trigger points question, double firing?? Options

[jeremiah98125]

I seem to have an issue with my injector trigger points on 72 1.7L. All 4 cylinders seem to be running a little rich which I think is another issue, but 2 of the diagonal ones (2+3) are super rich, they totally blacken the spark plugs within a few minutes. I pulled the distributer and cleaned up the trigger points with some contact cleaner and they looked fine to me. It seems from what I've read that they are double firing? What would cause this? Wondering what I should be looking for when I pull the distributor again, and how I can test them once removed? They have 60k miles on them, would a new set be worth the $$? thanks!

[pbanders]

Interesting discussion, a couple of comments. First, the the TC's are a simple, cheap spring switch. All such switches tend to have bounce, that's why the ECU has a debounce circuit. See:

http://members.rennlist.com/pbanders/ecu.htm#TL

That said, the debounce limit of the ECU TL circuit is limited, and if you've got a switch that has a really long bounce (probably has a defective spring), you can get two pulses. It's a simple enough matter to swap in a new switch (uh, you DO have a nearly full set of new or "tested good" FI parts on the shelf, right? (IMG:style_emoticons/default/smile.gif)) and see if it works.

BTW, normally to see switch bounce, you need an oscilloscope. If you're seeing it on an ohmmeter, then it's really messed up.

Last comment is on the MPS leak-down. I haven't updated my page with this data, but I've noticed two leak modes. When they leak down fast, it's a cracked diaphragm, it's got to be replaced. When it takes tens of seconds for it to leak 5 mmHg or so, the leak is probably coming from the adjustment screws. If you've got an MPS that's already had the epoxy removed around the full load stop, you can significantly decrease the leak by using a small screwdriver and layering some thick grease around the inner adjustment screw. I've done this myself and it seems to hold up for a long time. Regardless, the impact of a small leak on the operation of the MPS is minimal, because the motor has more than enough pumping capacity. Only when the diaphragm becomes cracked does the MPS have to be replaced.