'76 280Z Question on dist/manifold vacuum, dist timing, fuel pressure, brake booster

[FastWoman]

But Eric, you never tried my yogurt cup test! Seriously, when you do it, you'll immediately KNOW whether there's a leak (or a leak large enough to be of any importance)! I'm satisfied, now that Jenny has inflated her intake, that it's tight (within reason, notwithstanding a bit of blow-by past the valves and rings).

Jenny, the EGR makes no difference. You're good. Question answered: Your intake is tight. Yay!

Check your AZ distributor to be sure the shaft isn't bent/wobbly (which is a problem with some rebuilds). You can tell by seeing if the magnetic spur wobbles when it turns and/or the gap between it and the pickup varies as it turns. Also, in hind-sight, I would have asked your question about whether painting a part would void the warranty, and I'd paint that bugger before putting it on my car. (The vacuum advance doobob gets rusty very quickly.)

I don't think a compression test would be affected by valve lash, unless one of your rockers is adjusted too tight. (Two of mine were! Yikes!) Pre-loosen all your spark plugs, and retighten them just a little bit. Warm up your engine, and then shut it off. Secure the throttle wide open (e.g. bungie cord on the throttle linkage). Remove all the plugs. Then test compression in all your cylinders, one by one. Make certain you turn the engine the same number of cycles for each cylinder. (Each cycle will push the compression gauge needle a bit more.) I'd suggest maybe 5 cycles.

Making progress:

No vacuum leaks.

Cleaned up electrical connections.

AFM tested w/in specs, except for the air temp sensor. (Did you ever get that figured out?)

Soon to do valve lash and distributor (and timing).

Do your coolant temp sensor and thermotime switch test OK?

I'd re-test all your components from the level of the ECU connector, as that will also test all your connections and wiring.

You're actually getting pretty close.

[cozye]

But Eric, you never tried my yogurt cup test! Seriously, when you do it, you'll immediately KNOW whether there's a leak (or a leak large enough to be of any importance)!

Actually I have, but instead of using a yogurt cup, I used a flat section of gorilla tape to seal off the mouth of the throttle body, and I used 3 psi of air hose to inflate it. At first i just listened for leaks, then I would watch the tape bulge out from the pressure and see how long it would take to deflate. I've also done a normal "boost test", I've done smoke tests, carb spray test, blow with the mouth tests, and propane tests.. I was pulling my hair out trying to find a leak.

I was just offering an alternative to the carb spray idea that would reach hard to get to places

I agree though, It doesn't sound like she has a leak.

[cozye]

Jenny,

When you finish all the suggestions Sarah made, if we get to the conlcusion that those items are good, PM me your mailing address and I'll send you a potentiometer with bullet connectors on the end of it you can use to put inline with your water temp sensor. This will be a much better way to richen your mixture up for testing. It's only a 1000 ohms, and I needed about 1100 ohms on mine, which is why I have the extra. It will get you close enough for testing purposes though.

[FastWoman]

Eric, I had to add about 2.5 kOhms in series. Your 1k might work, but it also might not. I suppose there's also a possibility she's running rich, after all the cleaning and such, in which case she'd need a solution to lower the temp sender resistance. Hypothetically, if that were the case, I think she could install a second temp sender in an unused thermo housing hole (at least mine has one available) and wire the two in parallel. But we'll get to that eventually.

It's also possible some mechanic already installed a resistor in series. I say that because there was a fixed resistor soldered in series and wrapped inside my wiring harness.

Jenny, do you know how to solder electrical connections, use heat shrink, etc? If not, it's pretty easy to learn. Here you go...

This demo is overly compulsive, IMO, but it shows the process. No biggie -- even easier than shown.

Anyway, these are things to come. First complete the checklist, and then we'll do the final adjustments. :-)

[Jennys280Z]

cozye: Thank you for your offer! You guys are helping my car run better and that means a lot.

FastWoman: On your yogurt cup test results I should add, that when i inflated the manifold it felt pressurized. Then, the hose became exceedingly difficult to blow air into it and it stayed that way for as long as I continued to blow. This further indicated a tight setup to me. It was very uncomfortable to keep trying Remember I am your first data point for your experiment other than yourself!

General to all about the car: In limbo right now...AFM is fully cleaned, tested and adjusted and ready to install. But I'm puttering around in my off time retesting connectors a 3rd time after spraying them a final time with Dexoit, giving the outside of my AFM to TB boot (mine turned out to be in excellent condition) a nice dose of armor all, cleaning the innards to the throttle body door. There is still a ring of soot around the edges of the round flap though I've gotten all of it shiny clean save the rim of the circle. I might try a tiny screwdriver covered by a plush rag to finish the job. I used a few q-tips doused in carb cleaner but I don't want to get cotton in there by accident by rubbing too hard on the edges so it's stuff like this that slows me down.

In response to my problem in reply #12 of not being able to find 3/16" vacuum hose is because parts auto parts stores here don't have 3/16" vacuum hoses. The sizes are 5/32" and 7/32" which I used both to replace my vacuum lines. They were very tight but the fresh rubber was soft enough to stretch with no problem. The 7/32" is the purge line from the canister. Does anyone change their carbon canister filter? They have these for sale for a few bucks...is it worth doing?

Replacing my vacuum lines was easy and worth it, especially after i install my new distributor (vac advance again? yaay!).

My motor was 14 deg advance on the last tests I ran...I should have noted that. I'm going to fine tune it to 12.5 next time I start it up. Also it looks like this is about as far as I can rotate the distributor to advance it. This is kinda worrisome to me for some reason....is this normal (ie. can a normal distributor advance itself only about 15 degrees?)

[Jennys280Z]

Would you guys prime/paint my remanufactured brake booster?

It looks like I got a rebuilt booster that was rusted on the surface before they remanufactured it because it has some "speck" marks on the metal surface under the paint which looks suspiciously (exactly) like rust damage.

I don't want to happen to the booster on the left what happened to the one on the right. Ewww

[cozye]

FWIW, when my distributor had the stock inductor and pick up coil setup, it was almost rotated as far is it would go, I could get it to about 17 or 18 degrees advance. now that i switched over to an optical trigger ignition, the distributor is right in the middle of the range, and just about lined up with the mark on the bolt for 13 degrees advance.

[Zed Head]

Replacing my vacuum lines was easy and worth it, especially after i install my new distributor (vac advance again? yaay!).

My motor was 14 deg advance on the last tests I ran...I should have noted that. I'm going to fine tune it to 12.5 next time I start it up. Also it looks like this is about as far as I can rotate the distributor to advance it. This is kinda worrisome to me for some reason....is this normal (ie. can a normal distributor advance itself only about 15 degrees?)

j280Z, not really sure what you're saying here, but anyway, the vacuum and centrifugal advance happens inside the distributor (at your shiny new breaker plate with new ball bearings). The factory static advance (no vac or centrifugal/mechanical movement) should be 7 degrees, 1976, engine warmed up. That is what you are setting by rotating the distributor body at idle. Although, it is fairly common to run a few more degrees static advance.

The vacuum and centrifugal advances are not really "tunable" but can be changed with a little work. It would be interesting to know what your reman distributor has for these two, since I am pretty sure the reman companies standardized on some middle of the road numbers, as shown by their "compatibility" between many models that had different advance curves from the factory.

Anyway, for starters, you should probably set your static timing at 7 degrees per the FSM (10 degrees for CA model), especially since you may have been driving it with stuck advance mechanisms on your old distributor.

[Jennys280Z]

j280Z, not really sure what you're saying here, but anyway, the vacuum and centrifugal advance happens inside the distributor (at your shiny new breaker plate with new ball bearings). The factory static advance (no vac or centrifugal/mechanical movement) should be 7 degrees, 1976, engine warmed up. That is what you are setting by rotating the distributor body at idle. Although, it is fairly common to run a few more degrees static advance.

The vacuum and centrifugal advances are not really "tunable" but can be changed with a little work. It would be interesting to know what your reman distributor has for these two, since I am pretty sure the reman companies standardized on some middle of the road numbers, as shown by their "compatibility" between many models that had different advance curves from the factory.

Anyway, for starters, you should probably set your static timing at 7 degrees per the FSM (10 degrees for CA model), especially since you may have been driving it with stuck advance mechanisms on your old distributor.

Hi Zedhead! Not getting any vacuum advance from this distributor but the centrifugal advance works fine. But, if (either) advance mechanisms are stuck, wouldn't I compensate for that by increasing the advance?

The car idled better at 14 degrees advanced than 10 degrees where it was, but this is the case with the slightly lean condition I seem to be running at. I was intending to retard it back to ~12.5 after the next startup, or even perhaps back to 10, depending on how my clean and re-adjusted AFM has helped how it runs. Revved smoothly at 14 advance too. I didn't take it for a test drive though I wanted to.

On cleaning the fuel injector connectors, advancing the static timing from 10, and replacing the PCV valve, I took my manifold vacuum from 14.0-14.9"Hg to 14.9-15.3"Hg. What pieces of that improvement those changes individually made I don't know. My old PCV valve wasn't malfunctioning yet, though on shaking it, it felt a lot "heavier" than the new one which rattled willingly.

AFM is adjusted from ~2.5 teeth lean to ~0.5 teeth rich. Did some cleaning of the metal "tray" where the AFM bolts to, a single little rust spot got sanded cleaned and painted. o/w I'd have had my AFM on tonight sans the drying touchup paint.

There's a photo of my distributor's position at 10deg BTDC, I think on page #1 of this thread. I wondered if that looks in-line with what others have seen on their distributors.

[Jennys280Z]

FWIW, when my distributor had the stock inductor and pick up coil setup, it was almost rotated as far is it would go, I could get it to about 17 or 18 degrees advance. now that i switched over to an optical trigger ignition, the distributor is right in the middle of the range, and just about lined up with the mark on the bolt for 13 degrees advance.

I *MAYBE* could get 17-18 out of mine too. I'm not sure that it's as far as it will go. I didn't try to force it as far as it could go but it *looks* as if it's out of room to move or very nearly so.

[Jennys280Z]

Eric, I had to add about 2.5 kOhms in series. Your 1k might work, but it also might not. I suppose there's also a possibility she's running rich, after all the cleaning and such, in which case she'd need a solution to lower the temp sender resistance. Hypothetically, if that were the case, I think she could install a second temp sender in an unused thermo housing hole (at least mine has one available) and wire the two in parallel. But we'll get to that eventually.

It's also possible some mechanic already installed a resistor in series. I say that because there was a fixed resistor soldered in series and wrapped inside my wiring harness.

Jenny, do you know how to solder electrical connections, use heat shrink, etc? If not, it's pretty easy to learn. Here you go...

This demo is overly compulsive, IMO, but it shows the process. No biggie -- even easier than shown.

Anyway, these are things to come. First complete the checklist, and then we'll do the final adjustments. :-)

Awesome advice as always FastWoman. I think that thanks to you, I do better work (know what to watch out for -- so many helpful tips!)

I pulled all those bullet connectors off and cleaned them if that's where the inline resistor would go. There were no resistors on any of them but there was some corrosion.

I'm suspecting that maybe these problems with my car may have been brought to the surface by all of the electrical connectors I was cleaning. I found that my car was tuned up the wrong way (through the AFM wheel). I believe this was done because my mechanic (at that time) was fixing a rich running condition, and leaned it out by adjusting the wheel and installing hotter plugs.

When I cleaned all of these connectors (water temp, thermotime, ECU, CSV, TPS, etc) I believe I removed the actual cause of the rich condition and thus, inadvertently made my car run too lean. Logically it would seem to me, if unplugging the water temp sensor makes a car run very rich, then an oxidized connector would have higher resistance and logically create a slightly rich condition. While a fully-cleaned water temp sensor would be the leanest running case.

NGK GR5 plugs are not only hotter than OEM, but they have highly projected tips. Bigger tips than my BPR7ES's that are also projected (the P means a projected tip). This long nose is another way to get a little bit of additional spark advance. But perhaps these plugs would also be ideal to install to deal with a carbon fouled and rich running motor. Because they put the spark even closer to the piston head they might be effectively even "hotter" on the piston than a 5-heat rated plug without the long projection. GR5s are also a "V-power" plug with the V shaped tip which is alleged to deliver a better spark.

My water temp sensor and thermotime were the dirtiest connectors yet seen on my car. Fuel injector #1 which lives in the same neighborhood as those was pretty nasty and green also.

I agree with the conservative school of thought that says "don't mess with these AFMS". As owners we have time on our hands to be meticulous about the details, like keeping our electrics clean and our parts that wear out, fresh. If I was far more skilled and experienced with working on multiple Zs before, I might be proficient enough to do a little AFM tuning. But at my skill level, I think I'm best to just return it to its factory settings and just concentrate on the real problem that's somewhere else under the hood.

Edited January 6, 2011 by Jennys280Z

[Zed Head]

A three minute reply (when I started)! Must be cold and rainy in Oregon (where I am).

I thought that you said you were buying a new Autozone distributor back in Post #71? So I'm just suggesting being conservative until you know more about the advance curves on the new one. I don't know if you run Premium or Regular either (I'm assuming Premium?). If you give it too much static advance and you have aggressive advance curves and you ran Regular, you could get some knocking at part-throttle or wide open.

There were a wide variety of advance curves used for the different years of Z cars, and I've noticed the auto parts stores going with "close enough" for some parts (they call it SKU - Stock Keeping Unit - reduction in the business world, it saves money). Just look at the "compatibility" option on OReilly's web site.

I'm running 17 degrees on mine but I did get a bad tank of gas once and got a little bit of knocking at part throttle. But I also have a 78 mechanical curve with a 76 vacuum (Frankendistributor).

14 static would give you 34 total on a 1976 curve, so you're probably fine there. I can't tell if you're trying to get back to stock or if you're up for modifying until it runs the way you want it to. Either way is good, FW and cozye can get you there.

Edit - I actually started this before your last post...

Edited January 6, 2011 by Zed Head