restting cam sensor for "tuning" purposes

[ThikStik]

I have 2 ques re cam sensor. I have always had hi o2's and a bit of K at wot. Like 900 and 2-7 K. So, is it possible to tweak the cam sensor to cause the injectors to fire alittle sooner to burn that fuel. and ques 2: since the sensor is cam driven , which is timing chain driven, isint it prudent to check it every so often for correct setting?
TIA

 

[scottyb]

The crank sensor is the reference used to determine fuel and ignition timing.

The cam sensor is the reference that is used to determine which signal of the crank sensor is TDC #1. (in basic terms)

Moving the cam sensor will do nothing for performance. It only needs to be within the correct "window" so the ECM can know which stroke on the crank sensor is the one to fire on. Once you move it out of the window, it will not run.

There's a thread on turbobuicks.com - "cam sensor and timing Q" that opened my eyes on how it works. Take a look.

 

[broke1]

ThikStik,gimme a shout at 223-6181

 

[azgn]

you can unplug the cam sensor and run in batch fire if you want.......

 

[Nick Micale]

Originally posted by ThikStik
....... is it possible to tweak the cam sensor ....TIA

This has been debated over the years and contrary to the theory it cannot be "tweaked", I have found it sometimes helps.

With tolerance build up and different cam timing, like with aftermarket cam, moving it slightly off its normal position can help in idle and run modes.

The "procedure" is simple. With the engine running and the clamp loosened, move the sensor one way then the other to find where it runs best.

 

[boostcreep]

If it helps to move the sensor, what is changing

 

[ThikStik]

I figured after startup, it has done its job from an ignition sync standpoint...then, its job is to fire injectors at the correct time. Therefore it can be tweaked alittle to change injector timing. I know Ive heard of someones chip running better with a little different setting of it. ( what Nick was saying basically). I could experiment using chalk marks.
Thanks

Hey Broke1, Ill shout at ya i of these days.

 

[750H.P.V6]

Guy's,

I agree with Nick on this. When installing a longer duration cam the valve opens earlier and closes later. I have found that by advancing the cam sensor a bit helps driveabilty and idle quality on cars with large cams. I have a 224/224 solid roller cam and have found that 12 degrees after TDC rather than the factory setting of 25 degrees works best.

Neal

 

[ThikStik]

So advancing it does change something...But now that I think about it - DA! ...the wot 02's should not be affected by a sensor position change because the injectors are static at wot. Oh well, back to the drawing board.

 

[ijames]

The cam sensor provides the initial ignition-crank sensor sync so the ignition module can fire the first time, and then so long as the cam pulses are coming in they are used to continually resync the ignition. If you twist the cam sensor too far while the engine is running you make the crank sensor sync to the wrong cylinder and you get a misfire. You can see this jump with a timing light. Independently of all this going on in the ignition module, the cam sensor pulses are also fed to the ecm which uses them to sync the injector opening, so moving the cam sensor does change the timing between the injector opening and the intake valve opening. This makes a small difference at idle, especially with bigger injectors where the injector pulse width is getting very short, and virtually no difference at wot. After the engine is running if the cam sensor pulses stop, the ecm goes from sequential mode to batch fire mode (and sets an error code).

 

[boostcreep]

So the waveforms on the 'other' site are BS?? And here I thought I knew how to read them

 

[bsdlinux]

Re: Re: restting cam sensor for "tuning" purposes

Originally posted by Nick Micale
With tolerance build up and different cam timing, like with aftermarket cam, moving it slightly off its normal position can help in idle and run modes.

Nick,

How big do you think a cam would have to be to benefit from this tweaking. I have a 218/218 with 83 injectors.

 

[bruce]

Some years ago I played with the sensor timing, and in 2d increments never found anything that amounted to much on a small cammed motor.

At idle the injectors are firing at closed valves, with about a 2%DC. 2% of 360d of crankshaft rotation is a total of 7d or actually 14d for 720d since it's SEFI. IMO, stressing the O, I don't see where changing it 2-4d, out of a total of 720d is going to change much.

What I have found is that up to and including 60PPH injectors there's little change from batch fire to SEFI. The *double* firing of the injectors, and having twice as much atomization from that seems to more then make up for the *greater* PW calcualtions. And they're minute amounts.

And the large plenum, and low velocities at idle, are going to make for alot of *cross charge contamination*, between cylinders anyway.

But, like everything else on the net, you get what you pay for.

 

[ijames]

Originally posted by boostcreep
So the waveforms on the 'other' site are BS?? And here I thought I knew how to read them

You didn't give a link to the waveforms, so it took several searching sessions to find them. I was repeating what Tom Chou had told me several years ago (see the discussion there), and apparently he was incorrect about this as I do believe Dave's waveforms. In the ecm a sequencer circuit takes in the cam sensor signal and a trigger signal derived from the crank sensor signal and in turn provides timing signals to the chip which signals the injectors to fire. From the circuit it isn't possible to tell directly which controls the timing, but it would be much more complicated to use the cam sensor compared to the crank sensor so I think Occam's Razor clearly favors Dave's observations as well.

 

[750H.P.V6]

I'm confused.

Carl,

Since I wasn't able to locate the "waveform" discussion I guess I'm at sort of a loss. I know both yourself and Bruce have a much more intimate knowledge than myself of how the inputs from the crank and cam sensors are processed at the ECM. I have re-read what you stated and now I'm questioning whether or not cam sensor adjustment has an effect on ignition timing as well as injector timing. I believe that it doesn't. Can you clarify and or give a link to the "waveform" post.

THX
Neal

 

[ijames]

I'm sorry, Neal. I have a habit of closing windows as soon as I've finished reading them, without copying the url. You can't do searches at turbobuicks.com unless you are registered and I'm not, and I had to go through about 4 "other" Buick sites before I found the thread there, and I just didn't feel like wading back in the other night and finding the thread again when I realized that I didn't have the url. Here's the link: http://*********************/forums/showthread.php?threadid=17681 I was hoping the other poster would come back with the url (yeah, the answer to pretty much any question along the lines of "why did Carl do that?" is because I'm lazy ;-)).

Many people have verified that moving the cam sensor does not change the ignition timing, until you move it so far that the ignition module syncs to the wrong cylinder and the timing jumps 120 degrees (and it pops or misses or dies ). The question was what happens to the injector timing, and the belief was that this did move with the cam sensor. Dave Jones set up an ecm bench and used an oscilloscope to show that the relative timing between crank sensor pulse and injector pulse also does not change significantly as the cam sensor is moved. There is a small relative timing shift due to circuit propagation delay, which is constant and therefore translates into a varying number of crankshaft degrees as the rpm varies, but this is a tiny effect and has nothing to do with the cam sensor position. So the conclusion is that so long as the cam sensor is set suficiently far from the edges of the "window" that chain stretch and other mechanical motions can't make it move to the next window, it doesn't matter exactly where it really is because both ignition and injector timing will be controlled by the crank sensor.

Edit - and of course the silly censorship rules have just mangled the url anyway. Isn't this the land of free speech? The url is basically http://www.turbobuick$.com/forums/showthread.php?threadid=17681
where the $ needs to be replaced with an s, sigh.

 

[bruce]

If you convert the ecm into being romless there is a value you can change to offset the inj pulse from the ref pulse, or it was easy to change if your working with source code. The SEFI chip is programmed from the code. ie then if DEFI for some reason, the BPC is cut in half, and the SEFI chip bypassed.

At any large throttle opening at the higher RPM, the injector openings, and closings overlap so much of the intake valve timing, it hard to imagine much of a difference anyway.

But, I got another *thing* in the works to try and prove it one way or another for sure.

 

[scottyb]

on the "other" site, search for "cam sensor and timing Q"

 

[750H.P.V6]

That makes sense now

Carl / Bruce,

Thanks for the clarification. I guess in a nutshell the cam sensor tweaking I have done in the past is of no "real" value based on what you say. The cam sensor just sends the signal to the ECM to identify where the #1 cylinder is so the computer knows where to start the injector and timing sequences.

Happy Holidays (Merry Christmas actually but trying to be PC)

Neal