Holly_Hobby: primitive has octane question

[franksolich]

http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=310x825

Hmmmm.

Holly_Hobby  Donating Member  (1000+ posts) Thu Jan-31-08 07:33 PM
Original message

Octane question
   
Hi....I have a 2005 Chysler Pacific with 8,500 miles on it (I don't drive much). It's starting hard, no matter the temp outside. I have to push the gas peddle half way down to get it to start after it sits. I haven't used premium gas like the recommendation, I use the cheapest grade. Could this be causing the problem? Thanks.

There aren't many primitives knowledgeable about automobiles; only one showed up at this bonfire.

jimmil  Donating Member  (20 posts) Feb-26-08 02:31 PM
Response to Original message

1. Rather Doubtful...
   
Octane has more to do with the ability of gas to not auto-ignite when subjected to pressure. At startup there is really nothing there that octane really can effect. Things that do have an effect on startup, depending on the motor of course, could be something like the fuel pump. When the ignition is turned on the fuel pump pressurizes the system. You can check the fuel pressure by attaching a pressure tester on the fuel rail which has a nipple similar to what is on a tire to inflate it. Check to see if you have the proper pressure. If not then it can be the fuel pressure regulator or the actual fuel pump. More often than not it is the pump. If the car sometimes starts right up and other times not then it is highly suspected that the pump is slowly going out.

If the fuel pressure is good then you need to check various sensors that have an effect on the start procedure. The first thing that happens after you begin the cranking sequence is the crank sensor tells the computer where the crank is in relation to what phase of stroke it is in. Once the crank sensor detects the crank's position it tell the computer where it is and then the computer looks for the cam sensor impulses. Once the cam position is detected and read the computer can tell the fuel injectors when to fire as well as when to fire the spark. So you can start at the crank sensor and trouble shoot from there.

Something that can happen although not so very often is you can have a leaky injector that cause problems when starting. To test that you need to pull the injector fuse at the fuse panel. Then you try and start the car. If the engine fires ANY then you can be assured you have an injector that is leaking.

Okay, experts--is the jimmy primitive right or wrong?

[Chris_]

High Octane is more expensive, therefore better.

[Rebel]

Holly_Hobby  Donating Member  (1000+ posts) Thu Jan-31-08 07:33 PM
Original message

Octane question
   
Hi....I have a 2005 Chysler

Well, you've identified the problem. Next step is fixing it.

[Crazy Horse]

Not sure if the primitive is correct or not. The primitive is incorrect about the gas rsatings meaning nothing.............very bad advice not to follow the required, not recommended ratings. Running low octane in a high compression engine that says it needs 92/3 will cause detonation before the plug and be a knocking.

So seeing that the primitive thinks there is nothing different between the gas ratings...........yeah I feel with high confidence that it's wrong

[Uhhuh35]

The engine in her car is a 3.5 liter V 6 that has 10 to 1 compression ratio pistons! That's high!
Every car manual I've ever read recommends a certain octane rating. If you go off this recommendation and buy a lower grade fuel you could have starting and stalling problems. Some people will tell you that the higher cost of premium gas is offset by the better fuel economy. With the price of gas these days, premium isn't really a lot higher than regular is it?

Anyway, higher grades are meant for engines that have a higher compression ration so yes, it's probably causing the problem.

[Miss Mia]

The engine in her car is a 3.5 liter V 6 that has 10 to 1 compression ratio pistons! That's high!
Every car manual I've ever read recommends a certain octane rating. If you go off this recommendation and buy a lower grade fuel you could have starting and stalling problems. Some people will tell you that the higher cost of premium gas is offset by the better fuel economy. With the price of gas these days, premium isn't really a lot higher than regular is it?

Anyway, higher grades are meant for engines that have a higher compression ration so yes, it's probably causing the problem.

Agreed.  The manufacture recommends specific octanes for specific engines and performance. You should always use what's recommended. 

[Carl]

olly_Hobby  Donating Member  (1000+ posts) Thu Jan-31-08 07:33 PM
Original message

Octane question
   
Hi....I have a 2005 Chysler Pacific with 8,500 miles on it (I don't drive much). It's starting hard, no matter the temp outside. I have to push the gas peddle half way down to get it to start after it sits. I haven't used premium gas like the recommendation, I use the cheapest grade. Could this be causing the problem? Thanks.

This person may or may not be having an octane problem,I doubt it.
Old,dead,tarnished fuel is more likely a problem and in a fuel injected vehicle never touch the gas pedal when starting.

[Gwitness]

A weak fuel pump is a more likely cause.

[Chris_]

A weak fuel pump is a more likely cause.

Or....there is a loose fitting/pinhole somewhere on the injector rails, and the system is losing prime.....

doc

[Gwitness]

A weak fuel pump is a more likely cause.

Or....there is a loose fitting/pinhole somewhere on the injector rails, and the system is losing prime.....

doc

Possible...but highly unlikely...there would be a complaint of a raw gas smell....I've replaced a number of these pumps for just this very reason.

[RobJohnson]

olly_Hobby  Donating Member  (1000+ posts) Thu Jan-31-08 07:33 PM
Original message

Octane question
   
Hi....I have a 2005 Chysler Pacific with 8,500 miles on it (I don't drive much). It's starting hard, no matter the temp outside. I have to push the gas peddle half way down to get it to start after it sits. I haven't used premium gas like the recommendation, I use the cheapest grade. Could this be causing the problem? Thanks.

This person may or may not be having an octane problem,I doubt it.
Old,dead,tarnished fuel is more likely a problem and in a fuel injected vehicle never touch the gas pedal when starting.

I agree.  That would be the first place to check.

[RobJohnson]

A weak fuel pump is a more likely cause.

Or....there is a loose fitting/pinhole somewhere on the injector rails, and the system is losing prime.....

doc

Possible...but highly unlikely...there would be a complaint of a raw gas smell....I've replaced a number of these pumps for just this very reason.

Oh....a common problem? Well then that trumps my other post. I was thinking about it could be bad gas from sitting so long.

[Gwitness]

All fuel pumps fail...it's just a matter of when.

[RobJohnson]

All fuel pumps fail...it's just a matter of when.

Pretty much.

Especially when driving around with low amounts of fuel in tank all the time. On top of the wonderful quality of gas.