924Board.org

[leadfoot]

Cars back on the road...
Cold start is better than ever, starts first push of the button and purrs...
Problem was two of my plugs had internally broken down, worked fine cold but warm were misfiring badly... this resulted in the plugs going black and fouling very quickly.
Rotor was also out of phase by 22 deg and firing off the edge.
A reluctor has been used to filter the noise and I see maybe a single count if I stall the clutch.
Just need to have the cruise in 4th looked at and fuel enrichment on tip in adjusted ever so slightly richer, just a little too much fueling has been pulled out.
Easy enough to fix as I have the max power map and the fuel economy maps to work from now.
Stoked...
Leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[RC]

Thats cool Leadfoot.
Hope you can down tools and enjoy driving it for a while.

Champion plugs hey?

Expect the rotor was firing and arcing from the lagging or trailing edge? Does your EMS electronically retard timing with the dizzy set at max advance. Most systems using distributors (reluctor, hall effect or points) do, and the rotor problem you describe is quite common. Depending on which position you have locked the dizzy in the simplest solution may involve adding a trailing edge to the rotor. Can give you details if you haven`t already rectified this.

[endwrench]

Good to hear!

I fight bad spark plugs all the time. Some are just plain bad out of the box and others just seem to foul very easy. I have a hard time with this on my Porsche because I pull it in and out of the shop so many times without actually warming it. I think there is something in or lacking in todays fuel that fouls them so easily. Not like the old days when the actually showed deposits though. Can't clean'em either. I change plugs like underwear now!

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[Rasta Monsta]

Too heavy to push, eh Todd?



BTW are you going to Fernie?
_________________
Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[endwrench]

No, just too OLD!

Nope, no Fernie either Wish I could but I have too many other things nagging at me for my summer time. Have a good time without me

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[leadfoot]

Actually Bosch W3DC's, never had a problem with Bosch plugs before, NGK yes,
The dissy has be modified so that the bob weights are welded, and the one of the four prongs in the inductor setup has been split to reference No.1 at TDC.
This is called dual pulse triggering, so that if at a later date I choose to I can go with multi coil ignition.
What was happening is that my dissy rotor phasing was reset to 0 deg and not the 22deg that was needed, the spark output would have definately been running off the rotor button.

The ignition advance is then configured purely vs load vs rpm...

Any noise on the input trigger is counted and displayed on my hand controller which I have mounted in the center console. The 931 head with it's no.4 spark plug sit directly next to the output wires from the dissy and was racking up points like a good run on galaga.

Now i have a filter in place this massive amount of noise is gone... If I stall my car in the driveway (bad clutching from limited driving time) I get timstars IQ...

Going to take my tuner for a ride at some stage, figure it's safer to have someone else operate the PC whilst I drive...
Leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[RC]

Unusual for Bosch plugs hey Leadfoot ? Maybe you had a bad batch but aren`t they made in Asia now too? Quite cold ones youre running there but suppose you need that with the extra heat generated by the forced induction.

Recon Endwrench is on to something here too as no plugs seem to last as long as they used to. Put that down to cost cutting but may have more to do with the lack of lead? But thats another thread!

Dizzy. Sounds like the centrifugal is welded (never like that idea BTW) at max advance. What about the vac plate? Is that locked too and using MAP/ load or are you running with diaphragm vac/pressure advance/retard?

Take a look at this:

Thats a variable reluctor type pickup, probably similar to yours.
The coil and stator fingers are mounted on the vac advance plate whether you are moving it or not. The rotor fingers are attached to the shaft and rotate with the rotor.

This is essentially a 4 pole AC alternator. It produces a theoretically perfect sine wave. The amplitude (voltage) increases with RPM and so does the frequency, decreasing the wavelength. Most systems trigger when the signal changes phase, at the point after the fingers on rotor and stator meet and the wave peaks positive and is on the down slope. Some units trigger at the 0 volt point when the wave crosses from + to -.

Either way a split or forked prong, or most likely 1 prong on both stator and rotor, will not produce a CLEAN double pulse on #1. I dont know exactly what you have done here or how your system reads the waveform. Without an oscilloscope to SEE what is happening I can only assume that you have essentially a M type waveform superimposed over the positive peak. This MAY also be the NOISE that your system is picking up.

If you are still having any problems here it is possible to work around it one way or another depending on your system parameters, dizzy mods, filter design and your desires.

And the rotor button problem is an entirely separate issue, in essence caused by the position of the stator (vac advance) and its relationship
to the rotor fingers. Can post details if you really want them, as it is a mechanical/ electronic issue and not something that can successfully be tuned out.

Roger