Help! Diagnosis:Timing chain?
 

1978 CJ with 304 V8, been running fine.
Starts up from cold this morning.
Engine is running at ~3,000 rpm to warm up.
All is normal.
Take foot off gas pedal.
RPM drops and POW!
A single loud POP is heard.
The starter spins the engine, but the engine does not hit at all. No
funny sounds, just smooth engine starting, spinning sounds.

Hit the carb with a little starting fluid and it will hit a few times
and a distint 'whoosh' is heard intermittantly as the right front
cylinder hits.

My diagnosis guesses:
1) Timing chain broke or skipped a notch
2) Fuel pump broke (but it was replaced about 6 months ago)
3) Intake manifold gasket
4) Head gasket
5) Exhaust Manifold gasket

More serious engine problems (broken piston, head, crank, etc) don't
seem likely since there are no funning sound when cranking.

Oh great jeep wizards,
What is it?
What are the next things to do to diagnose it??

Thanks ever so much for the suggestions,
~steve

Re: Help! Diagnosis:Timing chain?
 

I would pop off the distributor cap and see if the rotor is turning.

That will quickly tell if the chain broke. You can also put the crank
pulley on the timing mark and verify the rotor is still pointing at #1
wire in the cap to see if it jumped. (or the opposite wire across from
#1.)

To check the slop in the timing chain, hand turn the engine to the
timing mark with the distributor cap off. Then turn it back the other
way while watching the rotor. As soon as the rotor starts turning the
other way, look at the timing marks and see how many degrees of slop you
have. Anything more than 15 or 20 deg and the chain is getting worn.

A pop can also be a coil exploding internally or an ignition module
blowing a cap or something. I would be pulling a plug wire to see if I
had spark.

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

River Horse wrote:
>
> 1978 CJ with 304 V8, been running fine.
> Starts up from cold this morning.
> Engine is running at ~3,000 rpm to warm up.
> All is normal.
> Take foot off gas pedal.
> RPM drops and POW!
> A single loud POP is heard.
> The starter spins the engine, but the engine does not hit at all. No
> funny sounds, just smooth engine starting, spinning sounds.
>
> Hit the carb with a little starting fluid and it will hit a few times
> and a distint 'whoosh' is heard intermittantly as the right front
> cylinder hits.
>
> My diagnosis guesses:
> 1) Timing chain broke or skipped a notch
> 2) Fuel pump broke (but it was replaced about 6 months ago)
> 3) Intake manifold gasket
> 4) Head gasket
> 5) Exhaust Manifold gasket
>
> More serious engine problems (broken piston, head, crank, etc) don't
> seem likely since there are no funning sound when cranking.
>
> Oh great jeep wizards,
> What is it?
> What are the next things to do to diagnose it??
>
> Thanks ever so much for the suggestions,
> ~steve

Re: Help! Diagnosis:Timing chain?
 

I would pop off the distributor cap and see if the rotor is turning.

That will quickly tell if the chain broke. You can also put the crank
pulley on the timing mark and verify the rotor is still pointing at #1
wire in the cap to see if it jumped. (or the opposite wire across from
#1.)

To check the slop in the timing chain, hand turn the engine to the
timing mark with the distributor cap off. Then turn it back the other
way while watching the rotor. As soon as the rotor starts turning the
other way, look at the timing marks and see how many degrees of slop you
have. Anything more than 15 or 20 deg and the chain is getting worn.

A pop can also be a coil exploding internally or an ignition module
blowing a cap or something. I would be pulling a plug wire to see if I
had spark.

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

River Horse wrote:
>
> 1978 CJ with 304 V8, been running fine.
> Starts up from cold this morning.
> Engine is running at ~3,000 rpm to warm up.
> All is normal.
> Take foot off gas pedal.
> RPM drops and POW!
> A single loud POP is heard.
> The starter spins the engine, but the engine does not hit at all. No
> funny sounds, just smooth engine starting, spinning sounds.
>
> Hit the carb with a little starting fluid and it will hit a few times
> and a distint 'whoosh' is heard intermittantly as the right front
> cylinder hits.
>
> My diagnosis guesses:
> 1) Timing chain broke or skipped a notch
> 2) Fuel pump broke (but it was replaced about 6 months ago)
> 3) Intake manifold gasket
> 4) Head gasket
> 5) Exhaust Manifold gasket
>
> More serious engine problems (broken piston, head, crank, etc) don't
> seem likely since there are no funning sound when cranking.
>
> Oh great jeep wizards,
> What is it?
> What are the next things to do to diagnose it??
>
> Thanks ever so much for the suggestions,
> ~steve

Re: Help! Diagnosis:Timing chain?
 

I would pop off the distributor cap and see if the rotor is turning.

That will quickly tell if the chain broke. You can also put the crank
pulley on the timing mark and verify the rotor is still pointing at #1
wire in the cap to see if it jumped. (or the opposite wire across from
#1.)

To check the slop in the timing chain, hand turn the engine to the
timing mark with the distributor cap off. Then turn it back the other
way while watching the rotor. As soon as the rotor starts turning the
other way, look at the timing marks and see how many degrees of slop you
have. Anything more than 15 or 20 deg and the chain is getting worn.

A pop can also be a coil exploding internally or an ignition module
blowing a cap or something. I would be pulling a plug wire to see if I
had spark.

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

River Horse wrote:
>
> 1978 CJ with 304 V8, been running fine.
> Starts up from cold this morning.
> Engine is running at ~3,000 rpm to warm up.
> All is normal.
> Take foot off gas pedal.
> RPM drops and POW!
> A single loud POP is heard.
> The starter spins the engine, but the engine does not hit at all. No
> funny sounds, just smooth engine starting, spinning sounds.
>
> Hit the carb with a little starting fluid and it will hit a few times
> and a distint 'whoosh' is heard intermittantly as the right front
> cylinder hits.
>
> My diagnosis guesses:
> 1) Timing chain broke or skipped a notch
> 2) Fuel pump broke (but it was replaced about 6 months ago)
> 3) Intake manifold gasket
> 4) Head gasket
> 5) Exhaust Manifold gasket
>
> More serious engine problems (broken piston, head, crank, etc) don't
> seem likely since there are no funning sound when cranking.
>
> Oh great jeep wizards,
> What is it?
> What are the next things to do to diagnose it??
>
> Thanks ever so much for the suggestions,
> ~steve

Re: Help! Diagnosis:Timing chain?
 

I would pop off the distributor cap and see if the rotor is turning.

That will quickly tell if the chain broke. You can also put the crank
pulley on the timing mark and verify the rotor is still pointing at #1
wire in the cap to see if it jumped. (or the opposite wire across from
#1.)

To check the slop in the timing chain, hand turn the engine to the
timing mark with the distributor cap off. Then turn it back the other
way while watching the rotor. As soon as the rotor starts turning the
other way, look at the timing marks and see how many degrees of slop you
have. Anything more than 15 or 20 deg and the chain is getting worn.

A pop can also be a coil exploding internally or an ignition module
blowing a cap or something. I would be pulling a plug wire to see if I
had spark.

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

River Horse wrote:
>
> 1978 CJ with 304 V8, been running fine.
> Starts up from cold this morning.
> Engine is running at ~3,000 rpm to warm up.
> All is normal.
> Take foot off gas pedal.
> RPM drops and POW!
> A single loud POP is heard.
> The starter spins the engine, but the engine does not hit at all. No
> funny sounds, just smooth engine starting, spinning sounds.
>
> Hit the carb with a little starting fluid and it will hit a few times
> and a distint 'whoosh' is heard intermittantly as the right front
> cylinder hits.
>
> My diagnosis guesses:
> 1) Timing chain broke or skipped a notch
> 2) Fuel pump broke (but it was replaced about 6 months ago)
> 3) Intake manifold gasket
> 4) Head gasket
> 5) Exhaust Manifold gasket
>
> More serious engine problems (broken piston, head, crank, etc) don't
> seem likely since there are no funning sound when cranking.
>
> Oh great jeep wizards,
> What is it?
> What are the next things to do to diagnose it??
>
> Thanks ever so much for the suggestions,
> ~steve

Re: Help! Diagnosis:Timing chain?
 

"River Horse" <hippo@comcast.net> wrote in message
news:JcGdndzfX69xUPPdRVn-iQ@comcast.com...
> 1978 CJ with 304 V8, been running fine.
> Starts up from cold this morning.
> Engine is running at ~3,000 rpm to warm up.
> All is normal.
> Take foot off gas pedal.
> RPM drops and POW!
> A single loud POP is heard.
> The starter spins the engine, but the engine does not hit at all. No
> funny sounds, just smooth engine starting, spinning sounds.
>
> Hit the carb with a little starting fluid and it will hit a few times
> and a distint 'whoosh' is heard intermittantly as the right front
> cylinder hits.
>
> My diagnosis guesses:
> 1) Timing chain broke or skipped a notch
> 2) Fuel pump broke (but it was replaced about 6 months ago)
> 3) Intake manifold gasket
> 4) Head gasket
> 5) Exhaust Manifold gasket
>
> More serious engine problems (broken piston, head, crank, etc) don't
> seem likely since there are no funning sound when cranking.
>
> Oh great jeep wizards,
> What is it?
> What are the next things to do to diagnose it??
>
> Thanks ever so much for the suggestions,
> ~steve

To check for a bad chain pull off the dist cap, crank the engine slowly by
hand with a socket on the crank bolt and try to line up 0 degrees TDC on the
crank and see if the rotor lines up on #1 cylinder. If everything turns and
the timing marks line up, then it isn't the chain, if the rotor isn't
turning, then the chain & gears are toast....$$$$$$$!

Most likely that's not the problem.
Check the basics: Is it getting air? Is it getting fuel? Is it getting
spark? Is it in time? If all of these are a "yes", then it should fire, but
might not run if the carb is knackered. Al;so, this could be as simple as
the + or - wires on the coil being loose, etc.

Re: Help! Diagnosis:Timing chain?
 

"River Horse" <hippo@comcast.net> wrote in message
news:JcGdndzfX69xUPPdRVn-iQ@comcast.com...
> 1978 CJ with 304 V8, been running fine.
> Starts up from cold this morning.
> Engine is running at ~3,000 rpm to warm up.
> All is normal.
> Take foot off gas pedal.
> RPM drops and POW!
> A single loud POP is heard.
> The starter spins the engine, but the engine does not hit at all. No
> funny sounds, just smooth engine starting, spinning sounds.
>
> Hit the carb with a little starting fluid and it will hit a few times
> and a distint 'whoosh' is heard intermittantly as the right front
> cylinder hits.
>
> My diagnosis guesses:
> 1) Timing chain broke or skipped a notch
> 2) Fuel pump broke (but it was replaced about 6 months ago)
> 3) Intake manifold gasket
> 4) Head gasket
> 5) Exhaust Manifold gasket
>
> More serious engine problems (broken piston, head, crank, etc) don't
> seem likely since there are no funning sound when cranking.
>
> Oh great jeep wizards,
> What is it?
> What are the next things to do to diagnose it??
>
> Thanks ever so much for the suggestions,
> ~steve

To check for a bad chain pull off the dist cap, crank the engine slowly by
hand with a socket on the crank bolt and try to line up 0 degrees TDC on the
crank and see if the rotor lines up on #1 cylinder. If everything turns and
the timing marks line up, then it isn't the chain, if the rotor isn't
turning, then the chain & gears are toast....$$$$$$$!

Most likely that's not the problem.
Check the basics: Is it getting air? Is it getting fuel? Is it getting
spark? Is it in time? If all of these are a "yes", then it should fire, but
might not run if the carb is knackered. Al;so, this could be as simple as
the + or - wires on the coil being loose, etc.

Re: Help! Diagnosis:Timing chain?
 

"River Horse" <hippo@comcast.net> wrote in message
news:JcGdndzfX69xUPPdRVn-iQ@comcast.com...
> 1978 CJ with 304 V8, been running fine.
> Starts up from cold this morning.
> Engine is running at ~3,000 rpm to warm up.
> All is normal.
> Take foot off gas pedal.
> RPM drops and POW!
> A single loud POP is heard.
> The starter spins the engine, but the engine does not hit at all. No
> funny sounds, just smooth engine starting, spinning sounds.
>
> Hit the carb with a little starting fluid and it will hit a few times
> and a distint 'whoosh' is heard intermittantly as the right front
> cylinder hits.
>
> My diagnosis guesses:
> 1) Timing chain broke or skipped a notch
> 2) Fuel pump broke (but it was replaced about 6 months ago)
> 3) Intake manifold gasket
> 4) Head gasket
> 5) Exhaust Manifold gasket
>
> More serious engine problems (broken piston, head, crank, etc) don't
> seem likely since there are no funning sound when cranking.
>
> Oh great jeep wizards,
> What is it?
> What are the next things to do to diagnose it??
>
> Thanks ever so much for the suggestions,
> ~steve

To check for a bad chain pull off the dist cap, crank the engine slowly by
hand with a socket on the crank bolt and try to line up 0 degrees TDC on the
crank and see if the rotor lines up on #1 cylinder. If everything turns and
the timing marks line up, then it isn't the chain, if the rotor isn't
turning, then the chain & gears are toast....$$$$$$$!

Most likely that's not the problem.
Check the basics: Is it getting air? Is it getting fuel? Is it getting
spark? Is it in time? If all of these are a "yes", then it should fire, but
might not run if the carb is knackered. Al;so, this could be as simple as
the + or - wires on the coil being loose, etc.

Re: Help! Diagnosis:Timing chain?
 

"River Horse" <hippo@comcast.net> wrote in message
news:JcGdndzfX69xUPPdRVn-iQ@comcast.com...
> 1978 CJ with 304 V8, been running fine.
> Starts up from cold this morning.
> Engine is running at ~3,000 rpm to warm up.
> All is normal.
> Take foot off gas pedal.
> RPM drops and POW!
> A single loud POP is heard.
> The starter spins the engine, but the engine does not hit at all. No
> funny sounds, just smooth engine starting, spinning sounds.
>
> Hit the carb with a little starting fluid and it will hit a few times
> and a distint 'whoosh' is heard intermittantly as the right front
> cylinder hits.
>
> My diagnosis guesses:
> 1) Timing chain broke or skipped a notch
> 2) Fuel pump broke (but it was replaced about 6 months ago)
> 3) Intake manifold gasket
> 4) Head gasket
> 5) Exhaust Manifold gasket
>
> More serious engine problems (broken piston, head, crank, etc) don't
> seem likely since there are no funning sound when cranking.
>
> Oh great jeep wizards,
> What is it?
> What are the next things to do to diagnose it??
>
> Thanks ever so much for the suggestions,
> ~steve

To check for a bad chain pull off the dist cap, crank the engine slowly by
hand with a socket on the crank bolt and try to line up 0 degrees TDC on the
crank and see if the rotor lines up on #1 cylinder. If everything turns and
the timing marks line up, then it isn't the chain, if the rotor isn't
turning, then the chain & gears are toast....$$$$$$$!

Most likely that's not the problem.
Check the basics: Is it getting air? Is it getting fuel? Is it getting
spark? Is it in time? If all of these are a "yes", then it should fire, but
might not run if the carb is knackered. Al;so, this could be as simple as
the + or - wires on the coil being loose, etc.

Re: Help! Diagnosis:Timing chain?
 

River Horse did pass the time by typing:
> 1978 CJ with 304 V8, been running fine.
> Starts up from cold this morning.
> Engine is running at ~3,000 rpm to warm up.
> All is normal.
> Take foot off gas pedal.
> RPM drops and POW!
> A single loud POP is heard.
> The starter spins the engine, but the engine does not hit at all. No
> funny sounds, just smooth engine starting, spinning sounds.

Any spark?

Take the primary off the coil stick an old spark plug in there then
and hold it about 1" from the block and have someone crank it.

> Hit the carb with a little starting fluid and it will hit a few times
> and a distint 'whoosh' is heard intermittantly as the right front
> cylinder hits.
>
> My diagnosis guesses:
> 1) Timing chain broke or skipped a notch

Off one notch would make your engine run like hell, but it would start.
Fully broken and your engine would probably not even crank or there would
be one hell of a grinding noise from the chain cover as the chain gets all
wrapped up.

> 2) Fuel pump broke (but it was replaced about 6 months ago)

Pull the fuel line, crank, check for fuel. What your describing could
be the fuel pump. Is it electric? Thought that old they were usually
mechanical.

> 3) Intake manifold gasket

It would still start but run lean or stall

> 4) Head gasket

Would still start but run poorly and you would either get white
smoke out the pipe (sucking coolant) and oil in the coolant.

> 5) Exhaust Manifold gasket

Still would start, but make a "farting" noise. Sorta like a diesel
running.. puffa puffa puffa

Not sure if the 304 is a non interference engine or not.
That just means if the timing chain goes your engine will not
eat itself by tring to comress an open valve. Very ugly.

I wouldn't suspect engine internals yet. Start with the electrical
including the ignition circuit.


--
DougW