

before you crank the engine, are the fuel jets actually spraying fuel onto closed butterflies in these tbi's?

 

makes sense on setting the choke, which i though was mostly automatic but i guess you could pursuade it by pushing the pedal, hecktorx.... but "to the floor"???

[GM-Tech]

Pumping the pedal with the engine not turning does nothing. Holding it to the floor is NOT like setting the choke. A choke shuts off air, causing engine vacuum to pull more fuel through the carb's venturi, making for a richer mixture.

 

What holding it to the floor actually does in most cases is force the system into what's called a "clear flood" mode, but only if the engine is cranking, i.e. turning over but not running. Basically, if the PCM sees the TPS at WOT and the engine is cranking (not running), it shuts off the fuel injectors to help clear a flooded engine.

 

No fuel is being sprayed unless the engine is turning. Unlike a carb that has an accelerator pump that squirts fuel every time you press the gas pedal, an injected engine does nothing unless the engine is running. That is, except for the "clear flood" mode and as mentioned, that shuts off the fuel, it doesn't send more.