KEjet Running fault

[mercmad6.3]

I have an unusual problem here which I cannot even find anyone else having the same problem.
The engine is a m117 a 330HP 10-1 comp. 560
It has two new fuel pumps, a new fuel tank and acumulator. New flex lines to the fuel head. new hard lines.
A new rheostat,
I had to replace the 8 pin ignition for a 4 pin type from a 420 because I couldn't find another 8 pin unit .
Injectors tested perfect.
new heat sensors .It has a air temp sensor in the intake snorkel.Unlike US versions.
new plugs and leads. Rotor and cap are new .
So all of the normal stuff has been done.
The fault
The engine starts and idles perfectly .
Open the throttle above idle and it back fires through the exhaust ,running as though a lead is crossed (new leads and plugs !) but above slight throttle it suddenly runs clean and revs perfectly. It only misfires like this at the same throttle position ,not at idle,or at full throttle. As this is the normal throttle position in town driving , it makes it undriveable . it doesn't appear to be running too lean as suggested in the WSM as it is actually a bit on the rich side.
Any ideas?

[ytech15]

Was it doing it before the EZL replacement? are you aware of the fact that different modules utilize different ignition maps? Is the duty cycle static or is it fluctuating?

[Diseasel300]

I'm sure there's a difference between a "4 pin" and "8 pin" EZL, otherwise why would there be different versions? Given that this sounds like an ignition issue, I'd go back and visit your replacement module.

[Frank Reiner]

mm:

The above comments would appear to be going in the right direction.
When the throttle is lifted from the idle position the idle signal to the EZL is removed, and less spark retard is applied. If the retard curve of the 420 EZL is not as aggressive as that of the 560 there may be an earlier spark (more advance).
If the distributor is positioned so that the rotor is too close to the previous terminal in sequence in the cap, a spark can occur in the wrong plug.

Try relocating the distributor about 10 degrees anti-clockwise; that will move the rotor closer to the "next" plug terminal, and away from the "last" terminal.
As engine speed increases the rotor centrifugal advance mechanism achieves the same result.

[mercmad6.3]

OK, I am getting a better idea so far on this.
The 4 pin and 8 pin share the same advance curves. the original 8 pin, no longer available new or used does have 12 separate curves built into it though which were modifiable by swapping over a plug in resistor on the module itself ,but the 420 type doesn't ,having only 6 different curves which are accessed by the adjustable pot in the passenger footwell. I've not had the need to touch those. The extra pins in the original unit are for the two knock sensors.
I was thinking the timing might possibly be able to be tweaked so I will put the light on it and check the operation as it goes from idle to part throttle. But that sounds the most plausible reason so far.
As an aside,a mate has removed the KEjet entirely and fitted the Kjet from a 380 to a spare 560 to see how the system likes it.

And, there is no lambda control or oxysensor on this version of 560 either.
Again many thanks!!!!

[mercmad6.3]

OK. thanks to the suggestions for checking out the ignition I spent a couple of minutes with a timing light .At idle the ignition was firing at 50 BTDC, when revved beyond idle the ignition advanced off the scale
The ignition is theoretically fixed by the module .I disconnected the vacuum line and the timing instantly changed to 10BTDC.
I reconnected it and tried retarding the distributor but it cut out.I then turned it to full advance and that fixed it! I have never had to do this before as the ignitions set them selves ...allegedly. Little wonder i couldn't get a handle on the damn thing.
Heres a video of it running now ,to partial throttle

https://youtu.be/U0JpQ9lcTQo

[Frank Reiner]

Originally Posted by mercmad6.3

OK. thanks to the suggestions for checking out the ignition I spent a couple of minutes with a timing light .At idle the ignition was firing at 50 BTDC, when revved beyond idle the ignition advanced off the scale
The ignition is theoretically fixed by the module .I disconnected the vacuum line and the timing instantly changed to 10BTDC.
I reconnected it and tried retarding the distributor but it cut out.I then turned it to full advance and that fixed it! I have never had to do this before as the ignitions set them selves ...allegedly. Little wonder i couldn't get a handle on the damn thing.
Heres a video of it running now ,to partial throttle

https://youtu.be/U0JpQ9lcTQo

mm:

A question:
Are you using the flywheel trigger? [It would appear that you are.]
If you are, the 50 degrees advance that you saw w/vacuum is the position of the trigger segments on the flywheel. The EZL then retards from that full advance point. When vacuum was removed from the EZL, it was interpreted as full load/full throttle, and the EZL retarded the spark.

When you moved the distributor, you did not change the advance/retard; there is no trigger in the distributor!
You did however index the cap terminals to the rotor. (see my post above)

[mercmad6.3]

That sounds right, the rotor was running between the cap lugs so the spark was bouncing around going to the wrong cylinders.