What does it mean if you have to press the gas pedal to get the car to start?

[haydenm315]

My car always starts right up on the first keyturn. The same isn't true if I somehow stall the car. This will usually occur in the morning if I'm not paying attention and am not gentle enough on the clutch and don't give enough gas. It will turn over a good bit before coming back to life. If I floor the gas pedal it roars right back to life. I've read that flooring the pedal on startup cuts off the fuel injectors. Does this mean my engine is flooded when it stalls?

 

[Yamaha V6]

No, flooring it doesn't cut off the fuel injectors, it tells the car to run in WOT, allowing the most air in to mix with the fuel already there.

When you flood a fuel injected car, mash & hold the gas until it fires (then obviously let off quickly). If you just turn the key, the mixture's too rich & it won't fire, especially since as you crank you're firing more fuel in there; the car isn't reading the mixture on startup since it's in open loop, so it doesn't adjust the fuel to lean it out so it can fire. Going to WOT allows it to fire.

 

[shojuan]

I always thought the computer cuts fuel when the TPS signal reads foot to the floor on startup? shrug

 

[stevetatro]

People who know much, much more about the SHO, and the FI system, than I do have stated that when the car's off, pushing the throttle to the floor cuts off the injectors.

This is handy becuase if you have a leaky injector and there's already fuel in the cylinder, when you go to start it there would be too much fuel in said cylinder. If you cut off the injectors and prevent additional fuel from being injected into the cylinder the cylinder can effectively burn the fuel that trickled in from the leaky injector.

Phew. I'm tired now.

 

[projectSHO89]

Per Charles Probst, SAE, on page 42 of "Ford Fuel Injection and Electron Engine Controls"
/quote
De-Choking

Under some conditions, cranking may "flood" the engine in spite of the best efforts of the fuel control system. "De-Choking" provides for cranking without fuel to dry out the plugs and cylinders. Cranking witht he accelerator held full down signals the system to de-choke.

/end of quote

Instructions for using the pedal to the floor technique are also in your owner's manual. Read it.

Steve

 

[Yamaha V6]

Ok, so the injectors don't actually fire. If that's true, how does the car know ignition from non-ignition (read this as, how does the car know that the starter isn't turning everything, vs. the combustion turning the engine over?)

If the fuel injectors are cut off & you keep the car floored, the amount of fuel already in the combustion chamber is used up VERY quickly. How then does the car fire & keep running (at WOT). Try it. Floor the car, start it, and it RUNS (and revs up very quickly, obviously). If the injectors are not firing, how does fuel get to the cylinder to combust? Osmosis?

It's got to be a pre-set no injector for X ignition cycles or something like that, otherwise I don't see how this would cause the car to start. Someone clue me in please.

 

[Mike Kopstain]

Fred, your obviously quite a ways farther up the totem pole of knowlegde than I am, but the way I understand it is that WOT or 4.5 - 5.0 volts from the TPS will shut the injectors off. The computer will know the engine is running on it's own power when it gets to a certain RPM and will start firing the injectors regardless of throttle position.

I just went out and verified this on the Vulcan ( ). Holding the pedal down results in no pulse signal to the injectors.

<small>[ March 28, 2003, 12:19 PM: Message edited by: Mikeys_Taurus ]</small>

 

[SHOZ123]

If you need to prove to yourself that the injectors are off when cranking the engine and the gas pedal is to the floor just try it. This is also a good way to pre-oil the engine before starting.

 

[projectSHO89]

The computer discriminates a cranking condition from a running condition by watching for an irregularly timed PIP signal.

Do yourself a favor, get the Probst manual. All of this is explained in it.

Steve

 

[Underdog]

Perhaps it's different in the later years. My 94' Helms manual states that 450 rpm is the magic number that tells the computer the engine is running.

 

[Doug Waschenko]

SHO throttle position sensors are whacky.
For some reason, under some conditions the driver needs to move the throttle, much like the car had a crburetor and you needed to pump it to start it, PARTICULARLY when the car is still cold, had been running for 30 seconds or so and you stall it from say letting out the clutch to fast.
Your mechanic will test it, tell you it's good and not to pump it, but trush me do it.
Sometimes the DIS module is responsible for this.
They tend to develop cracks in the plastic housing because of thier location on the intake manifold.
Sometimes you can test this by running the car in the dark with the hood open and you will "see" the arching in the module that you wouldn't ordinarilly find.
Good luck.

 

[Bizzy]

I've noticed that my sho many a times needs me to give the pedal a little push to open up the TB for it to kick over and start. This only happens when the engine is cold, when it's warm it starts right up without issue. Is it possible that my injectors might be leaking or have something stuck in there?

I do like that idea of flooring the pedal to pre-oil the engine. So if I were to floor the pedal before turning the key to any position, then start the engine if it fires right up then there's a good change that one or more of my injectors might be leaking? If in fact starting the car at WOT cuts the injectors.

 

[jasonty]

I just tried this on my junkyard 90, and my good 90, and they both started up, but not happily. I dunno, maybe they both have leaking injectors.

 

[projectSHO89]

If you have a continual need to apply partial throttle in order to get the engine started, your problem more likely is due to a failure in the Idle Air Bypass system.

At engine startup time, the IAB valve is commanded to the full open position. It supplies enough air around the closed throttle place to allow the engine to start in most cases. If the IAB valve were to stick, not open fully, or had the bypass passages otherwise clogged, there would be insufficient airflow to support the rich fuel/air mixture needed to start the engine under cold conditions. "Cold" in this sense means any engine that has not been run for 12 hours. A cold engine might be -20F in January in Canada or it might be 120+ under a broiling August sun in El Paso. Same thing to the computer. It's a "cold" engine until it reaches 195F.

By pressing slighly on the throttle, the operator is allowing a small amount of air to bypass the plate and it is intended that this procedure will help an engine start.

If all of you will open your owner's manual (those who have them) and read under the starting instructions, you will find that this advice is also included.

Steve W