Join 3,572 readers in helping fund MetaFilter (Hide)


Fuel injection huh?
October 1, 2012 11:58 AM   Subscribe

Mechanic-filter: AAA just fixed my car and I don't understand how. Explain it to me like I'm 5 years old.

Tried to start my car about 5 days ago and the engine would crank but the car wouldn't start. I was out of town and got back last night. Tried it again, same result. The boyfriend tried it, putting his foot on the gas, and got the same result. Called AAA to have them tow it to a shop. The tow truck driver asked if he could take a look at it. He got in the car, turned the key, put his foot on the gas (all the way to the floor) for about 15 seconds while the engine cranked, then lifted his foot up slightly. The engine caught and a puff of smoke came out the tailpipe. Turned the car off and restarted it a few times and it started like normal. He warned me not to put my foot on the gas or touch the gas pedal when the car was turned off, and said something about the fuel injection. I don't understand what any of this means! I've been driving for 16 years and have never had this happen before, and I don't put my foot on the gas when I'm starting the car. Can anyone walk me through what happened so I'll know what to do if it happens again? Car is a 2002 Ford Escort. Thanks!
posted by jabes to Travel & Transportation (14 answers total) 4 users marked this as a favorite
 
Sounds like a flooded engine.
posted by Partial Law at 12:05 PM on October 1, 2012 [1 favorite]


What it might be is that when you put your foot on the gas and start the car at the same time, you're sending lots and lots of gas into the engine cylinders and it coats the spark plug contacts. This makes it really difficult for the spark plugs to actually spark, so the gas doesn't ignite in the cylinders and start your car.

The computer in a fuel-injected car knows how much gas to send to the cylinders to get the car to start, but you said, "No! More gas! MOAR!"

I think by cranking it, the auto guy basically ran the pistons up and down without a lot of gas until the spark plugs dried out enough to fire.

So the moral of the story is, don't touch the gas pedal when you start the car.

I'm not sure why the engine was flooded to begin with, though.
posted by babbageboole at 12:11 PM on October 1, 2012 [1 favorite]


Flooding is common on carburetor'd engines, not so on injected ones. 2nding EFI- related weirdness.
posted by anti social order at 12:13 PM on October 1, 2012


Yep, you flooded the engine. I have no experience with this in cars, but I have a 1978 Vespa, and if I accidentally leave the gas valve on overnight, I have to kick and kick and kick (this is the equivalent of turning on the ignition) to "push" or cycle all the gas out before it'll start normally. When it finally does, the exhaust is a huge haze of white smoke for a few minutes.

I don't have the mechanical knowledge to go into specifics here, but I do know that all engines need a certain BLEND of gasoline and oxygen, and when you flood an engine you are giving it too much gasoline and not enough oxygen. This is why you have to cycle the flood out until you get back to the proper mix of air and gas. This is also why there is a lot of smoke — too much gas, not enough oxygen.
posted by Brittanie at 12:30 PM on October 1, 2012


Yep, when you flood a fuel injected car, you overcome it by holding the gas pedal down while you crank it over. Sounds counter-intuitive, but that is the way it works. (Same with an old crarb'd car, too, but who drives those anymore, right?)

Don't worry about it, though, as this is not part of the common knowledge skillset of driving a car.

In the old days, you would have to step on the gas a bit before trying to start a car. Some people still do this, which is why AAA told you not to.

In the future, though, as more and more cars are becoming drive by wire, you can step on the gas pedal all you want when it's off and nothing will happen, because the gas pedal is telling the computer what to do when the car is on, instead of being connected directly to the engine.
posted by TinWhistle at 12:32 PM on October 1, 2012


Yup. Flooded engine. With modern cars, don't touch anything when you try and start them other than the key (and the clutch if it is a manual). As mentioned, it gives the engine non-optimal fuelling while trying to start.

It doesn't coat anything on the spark plug, but it does put more fuel into the cylinder that is hard to remove for a cranking engine. You need a dry combustion chamber to give the correct air/fuel ratio to burn so any gas hanging around from weird throttle positions initially won't help the situation.
posted by Brockles at 12:37 PM on October 1, 2012


Ooops, I forgot to address WHY it happened in the first place.

Could be several things:

--You bumped the gas pedal when the car was off while you were getting out and didn't mean to or didn't realize it (or the floor mat got in the way and held the gas pedal down a bit).
--Something is stuck open in the EFI, in which case you are going to have the same problem later today or tomorrow. This will require a visit to the car doctor.

Hopefully it was the first option, but likely it could be the second, so be prepared for a repeat adventure.
posted by TinWhistle at 12:37 PM on October 1, 2012


It does sound like it was somehow flooded (i.e. there was too much fuel in the engine, so it could not ignite). Pressing the pedal and cranking the engine opens the throttle (i.e. lets in lots of air) and turns the engine over. That clears out the excess fuel and then the car can start.

All pressing the pedal will do on your car when it is off is open the throttle (just a valve that lets in more air). The fuel injection is controlled by a computer, so with no power, no computer, and so no fuel is injected. So something else caused the problem.

The AAA guy's belief about pressing the pedal while the car is off is a relic from the carburetor era. On more modern cars than yours, the pedal just sends a signal to the computer, so would do nothing at all when the car is off and likely would be completely ignored by the computer when starting.
posted by ssg at 1:08 PM on October 1, 2012


However, my understanding is that in a diesel-powered car you need to floor the gas pedal every time you start the engine. At least, that's what I learned to do in trucks, and it always worked. Whether it's the same for diesel-powered cars in these computer-managed days, I don't know, as I haven't driven one for a while.
posted by aqsakal at 1:34 PM on October 1, 2012


Definitely not for diesel cars. I'd be surprised if the pedal actually did anything at all while starting, but no reason to do it.
posted by ssg at 2:31 PM on October 1, 2012


Mechanic with 20 years experience weighing in here...I don't buy the flooding story. You tried to start the car and it wouldn't start, then you left it for 5 days. If it was flooded originally it wouldn't be flooded five days later. Any fuel in a cylinder w/ an open valve would have evaporated. The simplest cure for a flooded engine is just to walk away and try it again hours later.

In my opinion the AAA guy didn't fix or correct anything he just happened to have his hand on the key when it decided to start. If that is the case you have a problem that will show up again. I bet you have an electrical problem and a general rule of thumb is to rule out any electrical issues before troubleshooting a fuel circuit.

Has it been wet or rainy? A tiny crack in the distributor cap or damaged (old) spark plug cables can cause mysterious ignition gremlins. How long have you owned the car? It is a decade old, if it has been more than 4 or 5 years since the distributor cap, rotor, spark plug, and cables have been replace you should replace them now.

You should be able to get all of those parts for about $100 - $125 on-line. The work is pretty simple you could do it yourself w/ info you find on-line but an honest mechanic should do it for under $250 (i'm guessing here, don't know where you live).

If your ignition distribution parts are old they should be replaced as it will save you trouble in the future. If the problem shows up again at least you have taken the first step in a longer troubleshooting process and have more info you can give a mechanic.

While you are at it check how old the battery is. Winter is coming!
posted by pandabearjohnson at 2:41 PM on October 1, 2012 [3 favorites]


The procedure he did, where he held the pedal down to the floor, is a common thing in fuel injected cars. It tells the computer that you know it's flooded and to burn off all of that gas before injecting more. Wikipedia talks about it a little bit.

More modern cars wouldn't flood in the first place, but a 2002 could have worn injectors that could cause a flood.
posted by zrail at 2:45 PM on October 1, 2012


I agree with pandabearjohnson. Flooding doesn't happen alot with fuel injection. Pressing the gas pedal or not, it's all computer controlled and has a preset amount of fuel for starting. If this is becoming an intermittent or continuous problem...and eventually your car won't start at all...change up your ignition parts and if it's over 50/60k miles, change the ignition module too. That's about another $100 but your car won't run if it is beginning to fail.

Get a tune up and good luck to you!
posted by snsranch at 5:35 PM on October 1, 2012


My old car did that. Very long cranking times, almost to a point when battery would be about dead. It turned out to be that fuel pump was on the way out. This could be a cause too. It is very easy to check fuel pressure.

In all (most) vehicles, when their engine is flooded you need to floor the gas pedal when cranking. When you do that engine's computer doesn't inject any fuel so you can clear it out of the cylinders. This is how you start flooded fuel injected vehicles. Most of them, they might differ.

Yes, fuel injectors are computer controlled, but sometimes they leak fuel even when computer doesn't want them too and flood engines (they should not leak).

If the problem persists, I would do the cheapest things first if you were to DIY. Tune up (spark plugs and their wires, distributor cap, rotor. Then maybe fuel injectors.
posted by AdamG8GXP at 6:47 AM on October 2, 2012


« Older Does anyone know what the pian...   |  I really like some of the song... Newer »
This thread is closed to new comments.