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Sanity check on 280z FI tests


charliekwin

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Hi everyone,

 

My '78 has been running too rich to pass smog.  I've already gone through and replaced the coolant temp sensor, added a thermostat (a PO had removed it), replaced filters and plugs, replaced a few dodgy looking connections and tested fuel pressure.  It seems better, but by my highly-unscientific smell test (and headaches I get if I leave it running for too long) I think it still needs work.

 

This morning, I ran through the whole list of tests for high CO in The Bible.  I think I may have found my culprit!  The throttle valve switch test failed.  Any pressure on the throttle showed continuity between pins 3 and 18, which should only happen at WOT.  I popped off the case, and the two contacts seem very close together.

 

post-30129-0-74373900-1432320243_thumb.j

 

Before I start futzing with it, I'm hoping someone will confirm that:

 

1) This is indeed something I should be futzing with?  One of the plastic clips had already been snapped off and the connector clip was bent, so I'm rather certain a PO has had their fingers in here.

 

2) The best way to go about said futzing?  Atlantic Z says to loosen the screws and rotate the box, some other people have physically bent the contacts.  How much distance between the two should there be?

 

 

Results of the other tests, in case they have any value:

1-6 (coolant temp sensor) -- 2905 ohm (~65 degrees F) -- pass

1-4 (air temp sensor) -- 2870 ohm -- pass

1-1 (idle throttle switch) -- no continuity with throttle, continuity without throttle -- pass

1-2 (full throttle switch) -- no continuity without throttle, continuity with any throttle depression -- FAIL

1-3a (AFM) -- 183 ohm -- pass

1-3b (AFM) -- 187 ohm -- pass

1-3c (AFM) -- 103 ohm -- pass

3-2 (air regulator circuit) -- 12V -- pass

1-8 (air regulator & fuel pump circuit) -- .5 ohm -- pass

2-3a-f (injectors) -- 12V -- pass

 

 

Many thanks for reading!

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Nice work!.  In your picture it looks like 3 and 18 are open, and 2 and 18 are closed, which is correct for idle.  But you can see how it works, with the common center pin moving closer to 3 as the throttle opens, if I'm looking at it right.  You should be able to see it touch, and maybe even a tiny spark if you open the throttle with the key on.  But it looks like you should have some rotation possible before 3 and 18 contact.  You might check the connection itself for dirt and grime or a short.

 

It does look futzed with.  The two screws are different and one has been abused.  I would go ahead and loosen those two screws and adjust it until you get the right numbers, if you can.  That's an important circuit and could explain your problem.

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i believe the distance between the contacts is related to the point in the throttle application that the contacts close. in other words, it's not just a measurement of the gap, but a measurement of the timing of the switch closure in relation to your throttle position. bending the contacts can get you the gross adjustment if it's way off, then loosening the screws and twisting the assembly gives you fine adjustment to get it right where it should be.

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Looks like someone adjusted your "full throttle" contact points to work a lot sooner than they are supposed to. That will make you run rich right off of the idle circuit. You should not have any contact with the full throttle points until around 75% throttle. Im not at the house or I would tell you what page to look at in the FSM. You definitely need to adjust (bend) the full throttle contacts further away from the idle contact points. Make sure to hook up your ohm meter, you are looking for continuity around 75% of full throttle. Loosening the screws and adjusting the unit as a whole is only going to give you fine tuning which you can do later. I believe the FSM says 34 degrees which is "around" 75% throttle. Even if you just get it close it will be better than it is. It is way off from stock. I had to do the same thing when I bought a used one for my 77. If need be I can shoot you a pic of mine to help you gauge things. It's really a simple adjustment. 

 

"Idle" points should break almost immediately after coming off of idle. Something like 4 degrees. You could probably sneeze on the throttle to get that to happen. Hope this helps.

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Appreciate the help, and glad to know I wasn't of the mark here. I did some gentle bending and was able to adjust the contacts and confirmed with the multimeter that circuits stay open and closed more like they should. Currently getting a smog pretest to see how the numbers look.

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Congratulations. There are californians out there that have lost their sanity and their dignity and sold their cars for pennies on the dollar because they couldn't get their cars smogged.

 

The calif car i got had only the thermotime switch wires  switched with the temp sensor wires. Easy to do but hard for some people to spot.

There were 2 afm's in the back..  They always leave a trail of dissected afm's behind. :o

 

now whatever you do don't spray the top of the engine at the car wash. I'm guilty of that too.

Edited by hr369
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I'm in the Pasadena area, which is about as specific as I want to get on a public forum , but happy to connect via PM. I should probably look into any local Datsun clubs on the area.

I feel like it runs alright. Seems like it has a little miss or hesitation every so often, and it shakes a bit, but it's never died or stalled on me and pulls pretty well, so perhaps I'm just overtly critical of what a 40 year old motor should be doing. I have a short clip of it idling in my Boondoggle thread.

Edit: and I'll be sure to keep water away from the motor!!

Edited by charliekwin
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