How is my LJR even running?

Altonymous said:
Why do you think it would be physically impossible?
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The sprocket can fit on the cam in only 1 position. If the cam and sprocket are made correctly, when the marks on the cam sprocket are lined up with the crank sprocket, #1 has to be at TDC on compression.

While in that position, if you pull the chain and rotate the cam by 180, you'll be in the exact same position as if you just rotated the crank 1 revolution. The mark on the cam sprocket will be 180 from where you started but in relation to the pistons, it's exactly the same as leaving the chain in place and rotating the crank 1 turn.
 
Right.. and I'm betting the previous owner's shop did just this. I'm betting they pulled the chain... let the camshaft rotate.. when they went to put it back together they didn't check the stroke for compression.. and pointed the marks at each other while it was on the exhaust stroke. Slapped it together... turns the OPDA until it "worked" treating it like an old style distributor instead of the OPDA it is... and called it a day.
 
If the camshaft is 180 degrees off it just swaps the compression and ignition strokes with exhaust and intake strokes.

At that point the OPDA would have to stay with the camshaft.

I imagine the OPDA runs off the crankshaft so if the camshaft it 180 off the OPDA would have to be too.

Turning the camshaft back to where it belongs isn't an easy job.

After thinking about this, maybe it isn't too hard. Why don't I know whether it's an interference engine or not?

Correction: Just turn them back where they belong. the 4.0 is non-interference. I'd replace the chain while you're in there, who knows if it was even replaced by the guys that messed this up.
 
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Altonymous said:
pointed the marks at each other while it was on the exhaust stroke
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The position of the cam is what determines what piston is on compression. If the marks are aligned, and the parts (cam & sprockets) are made correctly, it is impossible for #1 to be anywhere other than at TDC on compression.
 
g.hayduke said:
The position of the cam is what determines what piston is on compression. If the marks are aligned, and the parts (cam & sprockets) are made correctly, it is impossible for #1 to be anywhere other than at TDC on compression.
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yes.. the position of the cam is what determines when it's on compression... but that doesn't mean the cam can't be 180 out.

If I'm wrong and I rotate the cam 180 degrees then install the chain while the marks are pointed at each other.. you're saying it shouldn't run. I'm getting closer to trusting myself and doing it. Guess we'll find out.
 
You can't rotate the cam 180 and have the marks match, one mark would be facing the wrong direction.

The OPDA only functions to determine if the camshaft is at zero degrees of rotation or 180 degrees. The crank sensor is used to determine all the spark timing. If the engine ran the OPDA is doing it's job and set correctly. There is no way possible for the crank sensor to determine if the cam is at 0 or 180 but those are the only two possibilities, it doesn't care if it is 0, -15, +15 it just tells the computer we are on 0 and not 180 and then the crank sensor does it's job. The ignition does not even fire until these two sensors have determined the cam orientation. While running the Jeep checks to make sure the sensor isn't bad. Also if the OPDA pulse transitions fall too close to TDC you'll get a code which is why allot of people get codes with different OPDA units.

If it runs forget about it, you got it right.


JEEPCJTJ said:
I imagine the OPDA runs off the crankshaft so if the camshaft it 180 off the OPDA would have to be too.
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Stop imagining things, it isn't helping anybody.
 
Altonymous said:
If I'm wrong and I rotate the cam 180 degrees then install the chain while the marks are pointed at each other.. you're saying it shouldn't run.
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Nope. I did not say it wouldn't run. In fact, I said it's common to have the OPDA 180 out and have the engine still run.

And I said it's impossible to have the cam 180 out since that is a normal, valid position where #6 is at TDC on compression. So you can rotate the cam 180 all day long as the cam sprocket mark is either pointing at the crank mark or pointing directly away from the crank mark. Either position is a valid position but the OPDA holes should only be aligned when the marks are pointing at each other, assuming cam & sprockets are made correctly.

pagrey said:
If it runs forget about it, you got it right.
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Not necessarily. If it throws codes intermittently, the timing could be the cause. It can run and still be off enough to throw codes and cause other issues.
 
Yeah I was missing the #6 part.. I am now testing compression on the correct cylinder... thanks!

So.. on #6 the marks on the sprockets align.. but the OPDA is 180 out. At least now I'm more comfortable saying the cam is setup correctly.

But that still leaves me with the Jeep won't run when the OPDA is not 180 out.. so what do I do?
 
Altonymous said:
But that still leaves me with the Jeep won't run when the OPDA is not 180 out.. so what do I do?
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So you have now confirmed that #1 is at TDC on compression when the marks are pointed exactly at each other?

And when you tried having the OPDA aligned correctly, did you exactly align the holes between the OPDA disk and the OPDA housing? If not, do that. Align the holes perfectly and tighten the clamp that holds the OPDA in place. Use something that's a snug fit in at least 1 of the OPDA holes to guarantee alignment.
 
Altonymous said:
So.. on #6 the marks on the sprockets align
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You're saying that #6 is at TDC on compression when the marks are pointing at each other? That makes no sense at all if that is the case. It would mean either the cam or the cam sprocket was made wrong, 180 out of phase.
 
g.hayduke said:
So you have now confirmed that #1 is at TDC on compression when the marks are pointed exactly at each other?

And when you tried having the OPDA aligned correctly, did you exactly align the holes between the OPDA disk and the OPDA housing? If not, do that. Align the holes perfectly and tighten the clamp that holds the OPDA in place. Use something that's a snug fit in at least 1 of the OPDA holes to guarantee alignment.
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No I have the marks pointing at each other when #6 is TDC on compression. Not #1.

I can't really do much with verifying the OPDA until I get it back together. So at this point I am just going to focus on that.
 
g.hayduke said:
You're saying that #6 is at TDC on compression when the marks are pointing at each other? That makes no sense at all if that is the case. It would mean either the cam or the cam sprocket was made wrong, 180 out of phase.
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Yeah and the FSM says to use #6... I thought it was #1... But I double checked the FSM and it says use #6.
 
Altonymous said:
But I double checked the FSM and it says use #6.
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Oh, really? It says when the marks are aligned, #6 should be on compression? In that case, my bad.

But I'm pretty sure the FSM says the OPDA holes should line up with #1 on compression, right?
 
g.hayduke said:
Not necessarily. If it throws codes intermittently, the timing could be the cause. It can run and still be off enough to throw codes and cause other issues.
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pagrey said:
While running the Jeep checks to make sure the sensor isn't bad. Also if the OPDA pulse transitions fall too close to TDC you'll get a code which is why allot of people get codes with different OPDA units.
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It would have been funny if you quoted my whole post, did you even read it or just get really excited when you found something to argue about?
 
Sure looks like.. and now I think we've figured out the confusion. So my OPDA is NOT 180 out.. because I have to turn it over one more time for the OPDA.





cps.png


cps-cont.png


valve-timing.png
 
pagrey said:
It would have been funny if you quoted my whole post, did you even read it or just get really excited when you found something to argue about?
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Not excited at all but will call BS on BS statements. Your BS statement is a popular statement made by many but always BS. Here's another one, also BS:
pagrey said:
If the engine ran the OPDA is doing it's job and set correctly.
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That 1 is also BS. Having an engine that runs is not necessarily the same as having it run right. And having the OPDA set close enough that the engine will run is not necessarily the same as having the OPDA "set correctly". This type of misinformation is rampant on the forums. I just call it out for what it is: BS & misinformation.
 
Altonymous said:
Sure looks like.. and now I think we've figured out the confusion. So my OPDA is NOT 180 out.. because I have to turn it over one more time for the OPDA.
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Good to know! But make sure the holes in the OPDA are perfectly aligned with #1 on TDC on compression.
 
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g.hayduke said:
Good to know! But make sure the holes in the OPDA are perfectly aligned with #1 on TDC on compression.
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Yeah, I'm going to find TDC on #6.. make sure I'm not off a tooth on the camshaft. Then once that's confirmed/fixed, by pulling the chain and rotating the camshaft slightly if it is off a tooth. Then I'll pull the sprockets and put the new sprockets and chain on.. rotate it over one more time.. ensure TDC on #1 and align the OPDA. If it goes into limp mode.. I'm going to drive to a local shop and have the cam signal reprogrammed so it's right.

That sound right?
 
Altonymous said:
have the cam signal reprogrammed so it's right
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Not exactly sure what this means but I'm guessing it's about using the scan tool to set the timing?

If you line up the holes in the OPDA perfectly with #1 at TDC on compression (1 crank rotation past having the marks lined up), that should be accurate but it's worth a try if you still have problems.

I don't think I've heard of anyone needing to do anything more than the mechanical alignment but that doesn't mean electronic timing is not needed at times.
 
g.hayduke said:
Not exactly sure what this means but I'm guessing it's about using the scan tool to set the timing?

If you line up the holes in the OPDA perfectly with #1 at TDC on compression (1 crank rotation past having the marks lined up), that should be accurate but it's worth a try if you still have problems.

I don't think I've heard of anyone needing to do anything more than the mechanical alignment but that doesn't mean electronic timing is not needed at times.
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Yeah I'm talking about the scan tool. Since I couldn't get it to run with the holes lined up... I had to misalign them to get it to run. I'm thinking that means I'm off a tooth or it I need to use the scan tool to get it running right with the holes aligned.
 
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