jeepeeyes proclaimed:

> Thanks for the responses.
> I think that I will take DougW's advice first and look at the spark
> plugs. I replaced all of them last year, but that does not mean one
> couldn't fail.
> Then, if they all look good, I will buy the stethoscope and carry it in
> the Jeep ('cause it always happens out in the boondies) and probe for
> the source of the knock the next time I hear it.
> Oh, by the way, I've already inspected the exhaust manifold and there
> seem to be no signs of cracks.
>
There are two major categories of mechanic stethoscopes. The
inexpensive ones are between $10 to $20 and are purely mechanical with
just air from the probe up to your ears--the earpieces are typically
earbuds. e.g. http://www.brandsonsale.com/ht-001057-images.html
For about $150, you can get the amplified version with the larger ear
mikes like a set of stereo headphones. e.g.
http://www.alltiresupply.com/p-OTC-3590.html

 

jeepeeyes proclaimed:

> Thanks for the responses.
> I think that I will take DougW's advice first and look at the spark
> plugs. I replaced all of them last year, but that does not mean one
> couldn't fail.
> Then, if they all look good, I will buy the stethoscope and carry it in
> the Jeep ('cause it always happens out in the boondies) and probe for
> the source of the knock the next time I hear it.
> Oh, by the way, I've already inspected the exhaust manifold and there
> seem to be no signs of cracks.
>
There are two major categories of mechanic stethoscopes. The
inexpensive ones are between $10 to $20 and are purely mechanical with
just air from the probe up to your ears--the earpieces are typically
earbuds. e.g. http://www.brandsonsale.com/ht-001057-images.html
For about $150, you can get the amplified version with the larger ear
mikes like a set of stereo headphones. e.g.
http://www.alltiresupply.com/p-OTC-3590.html

 

smack the cat. converter and see if it rattles if it does it is no good and
i have seen them make a noise that sounds just like a rod knockesp in the
trucks

jeepeeyes wrote:

> Hi group,
>
> I own a 2000 Jeep Wrangler 4.0 Automatic with about 70K miles on it.
> After a period of driving at slightly heavier than normal engine load
> on hot days, a knocking sound starts coming from the engine
> compartment.
>
> I think that the noise I've been experiencing is most likely coming
> from within the engine or maybe the transmission. The first time I'd
> experienced it I was driving through some sandy washes in Mojave. As
> the engine and transmission load in the sand increased the engine
> temperature went up (but well within the safe zone) and I started
> hearing at first a tapping noise that gradually grew louder to a
> pronounced knocking (like a small hammer hitting metal) in sync with
> the engine RPMs. I stopped and put the transmission in park with the
> engine idling, but the knocking continued. I opened the hood and tried
> to listen where the knocking was coming from. It was pretty loud and
> hard to tell where in the engine compartment it was coming from. It
> almost felt like I was hearing it louder from under the vehicle when I
> leaned down and listened to it from the side while looking at the
> transmission.
> At that time, I shut the engine off and waited for about 15 minutes.
> Then I started the engine and the knocking was gone. I continued
> driving slowly at lower gear in order to reduce the load on the engine,
> which seemed to help. But still the knocking would come back at times
> and I had to really slow down or stop for it to go away.
>
> The best guess, I figured from the frequency of the knock (about
> 8/sec), would point to a something occurring every other engine
> revolution like a valve.
>
> When I first got the Jeep a year ago, I had no trouble driving up a
> long hill on a paved road at a fairly normal rate of speed. Now a
> couple months ago, I experienced the knocking again as I drove on a
> road like that (paved, no sand) to the mountains on a hot day.
> Most recently, I started hearing the knocking slightly after a period
> of stop-and-go driving on pavement in rather benign hilly area.
>
> So the knocking seems to start after a period of heavier than normal
> engine load on hot days (though the engine temperature gauge always
> remains well within the safe zone).
>
> I would appreciate any ideas on what this might be and what if anything
> can be done about this.
>
> Thanks.

 

smack the cat. converter and see if it rattles if it does it is no good and
i have seen them make a noise that sounds just like a rod knockesp in the
trucks

jeepeeyes wrote:

> Hi group,
>
> I own a 2000 Jeep Wrangler 4.0 Automatic with about 70K miles on it.
> After a period of driving at slightly heavier than normal engine load
> on hot days, a knocking sound starts coming from the engine
> compartment.
>
> I think that the noise I've been experiencing is most likely coming
> from within the engine or maybe the transmission. The first time I'd
> experienced it I was driving through some sandy washes in Mojave. As
> the engine and transmission load in the sand increased the engine
> temperature went up (but well within the safe zone) and I started
> hearing at first a tapping noise that gradually grew louder to a
> pronounced knocking (like a small hammer hitting metal) in sync with
> the engine RPMs. I stopped and put the transmission in park with the
> engine idling, but the knocking continued. I opened the hood and tried
> to listen where the knocking was coming from. It was pretty loud and
> hard to tell where in the engine compartment it was coming from. It
> almost felt like I was hearing it louder from under the vehicle when I
> leaned down and listened to it from the side while looking at the
> transmission.
> At that time, I shut the engine off and waited for about 15 minutes.
> Then I started the engine and the knocking was gone. I continued
> driving slowly at lower gear in order to reduce the load on the engine,
> which seemed to help. But still the knocking would come back at times
> and I had to really slow down or stop for it to go away.
>
> The best guess, I figured from the frequency of the knock (about
> 8/sec), would point to a something occurring every other engine
> revolution like a valve.
>
> When I first got the Jeep a year ago, I had no trouble driving up a
> long hill on a paved road at a fairly normal rate of speed. Now a
> couple months ago, I experienced the knocking again as I drove on a
> road like that (paved, no sand) to the mountains on a hot day.
> Most recently, I started hearing the knocking slightly after a period
> of stop-and-go driving on pavement in rather benign hilly area.
>
> So the knocking seems to start after a period of heavier than normal
> engine load on hot days (though the engine temperature gauge always
> remains well within the safe zone).
>
> I would appreciate any ideas on what this might be and what if anything
> can be done about this.
>
> Thanks.

 

smack the cat. converter and see if it rattles if it does it is no good and
i have seen them make a noise that sounds just like a rod knockesp in the
trucks

jeepeeyes wrote:

> Hi group,
>
> I own a 2000 Jeep Wrangler 4.0 Automatic with about 70K miles on it.
> After a period of driving at slightly heavier than normal engine load
> on hot days, a knocking sound starts coming from the engine
> compartment.
>
> I think that the noise I've been experiencing is most likely coming
> from within the engine or maybe the transmission. The first time I'd
> experienced it I was driving through some sandy washes in Mojave. As
> the engine and transmission load in the sand increased the engine
> temperature went up (but well within the safe zone) and I started
> hearing at first a tapping noise that gradually grew louder to a
> pronounced knocking (like a small hammer hitting metal) in sync with
> the engine RPMs. I stopped and put the transmission in park with the
> engine idling, but the knocking continued. I opened the hood and tried
> to listen where the knocking was coming from. It was pretty loud and
> hard to tell where in the engine compartment it was coming from. It
> almost felt like I was hearing it louder from under the vehicle when I
> leaned down and listened to it from the side while looking at the
> transmission.
> At that time, I shut the engine off and waited for about 15 minutes.
> Then I started the engine and the knocking was gone. I continued
> driving slowly at lower gear in order to reduce the load on the engine,
> which seemed to help. But still the knocking would come back at times
> and I had to really slow down or stop for it to go away.
>
> The best guess, I figured from the frequency of the knock (about
> 8/sec), would point to a something occurring every other engine
> revolution like a valve.
>
> When I first got the Jeep a year ago, I had no trouble driving up a
> long hill on a paved road at a fairly normal rate of speed. Now a
> couple months ago, I experienced the knocking again as I drove on a
> road like that (paved, no sand) to the mountains on a hot day.
> Most recently, I started hearing the knocking slightly after a period
> of stop-and-go driving on pavement in rather benign hilly area.
>
> So the knocking seems to start after a period of heavier than normal
> engine load on hot days (though the engine temperature gauge always
> remains well within the safe zone).
>
> I would appreciate any ideas on what this might be and what if anything
> can be done about this.
>
> Thanks.