Rotor direction (distributor) - JeepForum.com
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post #1 of 83 Old 10-03-2021, 06:34 PM Thread Starter
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Rotor direction (distributor)

I feel like this should have been much easier to find but maybe I'm over thinking it.

Assuming everything has been "set up" correctly, with cyl 1 at TDC, what direction should the rotor be pointing? I'm trying to avoid some extra work, but in theory, if I know what direction the rotor is pointing at, I should also know what direction the distributor drive slot is pointing. I *think* based on where its sitting currently that the rotor is 90* from the slot(?)

Going off the attached image, if the slot is pointed as it should be the rotor (for whatever design reason) does not point in the same direction(?)

I'm trying to figure out if maybe the distributor is a tooth off in one direction or the other and its doing weird things to the fuel sync - I know, rotating the distributor doesn't let you fiddle with the timing as such, but I know it also needs to be installed correctly and I'm wondering if one of the shops I took it to did something stupid (or maybe I did, who knows at this point).

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post #2 of 83 Old 10-04-2021, 04:53 AM
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With cylinder #1 at compression stroke TDC, rotor should align perfectly with the slot in the cam sensor. Fuel sync needs to be as close to perfect as possible, and you need a suitable scan tool that has the ability to verify fuel sync.

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1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #3 of 83 Old 10-04-2021, 07:57 AM
HighLonesome
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Quote:
Originally Posted by variable View Post
I feel like this should have been much easier to find but maybe I'm over thinking it.

Assuming everything has been "set up" correctly, with cyl 1 at TDC, what direction should the rotor be pointing? I'm trying to avoid some extra work, but in theory, if I know what direction the rotor is pointing at, I should also know what direction the distributor drive slot is pointing. I *think* based on where its sitting currently that the rotor is 90* from the slot(?)

Going off the attached image, if the slot is pointed as it should be the rotor (for whatever design reason) does not point in the same direction(?)

I'm trying to figure out if maybe the distributor is a tooth off in one direction or the other and its doing weird things to the fuel sync - I know, rotating the distributor doesn't let you fiddle with the timing as such, but I know it also needs to be installed correctly and I'm wondering if one of the shops I took it to did something stupid (or maybe I did, who knows at this point).

If you set the motor to cyl 1 TDC, the rotor points to cyl 6, 90* exactly as you said.

If you pull the distributor, the slot points DIRECTLY at cyl 1, you can tell by eye if it's off a tooth.
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post #4 of 83 Old 10-04-2021, 08:50 AM Thread Starter
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Quote:
Originally Posted by Timo_90xj View Post
With cylinder #1 at compression stroke TDC, rotor should align perfectly with the slot in the cam sensor. Fuel sync needs to be as close to perfect as possible, and you need a suitable scan tool that has the ability to verify fuel sync.
I remember having something for this when we rebuilt the engine and I think it would tell me in degrees how close or far off I was but I can't for the life of me remember what I used or maybe rented. I don't see the option to do this in my snapon tool, though I would have thought it'd be fancy enough for that...

Quote:
Originally Posted by HighLonesome View Post
If you set the motor to cyl 1 TDC, the rotor points to cyl 6, 90* exactly as you said.

If you pull the distributor, the slot points DIRECTLY at cyl 1, you can tell by eye if it's off a tooth.
I guess I can rule that out then.

Thanks for the info guys!

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post #5 of 83 Old 10-04-2021, 10:34 AM
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I don't see the option to do this in my snapon tool, though I would have thought it'd be fancy enough for that..
Snap-on MT2500 can show fuel sync (engine idle needs to be at 1000rpm for the test, which MT2500 does automatically just like Chrysler DRB3), not sure how it is with the newer models but I'd be surprised if they can't do it.

Basic code readers usually don't know anything about fuel sync.

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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #6 of 83 Old 10-04-2021, 10:55 AM Thread Starter
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Quote:
Originally Posted by Timo_90xj View Post
Snap-on MT2500 can show fuel sync (engine idle needs to be at 1000rpm for the test, which MT2500 does automatically just like Chrysler DRB3), not sure how it is with the newer models but I'd be surprised if they can't do it.

Basic code readers usually don't know anything about fuel sync.
Hmm.... I guess I didn't look hard enough (the MT2500 is the one I have). Not the most intuitive tool, but I'll take a closer look anyway (and track down my manual).

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post #7 of 83 Old 10-04-2021, 10:05 PM Thread Starter
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Found it. Was starting me in the face. This thing is old enough that in one place it asks which baud rate to communicate at and when I saw "set sync signal", for some reason I confusing the setting location.

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post #8 of 83 Old 10-05-2021, 06:58 AM
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I thought you couldn’t/shouldn’t move a distributor on a Zj..???

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post #9 of 83 Old 10-05-2021, 07:17 AM
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Quote:
Originally Posted by JonMopar View Post
I thought you couldn’t/shouldn’t move a distributor on a Zj..???

You can, but shouldn't without a scan tool. I don't have one, so I center the distributor in the adjustment range. Has gotten me by for a long time.
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post #10 of 83 Old 10-05-2021, 09:28 AM
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Quote:
Originally Posted by JonMopar View Post
I thought you couldn’t/shouldn’t move a distributor on a Zj..???
Correct and incorrect. If you move it, you mess up fuel sync. If you need to reset fuel sync for reason or another, you MUST rotate distributor.

Rotating the distributor has absolutely nothing to do with ignition timing - it is used ONLY to adjust fuel synchronization. As has been mentioned, you basically have to use a scan tool for the job to set it correctly but you can eyeball it and get it close enough for the engine to run.

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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

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1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #11 of 83 Old 10-05-2021, 10:48 AM Thread Starter
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The fuel sync doesn't really tell you a whole lot either, it just tells you how many degrees off it is in one direction or the other - or something along those lines. I ran the sync test last night and it it sat firmly at zero, which for me I guess is good and bad - good that it's in the right position, bad in that that's yet another thing I can't blame for how things are running... (I keep hoping for it to be something that is relatively simple but that I've just completely overlooked).

I've got a new mopar crank and cam sensor coming, neither of which I really suspect as being 'bad', but the long term fuel trim seems to consistently end up +30-35% which always seemed odd to me as the tool says I'm running rich most of the time. I say odd because I can't tell if it reporting that its running rich is a result of being +30%, or if it's +30% AND it's running rich - confusing might be a more apt word. I take it to mean that it's either expecting more air than its getting, or it's unable to lean out the mixture or.... something.

I suppose I could intentionally mess up the fuel sync and see what happens, though if that resulted in everything suddenly running "the way it's supposed to", I'm not sure what I'd need to do with that data point... as well, it sounds like it wouldn't stay that way for long since the computer is just going to do whatever it wants anyway (which is clearly to scramble my brain).

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post #12 of 83 Old 10-05-2021, 12:07 PM
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ECM/ PCM cannot really adjust for incorrect fuel sync, because fuel sync signal is what the computer uses as a reference to start fuel injection sequence. It is the signal that tells computer the relationship between crankshaft, cam and when cylinder #1 is at TDC.

When was the last time you replaced your O2- sensor? What brand is it, and have you checked what kind of voltages you're seeing? If I'm not mistaken, Snap-On MT2500 is able to show live data for OBD1 -> you should be able to see the required values fairly easily when diagnosing things.

Are you still running your original fuel injectors? If so, any idea on their condition? LTFT being at +30-35% if I remember correctly is about the maximum both the older OBD1 (SBEC) and OBD2 (JTEC) can adjust to on these Jeeps.
LTFT should be well within +/-10% when things are working correctly, your computer is trying to compensate a LOT for constant lean condition - or trying to compensate for what it thinks is a lean condition.

This could be a sensor issue (manifold absolute pressure, intake air temp, O2- sensor, coolant temp), or fuel injector issue where injectors aren't providing enough fuel.

What kind of fuel mileage are you seeing?
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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

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1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #13 of 83 Old 10-05-2021, 01:27 PM Thread Starter
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Quote:
Originally Posted by Timo_90xj View Post
When was the last time you replaced your O2- sensor? What brand is it, and have you checked what kind of voltages you're seeing? If I'm not mistaken, Snap-On MT2500 is able to show live data for OBD1 -> you should be able to see the required values fairly easily when diagnosing things.

Are you still running your original fuel injectors? If so, any idea on their condition? LTFT being at +30-35% if I remember correctly is about the maximum both the older OBD1 (SBEC) and OBD2 (JTEC) can adjust to on these Jeeps.
LTFT should be well within +/-10% when things are working correctly, your computer is trying to compensate a LOT for constant lean condition - or trying to compensate for what it thinks is a lean condition.

This could be a sensor issue (manifold absolute pressure, intake air temp, O2- sensor, coolant temp), or fuel injector issue where injectors aren't providing enough fuel.

What kind of fuel mileage are you seeing?
When it's running well enough to not stall, freeway mileage is around 10.

As for the sensors, they've ALL been replaced (including the IAC), many of them multiple times with different brands - I try to get Mopar or NTK or WVE where possible. I just replaced the 02 sensor (for the 4th time this year) - the stupid rich condition keeps caking them over in soot. All NTK. I've also replaced and/or cleaned the spark plugs quite a few times as well.

Compression test was done not all that long ago, and the numbers were decent if I recall. I'm also not loosing any coolant and I don't think I'm burning much oil (aside from what drips out of who knows where onto the exhaust...)

Vacuum system is "good" as far as I can tell.

I did block off the EGR at the intake manifold - only so that I could eliminate that variable, once things are normal again (big if there..), I'll un-block it.

In case you're curious as well, I pulled the cat and swapped in a straight pipe to rule that one out too. I didn't think it was bad, but the fewer variables the better. I stuck this in my WTF thread, but I'll stick it here as well - the cat being removed makes it just audible enough for the mic on my phone to pick it up. I'll try and grab a video of the live data on the snapon, would be nice if I had a way of seeing all the fields at once instead of having to scroll through it (for the sake of taking videos).


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post #14 of 83 Old 10-05-2021, 01:28 PM
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Have you considered adding a wide band oxygen sensor to it? Not really a common thing for diagnostics but you've already ruled out a *lot* of things. Wide band kits are not too bad these days, down in the $160 range plus welding a new sensor bung in. That would tell you if your exhaust matches what the PCM is seeing.
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post #15 of 83 Old 10-05-2021, 03:22 PM Thread Starter
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Have you considered adding a wide band oxygen sensor to it? Not really a common thing for diagnostics but you've already ruled out a *lot* of things. Wide band kits are not too bad these days, down in the $160 range plus welding a new sensor bung in. That would tell you if your exhaust matches what the PCM is seeing.
I hadn't considered that. What kind of things would I be looking for? Just generally things that don't match up, or something specific? Any suggestions on a kit of some sort? There seems to be a pretty large selection out there...

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