H3 fuel grade question

[Ipedog]

Hi All -

What sort of fuel does the H3 need? Regular, Super?

I will be turning in my 4Runner in the spring and really like the looks of the H3. I test drove a Adventure/Lux yesterday and was impressed.

What I'm not sure I would be impressed with is having to fil up with Super every week. My guess is that gas prices will be at $3.00 to 3.50/gal for regular by this time next year. Adding $.50 to .75 on for super would be no fun.

Thanks -

Rob (Ipedog)
Looking forward to joining the Hummer Ranks

[Ipedog]

Hi All -

What sort of fuel does the H3 need? Regular, Super?

I will be turning in my 4Runner in the spring and really like the looks of the H3. I test drove a Adventure/Lux yesterday and was impressed.

What I'm not sure I would be impressed with is having to fil up with Super every week. My guess is that gas prices will be at $3.00 to 3.50/gal for regular by this time next year. Adding $.50 to .75 on for super would be no fun.

Thanks -

Rob (Ipedog)
Looking forward to joining the Hummer Ranks

[TigerH3]

I have been using regular with no problems. I was told by my dealership that the H3 only required regular unleaded.

[f5fstop]

Regular grade; 87 Octane

[HummBebe]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by f5fstop:
Regular grade; 87 Octane </div></BLOCKQUOTE>

f5fstop:

Do you know why they are running 87 in a engine that has a compression ratio over 10:1 ?

I was schooled that that was taboo....yet it seems to run fine!

[f5fstop]

Actually, I need to correct my statement, it actually reads, "87 Octane or higher."

The advancements in electronic sensors and control have allowed all the car manufacturers to allow engines to run on regular versus premium fuel. Knock sensors are more finely calibrated, engine control sensors have a better control over the power curve, fuel, timing, etc. Even the Vette I just traded in, could run on 87, the owner's manual just recommended 91.
I know from reading test reports on Cadillacs that have high compression and use 87, there is no noticeable increase in HP and definitely no increase in fuel mileage. I have not seen any studies done on this engine, but I know they have done them.
Since this is a high compression engine, there is no comment about how higher octane should not be used and may cause damage more than benefit the engine. So, it appears you could burn higher octane and not have a problem.

"I was schooled that that was taboo....yet it seems to run fine!"

I was schooled the same way, but things are changing so fast now that it is hard to keep up with the new technology.

[ChevyHighPerformance]

If the H3 is controlled similar to GM's other vehicles, there are two main spark tables: high octane and low octane. Here is a menu shot of a programming package used to program the PCM.

[ChevyHighPerformance]

The top left shows the two main timing tables. A typical timing table is shown below. The timing is a funtion of Engine RPM and cylinder airflow in g/cylinder.

[ChevyHighPerformance]

This was a high octane table. The low octane table will have lower timing throughout the table. As you drive, your knock sensor(s) will detect knock (before any audible knock) and will retard timing based on learned "cells". So your normal timing for these cells will be in between the high octance and low octane table. If certain conditions are present, the PCM will dump you to the low octane table if it assumes the you have a bad tank of gas - gas milage will suffer some. After filling up with a predetermiend amount of fuel, the learned timing values will reset and the timing will learn again. Ever feel that the vehicle is more peppy after a fill up? One reason is that the timing has been reset and the engine will produce a little more power.

GM has to design these tables to accomodate different elevations, temperatures (there are separate IAT and ECT timing adder tables), fuel quality (oxygenated or normal), etc.

You will get the best fuel economy when the timing is matched to the fuel quality. A good custom tuner can increase the target A/F ratio from 14.7 to about 14.9-15.0, add timing to the low octane and high octane timing tables (part throttle and WOT), and few other tricks to get better gas mileage while still maintaining acceptable emissions.

[HummBebe]

I asked the same question in an email to GM. They replied "Please refer to your owners mnual" LOL

I thought I wanted an answer....now I just feel old and out of it. :-)

But thank you, I can now look forward to a programmer for my H3.

I'm printing this and sending it to my POP. He is really a dinosaur. Bless his heart.


It's time to buck up little soldier

[f5fstop]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by ChevyHighPerformance:

You will get the best fuel economy when the timing is matched to the fuel quality. A good custom tuner can increase the target A/F ratio from 14.7 to about 14.9-15.0, add timing to the low octane and high octane timing tables (part throttle and WOT), and few other tricks to get better gas mileage while still maintaining acceptable emissions. </div></BLOCKQUOTE>

Good information, above my head, but I have a friend in Romulus MI who is in charge of some of this type of programming.

[mightypuck]

87 Octane...have even used Arco and it runs fine.

[Ipedog]

Thanks for all your replies (Some way more technical than I expected ).

The H3 looks even better now.

Thanks lots -

Rob (Ipedog)

[ChevyHighPerformance]

I guess I got a little carried away. 87 is OK. Unlike some of their compeition, GM did a good job with the programming to permit the high compression engine to run on 87 octane without the audible pinging.

[Ipedog]

In the first post of this message I guessed that gas prices would be at $3.00 to 3.50/gal in a year... I guess I was off a wee bit, like 51 weeks!

Rob (Ipedog)