1998 Grand 8 cyl 5.9

A few days ago I bought a '98 Grand Cherokee with 8Cyl 5.9 and now I
see that it might be necessary to use premium gas. Bad news but is it
true?

Ed wrote:
> A few days ago I bought a '98 Grand Cherokee with 8Cyl 5.9 and now I
> see that it might be necessary to use premium gas. Bad news but is it
> true?

It's true. The 5.9 needs higher octane but only if your getting ping.

Run it on the mid octane and if you get any pinging then add the higher
octane till it goes away.

Works like this.

1/2 gal of 87
+ 1/2 gal of 91
--------------- is
1 gal of 88

octane works in direct proportion.

p.s. gasoline is gasoline, there is no "premium" just additives
and octane booster that contrary to what some say actually lowers
the combustibilty of the fuel.

I run (on average) 92 octane. Which I get by pumping in alternating
fillups of 93 and 91 octane fuel.


--
-- DougW -- 93 ZJ 4.0 http://revbeergoggles.com
HESCO Supercharger - 300W IASCA Stereo - Edelbrock IAS Shocks
Gibson Exhaust - rear DCpower - custom gauge install - Stillen Rotors
Banks Header - and BEER, in the fridge!

I do a gas mileage and performance test.

I run a tank of regular and see what happens. In my CJ7's case the
sucker won't go over 65 mph, rattles like crap and only gets 250 miles
per 76 liter tank on regular. When I switch to premium, 3rd gear will
do 70+ mph, 4th buries the speedo and I don't have any urge to see what
5th will do. I then get 350 miles easy to a tank full. (I am comparing
tankfulls on long trips here, we put 3000 miles on the CJ7 this summer
on one trip)

With my Cherokee, it makes absolutely no difference at all.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Ed wrote:
>
> A few days ago I bought a '98 Grand Cherokee with 8Cyl 5.9 and now I
> see that it might be necessary to use premium gas. Bad news but is it
> true?

DougW wrote:
> Ed wrote:
>> A few days ago I bought a '98 Grand Cherokee with 8Cyl 5.9 and now I
>> see that it might be necessary to use premium gas. Bad news but is it
>> true?
>
> It's true. The 5.9 needs higher octane but only if your getting ping.
>
> Run it on the mid octane and if you get any pinging then add the
> higher octane till it goes away.
>
> Works like this.
>
> 1/2 gal of 87
> + 1/2 gal of 91
> --------------- is
> 1 gal of 88
^^---89
That is IF I actually could do math in my head. :/

--
Doug(mind like a steel trap. rusted shut)W

In message .com>, "Ed" wrote:

>A few days ago I bought a '98 Grand Cherokee with 8Cyl 5.9 and now I
>see that it might be necessary to use premium gas. Bad news but is it
>true?

The 5.9 came programmed to run premium, but can be reprogrammed to run on
regular.

bllsht wrote:
> In message .com>, "Ed" wrote:
>
> >A few days ago I bought a '98 Grand Cherokee with 8Cyl 5.9 and now I
> >see that it might be necessary to use premium gas. Bad news but is it
> >true?
>
> The 5.9 came programmed to run premium, but can be reprogrammed to run on
> regular.

Thanks to all who responded. I will use regular and see what happens
and the mention about reprogramming will take care of any problem.
Ed. Kelly

"Ed" > wrote in
ups.com:

>
> bllsht wrote:
>> In message
>> .com>, "Ed"
>> wrote:
>>
>> >A few days ago I bought a '98 Grand Cherokee with 8Cyl 5.9 and
>> >now I see that it might be necessary to use premium gas. Bad
>> >news but is it true?
>>
>> The 5.9 came programmed to run premium, but can be reprogrammed
>> to run on regular.
>
> Thanks to all who responded. I will use regular and see what
> happens and the mention about reprogramming will take care of any
> problem.

The need for premium is determined by combustion chamber
design and compression ratio, it would be more accurate to say it's
designed rather than programmed. If you run regular the engine will
knock, you won't know it because the knock sensors will retard the
spark which will reduce gas mileage and performance. If you
reprogram the computer to limit the spark advance (and there's no
need to do so, that's exactly what the knock sensor will do for you)
you'll accomplish the same thing, a loss of power and a reduction in
gas mileage.

Read Mike Romain's post where he says, "I run a tank of regular and
see what happens. In my CJ7's case the sucker won't go over 65 mph,
rattles like crap and only gets 250 miles per 76 liter tank on
regular. When I switch to premium, 3rd gear will do 70+ mph, 4th
buries the speedo and I don't have any urge to see what 5th will
do. I then get 350 miles easy to a tank full."

That may be a little more extreme that the results you'll have but
you get the idea, you should run premium.

We too have a '98 ZJ 5.9 Limited. Gas prices were higher when we bought it
than they are now. It is a 'weekend and trip' vehicle for us, not a daily
driver. Both of our daily beaters are Hondas.

It seems that middle grade gas might be OK but since our use of the beast is
limited we don't mind paying for premium.
FWIW I was told that the computer can be programmed for lower octane gas.

If you experiment with the different grades of gas I would appreciate
hearing your experiences.

Since I'm asking for your opinion, I would like to know about your shock
absorbers. I asked here about a month ago about what to put on my beast. I
went with the Edelbrock Performer IAS's. I am happy with them but only have
the originals to compare with. What shocks are on your ZJ? Do you like them?
Why / Why not?

Thanks,
dj

"XS11E" > wrote in message
...
> "Ed" > wrote in
> ups.com:
>
>>
>> bllsht wrote:
>>> In message
>>> .com>, "Ed"
>>> wrote:
>>>
>>> >A few days ago I bought a '98 Grand Cherokee with 8Cyl 5.9 and
>>> >now I see that it might be necessary to use premium gas. Bad
>>> >news but is it true?
>>>
>>> The 5.9 came programmed to run premium, but can be reprogrammed
>>> to run on regular.
>>
>> Thanks to all who responded. I will use regular and see what
>> happens and the mention about reprogramming will take care of any
>> problem.
>
> The need for premium is determined by combustion chamber
> design and compression ratio, it would be more accurate to say it's
> designed rather than programmed. If you run regular the engine will
> knock, you won't know it because the knock sensors will retard the
> spark which will reduce gas mileage and performance. If you
> reprogram the computer to limit the spark advance (and there's no
> need to do so, that's exactly what the knock sensor will do for you)
> you'll accomplish the same thing, a loss of power and a reduction in
> gas mileage.
>
> Read Mike Romain's post where he says, "I run a tank of regular and
> see what happens. In my CJ7's case the sucker won't go over 65 mph,
> rattles like crap and only gets 250 miles per 76 liter tank on
> regular. When I switch to premium, 3rd gear will do 70+ mph, 4th
> buries the speedo and I don't have any urge to see what 5th will
> do. I then get 350 miles easy to a tank full."
>
> That may be a little more extreme that the results you'll have but
> you get the idea, you should run premium.
>
>
>
>

"Doug" > wrote in
:

> FWIW I was told that the computer can be programmed for lower
> octane gas.

Correct, but as I said, it's a waste of time and money. The knock
sensor will do exactly the same thing, retard the spark with exactly
the same results, less performance and less gas mileage.

It's probably cheaper to run premium.

Some engines have low compression kits available for them, I'm not sure
the 5.9 is one of them. They may consist of low compression pistons or
different cylinder heads which are VERY costly and it would take years
to make up the cost in savings on gas price or there may be thicker
head gaskets available, still costly because of the labor involved but
much less than the other means of lowering compression...

Again, it's cheaper to run premium and make sure your *next* vehicle
runs on regular.

As for shocks, I have a lift mounted on the back of my Jeep to carry a
mobility scooter so I needed to get air adjustable rear shocks, that
very much limited my choice, I just got what was cheap.

My dad has one of those 'go-karts', and it is difficult for my mom and
sister to disassemble it when they go on a trip.

What lift do you have?
Wish you'd gotten something else?
Thoughts/comments?


"XS11E" > wrote in message
...
> "Doug" > wrote in
> :
>
>> FWIW I was told that the computer can be programmed for lower
>> octane gas.
>
> Correct, but as I said, it's a waste of time and money. The knock
> sensor will do exactly the same thing, retard the spark with exactly
> the same results, less performance and less gas mileage.
>
> It's probably cheaper to run premium.
>
> Some engines have low compression kits available for them, I'm not sure
> the 5.9 is one of them. They may consist of low compression pistons or
> different cylinder heads which are VERY costly and it would take years
> to make up the cost in savings on gas price or there may be thicker
> head gaskets available, still costly because of the labor involved but
> much less than the other means of lowering compression...
>
> Again, it's cheaper to run premium and make sure your *next* vehicle
> runs on regular.
>
> As for shocks, I have a lift mounted on the back of my Jeep to carry a
> mobility scooter so I needed to get air adjustable rear shocks, that
> very much limited my choice, I just got what was cheap.
>
>
>