Trying to assess the damage(sorry..long)

[RaveVibe]

I bought my 03 GT about a month ago, and so far have been enamored by its performance, comparatively.(my previous car was 94 grand am, so the Vibe might as well be racecar as far as I am concerned=) )However yesterday I took my car to the dealer for my first oil change (yes I drive quite a bit) and had a discussion with the previous owners son and received some troubling information. (both the son and father work at the dealership). Previously I had asked him what his father ran in the car, and he said he was pretty sure just regular. Since that day he has discussed the topic with his father, and yesterday informed me that he (dad) had asked some friends etc. and concluded that regular was fine, and that is what he ran. This was done for 54,000 miles. I have searched all the "premium fuel" threads, yet can find nothing as to the specificity of the damage in relation to the duration of the engines exposure to predetination. There is no pinging or knocking noise, but the only way I can think of to determine my loss is to drive another GT and compare. Perhaps the degree of hp loss would be too minute to even detect, but if running 91 or up is so imperative, what would 54K miles on an inferior octane do? Should I expect a shortened life span on my engine (this is my major concern)? Also I have been keeping up with gas mileage and it seems that even on the highway I get 30mpg at best, could this be a problem? I am truly sorry if this has already been addressed, and realize that I can hardly expect a technicians response as this is obviously very specific and complicated. Therefore I am merely asking for your generalizations and opinions, not a rock solid explanation, as such can hardly exist. Thanks in advance for any help , this forum as been an indispensable reference and the comradery and kindness shown here is not lost on me.

[GMJAP]

I believe the general consensus is that in a modern engine like the 2ZZ, the knock sensors and engine management computer will alter the timing to prevent any damage from occuring.

[coldmm803]

i agree with GMJAP about the sensors and such. i have a base 05 which is supposed to run on regular but over the past 2 months or so i began using 89 and my mpg has increased/ become more stable and acceleration is a bit smoother. when i first got my vibe i was getting about 34mpg on the highway but at some point my cat went bad which lowered my milage to about 28 highway (bad cat is a known issue) and since i got it replaced my milage didnt go up but then i started tryin 89 octane and my milage is back up to 33ish on the highway. good luck

[prathman]

I agree with GMJAP that as long as the knock sensor was doing its job there should be no damage. Of course while it was running regular the timing would have been retarded and therefore performance would have been less *at that time*. But if you now want the full performance just use the higher octane gas and the timing should adjust automatically to give you the proper performance.

[RaveVibe]

Wow thats a relief, by the way coldmm803, was the replacement of your cat covered by your warranty, I have the exdended 2 year if that makes a difference. That may be my problem with the gas, I am assuming the GM dealer could simply plug into the ecu to determine any problems with the cat, but if there is no "check engine" light on then the computer is not coding anything wrong, so how would they determine if the cat is faulty? Really the answer I am looking for is if this is a simple to find and solve thing or if it will be a pain to me.

[coldmm803]

my cat was replaced under a tsb linked below, not sure if the gt is covered yet. according to pontiacs site the highway milage for the new gt's is 32 so if your getting 30 your pretty close, before looking into a bad cat i'd increase the octane of the gas your using since the gt is ment for premium. of course from a price point of view going to premium will cost more but if it increases your milage you may actually save by spending that 20 or so cents more per gallon. by that i mean, if you put in 10 gallons @ $2.80 per of 87octane that same 10 gallons will cost $2 more if you get say 89 octane for $3 per gallon, so if your milage increases by 3 miles per gallon over 10 gallons you actually gain 1 gallon (30 miles more) of gas or $1 by getting better octane.but if you have a rotten egg smell when you should deff look into the cat other wise i'd wait a month of using better octane firsthttp://forums.genvibe.com/zerothread?id=20143

[northvibe]

yea the engine will in computer terms "clock down" so it is able to "limp" along with regular but now that you know, use premium all the time from now on. regular should be used in the GT (2zz) in only emergency situations, the engine is made to run premium. I dont see any damage as stated above.

[joatmon]

The car was designed to run on higher octane fuel, so that's what you should use. The knock sensors should theoretically adjust timing to prevent damage, but also if the car was driven agressively, theoretically some accelerated wear could have happened. As far as the cat going bad, they seem to fail in two ways. Mine stopped converting and the O23 sensors detected this and set a CEL. phm013's converters (note, plural) became restricted, affected mileage and performance, but never threw a CEL.I say put the right octane gas in for that car, maybe a tank or two, and see what the gas mileage does before worrying about the cat. WIth gas prices where they are, the difference between low and higher octane is not that significant, and besides, you bought the GT for the power, feed it what it needs for the best performance.

[goodvibe]

I never got 30 mpg in mine though it's hard not to have fun in a GT. You're fine.

[burkeyro]

I agree with the everyone else. We are running High Compression engines, With ALOT of electronic Fail Safes. If the previous owner used Regular and Mid grade and never got into LIFT RPM range, there really shouldn't be any problems, I detonated the Living CRAP out of my 82 Supra Engine (I had already Planned on Tearing it down) believe me you would Notice if there was something wrong. If you are really worried about it, take it to another mechanic and have them pull the Plugs and Scope each cylinder for Damage. Shouldn't cost too much or take too much time, All they do is pull the plug and Look in each cylinder with a Fibre Optic camera. Hell I'm only getting 27 Miles to the gallon, but I blame that on the Driver. HE HE HE I love my GT.

[RaveVibe]

Sorry, Ive been away for a while, and also that I did not clarify, I have ran 94 premium since the day I purchased the car, just the previous owner (car dealer) ignored the manual.