Discussion
personally, its always optimax for my Vette (C5) and the Monaro - same engine. The PCM strategy is to push the limits, until pinging etc causes it to say thats enough. It uses the long and short term fuel trims and knock retard function to get the best it can out of what you put in the tank. It takes up to 100 miles of driving to reach the optimum, or to recover it after a fill of regular. Logging live data and observing KR etc you can see the difference. And it does slightly improve mpg to offset the extra costs.
I saw a big difference as I problem with my vette LS1 engine where at 4/5000rpm with throttle full and open it would stutter as if it was being fed enough fuel.
100 Miles+ on higher Ron the problem hasnt been back since, I can only put this 4 month problem down to changing from unleaded up to super unleaded over night.
What do you reakon?
100 Miles+ on higher Ron the problem hasnt been back since, I can only put this 4 month problem down to changing from unleaded up to super unleaded over night.
What do you reakon?
l80ous said:
I saw a big difference as I problem with my vette LS1 engine where at 4/5000rpm with throttle full and open it would stutter as if it was being fed enough fuel.
100 Miles+ on higher Ron the problem hasnt been back since, I can only put this 4 month problem down to changing from unleaded up to super unleaded over night.
What do you reakon?
Sounds like theres a problem, was the low octane fuel stale? it should run fine on all unleaded. When misfiring, did she set any DTCs? try going back to 95 stuff and see if the prob returns. If it does, maybe some diagnostics are needed.
Fuel was used and topped up around once per week totaly usage through the winter she wasnt used much, so maybe your right can this make a difference?
Whats DTC's? I would answer that if i new what it means, dont know a great deal about cars but in this case probably dont understand the short-hand.
I might try going back, thats a good point, what could be wrong do you think? maybe new pluggs and leads are needed, that was orginally one thought of mine?
Whats DTC's? I would answer that if i new what it means, dont know a great deal about cars but in this case probably dont understand the short-hand.
I might try going back, thats a good point, what could be wrong do you think? maybe new pluggs and leads are needed, that was orginally one thought of mine?
l80ous said:
Whats DTC's?
DTC = Diagnostic Trouble Codes (displayed on the Driver Information Center, i.e. the display under your speedo)
There is a comprehensive list of DTCs here www.digitalcorvettes.com/forums/showthread.php?t=50748
Good luck....
Optimax has a higher octane which relates to knock retard because it burns slower and I believe releases a bit more power. What this means in practice is that when your knock sensors detect knock, the computer retards your timing to prevent it. Since higher octane fuel prevents knock, in theory, you will get more power. Your computer will have to "learn" this and will also have learnt your driving style to some degree so a change to Optimax should be done at the same time as resetting the computer or it will taks some time to do it.
A by-product of the higher power potential of Optimax is less throttle and most people find that their mpg improves by using it. So the increased cost is offset. When I supercharged my Mustang and switched to Optimax, the mpg stayed exactly the same despite having an extra 162bhp and I know from the forums that most Mustangs using 95 RON are getting far less mpg than me and I don't hang about.
Now I'm not sure about how correct this is but I read somewhere that biethanol fuel like Tesco 99 has the right octane but a lower calorific value (?)as it's vegetable based so it will do a lot less mpg than a non-biethanol fuel.
As with anything, you should monitor the performance after you reset the computer and also monitor your mpg as it may not actually work out any more expensive than cooking fuel.
See this thread if considering using biethanol based fuels: www.pistonheads.co.uk/gassing/topic.asp?t=252127&f=57&h=0
>> Edited by LuS1fer on Wednesday 19th April 08:16
A by-product of the higher power potential of Optimax is less throttle and most people find that their mpg improves by using it. So the increased cost is offset. When I supercharged my Mustang and switched to Optimax, the mpg stayed exactly the same despite having an extra 162bhp and I know from the forums that most Mustangs using 95 RON are getting far less mpg than me and I don't hang about.
Now I'm not sure about how correct this is but I read somewhere that biethanol fuel like Tesco 99 has the right octane but a lower calorific value (?)as it's vegetable based so it will do a lot less mpg than a non-biethanol fuel.
As with anything, you should monitor the performance after you reset the computer and also monitor your mpg as it may not actually work out any more expensive than cooking fuel.
See this thread if considering using biethanol based fuels: www.pistonheads.co.uk/gassing/topic.asp?t=252127&f=57&h=0
>> Edited by LuS1fer on Wednesday 19th April 08:16
LuS1fer said:
...a change to Optimax should be done at the same time as resetting the computer or it will taks some time to do it.
...you should monitor the performance after you reset the computer...
Wayne, when you talk about "resetting the computer, how is this done? Is there a way of returning to the factory default settings so that changes can be re-learnt?
I've just had a quick research on this point and it seems you can't reset it (unlike the Camaro and TA F-bodies where you pull a few fuses and default everything). It seems the C5 computer systems are a lot more tech and so, on the face of it, should be able to learn any changes pretty quickly. Disconnecting the batttery should have a similar effect I would guess but make sure your radio doesn't need a code before doing that.
Here is a useful site for clearing the C5 computer clutter but don't get hung up on it. Apparently a lot of the computer sensing is done by radio signals so even the presence of a mobile phone can set a code and why a good battery is so essential on a C5.
www.stengel.net/diccodes.htm
Here is a useful site for clearing the C5 computer clutter but don't get hung up on it. Apparently a lot of the computer sensing is done by radio signals so even the presence of a mobile phone can set a code and why a good battery is so essential on a C5.
www.stengel.net/diccodes.htm
Interesting one this.....
I always used 95 octane unleaded in the Z06 before it was modded and now with the turbos I only use 97 super.
I have to use 97 super in the Evo and different brands do make a difference to the mileage per tank that you get.
BP Ultimate returns about 210-230 miles per tank. Shell Optimax usually returns 220-230 per tank. The best I have found is Total 97 (called Exellium or something like that) returns up to 250 miles per tank and this is all from the same journey commuting over a one month period.
I always used 95 octane unleaded in the Z06 before it was modded and now with the turbos I only use 97 super.
I have to use 97 super in the Evo and different brands do make a difference to the mileage per tank that you get.
BP Ultimate returns about 210-230 miles per tank. Shell Optimax usually returns 220-230 per tank. The best I have found is Total 97 (called Exellium or something like that) returns up to 250 miles per tank and this is all from the same journey commuting over a one month period.
My Monaro loves that excellium, same engine as C5.
Returning to the original point, Fuel goes stale very quickly when left in the tank. Occasionally, the stuff is off when you buy it. A fuel refining customer of mine told me they put in an oxidising agent, so it has a short life. Stops people nicking their tankers and having free fuel for life !! They arent allowed to put it in 100LL Avgas for obvious reasons, so you know which tanker to pinch !!! Stale gas has a very low octane rating so knocks and pings start very early in the advance process. The PCM will pull back the sparks to kill the knock before it mashes the engine, you wont even hear it. But power will be well down and it may run badly at WOT/higher rpm under load. Resetting the PCM isnt really needed, but pulling the battery will clear the fuel trim tables back to starting point. See if you can replicate the fault. Check for codes, and if necessary, log some live pcm data during the malfunction, that should nail the prob. Check out www.autotap.com - every vette owner should buy one of these - cheap as chips and very good. BTW, I have no connection with them, but I use and like their products.
Hope that helps!
Returning to the original point, Fuel goes stale very quickly when left in the tank. Occasionally, the stuff is off when you buy it. A fuel refining customer of mine told me they put in an oxidising agent, so it has a short life. Stops people nicking their tankers and having free fuel for life !! They arent allowed to put it in 100LL Avgas for obvious reasons, so you know which tanker to pinch !!! Stale gas has a very low octane rating so knocks and pings start very early in the advance process. The PCM will pull back the sparks to kill the knock before it mashes the engine, you wont even hear it. But power will be well down and it may run badly at WOT/higher rpm under load. Resetting the PCM isnt really needed, but pulling the battery will clear the fuel trim tables back to starting point. See if you can replicate the fault. Check for codes, and if necessary, log some live pcm data during the malfunction, that should nail the prob. Check out www.autotap.com - every vette owner should buy one of these - cheap as chips and very good. BTW, I have no connection with them, but I use and like their products.
Hope that helps!
V7TTE said:
Wayne, when you talk about "resetting the computer, how is this done? Is there a way of returning to the factory default settings so that changes can be re-learnt?
I've looked and looked but I cant find the computer on my 1970 C3, I did find an Abacus though, will that do? Simple enough to reset as well, just slide all the balls to the left, or should it be the right??;D;D;D
BTW superunleaded works better in it!
G
VetteG said:
Wayne, when you talk about "resetting the computer, how is this done? Is there a way of returning to the factory default settings so that changes can be re-learnt?
I've looked and looked but I cant find the computer on my 1970 C3, I did find an Abacus though, will that do? Simple enough to reset as well, just slide all the balls to the left, or should it be the right??;D;D;D
BTW superunleaded works better in it!
G
I thought it was a slide-rule on the '70 model?
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