Performance effected by different octane? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

Reply
 
 
 
Thread Tools Search this Thread
Old 08-16-2004, 07:42 AM   #1
Member
Posts like a V-Tak
Thread Starter
 
Join Date: Jul 2004
Location: Detroit, MI
Posts: 49
Thanks: 0
Thanked 0 Times in 0 Posts
beakah is on a distinguished road
Default Performance effected by different octane?

I might be crazy, or my mind is so blew out trying to find my loss of power/stumble/hesitation at acceleration and while going 70mph, that I can't think right anymore. :o

Anyway I put 89 octane in the car yesterday just for a goof....and low and behold I'm not noticing my problem. I've only driven it twice since I put the gas in, so it might be premature, but I have not noticed any loss of performance. In fact, I'd say my original performance has come back.....but why and how??

What is the theory behind this? Is this possible?

My fuel economy has also gone down from 425 miles per tank to around 385 miles per tank if that helps. I put the new Delco O2 sensor and noticed no difference in fuel economy.

No SES light, cat is not clogged, new ICM and coils, full tune including wires, plugs, fuel filter, PCV, O2, 43 PSI at the fuel rail, cleaned FPR.
beakah is offline   Reply With Quote
Old 08-16-2004, 08:11 AM   #2
Senior Member
Posts like a Turbo
 
Join Date: Jul 2004
Posts: 226
Thanks: 0
Thanked 0 Times in 0 Posts
DJ SHO is on a distinguished road
Default

Try a PCM reset if you just did all this maintenance at once. The PCM might have adapted to the way things "used to be" and might take a long time to relearn.

The higher octane fuel will result in "normal" performance cabilities over the use of 87 octane, which retards timing to get rid of the pinging associated with the lower octane fuel. Lower octane fuel also makes the PCM back off boost a bit.

Anyone else agree with me? Or am I way off?
DJ SHO is offline   Reply With Quote
Old 08-16-2004, 01:42 PM   #3
Senior Member
True Car Nut
 
Join Date: Jun 2002
Location: Bedroom, Ontario
Posts: 3,266
Thanks: 0
Thanked 0 Times in 0 Posts
Drifter420 is on a distinguished road
Default

That is correct.. on a Supercharged engine.. higher octane will prevent pre-detonation and thus KR. It also burns more complete and slower. A lower octane 87 will burn hotter but less control. I noticed you said you're SE so 87 Octane is fine for you.. for Supercharged, the octane DEFINITELY affects fuel milage IMO. I"ve ran 91 Octane and get around 600KM per tank ( I never go to 1/8th.. usually in betwen 1/8th and 1/4 before fill up ) but running 94 Octane I"m gettin 650KM before 1/4 tank ( but I'm not on boost very often. )
Drifter420 is offline   Reply With Quote
Old 08-16-2004, 01:58 PM   #4
Senior Member
True Car Nut
 
Join Date: Jun 2003
Location: Purgatory
Posts: 6,313
Thanks: 0
Thanked 0 Times in 0 Posts
PontiacDad is on a distinguished road
Default

Well put drifter Thats exactly the way it works. If your car is getting Knock Retard depending on how much your getting the power will be very restrictive.
Every degree of kr takes away 1.5-2 Hp.....it can add up quickly.
PontiacDad is offline   Reply With Quote
Old 08-16-2004, 02:31 PM   #5
Member
Posts like a V-Tak
Thread Starter
 
Join Date: Jul 2004
Location: Detroit, MI
Posts: 49
Thanks: 0
Thanked 0 Times in 0 Posts
beakah is on a distinguished road
Default

Wow....this is really informative and has opened up a new door....

I believe there are two knock sensors on my 95 SE. One is right by the starter and the other is in the back of the engine by the oil pan....they both look the same and have a blue wire as my Haynes manual states. If any of this is in error please let me know....

My starter has a pretty long stud on it and it'* actually coming in contact with the connector to the knock sensor....it is pushed up right into it and is pushing the connector on an angle....it does not look good at all. I may have to cut the stud down with a saws-all. The connector itself could have a broke wire or something......but there is no SES light. I guess I really need to get this on a scantool......any other input please let me know.....
beakah is offline   Reply With Quote
Old 08-17-2004, 09:40 AM   #6
Senior Member
Posts like a Turbo
 
Join Date: Jul 2004
Posts: 226
Thanks: 0
Thanked 0 Times in 0 Posts
DJ SHO is on a distinguished road
Default

An open or short in the knock sensor wiring will most likely throw a code to the PCM, just like any other sensor. The PCM under stands which is which, meaning it understands voltage or frequency signals from a particular sensor'* signal line. It can tell the difference between the normal signal range, full short, or full open. IF it sees one of the two extremes, it should throw a code, and therefore a MIL. It should also throw a code, depending on the circuit parameters for monitoring, if the signal is past the tolerable range. I believe most knock sensors are only two-wire connectors so the voltage range should be between 0-5 volts, but since I'm new to GM'* and such this may be different. For the most part though you should get a MIL if the the knock sound, being picked up by the sensor, was very strong, or the signal was shorted. Since the motor has two of them, it might do some comparisons from the two sensors, meaning #1 heard the knock sound, but #2 didn't, so there must be a problem with #2, therefore throwing a DTC. From what I've read, most sensors will cause the MIL to illuminate, accept for most tranny codes, which still store a DTC, but don't illuminate the light. I think if there was an abnormal signal from the knock sensor, you'd see a MIL. But scan it anyways. Best thing to do if you have the means to do so.
DJ SHO is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Octane Points (Octane Boost) bandit General GM Chat 2 08-28-2007 11:21 PM
Trunk lid carpeting: different for different years? Bugsi General GM Chat 8 01-23-2006 08:18 PM
Octane rating & performance thought crzydmnd72 General GM Chat 11 03-21-2004 10:47 PM
Octane vze3r85p General GM Chat 29 10-22-2002 06:19 AM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 04:35 AM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.