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Discussion Starter · #1 ·
Hi all.

Ironically, noticed that this thread uses an image of mine:

http://forums.vwvortex.com/showthread.php?4170560-TECH-Timing-your-ABA ;) but rereading it shed some light.

On my ABA, if memory serves, the crank pulley and rotor line up to their marks but the cam is nearly one tooth off.

If the cam is out a little, the ECU doesn't notice this right? No DTC is thrown for the CMP so it seems the ECU is satisfied with the ignition timing from that standpoint.

I realize this is elementary stuff, but I'm still trying to nail down a slight intermittent performance issue and it sure feels like an ignition timing issue. IF the ECU noticed a difference in valve timing (can't see how it would) and was trying to compensate, am wondering if this would create intermittently correct timing advance.

Got my VCDS recently and am still learning it but will graph timing advance soon.

Thanks

Neil.
 

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When setting the timing, the rotor can be a little off and the ignition can adjust enough to keep the CPS happy. But if its at the tagged edge, a worn old belt might stretch and throw CEL. You can easily rephase the distributor by clocking it so the rotor lines up with the timing mark. But if you aren't throwing a CPS code then I dont think you ignition issue is timing belt related.
 

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Discussion Starter · #3 ·
thanks 911_fan

Since the rotor/crank pulley marks line up but cam "OT" marks don't, thought the end result would be similar to an incorrectly adjusted adjustable cam.

The engine has periods where it accelerates better (normal I guess) then periods where it won't. Not fuel quality related, no DTC's, all else seems ok and it seems totally random.:screwy:

Neil.
 

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The cam could actually be anywhere out of time and as long as the "cam position sensor" is clocked correctly and stays in phase with the crank sensor, the ecu will have no idea where the cam actually is in it's timing. (The motor might not run well if cam timing is way off, but the ECU would have no idea why and no code would/could be generated.) For the ECU, all the hall sender actually does is tell the ECU when it "sees" TDC for #1 to setup the injector firing sequence for the sequential injection, all the timing for the ignition comes from the crank position sensor and the toothed wheel. An OBDI ABA motor will run with the hall sender unplugged, it just reverts to batch firing for the injectors. And since the motor uses a dist to send the spark to the correct cylinder, not wasted spark nor coil on plug, the ECU doesn't need to know firing order for spark.
 

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Discussion Starter · #5 ·
ps2375: appreciate the explanations.

re: valve timing. This is kind of where I was headed in thought but wasn't totally clear. And I recall now re: the dist. hall. On one test run years back, I'd left it unplugged; the engine *totally* sucked on any inclines. Your point on ECU and valve timing makes sense now. I was a newb to belt installs at the time but really couldn't find a way to line up all 3 marks. In hindsight, I can see that if I get the cam and crank to line up, then I can index the dist. later (as per the thread I point to and 911' comment) I'm likely due for a new belt now (in terms of years) so hopefully will get all lined up exactly.

Would the knock sensor come into play if the valve timing was way off?

Can't get VCDS to open the Scope and track measuring blocks. (keep getting Windows error). When I do, I'll hopefully be able to nail down this weird MIL thing.
 
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