Is Premium Unleaded Necessary?

F

Fife

Registered
Hello,

Just looking for some opinion/s on fuel grade. My wife drives our stock 1994 Mark VIII to work (about 32 miles each way). We have always used premium unleaded in the car. Was wondering if using mid grade (89 octane) would cause any issues? She does not drive the car hard at all. I step down on it once in a great while. I have always heard that if the car does not knock then it does not need higher octane fuel. What do you think?

Thanks,
Fife
 
Short term use once and while will not be an issue. Long term useage will cause problems. You may also notice performance issues.
 
HAAHAHAHAHA.... I've used nothing BUT regular unleaded after about a year of high test after buying the car. My L/M dealer said THEY used nothing but regular the two years THEY drove the car as a picker-upper and suggested that I do the same.

I usually get about 26.6-27 on the highway and about 18 combined. Penny is the usual daily driver and all under 45MPH. I am the highway driver.......
 
Premium is recommended but not required. If the knock sensors are doing their job you wont hear any. The computer will detune the engine if knock is detected. So there will be a slight lose of power with lower grade gas if knock is detected.
 
From the owner's manual:​

Octane recommendations​

Your vehicle is designed to use
“Premium” gasoline for optimum
performance with an (R+M)/
2 octane rating of 91 or higher.
Gasolines with lower octance ratings
can be used, but performance may
decrease.​


FWIW, I'm all about performance, and my car is tuned for 93 octane, so that's what I run.
 
It was equated before that you only spend $1.26 (or something) PER TANK after the gas mileage vs. premium savings is factored in.

I skimp sometimes on my S2K too, haha.
 
The other factors in cost is probably longer engine life, less deposits from lower grade gas will buildup in the valves and engine will last much longer. My friend used premium on his pick up from day 1, and never has an issue, and 200,000 miles later, running smooth as day 1. I switched back to premium after hearing his explanation. And my added mileage offsets the costs almost completely.
 
^ +1

408K on my 95..all on exxon 93 octane.

at 150k my fuel pump died and exxon sent me 330.00 to pay for the pump replacement since I had never pumped anything except exxon 93 in my car and had 9ish years worth of fuel receipts to back it up.
which is why you should always get a gas receipt even if you pay cash.

the exxon guy tried to blame the rust in my tank, on my "tank", ya shoulda saw his face when I asked him to "puleeeeze splain to me" how a plastic gas tank..rusts.


only 93 for me, your mileage may vary, no warranty expressed or implied.
 
Hello.
I tried to use lower grade fuel in my '93. The engine threw the mother of all hissy fits about that. It took 3 tanks, from full to dry until it behaved normally again. I am far from an expert, but this was my experience. Chris
 
My navigator recommends premium and gets midgrade. I found that gas mileage didn't deteriorate with midgrade. It did with regular. So midgrade it is.

Light duty driving, low temperatures, regular is fine. High temperatures, high loads (esp at low RPM), go with premium.

If you're curious, do a tank or two of each, running the same loop in a similar driving style, and see if you can identify any consistent difference in mileage. Then go with what gets the better mileage.
 
How long does it take the car to adjust from 93 - 87 or visa versa?

Will the computers pretty much instantly make a change, or does it take time for them to 'learn?'
 
If pinging is detected via the knock sensors, the PCM retards timing at a preset rate - pretty much instantaneous. Fuel trims though are an adaptive process that takes several driving cycles, the details of which I would need to research - not so instantaneous.
 
There is an "Octane ajust plug" under the hood on the harness near the EEC-IV Test connector. Don't remember about plugged or unplugged, but it instantly changes the "start point" for all autoajustable values for 3 octane digits (from 91 Premium to 88 Regular for example). Harness plug color is black, 2 wires, DarkGreen & Grey/Red. At the left back side of the engine near windshield wiper motor & EAM solenoid(on the same harness) for the Gen2.
 
NickPims said:
There is an "Octane ajust plug" under the hood on the harness near the EEC-IV Test connector. Don't remember about plugged or unplugged, but it instantly changes the "start point" for all autoajustable values for 3 octane digits (from 91 Premium to 88 Regular for example). Harness plug color is black, 2 wires, DarkGreen & Grey/Red. At the left back side of the engine near windshield wiper motor & EAM solenoid(on the same harness) for the Gen2.
Click to expand...

I was told once by a reliable source, that the "octane plug" is not always what it says it is.
 
You must log in or register to reply here.
Back
Top