Fuel grade

[RERM]

Hi, I'm wondering if any of you have noticed the 3.8L in the Gen III Montero to be particularly dependant on the fuel grade. Let me explain, I have an '03 Limited that I ran Regular on all of last year, well, lately (last month or so) I've been getting a Check Engine light.(Code made my mechanic think it had to do with the cats, sorry but I forgot the code#). Well, the last month I've run 3 straight tanks of Premium (and one bottle of Octane booster) and voila!!! no more code!!!!

Are these engines THAT sensitive????

I mean, they run Montero/Pajero/Shogun's all over the world, in some pretty remote places, and they require Premium????

Seems strange to me...

Any thoughts?

 

[Michael Brown]

It should not be. I would believe that there is a dirty O2 sensor. Although mine has been showing a code since 2006 and I haven't had any issues running regular in the 3.5L.

 

[off-roader]

The minimum recommended fuel grade is usually indicated on the inside fuel door. Your owners manual should also tell you what fuel to run.

In my case, with my 96 which has the 3.5L dohc engine, it says 87 octane minumum and 91 octane recommended.

 

[SoCalMonty]

Seems like a coincidence. Any computer controlled car will pull back ignition timing to allow lower grade fuel, as not all regions sell the same octane. You may lose ~5 peak HP running 87 vs 91/92/93, but nothing to write home about.

If you're towing or frequently find yourself at full throttle, run premium. If you cruise and keep RPM's low, and you don't lug the engine much (1,000 lbs of cargo and climbing hills), you will be fine with lower.

I just run 89 in mine. No real reason other than compromise.

 

[off-roader]

Better smog results using premium though...

 

[RERM]

I doubt it's the O2 sensors as their all new!!!, might it just be the Costco gas I'm using?

 

[off-roader]

I doubt it's the O2 sensors as their all new!!!, might it just be the Costco gas I'm using?

I believe costco buys their gas from your local refineries. At least they do here in NorCal. Costco buys from the local Chevron refinery.

 

[Mudrunner]

Typically the only reason a certain fuel grade is required is because of performance applications, such as Turbos, superchargers, or high Compresion. The only other reason for a Higher octane will be because of reducing knock, this you will also be most common in V6 engine. The reason iirc is because they are off balance from that of an V8 with the 3 cylinders on each side, makes them unbalanced when the A/F mix is ignited.

 

[Monstero]

Compression on those motors is 10:1, If i remember right that is why they say higher octane. Always run premium in mine, when i run low grade poor girl sounded like a diesel. I know it would have adjusted eventually but I couldn't bear it....like nails on a chalk board to me. lol

 

[Mudrunner]

Compression on those motors is 10:1, If i remember right that is why they say higher octane. Always run premium in mine, when i run low grade poor girl sounded like a diesel. I know it would have adjusted eventually but I couldn't bear it....like nails on a chalk board to me. lol

lol I hate those sounds too!

 

[RERM]

How long should it take the computer to adjust when you change from Reg to Prem?, keep in mind I ran Reg for a year, and I've been running Prem for 3 tanks of gas...

 

[rockwood]

It's the additives that vary by brand.

 

[GFO]

Better smog results using premium though...

I'm about to get a smog check in a week or so; I know my cat is on the edge of dying as last check it barely passed. How much of a difference does premium make?

I normally run 89, sometimes I do 87.

 

[off-roader]

A few years back I went w/out doing anything (96SR w/ 188k miles). Failed smog test. I went back to the same smog shop (free retry) with a fresh tank of premium unleaded & did an oil change the night before. I passed ("by the hair of my chinny chin chin" as the saying goes).

HTH.

 

[RERM]

I got the codes (P0171 and P0172)

Keep in mind, I've already changed all four O2 sensors (with Denso's not Bosch), cleaned the MAF, checked the injectors (not clogged and working). Right now I can only figure it might be a dirty fuel filter....

PS. The Check Engine light keeps coming on and off. One day it's on, one its off...