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!

[realred914]

(IMG:style_emoticons/default/ar15.gif) worn trigger points have cuased rich running on several 914s I have delt with. I have had this failure much more often than then having them be poor contact (ie dirty or corroded contacts) just a fact of life as these cars age. this should be considered a consumable item, yes a long term consumable, but eventulally they all will wearout and bounceif you dont change them

what happens is the wear block that rides on the cam gets too small so that the points just barely open, eventullay the wear will be so great on the wear block that the dont open at all (ie no firing) but before they get that bad, they open with such a small gap (say for arguement sake they only open a max of .0005 inch when highly worn) now they can bounce and trigger double or more firings. if they barely open due to wear on the wear block they will bounce!!!!!!!

the wear block I have found should be considered at their limit when teh small taper on the nose of the wear block is worn away to be flat new ones should have a taper on the tip, wornout ones should be flat.

now if your in a bind money or time wise, you can try bending the points arm a bit to make them open a bit more, then you can get a bit more life out of them.

the symptom tends to be worse at high rpm so that if you bench test them by turning the dizzy by hand and test with an ohm meter they seem fine, but run them up at high speed, and they can bounce.
also when you mount the triger points you are able to , due to clearances in the holes the mounting screws go thru, you can slide the points back and forth a bit before you tighten down teh two retaining screws, I recomend you center them as much as possible before tightening them down. thus you will have a more simular gap on the two points, slide them to one side or the other and one set of points wil have a smaller gap, and hence that one will be more suspetable to failure first.
By hand rotating and watching ohm meter for open/closed contact and noting the postion of the cam (via the rotor) you can get them very centered (set them up by noting the cams rotation angle verse when they first open, then repaet on other set of points. and move the whole assembly back and forth until both sets of points open at exactly 180 Degrees from each other. if they are off center, they will not be opening exactly 180 from each other, and hence are not centered.

very simple to set them up right, this will ensure longest service life as both gaps will be maximized and both cams followers (wear blocks) spring pressure will be minimized for reduced overall wear.

little details like this set up proceedure will give you many many extra miles of driving before failure.

anyone can install a set of trigger points and blindly screw them in place. but your not just anyone, so take the time to get them dead centered.

PS if your points are getting dirty oily often then you may find you have poor crank case venting, and/or a worn dizzy shaft that allow oil / combustion gases to get on them form the crank case correct crank gas venting is more than just smog control, it helps make your car more reliable!!!!!
yes!!! swap the injector wires to test and isolate if it is an injector issue or double injection issue. ECU failure can happen, but is fairly rare, The firing siginal to the two power transistors (the electronic switch that fires them) is triggered by the trigger points. other inputs (such as head temp or mainifoold pressure, throotle postion) determine the firing pulse time, but the actual tirgger to fire is only from the trigger points. the pulse time should control all four injectors evenly. the trigger is the only thing that effects pairs of injectors

also you can test injector flow volume by removing all four and placing the end sof them in four graduated test tubes and crank teh motor for several seconds, then note if they all pump out eh same volume or not. a good source of graduated test tubes in sthe drug store, get the plastic baby liquid medicine tubes, they should have teaspoon of ml markings on them, get four of them and your good to go.
also make sure spray pattern is a nice even cone shape and note if any injector contiunes to weep fuel out when you turn ont eh fuel pump with out cranking the motor. a weeping injecotr will need clean or replace


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[jeremiah98125]

(IMG:style_emoticons/default/ar15.gif) worn trigger points have cuased rich running on several 914s I have delt with. I have had this failure much more often than then having them be poor contact (ie dirty or corroded contacts) just a fact of life as these cars age. this should be considered a consumable item, yes a long term consumable, but eventulally they all will wearout and bounceif you dont change them

what happens is the wear block that rides on the cam gets too small so that the points just barely open, eventullay the wear will be so great on the wear block that the dont open at all (ie no firing) but before they get that bad, they open with such a small gap (say for arguement sake they only open a max of .0005 inch when highly worn) now they can bounce and trigger double or more firings. if they barely open due to wear on the wear block they will bounce!!!!!!!

the wear block I have found should be considered at their limit when teh small taper on the nose of the wear block is worn away to be flat new ones should have a taper on the tip, wornout ones should be flat.

now if your in a bind money or time wise, you can try bending the points arm a bit to make them open a bit more, then you can get a bit more life out of them.

the symptom tends to be worse at high rpm so that if you bench test them by turning the dizzy by hand and test with an ohm meter they seem fine, but run them up at high speed, and they can bounce.
also when you mount the triger points you are able to , due to clearances in the holes the mounting screws go thru, you can slide the points back and forth a bit before you tighten down teh two retaining screws, I recomend you center them as much as possible before tightening them down. thus you will have a more simular gap on the two points, slide them to one side or the other and one set of points wil have a smaller gap, and hence that one will be more suspetable to failure first.
By hand rotating and watching ohm meter for open/closed contact and noting the postion of the cam (via the rotor) you can get them very centered (set them up by noting the cams rotation angle verse when they first open, then repaet on other set of points. and move the whole assembly back and forth until both sets of points open at exactly 180 Degrees from each other. if they are off center, they will not be opening exactly 180 from each other, and hence are not centered.

very simple to set them up right, this will ensure longest service life as both gaps will be maximized and both cams followers (wear blocks) spring pressure will be minimized for reduced overall wear.

little details like this set up proceedure will give you many many extra miles of driving before failure.

anyone can install a set of trigger points and blindly screw them in place. but your not just anyone, so take the time to get them dead centered.

PS if your points are getting dirty oily often then you may find you have poor crank case venting, and/or a worn dizzy shaft that allow oil / combustion gases to get on them form the crank case correct crank gas venting is more than just smog control, it helps make your car more reliable!!!!!
yes!!! swap the injector wires to test and isolate if it is an injector issue or double injection issue. ECU failure can happen, but is fairly rare, The firing siginal to the two power transistors (the electronic switch that fires them) is triggered by the trigger points. other inputs (such as head temp or mainifoold pressure, throotle postion) determine the firing pulse time, but the actual tirgger to fire is only from the trigger points. the pulse time should control all four injectors evenly. the trigger is the only thing that effects pairs of injectors

also you can test injector flow volume by removing all four and placing the end sof them in four graduated test tubes and crank teh motor for several seconds, then note if they all pump out eh same volume or not. a good source of graduated test tubes in sthe drug store, get the plastic baby liquid medicine tubes, they should have teaspoon of ml markings on them, get four of them and your good to go.
also make sure spray pattern is a nice even cone shape and note if any injector contiunes to weep fuel out when you turn ont eh fuel pump with out cranking the motor. a weeping injecotr will need clean or replace


(IMG:style_emoticons/default/smash.gif) (IMG:style_emoticons/default/smash.gif) (IMG:style_emoticons/default/screwy.gif) (IMG:style_emoticons/default/driving-girl.gif) (IMG:style_emoticons/default/santa_smiley.gif) (IMG:style_emoticons/default/beerchug.gif) (IMG:style_emoticons/default/smilie_pokal.gif) (IMG:style_emoticons/default/ar15.gif)

Well I pulled them out again, and I could actually see them double firing on the ohmmeter on one side while rotating the shaft quickly.. In 1 rotation, the meter needle would bounce twice as much as the other side. I think it's like you said they were barely opening. I guess I'll buy some new ones! Yay.. at least I know I need them now... In the meantime I bent the spring/clip thing like you suggested so they will open up more. Looks good on the meter now. I'll give her a proper flogging tomorrow and see how it goes. thanks for all the help fellas!