Jittery Timing

niduncan · Post by **niduncan** » Fri May 05, 2006 11:38 am

I have recently built and fitted a Megajolt using a MAP sensor.
When the timing marks are viewed, at idle, using a timing light and running EDIS only (no Megajolt connected) the timing is rock steady at 10degBTDC. With the Megajolt connected the timing mark tends to be jittery i.e. not steady any more. The ignition advances OK when the engine is revved, so the Megajolt seems to be working OK. The car also drives OK.

Do I have a problem or is this normal?

Oliver Sedlacek · Post by **Oliver Sedlacek** » Sat May 06, 2006 9:01 pm

On the tuning software are the MAP and RPM values steady or not? If the RPM leaps about then the megajolt may be picking up spikes. If the MAP value is fluctuating you may want to try damping the manifold signal. For diagnostic purposes you could try a flat map with a fixed advance at all locations to see if that makes a difference.

niduncan · Post by **niduncan** » Mon Jun 12, 2006 11:53 am

The jittery timing was being caused by the timing light getting confused by the waisted spark. The timing light I am using has an advance dial on it, when this dial is used the timing indicated by the marks on the crank pulley are incorrect. If the dial is set to zero then it works OK. I had initially set the position of the VR sensor with the timing light set to 10 degBTDC and then moved the VR sensor so that the TDC marks were aligned. With the timing light set to zero the timing indicated by the marks on the pulley was 4 degBTDC not 10. This has been confirmed by using a timing light without an advance dial as well.

Be careful when using timing lights with a waisted spark system!

MartinM · Post by **MartinM** » Mon Jun 12, 2006 2:20 pm

Interesting. Was it a Snap On?

I've been watching the Snap On advance timing lights on eBay and have bid for quite a few, but they go for silly money.

I don't think I'll bother anymore...presumably the rpm reading that the Snap On ones show is also wrong...

I can't believe that Snap On timing lights don't work with wasted spark systems properly

Post by **brentp** » Mon Jun 12, 2006 2:37 pm

That is good to know! I have an 'el cheapo' timing light with no advance dial, and it seems to work fine.

Glad you were able to figure it out!

Brent

chriscook · Post by **chriscook** » Mon Jun 12, 2006 5:07 pm

I think the newer ones will work. There was <a href="http://picasso.org/mjlj/?q=node/780">a thread on this a couple of weeks ago.</a> The problem is they don't ignore every other spark so display twice the rpm and twice the advance - so if your mental aritmetic is up to dividing by 2 then its not really a problem!

Chris

MartinM · Post by **MartinM** » Mon Jun 12, 2006 5:55 pm

Yeah I know - I made a right fool of myself on it as well!

Just three more things to add/ask:
- if you read the blurb on the Snap On advance timing lights, they say they only flash every other spark to save lamp life - so how does that work with wasted spark?
- they have a rpm display as well, specc'd to 10,000 rpm. So if if they measure twice the rpm, they are only good for 5,000 real rpm on a wasted spark system?
-are the newer ones (ie the ones that work) the MT2261 and the older ones (ie the ones that don't) the MT1261?

Post by **brentp** » Mon Jun 12, 2006 6:04 pm

So if they flash every other spark, you'd randomly align with the regular spark or wasted spark? does it even matter? - I'm thinking in 4 cylinder mode so it shouldn't matter in this case...

I think that xenon flashbulbs should be a thing of the past, I'd imagine that high powered white LEDs could do just as well and last basically forever..

Brent

Autosport Labs

Jittery Timing

Jittery Timing

What does the tuning software show?

Found the problem

Interesting.

That is good to know! I have

I think the newer ones will

Yeah I know - I made a right

So if they flash every other