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Timing light mystery?


kumfasa
Member


Galant VR-4 org Post #: 1238277 posted 06/30/17 07:48 PM     Remind Me!  Send Private Message   Edit Post      
Hi Guys,
I'll explain my situation and hopefully you can shed some light on why this is happening.

I have a 91 JDM vr4.
I have boost leak tested it many times but only to about 20psi. I have just increased my boost level to ~26psi and thought I better do a boost leak test to above that level to ensure I wasn't missing any other high pressure leaks.
I found a couple and fixed them. (Throttle body gaskets and biss o-ring).

While resetting my biss screw to hit 30 on the isc position I though it would be a good idea to check my base timing.
Hooked up the timing light and I can only get a clear and consistent light that actually revealed my crank pulley marks from the plug wire going to cylinder 4! (4 being at the thermostat end of the engine, furthest from the timing belt)
When I connect the timing light to the plug wires leading to cylinder 1,2 or 3 I get multiple strobes and cannot see the crank pulley marks anywhere even when moving the cam position sensor both ways until the engine start to stumble.

The car runs great with setting the timing to 5 BTDC off plug wire to cylinder 4 and has been dyno tuned to 250kw (335hp) in that setting.

I certainly don't think that my timing is out but why can I not get a good timing strobe from the cylinder 1 plug lead?



Even the wool your trying to pull over my eyes is 95% polyester.

Posts: 115 | From: Tauranga, New Zealand | Member Since: 02/28/15 | IP: (58.28.212.87) | Report this post to a Moderator

FlyingEagle
Doesn't Match Anything


Galant VR-4 org Post #: 1238279 posted 06/30/17 08:30 PM     Remind Me!  Send Private Message   Edit Post      
What you may be getting is this:

1 - 3 - 4 - 2

Waste spark ignition system. Fires every 360 degrees of crank rotation, versus only once every 720 (4 revolutions).

Cylinder 1 and 4 have identical location of piston. If cylinder one is firing, cylinder 4 is up top too, and vice versa.

Check to make sure your old school timing gun does not have a dial to play with timing advance/retard of the light firing sequence.

Some guns have problems with the magnetic pickup coil and the waste spark system ... maybe wires, maybe the gun sensitivity, but I have had trouble with guns to a degree but emissions test machine pickup coils were the worst offenders.



C53A 1 of the ~1500

Posts: 1505 | From: THE Ottawa | Member Since: 03/05/05 | IP: (108.162.128.106) | Report this post to a Moderator

kumfasa
Member


Galant VR-4 org Post #: 1238280 posted 06/30/17 10:03 PM     Remind Me!  Send Private Message   Edit Post      
Thanks for the info about guns. The gun I have is the cheapest chinese made thing in existence. And has no adjustment available.
I borrowed another gun (friendly neighbour) and tried again. Spot on 5 BTDC off both leads to Cyl 1 and 4.

Both guns were hooked up at the coil pack without taking the plug cover off the engine. The leads are quite close together there and I suspect some sort of interference with my cheap gun.
So I removed the plug cover and separated the plug wires and my gun reads 5 BTDC off both 1 and 4 also.

I guess you get what you pay for. For a tool that is so rarely used I couldn't justify spending a whole lot. (I should have just asked my neighbor in the first place. Or taken the 5 seconds to remove the plug cover)

Thanks for your help.



Even the wool your trying to pull over my eyes is 95% polyester.

Posts: 115 | From: Tauranga, New Zealand | Member Since: 02/28/15 | IP: (58.28.212.87) | Report this post to a Moderator

FlyingEagle
Doesn't Match Anything


Galant VR-4 org Post #: 1238299 posted 07/01/17 10:26 PM     Remind Me!  Send Private Message   Edit Post   
Glad it worked out. I would have suggested going direct at the spark plug boot lead in, but assumed you were already there; sorry I missed that.

Finicky electrical system with waste spark that I suspect wasn't around when the timing guns were invented. Le sigh.

Guess it is a good thing the leads aren't totally shielded!



C53A 1 of the ~1500

Posts: 1505 | From: THE Ottawa | Member Since: 03/05/05 | IP: (108.162.128.106) | Report this post to a Moderator


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