Timing ?

danncus · Post by **danncus** » Sat May 20, 2006 4:26 pm

Hi I have fitted the toothed wheel to my front pulley with missing tooth 90deg BTDC - but when running on edis only using my timing light ( with adjustable advance calc i am seeing a steady 20deg not 10 deg am i missing somthing?

danny

Kenn · Post by **Kenn** » Sat May 20, 2006 6:59 pm

The missing tooth should be set at TDC and the VR sensor should be 90 deg's befor the missing tooth when engines at TDC on a 4 cylinder engine.

danncus · Post by **danncus** » Sat May 20, 2006 9:07 pm

Kenn - yeh i've done that and it checks out when static. But when runnung with my timing light the spark to no. 1 cylinder is showing 20dag not 10 deg as expected

thanks
dan

Kenn · Post by **Kenn** » Sat May 20, 2006 9:12 pm

thats not what you've writen in your first post?

missing tooth must be set ATDC. as in not 90degs befor.

chriscook · Post by **chriscook** » Sun May 21, 2006 10:11 am

Does the timing light account for wasted spark operation? If not it will fire the strobe twice as often as it should and will indicate twice the actual advance. I had exactly this with a snap-on timing light i was using.

danncus · Post by **danncus** » Sun May 21, 2006 11:08 am

Superb! i was begining to think i was going mad!!! a can use more advance now!!

thanks chris

Oliver Sedlacek · Post by **Oliver Sedlacek** » Sun May 21, 2006 5:59 pm

I find it quite difficult to be sure exactly what point the VR sensor sees as it's reference angle. I suspect that you're just 10 degrees out. Can you move the VR sensor mounting by 10 degrees?

MartinM · Post by **MartinM** » Mon May 22, 2006 9:45 am

I *think* I'm with Oliver (it's an install error), but the comment amount the 'advance' timing lights has got me pondering.

I can't find anything on the web about these sort of lights reporting twice the advance in a wasted-spark setup - which is odd as I would have thought that this would be an incredibly common gotcha. Thinking about it, I might expect a 'flash' at 180 degrees out from the correct place due to the 'wasted' spark, but then again I read that the Snap On lights only flash every other spark, so that adds another complication to the pondering!

Obvious test is to measure the advance when the MJLJ is programmed to give say 25 degrees advance - if you measure 35 then it's an install error; if you measure 50, then I'm well confused!

Oliver Sedlacek · Post by **Oliver Sedlacek** » Mon May 22, 2006 2:02 pm

I don't believe that a timing light will give the wrong reading with a wasted spark ignition. It will fire twice as often, but that's not a problem as both firings should show the correct timing. On a normal ignition it fires once every two revolutions, on wasted spark it's once per revolution (twice as bright

).

I got bored with trying to install the trigger wheel at exactly the right angle. When I got it close enough, I just left it and now I adjust the whole map to compensate.

MartinM · Post by **MartinM** » Mon May 22, 2006 2:27 pm

I agree (now!). Both sparks are at the same BTDC for a given cylinder - it's just that the firing spark is when the cylinder is on the compression stroke, the non-firing spark is on the exhaust stroke.

I'm with the install error ....

chriscook · Post by **chriscook** » Mon May 22, 2006 5:26 pm

But if the timing light is getting a signal every 360 degrees instead of 780 degrees. it thinks the engine is going twice as fast as it is. The timing light I was using (admittedly old but working fine) reported the revs as twice the actual rpm..

The light i used you dialled in the advance figure and it advanced the flash accordingly. If it thinks 180degrees is 360degrees to advance the flash by 20degrees then it'll report 40degrees. When I mentioned this to some others they had had of the same problem with this particular light.

I had exactly this issue and as well as making sense it was confirmed on the rolling road with their newer timing light that understands wasted spark ignition. Mine said 26degrees, their's said 13degrees , the MJ said 14!

The OP's problem could be this or installation. As someone said set the timing to something different, say 15 degrees (not too much as you don't want detonation and it'll make it harder to start), and see if your light shows 25 degrees or 30 degrees.

<edit>
Quick google showed this:

http://www.stealth316.com/2-ignition-timing.htm (section 6)
and:
http://forum.vwsport.com/viewtopic.php? ... 116243b39c

Chris

Oliver Sedlacek · Post by **Oliver Sedlacek** » Tue May 23, 2006 8:27 am

My low tech timing light flashes when the spark happens, so it never gets confused. I can see how a light that uses time and RPM would give the behaviour you describe, so I think users should be careful that they understand how their light works.

danncus · Post by **danncus** » Wed May 24, 2006 10:41 am

i can believe a discrepancy of 1 - 4 deg, but not 10. with a map running advance of 30 deg and cranking at 5 deg surly i would be the first to know if somthing is amis? therefore it must be the lamp which is counting each spark and doubleing the advance ??

i do agree - i am amazed that no one has had the the same problem

Oliver Sedlacek · Post by **Oliver Sedlacek** » Wed May 24, 2006 2:18 pm

Can you try a different make or type of timing light? A local garage might help out for a small amount of cash.

Post by **brentp** » Wed May 24, 2006 5:25 pm

Right, you could even buy a generic timing light, test and return it for refund. Would like to know your findings!

Brent

Autosport Labs

Timing ?

Timing ?

The missing tooth should be

Kenn - yeh i've done that

@TDC NOT 90degs befor

Does the timing light

Superb! i was begining to

Probably just mounting tolerance

I think I'm with Oliver

Timing light and wasted spark

I agree (now!). Both sparks

But if the timing light is

High tech / low tech

i can believe a discrepancy

Maybe

Right, you could even buy a