distibutor problems

[ridin_Z_alb]

so i have a 77 280z that came stock with an auto. lucky i got a 83 zx with a 5 speed and swapped it. I am currently running off all the stock equipment from the 77. Weel anyways, i had it running like a charm the other day up to about 4 grand and then thin greyish white smoke just pores out the header ( rest of the exhaust hasent been hooked up yet). So i go sown to autozone and get a new rotor and cap. and the car doesnt fire. later on i found out it was the ecu wasnt plugged in . Well before i found that out i messed with this little thing in the dizzy under the reluctor called a contactor by the factory service manual. well on the plate its connected to, there are what looks to be timing marks on one side. my question is: What did i mess with? and what does it do?

 

thanks a lot guys,

albert

[AK-Z]

The distributor only fits one way. You adjust spark timing by loosening the mounting bolts and rotating it by hand while the engine is running.

 

The plate you messed with is I think part of the vacuum advance assembly.

[islanddozer]

Yes vacum advance. Is it possible you swapped a couple of spark plug wires ? Check firing order.

[ridin_Z_alb]

Thanks for the advice guys. I have found that the only problem was the firing order on the distibutor. I had to move it one over(ones now five four is now one). sorry im still kinda wondering what that plate does. does it control when the vacuum advance comes in? or possibly how much advance?

[islanddozer]

activated by vacum to adjust advance timing

hard on throttle produces increase vacum which will increase advance in timing

[blue72]

Are you talking about this little guy?

 

 

More vacuum = more timing. Unless the diaphragm inside is cracked. Then it is just a vacuum leak leaning out your engine.

It's a bit reversed from what islanddozer said though. At WOT you have almost no vacuum at all. As RPMs rise above a certain point centrifugal force increases your mechanical advance instead. The vacuum actuated dashpot does most of its work at lower rpms. Vacuum pulls that little arm away from the center of the distributor and turns the plate inside the dizzy to which it it attached thus advancing your timing. Again, if it's worn out the arm doesn't move and your engine will be running leaner than it should.

 

If it were me I'd try putting all of the spark plug leads back where they should be and loosening the adjusting screw on the base of the distributor. Then break out the timing light and see if you can't get the timing set to spec by rotating the dizzy and going from there.

[islanddozer]

according to chilton

the vacuum control consists of a diaphram, one side of which is connected via a small bore tube to a vacuum source and the other side to a magnetic pickup assembly. Vacuum in the intake manifold diaphram which varies with engine speed and throttle opening, causes the diaphram to move, which in turn, moves the magnetic pickup assembly, thus advancing or retarding the spark. The distributor vacuum advance is controlled by the spark timing control system

 

Don't think that is opposite of what I said. I was just keeping things simple. Just another reason why I am thinking about not helping anyone on here anymore.

[blue72]

Sometimes I have to be corrected to learn.

 

As long as we are talking about manifold vacuum and not ported vacuum then we are both accurate to a certain extent. Manifold vacuum is the source that should be used for vacuum advance on the distributor.

 

As islanddozer stated, under acceleration, in low and mid engine load the engine generates more vacuum. I double checked this a few minutes ago on my own vehicle with a vacuum gauge hooked up to the balance tube between my intake manifolds. Vacuum dropped off sharply when blipping the throttle, but opening the throttle and holding it open as rpm raised produced an increasing amount of vacuum. If your vacuum advance is working correctly then it is advancing the timing in conjunction with the mechanical advance under these conditions. Another item of note is that above about 10-15 inches of vacuum the arm attached to the diaphragm is fully retracted and no more additional vacuum advance is generated.

 

One condition in which little to no vacuum is produced is under wide open throttle. The vacuum advance arm relaxes when your really "giving it some welly". Since no vacuum advance is happening timing is advance purely by mechanical means.

 

The vacuum advance itself usually helps increase fuel efficiency and driveability. In the Z community it is common for the diaphragm to go south, so many of us (myself included until my parts arrive at the local Nissan dealership) are running around with the vacuum diaphragm disconnected from any vacuum source and the manifold ports plugged.

 

I rebuilt two different types of Z car distributors this week so the idea of how the parts inside work is fresh in my mind. The part I didn't know as much about was how engines generate different vacuum over their broad range of operating conditions. Thank you for pointing out our conflicting statements islanddozer. It is not my intention to lead anyone astray and I hope you will continue to contribute in the future.