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The Northstar has a very effective knock sensor that will retard the timing if it detects a spark knock. Premium is recommended for peak performance. I ran my '97 on regular for 3 years and never noticed any difference in mileage or performance. If you're gonna race it, use premium. If not regular will work just fine.

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I use mid grade in my 95 STS. I either go to the places that give you mid grade for the 87 octane price, or else I use coupons for mid grade and it ends up being the same price or cheaper depending on what I have for coupons.

I've used 87 octane in the 95 STS with no problems whatsoever.

WARNING: I'm a total car newbie, don't be surprised if I ask a stupid question! Just trying to learn.

Cheers!

5% discount code at RockAuto.com - click here for your discount!

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I use the mid grade, I find my car runs like a pig on regular. The knock sensor retards the timing in order to stop knocking, retarded timing results in less power. When the engine is hot I can get a momentary knock when I pull away from a light, then it stops when I use regular.

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I realize that all cars are different and what works in one, may or may NOT work well in another.

Rangers Cadillac runs great on Regular... mine don't. Body by Fisher uses mid-grade ok.

This is my second 2006 DTS. Owners manual says Premium is RECOMMENDED.

I have right at 52,000 miles on it and had almost 40,000 on the first one when it burned in my garage fire.

During the three years and about 90,000 miles, I tried running regular in them several times. This particular car DOES NOT LIKE regular. :D

I take a 10% to 15% hit in fuel mileage and a VERY NOTICEABLY hit in performance. Since Premium is only 10% to 15% higher than regular, it is almost exactly the same price as regular, per miles driven, when you consider the MPG hit I take using regular.

I would love to be able to run regular in it, and if I only drove it barely above an idle, down to the grocery store once a week and Darling Wife drove to the beauty shop once a week, I could probably get by with regular and never know the difference.

But I like road trips. :D:D That is how I put 90,000 miles in three years.

On trips, I tend to drive SLIGHTLY over the posted speeds... when it is safe to do so.

On two lane roads.. if I need to pass... I use WOT to get around them and get back in MY lane as soon as possible. :D It is safer to be in your own lane....plus it is fun to use WOT.

At WOT, the difference between regular really becomes apparent in my car. It is sluggish and does not make the same power it does on Premium.

This is just my opinion and feeling about how the different grades of fuel run in MY PARTICULAR car.

As I said in the beginning... each car is different. Yours may do just great on regular.

If you want to run regular...You may want to run three of four tanks and keep real good track of the mileage.

THEN try three of four tanks of Premium... and keep real good track of the mileage.

See if there is any difference in YOUR car.

Also find a safe place to test the power... if you are so inclined.

Test it with both regular and then with premium after you have used at least a half tank of Premium to give it time to adjust to the Premium after using regular.

As always ....YMMV. :D

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That said, last week I took a 1000 mile trip to Maine, and used Sunoco 93 since the gas prices came down, I got about 2 MPG better gas mileage and it rocketed up hills....

I think its necessary to do a test a couple of tanks of 87, 89, 91 then treat it to 93 and see what you think

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

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That said, last week I took a 1000 mile trip to Maine, and used Sunoco 93 since the gas prices came down, I got about 2 MPG better gas mileage and it rocketed up hills....

Mike,

If you get 2 MPG better on 93... and the car runs so much better... why use anything else? :D:D

At 2MPG better ....that is 40 extra miles on each 20 gallons you buy. So therefore, it takes about TWO MORE GALLONS of mid-grade to do the same thing that Premium does. Looks like the extra cost of the two extra gallons of Mid-Grade would offset the small price differential of the Premium.

Plus as you said... the car RUNS better.

That don't mean much to some...but it does to Certified Car Nuts like "ME". :D

Who "BUT" a nut would put a TUNE on a DTS? :D:D:D

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Thanks for doing the homework for me. The prices have come down so low that Premium is reasonable and it does run better, I have found myself with a heavy foot since I started using it. I almost got myself in trouble coming home, pulling a bone headed move... got very lucky... I have to be careful getting angry behind the wheel, it can get me in trouble.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

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Yessir....Anger and gasoline is kinda like gunpowder and alcohol....it's not a good mix at all.

If you don't mind me asking... what happened?

I also have to watch myself sometimes. I drive from 100 to sometimes 400 miles a day in the course of my job. Most of it in heavy traffic.

It is easy to get mad and irritated with some people. As I have got older... it is a little easier to just relax, give 'em a good cussing (of course they can't hear me but it makes ME feel better) and just let em go.

Thats if I am in the V6 Chevy Van. :D

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Well I came up behind a mini van, dragging in the left lane on the Belt Parkway, I had a guy up my butt, I pulled hard two lanes to the right to get by this minivan, into the slow lane, WOT'd, went by a car in the middle lane, pulled back into the fast left lane, and the JERK that was crawling all along, sped up seeing that I was trying to go by and we ALMOST hit, he sped up and almost caused a problem, but it was MY fault as the timing should have been way better, he was doing 50 when I made the move and I came back into his lane at 75 having passed a car in the middle lane and he was RIGHT THERE. I saw we were close and he must have died because he dropped WAY back after that, I am sure his wife gave him an earful... trying to block me.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

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Some people are just pure idiots.

I have some drivers almost everyday that speed up if they see you are going to pass them.

Another thing that pi$$e$ me off... you are going to do a normal lane change...traffic is not real heavy...you put on the turn signal to let the people in the other lane know you are going to change lanes, and then they SPEED UP (for no reason) and close up the hole you were going to get into. It is irritating as heck.

If I am in the big ole van...and if it is a little car (or a BMW) and i am feeling ornery, I just keep easing over like I don't see them...(but watching them closely in the mirrors) then they get on the horn... I keep easing over. They usually back off as I get just a few inches from them. :D Then they go around me in the other lane and USUALLY tell me I am NUMBER ONE. :D

At least that is what I think they mean... they are holding up one finger. :D

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I have just purchased a '95 STS with 140,000 miles and the owner claims to be operating it on regular fuel.

It runs well but what fuel should or must I be using considering the new fuel mixtures?

Does it say "Premium Required" by the fuel gauge or in the owner's manual? If so, I wouldn't use regular.

Know that the '98 and later Northstars compute the actual fuel octane and make appropriate adjustments to ignition timing, but not certain about earlier versions.

I have a '99 STS and except two tanks over the summer when I couldn't bear to pay over $5/gallon, have used premium exclusively. I didn't check mileage carefully with the two regular tanks, but could definitely tell a difference in performance as I was doing quite a bit of driving on winding two-lane roads and acceleration during passing was significantly less energetic. There's a long hill in town with high retaining walls on both sides of the road and I've never heard even a touch of knock when going up--yet it's VERY noticeable with my other vehicles in which I burn regular.

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All Northstars including PRE-98 have the KNOCK SENSOR other wise we would not have stated so.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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  • 4 weeks later...
All Northstars including PRE-98 have the KNOCK SENSOR other wise we would not have stated so.

I have a 95 STS that my son now drives. When I got it in 1998 or 1999 it had 98K miles on it , it had 178K miles when my son got it. I did not used premium fuel in it, somehow I was able the see with the OBD that someone had set the computer to run on 87 octane. I don't remember how I found it (I slept since than) and a friend of mind who had a 94 STS was set for 89 or 91 octane when we looked at his caddy. We tried to change his to 87 octane but were unable cause we didn't have a manual and didn't want to screw things up. I never had any trouble running 87 octane for 10 years I drove it.

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All Northstars including PRE-98 have the KNOCK SENSOR other wise we would not have stated so.

I have a 95 STS that my son now drives. When I got it in 1998 or 1999 it had 98K miles on it , it had 178K miles when my son got it. I did not used premium fuel in it, somehow I was able the see with the OBD that someone had set the computer to run on 87 octane. I don't remember how I found it (I slept since than) and a friend of mind who had a 94 STS was set for 89 or 91 octane when we looked at his caddy. We tried to change his to 87 octane but were unable cause we didn't have a manual and didn't want to screw things up. I never had any trouble running 87 octane for 10 years I drove it.

I think what you were seeing what the PCM adjusting itself to run on 87, it was NOT set there. If you check with your friend, I am sure he was running higher octane than 87, and the PCM set itself up to run the higher octane. I will confirm this in my 95 manual and get back to this thread.

The knock sensor senses knocking and retards the timing to eliminate knock. I had not heard of what you just reported, maybe the OBD 1 PCM had a TABLE for 87, one for 89 and one for 91+ that it followed.

BUT this was NOT a manual override

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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All Northstars including PRE-98 have the KNOCK SENSOR other wise we would not have stated so.

I have a 95 STS that my son now drives. When I got it in 1998 or 1999 it had 98K miles on it , it had 178K miles when my son got it. I did not used premium fuel in it, somehow I was able the see with the OBD that someone had set the computer to run on 87 octane. I don't remember how I found it (I slept since than) and a friend of mind who had a 94 STS was set for 89 or 91 octane when we looked at his caddy. We tried to change his to 87 octane but were unable cause we didn't have a manual and didn't want to screw things up. I never had any trouble running 87 octane for 10 years I drove it.

I think what you were seeing what the PCM adjusting itself to run on 87, it was NOT set there. If you check with your friend, I am sure he was running higher octane than 87, and the PCM set itself up to run the higher octane. I will confirm this in my 95 manual and get back to this thread.

The knock sensor senses knocking and retards the timing to eliminate knock. I had not heard of what you just reported, maybe the OBD 1 PCM had a TABLE for 87, one for 89 and one for 91+ that it followed.

BUT this was NOT a manual override

I know that you don't like Chilton Manuals, but that's were I found how to check it, plus all I had. My son is away at school and I gave him the manual to take with him, 95 manual doesn't cover my 2001. But I am sure that it was not the PCM adjusting itself, I read in that manual how to see what the computer was set for. It said something about the engine setting being adjusted for octane rating but did not say how to adjusted them that's why we didn't mess with my friends 94. My son should visit this week or next I will ask him to bring the manual and tell you how to do it. I am sure I am not lost in space!

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All Northstars including PRE-98 have the KNOCK SENSOR other wise we would not have stated so.

I have a 95 STS that my son now drives. When I got it in 1998 or 1999 it had 98K miles on it , it had 178K miles when my son got it. I did not used premium fuel in it, somehow I was able the see with the OBD that someone had set the computer to run on 87 octane. I don't remember how I found it (I slept since than) and a friend of mind who had a 94 STS was set for 89 or 91 octane when we looked at his caddy. We tried to change his to 87 octane but were unable cause we didn't have a manual and didn't want to screw things up. I never had any trouble running 87 octane for 10 years I drove it.

I think what you were seeing what the PCM adjusting itself to run on 87, it was NOT set there. If you check with your friend, I am sure he was running higher octane than 87, and the PCM set itself up to run the higher octane. I will confirm this in my 95 manual and get back to this thread.

The knock sensor senses knocking and retards the timing to eliminate knock. I had not heard of what you just reported, maybe the OBD 1 PCM had a TABLE for 87, one for 89 and one for 91+ that it followed.

BUT this was NOT a manual override

I know that you don't like Chilton Manuals, but that's were I found how to check it, plus all I had. My son is away at school and I gave him the manual to take with him, 95 manual doesn't cover my 2001. But I am sure that it was not the PCM adjusting itself, I read in that manual how to see what the computer was set for. It said something about the engine setting being adjusted for octane rating but did not say how to adjusted them that's why we didn't mess with my friends 94. My son should visit this week or next I will ask him to bring the manual and tell you how to do it. I am sure I am not lost in space!

Not trying to add fuel to the fire...so to speak...

I know that the 2006 and newer uses a different computer system than the older cars, and it is now SPLIT. One computer for the engine, and one computer for the transmission.

That being said, when I had my 2006 TUNED a while back...there were TWO FUEL TABLES in the engine computer...and mine was stuck on the LOW OCTANE table.

He changed it to the HIGH OCTANE table.

It is SUPPOSED to change automatically, depending on what fuel you are running.

I have always used PREMIUM fuel in it ...except for some experimenting I have done on long road trips.

As some of you may remember, I have always complained that this car did not have the same EAGER, HEY LETS GO, feeling, that my first 2006 DTS had.

IT DOES NOW. :D:D:D

As far as being able to MANUALLY CHANGE the fuel tables from the control panel in the dash, on an older car...I don't have a clue. I would kinda doubt it, since the computers are locked down so tight by GM.

I am just relating my experience on my 2006.

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All Northstars including PRE-98 have the KNOCK SENSOR other wise we would not have stated so.

I have a 95 STS that my son now drives. When I got it in 1998 or 1999 it had 98K miles on it , it had 178K miles when my son got it. I did not used premium fuel in it, somehow I was able the see with the OBD that someone had set the computer to run on 87 octane. I don't remember how I found it (I slept since than) and a friend of mind who had a 94 STS was set for 89 or 91 octane when we looked at his caddy. We tried to change his to 87 octane but were unable cause we didn't have a manual and didn't want to screw things up. I never had any trouble running 87 octane for 10 years I drove it.

I think what you were seeing what the PCM adjusting itself to run on 87, it was NOT set there. If you check with your friend, I am sure he was running higher octane than 87, and the PCM set itself up to run the higher octane. I will confirm this in my 95 manual and get back to this thread.

The knock sensor senses knocking and retards the timing to eliminate knock. I had not heard of what you just reported, maybe the OBD 1 PCM had a TABLE for 87, one for 89 and one for 91+ that it followed.

BUT this was NOT a manual override

I know that you don't like Chilton Manuals, but that's were I found how to check it, plus all I had. My son is away at school and I gave him the manual to take with him, 95 manual doesn't cover my 2001. But I am sure that it was not the PCM adjusting itself, I read in that manual how to see what the computer was set for. It said something about the engine setting being adjusted for octane rating but did not say how to adjusted them that's why we didn't mess with my friends 94. My son should visit this week or next I will ask him to bring the manual and tell you how to do it. I am sure I am not lost in space!

This is interesting and the first time I have heard this in the ten years I have been here. Maybe its possible that the OBD1 system has a setting, but I had never heard of this before. As far as has been discussed, the KNOCK SENSOR retards timing based on the detection of knocking.. This 'setting' in the PCM has never come up. I need to get my 94/95 manual back from my friend this weekend and have a look myself. I don't doubt you, its just that it has never come up before. Lets see what others have to say about it

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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This is interesting and the first time I have heard this in the ten years I have been here. Maybe its possible that the OBD1 system has a setting, but I had never heard of this before. As far as has been discussed, the KNOCK SENSOR retards timing based on the detection of knocking.. This 'setting' in the PCM has never come up. I need to get my 94/95 manual back from my friend this weekend and have a look myself. I don't doubt you, its just that it has never come up before. Lets see what others have to say about it

It will be very interesting to find out if the fuel tables are MANUALLY ADJUSTABLE.

That would let anyone who wanted to run regular...and didn't care about the little extra power that you MAY get from PREMIUM..run REGULAR if they want to.

And on the other hand, if someone wanted it to BE ALL THAT IT CAN BE...they could adjust the fuel table to PREMIUM ONLY. :D

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This is interesting and the first time I have heard this in the ten years I have been here. Maybe its possible that the OBD1 system has a setting, but I had never heard of this before. As far as has been discussed, the KNOCK SENSOR retards timing based on the detection of knocking.. This 'setting' in the PCM has never come up. I need to get my 94/95 manual back from my friend this weekend and have a look myself. I don't doubt you, its just that it has never come up before. Lets see what others have to say about it

It will be very interesting to find out if the fuel tables are MANUALLY ADJUSTABLE.

That would let anyone who wanted to run regular...and didn't care about the little extra power that you MAY get from PREMIUM..run REGULAR if they want to.

And on the other hand, if someone wanted it to BE ALL THAT IT CAN BE...they could adjust the fuel table to PREMIUM ONLY. :D

So what we are saying here is that an engine can be SET to run on regular, with no intervention from the knock sensor? Why have a knock sensor then? So if the PCM is SET to run on regular does this take the knock sensor out of the equation? This thought is very new to me, having been around the guru for 6 or so years I don't think this ever came up, as far as I knew the PCM detected knocking via the knock sensor and then retarded timing to compensate. So we are saying that the PCM is set to 87, and even though CONDITIONS will allow the timing to be more advanced the PCM has been defaulted to 87 and thereby a forced retarded timing? THAT thought sounds VERY VERY antiquated to me and that method sounds too elementary, that method sounds STUPID to me, and to me there is NOTHING STUPID about the NORTHSTAR. With the knock sensor method the timing is retarded on a sliding scale as needed, not a POSTED spec. Many NSs will run fine on 87 in winter temps but knock like hell in summer temps on 87, so to POST an 87 in the PCM sounds very SIMPLISTIC.

I might contact the guru for a clarification on this since I am thinking about buying Mac's Eldorado.. and this thougth differs from anything I had heard prior..

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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So what we are saying here is that an engine can be SET to run on regular, with no intervention from the knock sensor? Why have a knock sensor then? So if the PCM is SET to run on regular does this take the knock sensor out of the equation? This thought is very new to me, having been around the guru for 6 or so years I don't think this ever came up, as far as I knew the PCM detected knocking via the knock sensor and then retarded timing to compensate. So we are saying that the PCM is set to 87, and even though CONDITIONS will allow the timing to be moved higher the PCM has been defaults to 87 and thereby a retarded timing? THAT thought sounds VERY VERY antiquated to me and that method sounds too elementary, that method sounds STUPID to me, and to me there is NOTHING STUPID about the NORTHSTAR.

I might contact the guru for a clarification on this since I am thinking about buying Mac's Eldorado.. and this thougth differs from anything I had heard prior..

Mike,

Nope...I am not saying there will be no intervention from the knock sensor.

My knock sensor still functions just as it was designed to.

During WOT takeoffs...it even senses severe WHEELHOP as knocking and pulls timing. :D:D

If it didn't function properly, the ECM would keep advancing the timing till it hit the built in limits or the engine self destructed from preignition.

I was just saying...on MY CAR...there is two fuel/timing tables built into the ECM.

It is supposed to change from one to the other, back and forth, AUTOMATICALLY, as needed, based on fuel, driving conditions and sensed spark knock (or lack thereof) and multiple other factors, all by itself.

Mine was somehow STUCK in the low octane table, which explains much of the differences between this car and my first one.

He changed it to the HIGH octane table, but I don't think it is LOCKED to the high octane table.

I will be seeing him Sat...midday...to have a couple more tweaks done to the car. I want the 2/3 shift firmed up just a tad more and want the TCC adjusted to hold better and not unlock so easy when driving.

I will ask for more explanation of the fuel/timing tables and exactly what he did to it.

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Thanks, I am in the process of contacting the guru on this

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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OK I asked the guru to stop by and to give us his thoughts on this, I don't know if he will be able to do so, but we will see. It was be exciting to have him stop by. Mike

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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OK I asked the guru to stop by and to give us his thoughts on this, I don't know if he will be able to do so, but we will see. It was be exciting to have him stop by. Mike

THATS GREAT.

I am looking forward to it.

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