Car Jerking when Accelerating

[chinkywinky]

So when i drove the car today it kept jerking when I was accelerating. It's like I was loosing power. I was running on almost empty gas but when I filled up it was ok. I'm hoping it's only because I was almost at empty. What could be the other causes of that?

[Monkman33]

It was fuel starvation. I recommend you don't let happen again. It can cause detonation.

[prrex4ever]

I have always heard that anything less than 1/4 tank is cause for concern for fuel starvation.

[rx4ur7]

I do not think that is true. We ran three cars in the Firehawk and Toyo IMSA series and never lost a motor to fuel starvation related detonation. These cars were run at speed, WOT, until they started to stumble, (BTW That was more than likely the jerking you had) they would then come in for fuel. Taking on nearly a full tank. These were 6 to 24 hr races.

I do not recommend it but I do not think that is the issue. My experience is that it has been more related to add-ons, control system setting, overboosting or the steering wheel control nut.

As stated I still do not recommend that you run them dry or low. I recommend keeping the tank full. For one, you maintain the handle of the car. Two, low fuel levels will build up more pressure in the tank from expanding gases putting more stress on the evap system and in extreme cases causing the tank to expand and break the baffles loose interally. (has happened I have replaced them)

Another thing is that low fuel has tendancy to build water condensation in the tank. Very common in hot climates with extreme temperature changes. Humid climates even more so.

That being said, maybe some of the fuel starvation detonation theory could be related not only the 4 I mentioned above but add to that pumping water into the compustion chamber instead of fuel?

In conslusion,
Keep it topped off with good fuel
Keep the filter clean
Use Redline SI-1 treatment once a year
If using aftermarket control systems, make sure you have good maps.

[chinkywinky]

Thanks guys. She seems ok now.

[Monkman33]

rx4ur7,

I do not wish to attempt to discount your experience, however, perhaps we are talking about two different applications regarding fuel starvation. One is under Naturally aspirated conditions, the other, under boost. Fuel starvation can easily lead to a detonation under boost due to the pump not being able to retain full pressure. As the pressure drops (which is not instantaneous in any way) there are multiple firing cycles in which the air/fuel ratio is at a dangerous lean condition. This is where the detonation happens. After the rail pressure drops below a certain point, the afr becomes too lean to even ignite, in which case you have a definite stumble/misfire scenario. I have watched the fuel pressure drop in a vehicle under fuel starvation conditions and heard definite pinging before it went to a straight missing.

Again, with complete regards to someone with much more actual racing experience than myself, I just feel we are looking at two different situations.

[rx4ur7]

Yes Monkmon33, you are correct in that light everything you state is true.

I was just referring to fuel level in tank in stock based applications as being the cause.

In my experience modifications done by many DIYs that are not done with a lot of thought in mind in that overboosting, insufficient fuel delivery and/or proper safeguards being taken usually lead to fuel starvation and resulting engine failure due to detonation.

Whilst properly built and maintained vehicles very rarely do. A bad fuel pump, clogged filter, injector or failure of control system would be one of those. Although blocked filters or injectors can usually be attributed to human error.

BTW-The IMSA and Firehawk cars were stock FD3S so it is a testimony on how well engineered the factory vehicle is when maintained properly.

So actually we agree, not enough fuel NA or turbo will cause the round motor to rattle resulting in $$$ for your local builder.

[powerhouse]

Lets get the monkey on the right banana tree.
1. Run out of gas, NO detonation.
2. Run on lean gas, "Kaboom"

Run out of gas at low RPM . a possible sputter before you stall.
Run out of gas at high RPM. burrrrrrrrrrrrrr if you know what i mean.

[Monkman33]

Originally Posted by powerhouse

Lets get the monkey on the right banana tree.
1. Run out of gas, NO detonation.
2. Run on lean gas, "Kaboom"

Run out of gas at low RPM . a possible sputter before you stall.
Run out of gas at high RPM. burrrrrrrrrrrrrr if you know what i mean.

Problem with your "run out of gas" issue:
You never go from full pressure and proper AFR's to zero fuel within a millisecond. you get air in the lines as the pump runs out of fuel to pressurize the system. As the pressure drops, your injector pulse-widths stay the same. Thus injecting a leaner mixture, which can cause detonation if it gets too lean. Then as the pressure keeps dropping or fluctuating depending on where the remaining fuel in the tank is being moved to (based on the movement of the vehicle) the car will run worse and worse. Again, not enough pressure means less fuel, means leaner AFR's, means higher chance of detonation.

That is the problem with fuel starvation... you never JUST run out.

[Monkman33]

Originally Posted by rx4ur7

Yes Monkman33, you are correct in that light everything you state is true.

I was just referring to fuel level in tank in stock based applications as being the cause.

In my experience modifications done by many DIYs that are not done with a lot of thought in mind in that overboosting, insufficient fuel delivery and/or proper safeguards being taken usually lead to fuel starvation and resulting engine failure due to detonation.

Whilst properly built and maintained vehicles very rarely do. A bad fuel pump, clogged filter, injector or failure of control system would be one of those. Although blocked filters or injectors can usually be attributed to human error.

BTW-The IMSA and Firehawk cars were stock FD3S so it is a testimony on how well engineered the factory vehicle is when maintained properly.

So actually we agree, not enough fuel NA or turbo will cause the round motor to rattle resulting in $$$ for your local builder.

Sounds good to me. :-) As I said before, I believe you have MUCH more actual racing and tuning experience than myself, so I did not intend to discredit you in any way.