I am operating my ancient Pathpuppy (6 cyl. manual transmission, U.S. emissions set-up) for which I no longer have a manual. I remember that it said to use 91 octane, but I cannot remember if that was a requirement or a recommendation. Is there someone out there with the information to set me straight?
The car will probably tell you. At the gas cap or in your instrument cluster near the gas gage, does it say premium unleaded only or unleaded only? If it says unleaded only then you can put 87 octane.
CD
I have been running my 1994 PF (214K) since new on 87 octane. Have had no engine problems at all. The old girl is on her fourth timing belt. I'm keeping her until she dies. Its been a good machine.
My '95 drinks 87 all the time without issue. I do use 91 when I tow though.
As far as a drop in performance with the AC on, my truck is horrible to drive with the AC on. Shifting is difficult (5 speed), and acceleration is non-existent. I normally only use AC on the highway as a result. This has been my experience with almost all my cars though.
DS
A power loss is expected as the engine adjusts to the lower octane fuel.
CD
I use my 97 pickups AC all the time when the weather is hot. Since it only has the 4 cyl 2.4 liter engine, the AC does cut down on the acceleration and increases the fuel consumption. Whenever I need the lost power to merge on to a highway or climb a hill, I just hit the AC button to shut it down until I have merged or reached the crest of the hill.
Are you sure the PCM for your truck doesn't already do this for you? I know that for my current Nissan Frontier and Ford Fusion, the PCMs automatically disengage the A/C compressor when you floor the accelerator. I thought this was a pretty standard arrangement for the last 12+ years. Before PCMs became common, you could buy vacuum controlled switches that did the same thing. I added one to a 1981 Audi I owned. You spliced it into the circuit that controlled the A/C clutch. Anytime the vacuum dropped below a certain level (indicating a nearly wide open throttle) the switch would open and cut power to the A/C clutch, which removed the A/C power drain.
For all the talk about automobile A/C using a lot of energy, I've never been able to see much of a difference in fuel economy between summer and winter driving. In fact, it seems that my worst fuel economy is in spring and fall months, when the A/C is used less and the gas should still be the warm weather blend. It has been a long time since I have owned a car where I could tell that the A/C compressor was even engaged. The Audi had a five cylinder 2.2L engine, and I don't think having the A/C cutout switch made much of a difference in performance. My SO has an '07 RAV 4 cylinder. The only time you see any problem related to the A/C is when you try to cruise at around 60 mph with the A/C on. The slightest incline makes the cruise control go wild. It downshift, floor the throttle, then immediately upshifts and basically jerks you all over the place. If you turn the A/C off, this doesn't happen. Or if you just cruise at 65 instead of 60, it doesn't happen. I figure it is just bad programming.
Ed
on 6/18/2008 10:12 AM C. E. White said the following:
I have the cheap XE model with 5 speed stick shift. No power anything (except for aftermarket keyless entry, which I installed myself) and no cruise. If my truck does have PCM, it has never worked. When the gas is floored and the AC is on, if I hit the AC button, I can feel the added power and acceleration as the AC shuts off.
This just reminded me of another problem. See separate post, not related to this problem.
I have found that as the spark plugs reach the end of their life, the on/off power fluctuation from the AC compressor engaging/dis-engaging tends to get much more apparent, annoyingly so. It's like the car's computer is working that much harder to compensate for the wider gapped and worn out plugs.
CD
Sure!
I see, Bill. Now that you've retired from Microsoft you have time to post to the newsgroups and help out the less fortunate -- like me? ;^)
Andrew:
Not sure... but I think any '91 is going to have a knock sensor and the computer will automatically retard the spark when knock occurs from lower octane gas.
With most cars that recommend 91 octane, you get better performance and thus better milage with 91 vs 87. The better performance includes higher mpg which actually makes premium cheaper.
The break even point is usually less than 1 mpg - in other words, if
87 octane gas costs you 1 mpg then you are losing money with Regular. EX - the .20 cent difference in price is now only about a 4% cost increase for Premium if a car getting 25mpg drops lower than 24mpg, you lose money. Depending on how & where you drive, you can lose a lot more than 1 mpg.Also, I don't know what kind of mileage you get, or how many miles you drive per year. But, do a rough calculation and see how many gallons of gas you use per year. For example, if you drive 14K miles per year and get 25mpg, you use 560 gallons per year. That comes out to $112 per year extra cost for premium. Not much of a savings... and you lose power... and if you lose mileage you likely lose money too.
I am a low-mileage driver; in the 14 years I have owned it I have put on less than 140,000 Km (I bike or bus to commute). I am also fairly good at driving efficiently, and have coaxed 100 Km out of less than 11 litres of fuel. City driving tends to draw more than 13 litres per 100 Km. I have gone back to 91 octane because, quite frankly, I did not like the loss of power when trying to merge with traffic.
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