Little Trucks, Big World
Spark Timing Control
Anyone have their emissions sticker still on their hoods? California (or federal). Preferably '84 and up but any year is good too.
Can you look and see if it says to remove the vacuum advance hose to distributor when setting the timing? Some years may or may not but it will settle an argument at best or teach me something at the worst.
Thanks... mike
Replies to This Discussion
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Permalink Reply by Tommy Perkins on
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Permalink Reply by Aaron Roth on -
Does it matter if itt is state or federal ?
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Permalink Reply by datzenmike on
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Thanks Tommy, anyone else?
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Permalink Reply by Chris on
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Not the sticker but the back page of FSM
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Quick Reference back Page.jpg, 181 KB
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It's in the FSM in the EF & EC section near the TVV thermal vacuum valve. Need to know if it says to remove the vacuum advance hose to set the timing on Z24 and Z20 motors Z22 are good to..
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Found it in my 85 FSM.it says to disconnect vacuum hose from distributor vacuum controller,and plug hose with proper plug.Run engine at about 2,000 rpm for about 2 minutes under no load.Then,run engine at idle speed and ensure that engine speed is below 1000 rpm.race engine two or three times under no load,Then run idle speed for one minute.Check ignition with timing light.3+-2 B.T.D.C.(AT;in drive)adjust as necessary,connect distributor vacuum hose,race engine two or three times under no load and run engine at idle speed.Check idle speed.M/T700+-100RPM(2wd)800+-100rpm(4wd)AT;650+-100RPM in drive.
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Permalink Reply by Patrick Smith on
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Mike, my federal 1982 emissions tag said to disconnect the vacuum advance.
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Wasn't that why there was a loop on the front of the air cleaner housing. That loop was the ported vacuum supply to the distributor vacuum advance. Only logical reason for its existence would be to easily disconnect the vacuum advance for timing setting.
Of course, if a person has a throttle body injected Z24i, the distributor uses a crank angle sensor, and there is no advance mechanisms at all. Typically post 1990 Nissans require you to disconnect the throttle position sensor to put the engine into set timing mode. Not sure, but I think the TBI trucks are similar. Truth is, there is a flow chart of things to do to properly set timing on most any ECCS driven Nissan. Sorry to go off topic.
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You see I was under the impression that the whole reason for ported vacuum is so there is none at idle so that the dizzy runs at static 3 degrees to reduce idle emissions.
So what does a properly timed engine read if the vacuum line isn't disconnected.... how much higher does it read if any???
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Honestly, I've had it connected and disconnected and as long as base idle was right, they set exactly the same. We talk about disconnecting the vacuum advance all the time in the auto industry, on all brands of cars. I think it is simply precautionary. It could also be to eliminate any potential of vacuum messing up your readings, even though a properly idling carburetor won't have ported vacuum present.
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Permalink Reply by Joe Wilson on
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I get about 4 inches of vacuum at 825rpm idle from my ported vacuum. It's not enough to advance the timing though. Reads the same whether or not it's disconnected. I think, like Patrick said, it's just to reduce room for error.
Good call on the loop near the air cleaner, it didn't occur to me that it was for easier disconnect.
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Joe, that is exactly how I would expect it to work. I have someone that sets it to 3 degrees with it off and plugged but it immediately jumps way up when connected. Must either have the idle too high or the vacuum is leaking in somehow.
Well thanks guys.
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