This Is Weird

[Tungsten]

This has probably been mentioned somewhere before but here it goes...

 

If I run 87 octane gas, my truck doesn't detonate (have pre-ignition) or anything like that. However if I use 89 octane gas, the truck drives much nicer; the acceleration feels smoother and the idle is slightly lower. There is absolutely no difference in MPG between the two for me. Currently, I run the engine timing at 15 deg BTDC. I think this is the OEM specification for the VG30E. Also, I have a custom exhaust with short-tube headers if that makes any difference. I know for the VG33E the recommended octane is 89. I did try premium gas and as expected the engine had lag.

 

Should I keep running 89 then or is 87 the better choice? Should I leave the timing where it is?

I am aware of carbon deposits increasing compression but my engine is relatively clean on the inside.

Edited April 5, 2010 by Tungsten

[MY1PATH]

This is a normal symptom for a vehicle with intake, headers & exhaust

above idle mixture is atomized better so the higer octane does not burn as slow as it would in a stock engine. at idle it may be buring to late and thus lowering your idle.

choices:

1. You can try a base timing of 16 deg to help your idle if you wish to keep running 89(the ecu will resume its normal ignition curve once you step on the gas so
2. only idle is changed) I don't think the added cost of 89 is worth what it does...
3. -you can run 89 as is, I don't think the added cost of 89 is worth what it does...
4. -you can mix octane by pumping 1/4 tank of 89 every other fill. (this has provided good results for me)
5. -you can just run 87 and possibly changing timing to 14 deg may have the same smoothing effect(more cost effective)
6. -you can run 87 as is, this is the simplest choice and is cost effective. Your engine will not suffer.

 

I been going with option 4 for a long time. when I got my MSD in I things got even smoother so I went to option 5 and things stayed smooth. I save more $ this way too.

[Tungsten]

ok thanks, so two things

 

1. I do like the low idle, it has no negative effect on anything.

2. I don't mind paying for 89 as it has detergents in it to help clean up the engine along the way.

 

So I will keep doing what I'm doing then.

[Tungsten]

ok more weirdness

 

I noticed that on 87, the truck runs ok when its stone cold but as it warms up performance deteriorates.

However on 89, the truck runs like @!*% when its cold, if I give it a little gas the rpms go up a bit and then drop right away as if the engine wasn't getting enough fuel but after warming up it runs fine.

 

I think the ECCS is doing something here. Maybe auto timing advance and retard?

 

Should I do something about the warm-up issue or just leave it?

[adamzan]

Drive up here and we'll fix it.

[msavides]

I have had zero success adjusting timing on my truck. every time I try to adjust it it moves then goes right back to 15, i then turn the dist again it move for a sec then goes right back to 15. So i don't think adjusting it will help. I think the ecu corrects it.

 

When I was doing a tune up I read the proper way to adjust the base timing is to disconnect the harness plug from the Throttle position sensor, and that disables the auto timing adjustment then you adjust the timing to as close to 15 BTDC as possible. as soon as you reconnect the TPS it adjusts itself anyways.

 

I am not 100% sure if this is correct operation, This is from my experiences with my truck.

 

Mark

[Tungsten]

yes that is correct the timing is controlled by some loop back and has to do with the CPS

i guess ill keep using 89 and ignore that problem

 

maybe a mix of 87 and 89 will help

 

such is the case of the VG30E with intake, headers, and a sport exhaust

 

how about an ECU upgrade?

Edited April 8, 2010 by Tungsten

[msavides]

yes that is correct the timing is controlled by some loop back and has to do with the CPS

i guess ill keep using 89 and ignore that problem

 

maybe a mix of 87 and 89 will help

 

such is the case of the VG30E with intake, headers, and a sport exhaust

 

how about an ECU upgrade?

 

 

If you do not already have a factory service manual get one.

 

It has detailed instructions on how to set you base idle and troubleshooting for figuring out your idle. you also have an aac valve that controls your idle. I just went through some wacky unstable idling problems that turned out to be my Throttle Position Sensor. your problem seems to be with your cold idle and there is really good troubleshooting for that. you could even look at the 1995 manual that in online in pdf format, I don't think there was any troubleshooting differences between 91 and 95.

 

Mark

[Chriskaw440]

I've heard all the octane banter here also....but my 1990 always runs much better on premium. Even with the new knock sensor and no error codes....everything in good shape etc etc.

 

87 or 89.....under load....mine knocks still/runs noisier. So I just pay the extra few cents and live with it. with 250,000+ miles on it....she keeps on going and I just changed all the spark

plugs last month when I replaced my lifters....they all had perfect "wear" on them. About 350 miles to a tank of gas give or take driving conditions.

 

As I understood it on these rides, the timing is electronically controlled so I never mess with it....

 

Need to replace my TPS sometime but I hear it's a bitch to get it adjusted right...and I've heard that its easy....which is it? I've never replaced one.

 

-Chris

[msavides]

I've heard all the octane banter here also....but my 1990 always runs much better on premium. Even with the new knock sensor and no error codes....everything in good shape etc etc.

 

87 or 89.....under load....mine knocks still/runs noisier. So I just pay the extra few cents and live with it. with 250,000+ miles on it....she keeps on going and I just changed all the spark

plugs last month when I replaced my lifters....they all had perfect "wear" on them. About 350 miles to a tank of gas give or take driving conditions.

 

As I understood it on these rides, the timing is electronically controlled so I never mess with it....

 

Need to replace my TPS sometime but I hear it's a bitch to get it adjusted right...and I've heard that its easy....which is it? I've never replaced one.

 

-Chris

 

 

I guess it depends on your luck. I had no such luck. It took me 2 hours. and about 60 attempts to get it correctly set. See here for my tips

 

http://www.nissanpathfinders.net/forum/index.php?showtopic=25451&st=20

 

 

Mark

Edited April 12, 2010 by msavides

[Tungsten]

I've heard all the octane banter here also....but my 1990 always runs much better on premium. Even with the new knock sensor and no error codes....everything in good shape etc etc.

 

87 or 89.....under load....mine knocks still/runs noisier. So I just pay the extra few cents and live with it. with 250,000+ miles on it....she keeps on going and I just changed all the spark

plugs last month when I replaced my lifters....they all had perfect "wear" on them. About 350 miles to a tank of gas give or take driving conditions.

 

As I understood it on these rides, the timing is electronically controlled so I never mess with it....

 

Need to replace my TPS sometime but I hear it's a bitch to get it adjusted right...and I've heard that its easy....which is it? I've never replaced one.

 

-Chris

 

I don't know if there will be any advantage of running Premium here. I don't think the compression is high enough to give you more power on premium in this engine.

[MY1PATH]

Octane is not power. Premum is not faster or stronger its actually slower. Octane is resistance to detonation. Higer compression ratios are what make more power. If that power cannot be harnessed becasue the fuel is burning to fast(may just need less timing) or because it is detonating (ecu retards timing and offsets fuel ratio) then yes Higher octane will be needed and it will feel like it has more power ONLY because the engine is running properly now.

[Tungsten]

i just filled up on 89 again

i got an average of 16.5 mpg from daily driving

[Toby]

i just filled up on 89 again

i got an average of 16.5 mpg from daily driving

 

I fill up on 87 and I average around 20/21 with no mods. I put anything higher than 87 in it and it freaks out and runs horrible.

[Tungsten]

i bet you aren't modified because mine used to do really well with 87 too

now its rough with 87 but smooth with 89

 

i think Precise1 has a similar setup to mine and gets the same MPGs but i don't know with what octane

 

if i drive slow, i can get as much as 25 mpg

Edited April 16, 2010 by Tungsten

[Toby]

I fill up on 87 and I average around 20/21 with no mods. I put anything higher than 87 in it and it freaks out and runs horrible.

 

lol

[Tungsten]

been a long night...

[Precise1]

i bet you aren't modified because mine used to do really well with 87 too

now its rough with 87 but smooth with 89

 

i think Precise1 has a similar setup to mine and gets the same MPGs but i don't know with what octane

 

if i drive slow, i can get as much as 25 mpg

My mods are a lift, MT tires, headers, 2.25" piping with a high flow cat. Around town I get 14-15mpg, no trips yet. I think I may have a sensor issue or small exhaust leak though.

 

Tungsten, you can get 25 mpg?? I really find that hard to believe...

 

B

[Tungsten]

so what octane do you run?

 

yea i can get some pretty good gas miles out of it

i drive around 300 miles a week and end the week with 1/4 tank left

[ahardb0dy]

I've noticed when ever I use premium it seems I get less MPG for what ever reason??

[92Pathmaker]

I run 91 because of the cams. I get 14mpg all city and usually 22-25mpg all highway

[nismothunder]

Hell,fill it up with some nitro and see what it does,you'll have a hell of a time for aboot 30 miles(or until the head gasket/rings give out)

[Tungsten]

I run 91 because of the cams. I get 14mpg all city and usually 22-25mpg all highway

 

filled up on 89 today, 13 gals of it

from what the odometer says i had 256 miles after the fill-up before this one

 

so i averaged in at 19 mpg, which was both city and highway (mostly city), pretty good

yes i can get 20-25 mpg highway and i can get away with the 2.00" pipe from the headers down

this engine does not respond well to mods anyway, those valves are tiny

 

the weird cold engine problem is actually starting to go away which is very weird lol

maybe the warmer season is helping

 

Hell,fill it up with some nitro and see what it does,you'll have a hell of a time for aboot 30 miles(or until the head gasket/rings give out)

 

lol something tells me you tried it

[MY1PATH]

I've noticed when ever I use premium it seems I get less MPG for what ever reason??

AGAIN

OCTANE IS resistantce to detonation thru a slower burn.

your mpgs go down because your gas is not burning fast enough.

[ahardb0dy]

ok, thanks for the explanation