Hmm, neat. Thanks!

"bllsht" <nospam@dot.net> wrote in message
news:6fi3q2pautrue37o9cssrja8cuf5vvc8b8@4ax.com...
> The FSM is a good source for repair info, but it doesn't go into all
> of the details.
>
> The 4.0L uses a waste spark system. That is it uses one coil to fire a
> pair of spark plugs simultaneously. One on the compression stroke and
> the other being wasted on the exhaust stroke. One post of the coil
> fires with positive potential and the other negative.
>
> A picture will make it easier. Scroll down to the DIS section for an
> illustration of what goes on.
>
> http://www.motorage.com/motorage/art....jsp?id=140913
>
>
> On Sun, 7 Jan 2007 22:28:31 -0500, "Matt Macchiarolo"
> <matt@nospamplease.com> wrote:
>
>>Just out of curiosity, what's your source for this? I know the packs fire
>>two sets of plugs but I wasn't aware it fired pos/neg, and there's no
>>mention of it in the FSM that I can find.
>>
>>"bllsht" <nospam@dot.net> wrote in message
>>news:t1t2q2daj61omiaa6ammb7br9fs4k1te9r@4ax.com. ..
>>. For each pair of cylinders, one plug is always fired
>>> negatively, and the other positively. That is, one fires from the
>>> center eletrtode to the outer electrode, and the other fires from the
>>> outer to the center. It's a series circuit. Open a series circuit and
>>> no current flows.
>>>
>>>
>>>
>>

 

Hmm, neat. Thanks!

"bllsht" <nospam@dot.net> wrote in message
news:6fi3q2pautrue37o9cssrja8cuf5vvc8b8@4ax.com...
> The FSM is a good source for repair info, but it doesn't go into all
> of the details.
>
> The 4.0L uses a waste spark system. That is it uses one coil to fire a
> pair of spark plugs simultaneously. One on the compression stroke and
> the other being wasted on the exhaust stroke. One post of the coil
> fires with positive potential and the other negative.
>
> A picture will make it easier. Scroll down to the DIS section for an
> illustration of what goes on.
>
> http://www.motorage.com/motorage/art....jsp?id=140913
>
>
> On Sun, 7 Jan 2007 22:28:31 -0500, "Matt Macchiarolo"
> <matt@nospamplease.com> wrote:
>
>>Just out of curiosity, what's your source for this? I know the packs fire
>>two sets of plugs but I wasn't aware it fired pos/neg, and there's no
>>mention of it in the FSM that I can find.
>>
>>"bllsht" <nospam@dot.net> wrote in message
>>news:t1t2q2daj61omiaa6ammb7br9fs4k1te9r@4ax.com. ..
>>. For each pair of cylinders, one plug is always fired
>>> negatively, and the other positively. That is, one fires from the
>>> center eletrtode to the outer electrode, and the other fires from the
>>> outer to the center. It's a series circuit. Open a series circuit and
>>> no current flows.
>>>
>>>
>>>
>>

 

Hmm, neat. Thanks!

"bllsht" <nospam@dot.net> wrote in message
news:6fi3q2pautrue37o9cssrja8cuf5vvc8b8@4ax.com...
> The FSM is a good source for repair info, but it doesn't go into all
> of the details.
>
> The 4.0L uses a waste spark system. That is it uses one coil to fire a
> pair of spark plugs simultaneously. One on the compression stroke and
> the other being wasted on the exhaust stroke. One post of the coil
> fires with positive potential and the other negative.
>
> A picture will make it easier. Scroll down to the DIS section for an
> illustration of what goes on.
>
> http://www.motorage.com/motorage/art....jsp?id=140913
>
>
> On Sun, 7 Jan 2007 22:28:31 -0500, "Matt Macchiarolo"
> <matt@nospamplease.com> wrote:
>
>>Just out of curiosity, what's your source for this? I know the packs fire
>>two sets of plugs but I wasn't aware it fired pos/neg, and there's no
>>mention of it in the FSM that I can find.
>>
>>"bllsht" <nospam@dot.net> wrote in message
>>news:t1t2q2daj61omiaa6ammb7br9fs4k1te9r@4ax.com. ..
>>. For each pair of cylinders, one plug is always fired
>>> negatively, and the other positively. That is, one fires from the
>>> center eletrtode to the outer electrode, and the other fires from the
>>> outer to the center. It's a series circuit. Open a series circuit and
>>> no current flows.
>>>
>>>
>>>
>>

 

Hi all, here is an update on my 2001 TJ from a previous reply in this
thread. After replacing the broken bridge and reassembling the rocker, a
test drive showed some improvement but the Jeep threw the P0302 engine code
again. After several days of digging into possibilities and a few calls to
Chrysler, the guys finally dug out the problem. The cam had a bad lobe on
one of the number two valves. I now have a pretty much rebuilt top end, new
lifters, cam, rockers, timing chain and gears, etc.. They showed me the old
cam and, while the Chrysler tech wouldn't admit a bad heat treat to begin
with, he did say that he has seen a "few" but they are not common to have go
bad. The TJ came home today, runs great, nice and quiet, smooth at idle and
driving speeds. I'm just over $700 lighter in the wallet but I should be
able to run this engine til I decide I need a newer Jeep. Just wanted to
let the group know the update on my problem about my misfire.
Les

"01XJ" <adam.tsacoumangos@gmail.com> wrote in message
news:1167779855.090317.153570@v33g2000cwv.googlegr oups.com...
>I just started experiencing a rough idle on my 2001 Cherokee (78k
> miles). My engine light went on a little after that with the P0303
> code. I just replaced the spark plugs, but that didn't help anything.
> I was
> thinking about changing the ignition coil or fuel injector. One other
> possibility I was
> thinking was checking the cylinder compression (maybe a gasket leak?).
> Anyone have any suggestions?
>

 

Hi all, here is an update on my 2001 TJ from a previous reply in this
thread. After replacing the broken bridge and reassembling the rocker, a
test drive showed some improvement but the Jeep threw the P0302 engine code
again. After several days of digging into possibilities and a few calls to
Chrysler, the guys finally dug out the problem. The cam had a bad lobe on
one of the number two valves. I now have a pretty much rebuilt top end, new
lifters, cam, rockers, timing chain and gears, etc.. They showed me the old
cam and, while the Chrysler tech wouldn't admit a bad heat treat to begin
with, he did say that he has seen a "few" but they are not common to have go
bad. The TJ came home today, runs great, nice and quiet, smooth at idle and
driving speeds. I'm just over $700 lighter in the wallet but I should be
able to run this engine til I decide I need a newer Jeep. Just wanted to
let the group know the update on my problem about my misfire.
Les

"01XJ" <adam.tsacoumangos@gmail.com> wrote in message
news:1167779855.090317.153570@v33g2000cwv.googlegr oups.com...
>I just started experiencing a rough idle on my 2001 Cherokee (78k
> miles). My engine light went on a little after that with the P0303
> code. I just replaced the spark plugs, but that didn't help anything.
> I was
> thinking about changing the ignition coil or fuel injector. One other
> possibility I was
> thinking was checking the cylinder compression (maybe a gasket leak?).
> Anyone have any suggestions?
>

 

Hi all, here is an update on my 2001 TJ from a previous reply in this
thread. After replacing the broken bridge and reassembling the rocker, a
test drive showed some improvement but the Jeep threw the P0302 engine code
again. After several days of digging into possibilities and a few calls to
Chrysler, the guys finally dug out the problem. The cam had a bad lobe on
one of the number two valves. I now have a pretty much rebuilt top end, new
lifters, cam, rockers, timing chain and gears, etc.. They showed me the old
cam and, while the Chrysler tech wouldn't admit a bad heat treat to begin
with, he did say that he has seen a "few" but they are not common to have go
bad. The TJ came home today, runs great, nice and quiet, smooth at idle and
driving speeds. I'm just over $700 lighter in the wallet but I should be
able to run this engine til I decide I need a newer Jeep. Just wanted to
let the group know the update on my problem about my misfire.
Les

"01XJ" <adam.tsacoumangos@gmail.com> wrote in message
news:1167779855.090317.153570@v33g2000cwv.googlegr oups.com...
>I just started experiencing a rough idle on my 2001 Cherokee (78k
> miles). My engine light went on a little after that with the P0303
> code. I just replaced the spark plugs, but that didn't help anything.
> I was
> thinking about changing the ignition coil or fuel injector. One other
> possibility I was
> thinking was checking the cylinder compression (maybe a gasket leak?).
> Anyone have any suggestions?
>

 

Les,

Thanks for the follow up.

Carl


"Les" <wiedrick@twcny.rr.com> wrote in message
news:45a45c4e$0$8920$4c368faf@roadrunner.com...
> Hi all, here is an update on my 2001 TJ from a previous reply in this
> thread. After replacing the broken bridge and reassembling the rocker, a
> test drive showed some improvement but the Jeep threw the P0302 engine
> code again. After several days of digging into possibilities and a few
> calls to Chrysler, the guys finally dug out the problem. The cam had a bad
> lobe on one of the number two valves. I now have a pretty much rebuilt top
> end, new lifters, cam, rockers, timing chain and gears, etc.. They showed
> me the old cam and, while the Chrysler tech wouldn't admit a bad heat
> treat to begin with, he did say that he has seen a "few" but they are not
> common to have go bad. The TJ came home today, runs great, nice and
> quiet, smooth at idle and driving speeds. I'm just over $700 lighter in
> the wallet but I should be able to run this engine til I decide I need a
> newer Jeep. Just wanted to let the group know the update on my problem
> about my misfire.
> Les
>
> "01XJ" <adam.tsacoumangos@gmail.com> wrote in message
> news:1167779855.090317.153570@v33g2000cwv.googlegr oups.com...
>>I just started experiencing a rough idle on my 2001 Cherokee (78k
>> miles). My engine light went on a little after that with the P0303
>> code. I just replaced the spark plugs, but that didn't help anything.
>> I was
>> thinking about changing the ignition coil or fuel injector. One other
>> possibility I was
>> thinking was checking the cylinder compression (maybe a gasket leak?).
>> Anyone have any suggestions?
>>
>
>

 

Les,

Thanks for the follow up.

Carl


"Les" <wiedrick@twcny.rr.com> wrote in message
news:45a45c4e$0$8920$4c368faf@roadrunner.com...
> Hi all, here is an update on my 2001 TJ from a previous reply in this
> thread. After replacing the broken bridge and reassembling the rocker, a
> test drive showed some improvement but the Jeep threw the P0302 engine
> code again. After several days of digging into possibilities and a few
> calls to Chrysler, the guys finally dug out the problem. The cam had a bad
> lobe on one of the number two valves. I now have a pretty much rebuilt top
> end, new lifters, cam, rockers, timing chain and gears, etc.. They showed
> me the old cam and, while the Chrysler tech wouldn't admit a bad heat
> treat to begin with, he did say that he has seen a "few" but they are not
> common to have go bad. The TJ came home today, runs great, nice and
> quiet, smooth at idle and driving speeds. I'm just over $700 lighter in
> the wallet but I should be able to run this engine til I decide I need a
> newer Jeep. Just wanted to let the group know the update on my problem
> about my misfire.
> Les
>
> "01XJ" <adam.tsacoumangos@gmail.com> wrote in message
> news:1167779855.090317.153570@v33g2000cwv.googlegr oups.com...
>>I just started experiencing a rough idle on my 2001 Cherokee (78k
>> miles). My engine light went on a little after that with the P0303
>> code. I just replaced the spark plugs, but that didn't help anything.
>> I was
>> thinking about changing the ignition coil or fuel injector. One other
>> possibility I was
>> thinking was checking the cylinder compression (maybe a gasket leak?).
>> Anyone have any suggestions?
>>
>
>

 

Les,

Thanks for the follow up.

Carl


"Les" <wiedrick@twcny.rr.com> wrote in message
news:45a45c4e$0$8920$4c368faf@roadrunner.com...
> Hi all, here is an update on my 2001 TJ from a previous reply in this
> thread. After replacing the broken bridge and reassembling the rocker, a
> test drive showed some improvement but the Jeep threw the P0302 engine
> code again. After several days of digging into possibilities and a few
> calls to Chrysler, the guys finally dug out the problem. The cam had a bad
> lobe on one of the number two valves. I now have a pretty much rebuilt top
> end, new lifters, cam, rockers, timing chain and gears, etc.. They showed
> me the old cam and, while the Chrysler tech wouldn't admit a bad heat
> treat to begin with, he did say that he has seen a "few" but they are not
> common to have go bad. The TJ came home today, runs great, nice and
> quiet, smooth at idle and driving speeds. I'm just over $700 lighter in
> the wallet but I should be able to run this engine til I decide I need a
> newer Jeep. Just wanted to let the group know the update on my problem
> about my misfire.
> Les
>
> "01XJ" <adam.tsacoumangos@gmail.com> wrote in message
> news:1167779855.090317.153570@v33g2000cwv.googlegr oups.com...
>>I just started experiencing a rough idle on my 2001 Cherokee (78k
>> miles). My engine light went on a little after that with the P0303
>> code. I just replaced the spark plugs, but that didn't help anything.
>> I was
>> thinking about changing the ignition coil or fuel injector. One other
>> possibility I was
>> thinking was checking the cylinder compression (maybe a gasket leak?).
>> Anyone have any suggestions?
>>
>
>

 

I just talked to the dealer who said the heat shield had been put on
the intake to prevent overheating injector #3. I guess it rules that
one out. I'll try looking at the injector this weekend. I'll wait on
checking the coil since it would most likely affect 2 cylinders,
although I'll keep it in the back of my head to not rule it out
completely.

Thanks everyone.

On Jan 9, 10:07 pm, "Carl" <carlsai...@hotmailREMOVE.com> wrote:
> Les,
>
> Thanks for the follow up.
>
> Carl
>
> "Les" <wiedr...@twcny.rr.com> wrote in messagenews:45a45c4e$0$8920$4c368faf@roadrunner.co m...
>
> > Hi all, here is an update on my 2001 TJ from a previous reply in this
> > thread. After replacing the broken bridge and reassembling the rocker, a
> > test drive showed some improvement but the Jeep threw the P0302 engine
> > code again. After several days of digging into possibilities and a few
> > calls to Chrysler, the guys finally dug out the problem. The cam had a bad
> > lobe on one of the number two valves. I now have a pretty much rebuilt top
> > end, new lifters, cam, rockers, timing chain and gears, etc.. They showed
> > me the old cam and, while the Chrysler tech wouldn't admit a bad heat
> > treat to begin with, he did say that he has seen a "few" but they are not
> > common to have go bad. The TJ came home today, runs great, nice and
> > quiet, smooth at idle and driving speeds. I'm just over $700 lighter in
> > the wallet but I should be able to run this engine til I decide I need a
> > newer Jeep. Just wanted to let the group know the update on my problem
> > about my misfire.
> > Les
>
> > "01XJ" <adam.tsacouman...@gmail.com> wrote in message
> >news:1167779855.090317.153570@v33g2000cwv.googleg roups.com...
> >>I just started experiencing a rough idle on my 2001 Cherokee (78k
> >> miles). My engine light went on a little after that with the P0303
> >> code. I just replaced the spark plugs, but that didn't help anything.
> >> I was
> >> thinking about changing the ignition coil or fuel injector. One other
> >> possibility I was
> >> thinking was checking the cylinder compression (maybe a gasket leak?).
> >> Anyone have any suggestions?