timing has to be done when changing Distributor Cap?
All Star
Joined: Jan 2009
Posts: 907
Likes: 2
From: Corrales, New Mecico
It's all right here, link was posted before.
http://www.noid.org/~lj/PCM%20Tutorial/PCMtutorial.htm
But you're going to have to read every page. MSD has some info too.
Try some of the Megasquirt web sites.
We have been saying, (and you have been ignoring) that every sensor plays a roll into when the PCM knows to fire an injector. If you replace the PCM, it learns everything about your vehicle, and what it can't learn the dealer has to plug in with a DRB. But it's a computer. Which is why you unplug the PCM after a mod so the computer will reboot and learn.
Like I said, don't over simplify this, it's not just one thing.
http://www.noid.org/~lj/PCM%20Tutorial/PCMtutorial.htm
But you're going to have to read every page. MSD has some info too.
Try some of the Megasquirt web sites.
We have been saying, (and you have been ignoring) that every sensor plays a roll into when the PCM knows to fire an injector. If you replace the PCM, it learns everything about your vehicle, and what it can't learn the dealer has to plug in with a DRB. But it's a computer. Which is why you unplug the PCM after a mod so the computer will reboot and learn.
Like I said, don't over simplify this, it's not just one thing.
Legend
Joined: May 2005
Posts: 8,663
Likes: 8
From: Central Oklahoma
I'd have to say it's all in the timing. The pcm doesn't remember or need a signal to know which injector to fire. The pcm is assuming the timing is right, and automatically activates the required injector. The cam and crank sensors tell the pcm what position they are in for spark, and the programming takes care of which injector to activate.
Record Breaker
Joined: Mar 2009
Posts: 2,181
Likes: 3
From: Battle Ground WA
So how about it; can anyone answer the question?
Again:
" ... the spark side is easy to understand because the PCM doesn't need to keep track of which cylinder needs a spark; the distributor takes care of that; and the orientation between cam and crank never changes under normal circumstances.
So what happens when you replace your PCM, for example. How does the new one know which injector is which? It just seems to me that for injector purposes, the PCM would need to be told which cylinder is which, at least on occasion.
.... (exactly) how would the hypothetical new PCM know which injector to fire".
Last edited by HeyYou; Oct 28, 2011 at 03:01 PM. Reason: Some commments removed from quote.
Retired Moderator - RIP
Joined: May 2008
Posts: 18,729
Likes: 17
From: NH
Not exactly. When the engine is assembled the crank is turned so that the rotor points to #1 cylinder. Also note that the cam sensor has a notch that is clearly marked #1 (or something to that affect) that lines up with the distributor body. Once those parameters have been established, the PCM then receives the proper signals from both the cam sensor as well as the flywheel sensor telling it when to fire the injectors.
That's what I'm saying. All that has to be right for the pcm to send the signal to the correct injector. Cam sensor is marked for proper alignment purposes. As in TDC. It doesn't tell the pcm which cylinder its on, except of course #1. That's when the programming comes into play and automatically know's which injector to fire next, according to the firing order.
OK, this is pretty much what I've been looking for:
From VW: "Also note that the cam sensor has a notch that is clearly marked #1 (or something to that affect) that lines up with the distributor body. Once those parameters have been established, the PCM then receives the proper signals from both the cam sensor as well as the flywheel sensor telling it when to fire the injectors".
And from Hahns: The PCM knows the firing order, the cam sensor tells it which 4 cylinders are up next, it then pulses each injector output in the correct order in conjuntion with the crank sensor signal.
And from Z: "Cam sensor is marked for proper alignment purposes. As in TDC. It doesn't tell the pcm which cylinder its on, except of course #1."
So, I think this is the missing piece that I've been asking about. The cam sensor sends a signal to the PCM every time the firing order restarts (as opposed to the crank sensor that just sees "nameless" cylinders).
So: new PCM is installed. Computer "says" to itself, "hmm, the engine is cranking, but I have no idea which injector to fire, being new around here. I'll wait until the cam sensor tells me that #1 is ready to fire, then I'll activate the #1 injector, and tell the coil to build up a spark and send it to the distributor" (which delivers it to the correct cylinder).
Adobedude: "We have been saying, (and you have been ignoring) that every sensor plays a roll into when the PCM knows to fire an injector. If you replace the PCM, it learns everything about your vehicle ..."
I haven't been ignoring anything. If anything, you've been ignoring what I've been saying. And is it your contention that when you put in a new PCM, there's a sensor somewhere that tells it "hey, injector 5 is the next one to fire"? If so, I'd like to know how that works.
Come on guys, give me a break. I know more than a lot of you think I know, and I also like to understand things on a very deep level, which some people seem to mistake for a general lack of understanding.
The purpose of these forums are to learn and share, and I think a lot of us just learned something. Insulting and/or ridiculing people works against the interests of a forum, because people will be less willing to ask questions or share information for fear of being attacked. Some of you, and you know who you are, could stand to step up your game a bit.
From VW: "Also note that the cam sensor has a notch that is clearly marked #1 (or something to that affect) that lines up with the distributor body. Once those parameters have been established, the PCM then receives the proper signals from both the cam sensor as well as the flywheel sensor telling it when to fire the injectors".
And from Hahns: The PCM knows the firing order, the cam sensor tells it which 4 cylinders are up next, it then pulses each injector output in the correct order in conjuntion with the crank sensor signal.
And from Z: "Cam sensor is marked for proper alignment purposes. As in TDC. It doesn't tell the pcm which cylinder its on, except of course #1."
So, I think this is the missing piece that I've been asking about. The cam sensor sends a signal to the PCM every time the firing order restarts (as opposed to the crank sensor that just sees "nameless" cylinders).
So: new PCM is installed. Computer "says" to itself, "hmm, the engine is cranking, but I have no idea which injector to fire, being new around here. I'll wait until the cam sensor tells me that #1 is ready to fire, then I'll activate the #1 injector, and tell the coil to build up a spark and send it to the distributor" (which delivers it to the correct cylinder).
Adobedude: "We have been saying, (and you have been ignoring) that every sensor plays a roll into when the PCM knows to fire an injector. If you replace the PCM, it learns everything about your vehicle ..."
I haven't been ignoring anything. If anything, you've been ignoring what I've been saying. And is it your contention that when you put in a new PCM, there's a sensor somewhere that tells it "hey, injector 5 is the next one to fire"? If so, I'd like to know how that works.
Come on guys, give me a break. I know more than a lot of you think I know, and I also like to understand things on a very deep level, which some people seem to mistake for a general lack of understanding.
The purpose of these forums are to learn and share, and I think a lot of us just learned something. Insulting and/or ridiculing people works against the interests of a forum, because people will be less willing to ask questions or share information for fear of being attacked. Some of you, and you know who you are, could stand to step up your game a bit.
Last edited by John D in CT; Oct 28, 2011 at 01:15 PM. Reason: Changed "Merc" to "Adobedude"
Champion
Joined: Oct 2009
Posts: 4,717
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From: N/A
So my thoughts on this,
The firing order is always the same it never changes, so I would say it is burnt on the pcm. I don’t think I remembers what the last injector fired was, I think it gets trigged off cyld 1 when turning over, it then knows the rest of the set firing order.
The firing order is always the same it never changes, so I would say it is burnt on the pcm. I don’t think I remembers what the last injector fired was, I think it gets trigged off cyld 1 when turning over, it then knows the rest of the set firing order.
Last edited by merc225hp; Oct 28, 2011 at 12:59 PM.
So my thoughts on this,
The firing order is always the same it never changes, so I would say it is burnt on the pcm. I don’t think I remembers what the last injector fired was, I think it gets trigged off cyld 1 when turning over, it then knows the rest of the set firing order.
The firing order is always the same it never changes, so I would say it is burnt on the pcm. I don’t think I remembers what the last injector fired was, I think it gets trigged off cyld 1 when turning over, it then knows the rest of the set firing order.
Last edited by John D in CT; Oct 28, 2011 at 01:06 PM.
Whoops, I sure did. That was Adobedude - sorry. Fixed it.
Last edited by John D in CT; Oct 28, 2011 at 01:16 PM.
Administrator
Joined: Apr 2010
Posts: 87,409
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From: Clayton MI
Crank Sensor tells the PCM when "a" cylinder is in firing position. Initially, it doesn't know WHICH cylinder it is, until the Cam sensor (in the dist) changes state. Then, which way it is going (on to off, or, off to on) tells it which cylinder is up. At initial startup, the PCM doesn't know squat about there the engine is in relation to which cylinder is where, it NEEDS the cam sensor to change state once before it actually knows enough to start running the engine. Fortunately, that is only one crankshaft revolution. (crank goes around twice, for one revolution of dist.) So the PCM figgers it out pretty quick.
PCM doesn't care which cylinder it is firing the coil for. It isn't relevant. Distributor handles that task, PCM DOES care about which injector it should fire though. (sequential fuel injection, not batch fire....) That is the critical bit here, and that is what the cam sensor is for. Turning the distributor will have zero direct effect on ignition timing. The crank sensor is fixed, and it is the sole arbiter of ignition timing. (relative to engine temp, rpm, etc......) All else being equal, turning the distributor does nothing to spark timing. Altering the relationship between the terminal on the cap, and the rotor tip doesn't alter when the PCM fires the coil, might just alter where on the rotor tip the spark jumps from though..... but, if the PCM thinks it should be firing the coil at 10* BTDC, moving the distributor doesn't alter where the PCM thinks 10* BTDC is. That's all the crank sensor.
PCM doesn't care which cylinder it is firing the coil for. It isn't relevant. Distributor handles that task, PCM DOES care about which injector it should fire though. (sequential fuel injection, not batch fire....) That is the critical bit here, and that is what the cam sensor is for. Turning the distributor will have zero direct effect on ignition timing. The crank sensor is fixed, and it is the sole arbiter of ignition timing. (relative to engine temp, rpm, etc......) All else being equal, turning the distributor does nothing to spark timing. Altering the relationship between the terminal on the cap, and the rotor tip doesn't alter when the PCM fires the coil, might just alter where on the rotor tip the spark jumps from though..... but, if the PCM thinks it should be firing the coil at 10* BTDC, moving the distributor doesn't alter where the PCM thinks 10* BTDC is. That's all the crank sensor.