Interstate Trouble

Greetings.

I have a 92 YJ 4.0 with 31s on it. I bought it with 120K and have put
maybe 5K more on it. Yesterday I thought it would be a good idea to
take it down I-80 for a weekend visit to a town 3 hours away. Unlike
most Wyoming 1-80 days it wasn't TOO windy, but the Jeep was having a
hell of a time. I figured it was the fact that my Jeep came with 3.07
gears and those leave me without 5th gear... But as I kept going it
kept sucking gas. I stopped real quickly and I noticed that the piston
slap seemed much louder and my oil pressure was low.. When I kept going
the pressure came back up to normal, but it kept sucking gas. In 60
miles I used about 25 bucks in gas.

So my question is. Is this a problem due to 3.07 gears that I need to
fix, or a problem with the engine, or both. When I gave up the quest it
slapped hard for awhile then it sounded normal after a bit. My temp was
normal and the oil level is good. I'm using syn 10-30. I'm guessing
that a re-gear would do the trick, but I want to see you all think. In
town and up till now the Jeep has run very good. The only problem I
have ever noticed is that when I run on the highway for a short time
and then stop I can smell a gassy smell.

Thanks for helping
D

Next time put your street tires back on.
God Bless America, ßill O|||||||O
http://www.billhughes.com/

Dave Jost wrote:
>
> Greetings.
>
> I have a 92 YJ 4.0 with 31s on it. I bought it with 120K and have put
> maybe 5K more on it. Yesterday I thought it would be a good idea to
> take it down I-80 for a weekend visit to a town 3 hours away. Unlike
> most Wyoming 1-80 days it wasn't TOO windy, but the Jeep was having a
> hell of a time. I figured it was the fact that my Jeep came with 3.07
> gears and those leave me without 5th gear... But as I kept going it
> kept sucking gas. I stopped real quickly and I noticed that the piston
> slap seemed much louder and my oil pressure was low.. When I kept going
> the pressure came back up to normal, but it kept sucking gas. In 60
> miles I used about 25 bucks in gas.
>
> So my question is. Is this a problem due to 3.07 gears that I need to
> fix, or a problem with the engine, or both. When I gave up the quest it
> slapped hard for awhile then it sounded normal after a bit. My temp was
> normal and the oil level is good. I'm using syn 10-30. I'm guessing
> that a re-gear would do the trick, but I want to see you all think. In
> town and up till now the Jeep has run very good. The only problem I
> have ever noticed is that when I run on the highway for a short time
> and then stop I can smell a gassy smell.
>
> Thanks for helping
> D

I wonder if you might have a stuck injector and when the engine is
working hard like that the oil is getting diluted. That would explain
the gassy smell, the low oil pressure, and the louder piston slap. I
had that happen in a VW years ago (I know<G>).

You might also have a sensor (temp sensor?) that is bad and confusing
the computer into making the engine run really rich.

Jeff DeWitt

Dave Jost wrote:
> Greetings.
>
> I have a 92 YJ 4.0 with 31s on it. I bought it with 120K and have put
> maybe 5K more on it. Yesterday I thought it would be a good idea to
> take it down I-80 for a weekend visit to a town 3 hours away. Unlike
> most Wyoming 1-80 days it wasn't TOO windy, but the Jeep was having a
> hell of a time. I figured it was the fact that my Jeep came with 3.07
> gears and those leave me without 5th gear... But as I kept going it
> kept sucking gas. I stopped real quickly and I noticed that the piston
> slap seemed much louder and my oil pressure was low.. When I kept going
> the pressure came back up to normal, but it kept sucking gas. In 60
> miles I used about 25 bucks in gas.
>
> So my question is. Is this a problem due to 3.07 gears that I need to
> fix, or a problem with the engine, or both. When I gave up the quest it
> slapped hard for awhile then it sounded normal after a bit. My temp was
> normal and the oil level is good. I'm using syn 10-30. I'm guessing
> that a re-gear would do the trick, but I want to see you all think. In
> town and up till now the Jeep has run very good. The only problem I
> have ever noticed is that when I run on the highway for a short time
> and then stop I can smell a gassy smell.
>
> Thanks for helping
> D
>

Bill, the street tires are long gone.

Jeff, would it explain low oil pressure only when idling? How do I
check it? The sensor I need a computer to check, but I'd like to avoid
taking it to the Jeep shop. The guys there will tell me that I need
Mopar parts by the crate load.

Thanks,
D

What was your engine rpm at, say sixty? I am thinking that 3.07 gears and
31 inch tires might be too much for even fourth gear. If so, then regearing
would fix a lot. Street tires would help too, if you want to run it on the
street.

Earle

"Dave Jost" > wrote in message
oups.com...
> Greetings.
>
> I have a 92 YJ 4.0 with 31s on it. I bought it with 120K and have put
> maybe 5K more on it. Yesterday I thought it would be a good idea to
> take it down I-80 for a weekend visit to a town 3 hours away. Unlike
> most Wyoming 1-80 days it wasn't TOO windy, but the Jeep was having a
> hell of a time. I figured it was the fact that my Jeep came with 3.07
> gears and those leave me without 5th gear... But as I kept going it
> kept sucking gas. I stopped real quickly and I noticed that the piston
> slap seemed much louder and my oil pressure was low.. When I kept going
> the pressure came back up to normal, but it kept sucking gas. In 60
> miles I used about 25 bucks in gas.
>
> So my question is. Is this a problem due to 3.07 gears that I need to
> fix, or a problem with the engine, or both. When I gave up the quest it
> slapped hard for awhile then it sounded normal after a bit. My temp was
> normal and the oil level is good. I'm using syn 10-30. I'm guessing
> that a re-gear would do the trick, but I want to see you all think. In
> town and up till now the Jeep has run very good. The only problem I
> have ever noticed is that when I run on the highway for a short time
> and then stop I can smell a gassy smell.
>
> Thanks for helping
> D
>

Dave,

I'm not sure about the oil pressure. It might be that you have a good
tight engine and even with the oil thinned out the upper pressure is
still being limited by the oil pressure relief valve, but when the
engine is idling the pump isn't spinning nearly as fast and the pressure
is far more dependent on the viscosity of the oil.

I haven't tried this on a Jeep but if you can remove the injectors from
the cylinder head but still have the fuel and electrical connected
switch the ignition on so the fuel system pressurizes and then check the
injectors. They should all be tight and dry. Any that have fuel coming
out of them are bad.

Some of the guys in the newsgroup must be real experts on these systems
and can tell you for sure if I know what I'm talking about, as I said I
haven't had to do this on a Jeep.

300,000 miles and no problems with the fuel system, exhaust, AC, heater,
suspension, transmission, universal joints...

Jeff DeWitt

Dave Jost wrote:
> Bill, the street tires are long gone.
>
> Jeff, would it explain low oil pressure only when idling? How do I
> check it? The sensor I need a computer to check, but I'd like to avoid
> taking it to the Jeep shop. The guys there will tell me that I need
> Mopar parts by the crate load.
>
> Thanks,
> D
>

Lugging the engine for sixty miles straight is going to cause your
oil to exceed it's operating temperature limits and it will be too thin
to have oil pressure at idle.
God Bless America, ßill O|||||||O
http://www.billhughes.com/

Dave Jost wrote:
>
> Bill, the street tires are long gone.
>
> Jeff, would it explain low oil pressure only when idling? How do I
> check it? The sensor I need a computer to check, but I'd like to avoid
> taking it to the Jeep shop. The guys there will tell me that I need
> Mopar parts by the crate load.
>
> Thanks,
> D

"Earle Horton" > wrote:

>What was your engine rpm at, say sixty? I am thinking that 3.07 gears and
>31 inch tires might be too much for even fourth gear.

I don't think that's it. I ran 31's on my TJ with 3.07s and while 5th
gear was only for downhills, and there was alot of clutch slipping to
launch, it was nothing like he's describing. My milage improved 1-2
mpg when I went to 4.10.

The OP was getting 6mpg - can't blame that on the tires.

I run the same 3.07 and 31" tires. 4th gear is about 2100 at 60 and 2500
at 70. 5th gear is ridiculous: 1500 and 1750 at 60 and 70 respectively.
The 2500 is a bit higher than I would like for steady crusising but not
bad.

Earle Horton wrote:
> What was your engine rpm at, say sixty? I am thinking that 3.07 gears and
> 31 inch tires might be too much for even fourth gear. If so, then regearing
> would fix a lot. Street tires would help too, if you want to run it on the
> street.
>
> Earle
>
> "Dave Jost" > wrote in message
> oups.com...
>
>>Greetings.
>>
>>I have a 92 YJ 4.0 with 31s on it. I bought it with 120K and have put
>>maybe 5K more on it. Yesterday I thought it would be a good idea to
>>take it down I-80 for a weekend visit to a town 3 hours away. Unlike
>>most Wyoming 1-80 days it wasn't TOO windy, but the Jeep was having a
>>hell of a time. I figured it was the fact that my Jeep came with 3.07
>>gears and those leave me without 5th gear... But as I kept going it
>>kept sucking gas. I stopped real quickly and I noticed that the piston
>>slap seemed much louder and my oil pressure was low.. When I kept going
>>the pressure came back up to normal, but it kept sucking gas. In 60
>>miles I used about 25 bucks in gas.
>>
>>So my question is. Is this a problem due to 3.07 gears that I need to
>>fix, or a problem with the engine, or both. When I gave up the quest it
>>slapped hard for awhile then it sounded normal after a bit. My temp was
>>normal and the oil level is good. I'm using syn 10-30. I'm guessing
>>that a re-gear would do the trick, but I want to see you all think. In
>>town and up till now the Jeep has run very good. The only problem I
>>have ever noticed is that when I run on the highway for a short time
>>and then stop I can smell a gassy smell.
>>
>>Thanks for helping
>>D
>>
>
>
>

I get the best gas mileage keeping mine at 2300 to 2500 rpm.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

RoyJ wrote:
>
> I run the same 3.07 and 31" tires. 4th gear is about 2100 at 60 and 2500
> at 70. 5th gear is ridiculous: 1500 and 1750 at 60 and 70 respectively.
> The 2500 is a bit higher than I would like for steady crusising but not
> bad.
>
> Earle Horton wrote:
> > What was your engine rpm at, say sixty? I am thinking that 3.07 gears and
> > 31 inch tires might be too much for even fourth gear. If so, then regearing
> > would fix a lot. Street tires would help too, if you want to run it on the
> > street.
> >
> > Earle
> >
> > "Dave Jost" > wrote in message
> > oups.com...
> >
> >>Greetings.
> >>
> >>I have a 92 YJ 4.0 with 31s on it. I bought it with 120K and have put
> >>maybe 5K more on it. Yesterday I thought it would be a good idea to
> >>take it down I-80 for a weekend visit to a town 3 hours away. Unlike
> >>most Wyoming 1-80 days it wasn't TOO windy, but the Jeep was having a
> >>hell of a time. I figured it was the fact that my Jeep came with 3.07
> >>gears and those leave me without 5th gear... But as I kept going it
> >>kept sucking gas. I stopped real quickly and I noticed that the piston
> >>slap seemed much louder and my oil pressure was low.. When I kept going
> >>the pressure came back up to normal, but it kept sucking gas. In 60
> >>miles I used about 25 bucks in gas.
> >>
> >>So my question is. Is this a problem due to 3.07 gears that I need to
> >>fix, or a problem with the engine, or both. When I gave up the quest it
> >>slapped hard for awhile then it sounded normal after a bit. My temp was
> >>normal and the oil level is good. I'm using syn 10-30. I'm guessing
> >>that a re-gear would do the trick, but I want to see you all think. In
> >>town and up till now the Jeep has run very good. The only problem I
> >>have ever noticed is that when I run on the highway for a short time
> >>and then stop I can smell a gassy smell.
> >>
> >>Thanks for helping
> >>D
> >>
> >
> >
> >