1. Welcome to TechPowerUp Forums, Guest! Please check out our forum guidelines for info related to our community.

Quick car question

Discussion in 'General Nonsense' started by kwchang007, Sep 20, 2008.

  1. flashstar New Member

    Joined:
    Dec 28, 2007
    Messages:
    743 (0.32/day)
    Thanks Received:
    56
    "The octane rating is a measure of the resistance of gasoline and other fuels to detonation (engine knocking) in spark-ignition internal combustion engines. High-performance engines typically have higher compression ratios and are therefore more prone to detonation, so they require higher octane fuel. A lower-performance engine will not generally perform better with high-octane fuel, since the compression ratio is fixed by the engine design."

    "Many high-performance engines are designed to operate with a high maximum compression and thus demand high-octane premium gasoline. A common misconception is that power output or fuel mileage can be improved by burning higher octane fuel than a particular engine was designed for. This is not true. The power output of an engine depends in part on the energy density of its fuel, but similar fuels with different octane ratings have similar density. Since switching to a higher octane fuel does not add any more hydrocarbon content or oxygen, the engine cannot produce more power."

    "Most fuel stations have two storage tanks (even those offering 3 or 4 octane levels), and you are given a mixture of the higher and lower octane fuel. Purchasing premium simply means more fuel from the higher octane tank. The detergents in the fuel are the same, Premium does not "burn cleaner.""

    Wikipedia

    You need an engine with a higher compression ratio to burn all of the higher octane gas. The ECU has little to do with it. You can always rebuild an engine to a higher compression ratio but there is no need to use high octane gas in a regular untuned engine. I need high octane because my engine has a 10.5:1 compression ratio...

    The sound could really be anything though. Do a thorough seafoam cleaning through the brake booster line and crank case. Don't forget to change your oil right after you do this.
    Last edited: Sep 21, 2008
  2. JC316

    JC316 Knows what makes you tick

    Joined:
    Jan 24, 2006
    Messages:
    9,357 (3.11/day)
    Thanks Received:
    902
    On a DOHC, the base timing is controlled by various electronic means. Camshaft position sensor, Crankshaft position sensor, and the ECM. If any of those are going out, the car wont start at all, or run for a bit and then die.

    Fuel pump and filter, I doubt seriously because it would be getting LESS gas at higher RPM's, thus making the car run worse. On top of that, it should fire off a lean condition code.

    It is so hard to diagnose a noise without hearing it, especially on a car since there is so much it can be. From cold carbon rap, to a timing tensioner rattling, to a rod knocking, to a paranoid owner. Each has it's own distinct sound (or lack thereof).
  3. kwchang007

    kwchang007 New Member

    Joined:
    Jan 27, 2007
    Messages:
    3,979 (1.51/day)
    Thanks Received:
    185
    Location:
    Severn, MD, USA.
    lol paranoid owner might be me...maybe it's the fact that the other two cars we have, have like 60 and 100 k less than my car so I'm just freaking out cause it doesn't sound as smooth, but at any rate, I will get a sound recording.

    About the Octane thing, it could use less fuel because it has a higher octane rating, I mean I know octane is knock resistance....and wikipedia says engine knock can be prevented by raising the fuel:air ratio...
  4. Steevo

    Steevo

    Joined:
    Nov 4, 2005
    Messages:
    7,990 (2.58/day)
    Thanks Received:
    1,084
    Get your engine mounts replaced. There is a TSB about it from Ford, however they choose to do nothing but let them break and make people pay.
    10 Million points folded for TPU
  5. JC316

    JC316 Knows what makes you tick

    Joined:
    Jan 24, 2006
    Messages:
    9,357 (3.11/day)
    Thanks Received:
    902
    It could be that, but you should feel the engine rock when you give it some gas, or it should vibrate like crazy.
  6. Steevo

    Steevo

    Joined:
    Nov 4, 2005
    Messages:
    7,990 (2.58/day)
    Thanks Received:
    1,084
    Only at a couple specific RPM bands will the engine vibrate, otherwise it just feels funny and runs like shit as the knock detection thinks it is knocking at a idle and moves the timing as far forward as possible.


    My brother had one and just bought another, eww.
    10 Million points folded for TPU
  7. Deusxmachina

    Deusxmachina New Member

    Joined:
    Jan 21, 2008
    Messages:
    526 (0.23/day)
    Thanks Received:
    55
    Years ago, only higher octanes had any cleaning detergents in them, so using higher octane did indeed help keep things clean. Nowadays, all octanes have the detergents. On a related note, ethanol was mentioned, and I don't know about all states, but in my state premium fuel has no ethanol in it. So, people who don't want even 10% ethanol in their cars may want to buy premium for that reason.

    I personally think there is little benefit for most people in using a higher octane than the car requires. People with high compression or turbocharged/supercharged cars may notice an improvement, but those engines aren't in most cars and are probably already getting premium. But... YMMV. Take note of your mpg, and if using premium ups the mpg, well then there you go. If it doesn't, well then there you go.

    For this Mercury, sometimes you just have to keep driving a car and let it get worse so you can then better diagnose it. If you don't get any check engine codes, that can be rough until you do. My first thought was maybe an intake leak of some kind, maybe the intake manifold gasket, or even low compression in one cylinder, but if the car is fine off-idle, then that's more curious. I've also personally had cars with an iffy idle but drove fine otherwise, and it was a bad spark plug wire.

    If it idles fine when cold but then starts getting rough when it warms, then it's probably a sensor of some kind or other. Because when the car is cold, it is operating off of fixed values for the sensors because the car isn't warm enough yet to go into closed-loop mode to use most sensors. If it idles rough when cold, I'd lean more towards a non-sensor fix of some kind.

    Oh yeah, seafoam. Many people use automatic transmission fluid instead. I probably wouldn't even bother putting any of it in the crankcase. The biggest gains are putting it directly into the intake manifold area while the car is running. It'll loosen all that carbon and gunk on top of the pistons and everywhere else. Do read up on this stuff before attempting. It's not something you want to do without knowing what you are doing. There's a chance you can vaporlock the engine, etc.
  8. kwchang007

    kwchang007 New Member

    Joined:
    Jan 27, 2007
    Messages:
    3,979 (1.51/day)
    Thanks Received:
    185
    Location:
    Severn, MD, USA.
    Uhh I think I'll stay away from seafoam and the auto transmission fluid stuff. If the point is to de-carbonize it I'll get a shop to do that. I'll make sure to get a audio clip tomorrow after the engine's warm, and it
  9. TheMailMan78

    TheMailMan78 Banstick Dummy

    Joined:
    Jun 3, 2007
    Messages:
    20,635 (8.20/day)
    Thanks Received:
    7,244
    Unless you have flashed the brain I wouldn't recommend changing octane in your car. In some of the newer engines you could be doing more damage than good.
  10. kwchang007

    kwchang007 New Member

    Joined:
    Jan 27, 2007
    Messages:
    3,979 (1.51/day)
    Thanks Received:
    185
    Location:
    Severn, MD, USA.
    Uhh this engine design dates back to at least 1994....
  11. imperialreign

    imperialreign New Member

    Joined:
    Jul 19, 2007
    Messages:
    7,043 (2.85/day)
    Thanks Received:
    909
    Location:
    Sector ZZ₉ Plural Z Alpha

    you do not need a higher-compression motor to burn all of the fuel spray with higher octane fuel


    I re-iterate, if you do run higher octane fuel, the PCM will see the difference in burn time through input from the O2 sensors, they'll indicate a rich condition. To compensate, the PCM will shorten the fuel injector dwell time, which means that the injectors aren't spraying fuel for as long a period of time as they were prior.

    Spraying less fuel per pulse width can equate to a net fuel economy gain, as it's taking you longer to go through the same amount of fuel as before.


    Again, the longer burn time of higher octane fuel also raises cylinder temperatures, which diminishes carbon byproduct build up on top of the piston and the cylinder/valves. Less carbon detritis inside the cylinder, the more fuel that is actually consumed during combustion, meaning the more efficient the combustion process is (if 100% is sprayed, and 100% is burned is more efficient than 100% spray : 90% burn).


    If you have a high compression motor, though - you do need higher octane fuel.
  12. imperialreign

    imperialreign New Member

    Joined:
    Jul 19, 2007
    Messages:
    7,043 (2.85/day)
    Thanks Received:
    909
    Location:
    Sector ZZ₉ Plural Z Alpha

    I wanted to comment on this one here, too


    in regards to to octane rating - once the PCM has learned driveability and fuel trim on higher octane, you should be able to notice that the motor feels smoother, idles a bit smoother, etc - enough so that when you go back to regular you'll feel a difference. If you've done a decarb (which is a good idea on a car with more thank 60k miles), and then put premium in, it'll take a few tanks for the PCM to relearn fuel trim, etc. Or, you can do as Wile E mentioned (which I completely forgot about earlier), and reset the PCM's learned fuel trim - just disconnect the negative cable on the battery and the PCMs learned stats will reset. It'll take about one tank (or a few drive cycles) for the PCM to learn fuel trim base from here, as now it's running on 100% stock programming fuel maps.




    But, in regards to the seafom, tranny fluid - if you add any of these substances directly to the crankcase via the oil fill . . . DO NOT drive the vehicle like this!!!! I cannot stress this enough! These additives are meant to clean sludge and deposist, and do not have the viscosity needed to prevent damage to a motor, which will inevitably occur should you take the car around the block like that.


    Still, on a motor with 80k+ miles, that hasn't seen regular 3000 mile oil changes, I DO NOT recommend adding any cleaners to the crankcase. If there are a lot of hard-carbon deposits and sludge, they can break free and end up in the oil pan - from there, they are sucked into the oil-sump and block the mesh screen. Also, depending on the design of the oil drain plug, a lot of the crud that ends up in the bottom of the pan might not come out when you drain the motor (Chryslers are notorious for this design).

    I stress that the best way to clean a motor is with patience and time - use high quality oil and filters, and change the oil regularly. If the motor is that nasty, start changing the oil every 1000-1500 miles. Hot, clean oil will slowly break up the crud on a minute level, and will be suspended within the oil itself, to be trappped by the filter.
  13. TheMailMan78

    TheMailMan78 Banstick Dummy

    Joined:
    Jun 3, 2007
    Messages:
    20,635 (8.20/day)
    Thanks Received:
    7,244
    Again I would look into what your timing is set up for. Not all MAF and PCM will do what imperialreign says. Some aint that smart. Be careful when changing octane's is all I'm saying.
  14. kwchang007

    kwchang007 New Member

    Joined:
    Jan 27, 2007
    Messages:
    3,979 (1.51/day)
    Thanks Received:
    185
    Location:
    Severn, MD, USA.
    Well if worst comes to worst it'd just run the same as regular right?
  15. imperialreign

    imperialreign New Member

    Joined:
    Jul 19, 2007
    Messages:
    7,043 (2.85/day)
    Thanks Received:
    909
    Location:
    Sector ZZ₉ Plural Z Alpha
    you're right . . . 1995 and earlier vehicles (OBD I), in particular domestics.

    if you're vehicle is 1996 and newer (OBD II), it'll figure it out, trust me.
  16. kwchang007

    kwchang007 New Member

    Joined:
    Jan 27, 2007
    Messages:
    3,979 (1.51/day)
    Thanks Received:
    185
    Location:
    Severn, MD, USA.
    Well wait, I'm not sure which one mine is. It's a 2000 model year, but I think there were models before 1996...
  17. TheMailMan78

    TheMailMan78 Banstick Dummy

    Joined:
    Jun 3, 2007
    Messages:
    20,635 (8.20/day)
    Thanks Received:
    7,244
    Run what is recommended for your engine. I am willing to bet good money your problem isnt octane related.
  18. TheMailMan78

    TheMailMan78 Banstick Dummy

    Joined:
    Jun 3, 2007
    Messages:
    20,635 (8.20/day)
    Thanks Received:
    7,244
    05 to 09 Mustangs don't. You gotta flash the brain. Its not like it used to be man. These car makers are going backwards.
  19. kwchang007

    kwchang007 New Member

    Joined:
    Jan 27, 2007
    Messages:
    3,979 (1.51/day)
    Thanks Received:
    185
    Location:
    Severn, MD, USA.
    Probably not to be honest....but high octane won't hurt, especially if in the end it comes out to be the same in terms of money.
  20. imperialreign

    imperialreign New Member

    Joined:
    Jul 19, 2007
    Messages:
    7,043 (2.85/day)
    Thanks Received:
    909
    Location:
    Sector ZZ₉ Plural Z Alpha
    doesn't matter. 1996 was a federal mandatory change for all OEMs. All vehicles for the 1996 model year had to be compliant with OBD II specifications and reulations.

    that to me just doesn't make sense - simply because not all 87 octane burns the same, and burn characteristics are different from one fuel manufacturer to the next.

    which Ford motors in particular in the mustangs, all of 'em, or just the v8s?
    kwchang007 says thanks.
  21. Deusxmachina

    Deusxmachina New Member

    Joined:
    Jan 21, 2008
    Messages:
    526 (0.23/day)
    Thanks Received:
    55
    Except in rare cases, yeah.

    Come to think of it, there's a possibility that premium fuel with no ethanol (not sure if your local gas has 10% ethanol or not) could give higher mpg simply due to no ethanol in it since ethanol requires more fuel than non-ethanol for the same power.
  22. TheMailMan78

    TheMailMan78 Banstick Dummy

    Joined:
    Jun 3, 2007
    Messages:
    20,635 (8.20/day)
    Thanks Received:
    7,244
    Not sure to be honest. The thing is if you run a high octane in the 4.6 it doesn't burn off. After a while it will leave crud. I don't know why they did this but its a pain in the ass. Lets say you put a CAI on. The PCM wont even tell the MAF to adjust and you'll end up running REALLY lean. I mean lean to the point you F$%K up the engine. Papa Ford "upgraded" the PCM to a PowerPC cpu believe it or not. Since then the damn thing is a bitch to tune right.

    Every time I talk to the guys at steeda they all agree "fords new PCM sucks". Now they make a newer version in the "Bullet" edition PCM that will sense an octane change but its only for manuals with a particular gear ratio. I'm sure by 2010 they will make this the norm. At least I hope so because right now it seems like I'm flashing the brain everytime I open the damn door.
  23. Wile E

    Wile E Power User

    Joined:
    Oct 1, 2006
    Messages:
    24,324 (8.81/day)
    Thanks Received:
    3,776
    No you don't need high compression. Advanced timing will also require higher octane fuel. It's one of the first things most Mustang owners will do to their car, right after ripping out the air intake silencer. It's worth up to 10-15HP at the wheels, depending on how far your engine will let you advance the timing (much like a cpu or gfx card, every engine is different, even if it's the same model). They have a 9:1 compression ratio also. What you are forgetting, is that advancing the timing raises the dynamic compression ratio, which is infinitely more important than static compression ratios. On the flipside of that coin, you can tune a 13:1 compression motor to run on 87oct if you want to. (Don't know why you would tho, the timing curves would be abysmal)

    Other examples of things that raise dynamic compression ratios are cam changes, turbos, superchargers, nitrous, etc., etc. Would you run a turbo car on 87oct if it had a 8:1 compression ratio? If so, have fun rebuilding your engine.

    I tuned and raced Mustangs for 10 years out of the family garage. I have run the back to back dyno tests myself to see the difference with my own eyes between stock timing, and advanced timing with high octane. The wiki article is incomplete in that respect.

    Do yourself a favor, and talk to a real drag racer or engine builder, you know, the people that do these things for a living, and see what they tell you.


    As far as putting high octane in this Mystique, it should be before Ford made the switchover to the newer style PCM (like that found in the S197). It should adapt to new fuel octanes. But I would be willing to wager money it doesn't do anything for the rough idle of this car.

    I'm still guessing IAC motor. It's on the side of the throttlebody on Fords, generally held on by 2 bolts. It has both a vacuum line and a plastic plug with 2 wires. It looks like this.

    [​IMG]

    The gasket should be a couple dollars max, and Carb cleaner is Carburetor Cleaner. Can be bought at the auto parts store along with the gasket.


    Although Stevo did bring up an interesting point about the engine mounts.
    Last edited: Sep 22, 2008
  24. imperialreign

    imperialreign New Member

    Joined:
    Jul 19, 2007
    Messages:
    7,043 (2.85/day)
    Thanks Received:
    909
    Location:
    Sector ZZ₉ Plural Z Alpha
    Sounds like Ford :p


    I swear, their engineers do stuff that just doesn't make sense . . . it's as if they have inspire their engineers with motivational posters like this:

    [​IMG]
  25. JC316

    JC316 Knows what makes you tick

    Joined:
    Jan 24, 2006
    Messages:
    9,357 (3.11/day)
    Thanks Received:
    902
    I have rarely seen a motor that would be that sludged up, if they did even basic maintenance on it, then it won't be that bad. I tossed some seafoam in the crank of a 99 taurus and a 96 Geo metro to shut the lifters up. Both had 120K on them and both are still running fine. I did kill the previous motor in that 99 taurus, but it hadn't had an oil change in 4 years and had been running 90w gear oil, so it was FUBAR anyway.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guest)

Share This Page