Jeeps Canada - Jeep Forums - 1998 Grand 8 cyl 5.9

Jeeps Canada - Jeep Forums (https://www.jeepscanada.com/)

- Jeep Mailing List (https://www.jeepscanada.com/jeep-mailing-list-32/)

- - 1998 Grand 8 cyl 5.9 (https://www.jeepscanada.com/jeep-mailing-list-32/1998-grand-8-cyl-5-9-a-40902/)

Re: 1998 Grand 8 cyl 5.9

In message <1158268539.893721.123660@b28g2000cwb.googlegroups .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.

Re: 1998 Grand 8 cyl 5.9

bllsht wrote:
> In message <1158268539.893721.123660@b28g2000cwb.googlegroups .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

Re: 1998 Grand 8 cyl 5.9

"Ed" <dorlyed@yahoo.com> wrote in
news:1158322821.028781.232450@i3g2000cwc.googlegro ups.com:

>
> bllsht wrote:
>> In message
>> <1158268539.893721.123660@b28g2000cwb.googlegroups .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.

Re: 1998 Grand 8 cyl 5.9

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" <xs11eNO@SPAMyahoo.com> wrote in message
news:Xns983F996ED713Exs11eyahoocom@70.168.83.30...
> "Ed" <dorlyed@yahoo.com> wrote in
> news:1158322821.028781.232450@i3g2000cwc.googlegro ups.com:
>
>>
>> bllsht wrote:
>>> In message
>>> <1158268539.893721.123660@b28g2000cwb.googlegroups .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.
>
>
>
>