Ok, I've been trying to wrap my head around some things, maybe someone can shed some light.. First, I'm in a 93 ZJ 5.2L that I just rebuilt - pretty much new everything, including heads.
As has been stated countless times by countless people, the ignition timing is controller by the computer.
Here's what I don't get.. The distributor is mechanical. Its basically 'connected' to the cam shaft which means the rotor moves at whatever rate the camshaft moves (ignoring linear/angular velocities etc. - point being that that movement isn't controlled so to speak). The width of the [brush] on the rotor can't be more than a few degrees worth of the rotation. How is it possible for the computer to control the ignition timing short of not firing at all on a cylinder?
I get that the cam sensor basically controls the fuel injection timing, or rather feeds data to the computer about when/how long to inject fuel.
Perhaps the problem is in the terminology: the "ignition timing" is computer controlled in that it controls the fuel/air ratio, but the "spark" timing is adjustable by spinning the distributor. The problem with this (in my mind) is that since they're all tied together in that the computer has to make a decision, the end result would be that the distributor position effectively does control the ignition timing, albeit semi-indirectly.
If you go under the assumption that everything is working properly *except* your distributor isn't lined up quite right, it would seem to follow that the computer wouldn't be able to 'fix' it by changing something, but could keep the engine running by leaning out the fuel mix or some such. It would also then seem to follow that for the engine to run *correctly* - meaning the only variable in the equation being things like, load, temperature, air flow/pressure (altitude/air density) - the distributor would have to be lined up correctly without the computer having to try and compensate for me not getting it right.
Am I making sense or have I misunderstood something?
If the above assumptions are correct, what exactly is the correct alignment procedure? To my knowledge, with Cyl 1 at TDC at the top of the compression stroke (TDC also meaning that the big groove lines up with the TDC mark on the timing cover), you drop the oil pump/distributor gear in so that the key in the gear essentially draws a line to cyl 1. You then align the distributor (which contrary to both the FSM and my Haynes manual does NOT have any markings on it an neither does the cam sensor plate - at least in my year(?)) so that the rotor is pointing at the Cyl 1 position on the cap.
Having been trying to get this right for a while now (I some how managed to pass smog with flying colors...), I came across a Service Bulletin about improperly indexed distributors that basically says to use the V8 mark on the balancer and measure the voltage from the cam sensor and spin the distributor back and forth till you're as close to the threshold of ~0v and 5v as possible. What I don't quite get is this line: "The following procedure is an alternative to the indexing procedure outlined in the service manual." So... which is it? Both? I'm assuming then that the threshold (I haven't actually looked) would line up with the position of the rotor?
The cam sensor is really an on/off switch. I mean, its a hall effect sensor etc... but the effect is that the computer wants a 1 or a 0, and the arc width of the 1 and the 0 is 180*, so for half the rotor rotation is on, the other half its off (effectively). Which would imply that wiring headaches and crosstalk issues aside, you could essentially not care at all about indexing the distributor gear properly so long as you could spin the distributor to line up the rotor with the cyl 1 position of the cap.
Sorry this is a bit long - I'm working some of this out as I go...
If I'm understanding correctly, the underlying reason why the distributor "doesn't" control ignition timing is because every time you move it, the computer has to think about it and update some value stored somewhere about some bit of data and decide if it wants to change things - which could potentially be a while (also implying that resetting the ECU might be the quickest way to see any effect of changing the distributor position).
I swear there's an actual question in there somewhere :fish:
My symptoms are that without a particular pattern, it takes a lot of turning over before the engine will start, and it sort of (looking for the best way to describe this)... well its like if you're doing 75 on the freeway in a manual transmission, you're in top gear, you put the clutch in and turn the engine off, then let the clutch out (assuming the key is still in the on position) and the engine just sort of picks up where it left off. Somewhat unceremonious. Wouldn't exactly call it 'coming to life', though it idles consistently in the ~600rpm range with an occasional miss (I think thats just a jeep thing).
The previous engine - with bad compression and leaky valves - had some balls. Not big ones, but noticeably more than post rebuild. It feels like its either not getting enough fuel or getting too much fuel. MPG is not noticeably better - not that I was expecting great mileage, but I was expecting it to be better than the old one. Getting about 11-12 HWY...
So in summary - hard to start, a bit gutless, bad mileage.
Describes the symptoms of a variety of sensors that I've looked up and already replaced (again). I have a few tests that I want to run despite this along with improving the ground connections - though they don't look all that bad, more of a 'for good measure' thing.
Thoughts? Answers? Questions? Drive by shootings? Apologies for tl;dr...
As has been stated countless times by countless people, the ignition timing is controller by the computer.
Here's what I don't get.. The distributor is mechanical. Its basically 'connected' to the cam shaft which means the rotor moves at whatever rate the camshaft moves (ignoring linear/angular velocities etc. - point being that that movement isn't controlled so to speak). The width of the [brush] on the rotor can't be more than a few degrees worth of the rotation. How is it possible for the computer to control the ignition timing short of not firing at all on a cylinder?
I get that the cam sensor basically controls the fuel injection timing, or rather feeds data to the computer about when/how long to inject fuel.
Perhaps the problem is in the terminology: the "ignition timing" is computer controlled in that it controls the fuel/air ratio, but the "spark" timing is adjustable by spinning the distributor. The problem with this (in my mind) is that since they're all tied together in that the computer has to make a decision, the end result would be that the distributor position effectively does control the ignition timing, albeit semi-indirectly.
If you go under the assumption that everything is working properly *except* your distributor isn't lined up quite right, it would seem to follow that the computer wouldn't be able to 'fix' it by changing something, but could keep the engine running by leaning out the fuel mix or some such. It would also then seem to follow that for the engine to run *correctly* - meaning the only variable in the equation being things like, load, temperature, air flow/pressure (altitude/air density) - the distributor would have to be lined up correctly without the computer having to try and compensate for me not getting it right.
Am I making sense or have I misunderstood something?
If the above assumptions are correct, what exactly is the correct alignment procedure? To my knowledge, with Cyl 1 at TDC at the top of the compression stroke (TDC also meaning that the big groove lines up with the TDC mark on the timing cover), you drop the oil pump/distributor gear in so that the key in the gear essentially draws a line to cyl 1. You then align the distributor (which contrary to both the FSM and my Haynes manual does NOT have any markings on it an neither does the cam sensor plate - at least in my year(?)) so that the rotor is pointing at the Cyl 1 position on the cap.
Having been trying to get this right for a while now (I some how managed to pass smog with flying colors...), I came across a Service Bulletin about improperly indexed distributors that basically says to use the V8 mark on the balancer and measure the voltage from the cam sensor and spin the distributor back and forth till you're as close to the threshold of ~0v and 5v as possible. What I don't quite get is this line: "The following procedure is an alternative to the indexing procedure outlined in the service manual." So... which is it? Both? I'm assuming then that the threshold (I haven't actually looked) would line up with the position of the rotor?
The cam sensor is really an on/off switch. I mean, its a hall effect sensor etc... but the effect is that the computer wants a 1 or a 0, and the arc width of the 1 and the 0 is 180*, so for half the rotor rotation is on, the other half its off (effectively). Which would imply that wiring headaches and crosstalk issues aside, you could essentially not care at all about indexing the distributor gear properly so long as you could spin the distributor to line up the rotor with the cyl 1 position of the cap.
Sorry this is a bit long - I'm working some of this out as I go...
If I'm understanding correctly, the underlying reason why the distributor "doesn't" control ignition timing is because every time you move it, the computer has to think about it and update some value stored somewhere about some bit of data and decide if it wants to change things - which could potentially be a while (also implying that resetting the ECU might be the quickest way to see any effect of changing the distributor position).
I swear there's an actual question in there somewhere :fish:
My symptoms are that without a particular pattern, it takes a lot of turning over before the engine will start, and it sort of (looking for the best way to describe this)... well its like if you're doing 75 on the freeway in a manual transmission, you're in top gear, you put the clutch in and turn the engine off, then let the clutch out (assuming the key is still in the on position) and the engine just sort of picks up where it left off. Somewhat unceremonious. Wouldn't exactly call it 'coming to life', though it idles consistently in the ~600rpm range with an occasional miss (I think thats just a jeep thing).
The previous engine - with bad compression and leaky valves - had some balls. Not big ones, but noticeably more than post rebuild. It feels like its either not getting enough fuel or getting too much fuel. MPG is not noticeably better - not that I was expecting great mileage, but I was expecting it to be better than the old one. Getting about 11-12 HWY...
So in summary - hard to start, a bit gutless, bad mileage.
Describes the symptoms of a variety of sensors that I've looked up and already replaced (again). I have a few tests that I want to run despite this along with improving the ground connections - though they don't look all that bad, more of a 'for good measure' thing.
Thoughts? Answers? Questions? Drive by shootings? Apologies for tl;dr...
Distributor/Ignition/Fuel Injection timing
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