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Old 08-10-2007, 09:55 PM   #11
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I've mostly worked on Chevys, and (IIRC) the target idle is dynamicly calculated to the MAP, CSS, MAF, IAT and CTS datastreams when TPS is 0. The Chevy Silverado Vortec PCM's like 575 rpm.
Maybe the old plugs caused a very very minor misfire and the CSS caught it so it raised RPM to cancel the loss out.
I'm not sure what would give the PCM reason to retrain itself after new plugs were installed tho?


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Why is your Cavalier idling at a lower RPM? Far as I know its a computer controlled vehicle, so its idle should be more or less hard coded into the ECU. Logically speaking, plugs shouldn't change your idle speed
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Old 08-10-2007, 10:03 PM   #12
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Quote:
Originally Posted by n0rt0npr0 View Post
I've mostly worked on Chevys, and (IIRC) the target idle is dynamicly calculated to the MAP, CSS, MAF, IAT and CTS datastreams when TPS is 0. The Chevy Silverado Vortec PCM's like 575 rpm.
Maybe the old plugs caused a very very minor misfire and the CSS caught it so it raised RPM to cancel the loss out.
I'm not sure what would give the PCM reason to retrain itself after new plugs were installed tho?
I just put the question in to Brisk, maybe they will have something to say...
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Old 08-11-2007, 12:05 AM   #13
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OK, here is what my man Martin @ Brisk has to say. BTW, these guys treat me right, I had a reply to my e mail w/i a couple of hours!

Hi Bob,
The spark on the LGS plugs is better exposed and will jump to one of the 4 electrodes wherever it is the easiest in each ignition event (unless you have MSD that generates 3 sparks where each can go to different ground electrode). The area where is less fuel droplets (atomized fuel molecules) is less conductive and harder to ignite, therefore the spark will occur in direction of least resistance at place most favorable for the air/ fuel ignition.
This contributes to more stable ignition process and less variation between each ignition cycle.

The PCM or ECM have preset limit for desired RPM that is trying to maintain by constantly regulating the amount of air that enters the engine around the throttle valve trough air bypass valve (idle air control solenoid). Since there is less variation between each ignition events the engine runs smoother and the PCM or ECM have to do less correction by the air bypass valve (idle air control solenoid) and other outputs based on information from ECM / PCM inputs.
Less variation between each ignition cycle = less ECM / PCM correction = smoother, low RPM limit idle.

May be you have in past experienced on some of EFI vehicles surging condition where engine RPM is high and constantly goes up and down. That is engine PCM / ECM constantly trying to keep engine RPM within preset limits. Most vehicles 1994 and up utilize sophisticated OBD II diagnostic system which can detect incomplete combustion process far before it become noticeable to the driver as a missfire. Some OBD II systems are set to set engine light on with a missfire code for individual cylinder when only 5% missfire occur in any of the engine cylinders. That is determined by ECM / PCM monitoring frequency change (time) between pulses from the Crankshaft position sensor.
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Old 08-11-2007, 01:47 PM   #14
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That's cool that he answered you quickly. Glad to see a reason behind the lowered rpms.

[QUOTE=unstable bob;67709]Most vehicles 1994 and up utilize sophisticated OBD II diagnostic system which can detect incomplete combustion process far before it become noticeable to the driver as a missfire.QUOTE]

I would consider 1996 the starting point where you could say most vehicles..
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Old 08-11-2007, 05:51 PM   #15
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[QUOTE=baddog671;67783]That's cool that he answered you quickly. Glad to see a reason behind the lowered rpms.

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Most vehicles 1994 and up utilize sophisticated OBD II diagnostic system which can detect incomplete combustion process far before it become noticeable to the driver as a missfire.QUOTE]

I would consider 1996 the starting point where you could say most vehicles..
Yeah, I think yer right about OBD II coming on in '96. I had a 94 Trans Am that was still OBD I.
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Old 08-11-2007, 05:54 PM   #16
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some engines REALLY don't like surface gap/ side-firing spark plugs and run like crap on them.

just a little note

Jeff
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Old 08-11-2007, 05:58 PM   #17
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some engines REALLY don't like surface gap/ side-firing spark plugs and run like crap on them.

just a little note

Jeff
Mine seems to be running very well, so I'm happy with the plugs.
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Old 08-11-2007, 06:51 PM   #18
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thats all the really counts isn't it?

some engines like or even NEED surface gap it just depends on the engine

Jeff
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Old 08-26-2007, 05:59 PM   #19
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I ditched the fancy factory platinums in my Focus for some copper cores...the car doesn't get any better FE, but it does seem to idle smoother, respond more quickly, and the bucking and surging inherant to the stock ECU also seems to be reduced. I also increased the gap from .055" to .060" per the advice of fellow SVT owners.
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Old 09-19-2007, 01:00 PM   #20
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I haven't tried a set of brisks for FE yet, but I can say from personal experience, that they do show an increase on the dyno when compared to other top brand plugs (all plugs were fresh).
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