Myth!!!!! Octane 99 and prior VS 00+
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Northstar Engines and System Technical Discussion Discussion, Myth!!!!! Octane 99 and prior VS 00+ in Cadillac Engine Technical Discussion; This may get moved to tech tips, but I think it needs to be here. . 99 information first. Big ...
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    AJxtcman's Avatar
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    Myth!!!!! Octane 99 and prior VS 00+

    This may get moved to tech tips, but I think it needs to be here.
    .
    99 information first. Big Myth!
    .
    Octane Description
    Octane is a measure of a fuel's ability to resist spark knock. Spark knock occurs in the combustion chamber just after the spark plug fires, when the air/fuel mixture in the cylinder does not completely burn. The remaining mixture spontaneously combusts due to temperature and pressure. This secondary explosion causes a vibration that is heard as a knock (ping). Fuel with a high octane number has a greater resistance to spark knock. This vehicle requires 91 octane ([R+M]/2 method) in order to ensure proper performance of the fuel control system. Using fuel with an octane rating lower than 91 can create spark knock, which would cause the PCM to retard ignition timing to eliminate the knock. In a case such as this, poor engine performance and reduced fuel economy could result. Also, in severe knock cases, engine damage may occur.

    Knock Sensor (KS) System Description
    Varying octane levels in gasoline can cause detonation in high performance engines. Detonation is sometimes called spark knock. Spark knock causes the pistons and rings to vibrate and rattle producing the spark knocking sound.

    To control spark knock a Knock Sensor (KS) is used. This system is designed to retard spark timing to reduce spark knock in the engine. This allows the engine to use maximum spark advance to improve driveability and to improve fuel economy.

    The Knock Sensor (KS) system has two major components:

    The KS module.
    The Knock Sensor (KS).
    The knock sensor is mounted into the engine block under the intake manifold. The knock sensor produces an AC voltage which increases with the severity of the knock. This signal voltage inputs to the Powertrain Control Module (PCM). The PCM then adjusts the Ignition Control (IC) to reduce spark knocking.

    This powertrain system runs several tests of the Knock Sensor system. A fault in the KS system will PCM DTCs P0325 will detect KS Module or PCM faults, P0326 will detect low octane fuel or engine noise and P0326 will detect Knock Sensor and/or circuit faults.

    Fuel Specifications
    Use premium unleaded gasoline rated at 91 octane or higher for best performance. You may use middle grade or regular unleaded gasolines, but your vehicle may not accelerate as well.

    Be sure the posted octane for premium is at least 91 (at least 89 for middle grade and 87 for regular). If the octane is less than 87, you may get a heavy knocking noise when you drive. If it's bad enough, it can damage your engine.

    If you're using fuel rated at the recommended octane or higher and you hear heavy knocking, your engine needs service. But don't worry if you hear a little pinging noise when you're accelerating or driving up a hill. That's normal, and you don't have to buy a higher octane fuel to get rid of pinging. It's the heavy, constant knock that means you have a problem.
    .
    .
    On the Tech II it shows Octane Level and the PCM adjust for it!!!!

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    msta293412 is offline Cadillac Owners Fanatic
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    Re: Myth!!!!! Octane 99 and prior VS 00+

    So my 2001 STS, witch is designed to run good on 87 octane, will run better with 93 octane?.....are you sure?

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    Re: Myth!!!!! Octane 99 and prior VS 00+

    Quote Originally Posted by msta293412 View Post
    So my 2001 STS, witch is designed to run good on 87 octane, will run better with 93 octane?.....are you sure?
    My Computer stopped responding. I had all the 2000+ and was adding the pictures. I opened the Task Manager and found a program running for Programing PCM's. I opened it last night and it did not close.
    .
    I will reload the info now.

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    Re: Myth!!!!! Octane 99 and prior VS 00+

    Definetly let me know....

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    Re: Myth!!!!! Octane 99 and prior VS 00+

    2000+ GM SERVICE INFORMATION FROM GM & FSM.
    .
    Octane description
    Octane is a measure of a fuel's ability to resist spark knock. Spark knock occurs in the combustion chamber just after the spark plug fires, when the air/fuel mixture in the cylinder does not completely burn. The remaining mixture spontaneously combusts due to temperature and pressure. This secondary explosion causes a vibration that is heard as a knock (ping). Fuel with a high octane number has a greater resistance to spark knock. This vehicle requires 91 octane ([R+M]/2 method) in order to ensure proper performance of the fuel control system. Using fuel with an octane rating lower than 91 can create spark knock, which would cause the PCM to retard ignition timing to eliminate the knock. In a case such as this, poor engine performance and reduced fuel economy could result. Also, in severe knock cases, engine damage may occur.

    Knock Sensor (KS) System
    Purpose
    Varying octane levels in todays gasoline may cause detonation in some engines. Detonation is caused by an uncontrolled explosion (burn) in the combustion chamber. This uncontrolled explosion could produce a flame front opposite that of the normal flame front produced by the spark plug. The rattling sound normally associated with detonation is the result of two or more opposing pressures (flame fronts) colliding within the combustion chamber. Though light detonation is sometimes considered normal, heavy detonation could result in engine damage. To control spark knock, a knock sensor (KS) system is used. This system is designed to retard spark timing when spark knock is detected in the engine. The KS system allows the engine to use maximum spark advance for optimal driveability and fuel economy.

    Operation
    The PCM uses a knock sensor (KS) to detect abnormal vibration in the engine (detonation/spark knocking). Mounted in the engine block, under the intake manifold, the knock sensor produces an AC signal at all engine speeds and loads. The PCM then adjusts the spark timing based on the amplitude and frequency of the KS signal.

    A knock sensor module is no longer used to diagnose the knock sensor system. The circuitry is integrated into the PCM. The PCM uses the knock sensor signal to calculate an average voltage. Then, the PCM assigns a voltage range above and below the average voltage value. The PCM checks the knock sensor and related wiring by comparing the actual knock signal to the assigned voltage range. A normal knock sensor signal should vary outside the assigned voltage range (as shown in the normal knock sensor figure). If PCM detects a signal voltage within the assigned voltage range, DTC P0327 will set (as shown in the abnormal knock sensor figure).

    1.gif
    (1) Upper Fail Region
    (2) Knock Sensor Calculated Average
    (3) Knock Sensor Signal (Normal)
    (4) Lower Fail Region


    2.gif
    (1) Upper Fail Region
    (2) Knock Sensor Calculated Average
    (3) Knock Sensor Signal (Failed)
    (4) Lower Fail Region

    Diagnosis
    If the PCM malfunctions in a manner which will not allow proper diagnosis of the KS circuits, DTC P0325 will set.

    DTC P0327 is designed to diagnose the knock sensors, and related wiring. Problems encountered with the KS system should set a DTC. However, refer to Detonation/Spark Knock in Symptoms if no DTC sets, and the customers complaint of detonation points to the KS system.

    Fuel Specifications
    Use premium unleaded gasoline rated at 91 octane or higher for best performance. You may use middle grade or regular unleaded gasolines, but your vehicle may not accelerate as well.


    Be sure the posted octane for premium is at least 91 (at least 89 for middle grade and 87 for regular). If the octane is less than 87, you may get a heavy knocking noise when you drive. If it's bad enough, it can damage your engine.

    If you're using fuel rated at the recommended octane or higher and you hear heavy knocking, your engine needs service. But don't worry if you hear a little pinging noise when you're accelerating or driving up a hill. That's normal, and you don't have to buy a higher octane fuel to get rid of pinging. It's the heavy, constant knock that means you have a problem.

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    Re: Myth!!!!! Octane 99 and prior VS 00+

    You can run lower octane in the 99 and prior just like a 00+.

    00+ Compression Ratio 10.0:1
    99 Compression Ratio 10.3:1

    .3 is not going to make the differnce that everyone states. The PCM has the ability to adjust for the Octane level and has since 96 or even before that. If the 99 had to have Premium and the 00 did not it would have been in the PCM program and I just don't see that it is not in the 99 program.

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    Re: Myth!!!!! Octane 99 and prior VS 00+

    Yeah, we all know you can run regular in the '99 and prior year cars....many people here do, and have for years....I don't because I like having the maximum level of power on tap at all times.....retarded timing is for losers...

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    Re: Myth!!!!! Octane 99 and prior VS 00+

    but isnt better octane gas better for ur car, like against sludge buildup in the engine..whutever the case i still use supreme...come one its a cadillac not a honda.

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    Re: Myth!!!!! Octane 99 and prior VS 00+

    Quote Originally Posted by 3rd Coast Balla View Post
    but isnt better octane gas better for ur car, like against sludge buildup in the engine..whutever the case i still use supreme...come one its a cadillac not a honda.
    Actually Premium will cause more combustion chamber deposits.
    Top tier maybe an exception to that.

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    Re: Myth!!!!! Octane 99 and prior VS 00+

    Quote Originally Posted by danbuc View Post
    Yeah, we all know you can run regular in the '99 and prior year cars....many people here do, and have for years....I don't because I like having the maximum level of power on tap at all times.....retarded timing is for losers...
    I see it in threads all the time.
    My 00+ can run regular because they changed the compression ratio.
    .
    You must not understand the timing of a Northstar because it retards it constanly as you drive. It runs up and down.

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    Re: Myth!!!!! Octane 99 and prior VS 00+

    No wonder, I seem to see performance improvement when I run 93....I thought iot was in my head, beacause I usually run 87....some one told me running 93 would hurt performance because , my timing was set for 87.....silly I guess, now that I understand the pcm adjusts for octane, temp, etc...

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    Re: Myth!!!!! Octane 99 and prior VS 00+

    My '97 couldn't even run midgrade without a noticeable performance lag. Throttle response was very soft, even on midgrade. It definitely ran the best on premium.

    My '01 has never seen anything but regular, and it runs fantastic on regular. It may run even better on premium, I don't know.

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    Re: Myth!!!!! Octane 99 and prior VS 00+

    Quote Originally Posted by AJxtcman View Post
    I see it in threads all the time.
    ...
    You must not understand the timing of a Northstar because it retards it constanly as you drive. It runs up and down.
    Duh. All engines do. Retard timing = smoother operation. Timing turns back when power is not needed, and the ratio of throttle position to RPM remains static for a long time. The point is that with lower octane fuel it will retard it more. This has a noticable effect on city mileage in my experience. highway doesn't change as much, but in stop and go traffic, the higher octane fuel makes a big difference.

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    Re: Myth!!!!! Octane 99 and prior VS 00+

    I have been running 93 since the beginning of this thread.....and I do notice a improvement of overall performance over running 87.......GRAET.....I dont care about $, Im gonna use 93 from now on!

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    Re: Myth!!!!! Octane 99 and prior VS 00+

    I've data logged my 01 eldo for WOT timing on 87, 93, 94, & 97 octanes. (running the tank nearly dry each time to help insure an accurate rating)
    My timing max's out at 31BTDC no matter what fuel is used. The O2's read the same as well.

    However I have seen a repeatable 2-ish mpg difference in using 87 vs 93. So I'd conclude that at WOT there is not a difference (on my 01) but at part throttle there is. (There is just no way to get a accurate comparison at part throttle because of operatng conditions and throttle angle)

    btw, If any of you guys can see your timing live. It's amazing to watch! Just putting around town at 30-40mpg I've seen it go over 50btdc. No other car I've read does that.

    Rich

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