Unstable timing, crappin out @ lo rpm

[Joffrey]

My recently assembled MS II (ini 2.3) works fine controlling fuel only but when I use it to control timing, the timing is less stable. low rpm is difficult to maintain. It sounds like it's not running on all cylinders if I let the rpm drop under 1200 rpm. Over 1200 rpm it is stable enough to check the timing, but it still jumps around a bit. Sometimes it dies when I try to drive it. Almost seems like it's going lean, but the VE table is fine when I don't use ms to control spark. Voltage may factor in somewhere - sometimes it runs worse or stalls when the electric radiator fan kicks on. I've been reading the forums and manuals and tweaking for days. I've made some progress but I still can't match the timing stability and idle quality of the stock ignition. I have the VR signal from the locked distributor split to both the MS II and the stock bosch module. There are no tach spikes. I could use a list of things to check. Thanks!

[bleoh]

Try different predictor algarithms, Last Interval worked best for me. Make sure your VR sensor is wired correctly - switch + and - to see if that changes anything. I am also finding that mine works better with negative trigger offset (I just have to use "calculated" to fire it when cranking). Good luck.

Brian

[Joffrey]

Thanks for the reply. I think I was wrong in saying the timing was jittering. Now I think the spark was cutting out or too weak and was confusing my cheap timing light. One thing I noticed was that the voltage to MS jittered around by at least a volt and has a volt or two less than the battery. TPS would also jitter a little, but not enough to trigger accel enrichment. Cleaning the main MS fuse stablized the voltage. I also added extra grounding points. The "performance" coil also may have been weak. it leaked oil last year. I replaced it with an 18 year old yugo coil that makes a nice 3/4 inch spark. It seems to be working fine now, but it was intermitant for a while so I still don't trust it 100%. This is my daily driver and I don't always have time to swap out distributers. I set the whole timing table to 0 and trigger offset to 0 so I can use the standard distributer while I test the MS coil driver and switch back with one wire if I have any problem with it. I can actually switch wires while it's running without the engine missing a beat. Timing light shows the same timing triggered by MS as it does when the coil is triggered by the stock module so I think the trigger point,vr wires and predictors are set right. I wonder if anyone else runs a distibuter that still has mechanical and vac advance enabled though MS? Seems like an easier starting point for working the bugs out, yet you can still tweak it.