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

[Jennys280Z]

Other ideas swimming in my head:

Dist vacuum advance (wouldn't be an issue at idle however it would mess up my performance under load; my car runs like a helicopter at different amounts of throttle/load)

Valve cover gasket (I guess I will have to replace this anyway once I take the cover off to inspect the valve train, cam timing, chain, et al. Hope there's a good rubber one that I can keep using after continously going in there)

Harmonic balancer drift/retarded ignition timing

PCV hose (doubt it; passed the choke cleaner test)

Dipstick seal (feels like it always did, highly doubt it's an issue)

Oil Cap (no rubber gasket or O-ring of any kind?; just plastic cap to aluminum cover like it always was). But this feels very tight, passed the choke cleaner test...seriously doubt it's an issue.

Air Filter

Stuck/burned valve (I seriously doubt this...or any other major mechanical problem).

Fuel injector connector corrosion (all injectors got 10.9V from the ECU when the battery was charged to about 11.2V), but I suppose this doesn't rule out corrosion increasing the resistance and thus lowering the current, and by extension the fuel spray as ordered by the ECU.

Fuel injectors dirty/clogged/leaking (no external fuel leaks anywhere...car doesn't leak a drop of anything else for that matter).

There's no coolant in my oil, no oil in my coolant, no gas in my oil, and no strange noises coming from the engine that I can tell, save the "valve rattle" that I've always heard and consider to be normal.

The AFM electrical connector looks impossible to get to without taking off the boots and AFM completely first. It's a real drag that the wonderful engineers at Nissan put that thing so hideously out of sight and reach.

Clogged exhaust. (seriously doubt this...I'll do the vacuum test for it that AtlanticZ recommends next time I start the motor just to rule it out...rev and hold 2500RPM for 15 seconds...if vacuum drops off -> clogged exhaust).

Compression test (I bought an Actron gauge kit a while ago...I'll do this before my next oil change and likely on the same day I adventurously remove my valve cover since I'll have my spark plugs out anyway to turn the motor to TDC) I expect to see low numbers (commensurate to an engine with well over 100k miles) that are close together.

Any other better ideas to consider first...electrical tests I can do with my multimeter etc., please advise!

To summarize my issues again: My car starts up and has 10inHg vacuum @ 800RPM at the rear of the intake manifold for about 20-30 seconds, then it bogs down to 5-7inHg and the RPM drops down to 500-600RPM until the motor warms up. When it's at 170deg, I get 15inHg +/- 0.5in. My motor is running lean (at least slightly), and has a very obvious Vvvv-vvvv-vvvv-vvvv behavior instead of a smooth Vvvvvvvvvvvvvvvvv that I know this motor is capable of. Tailpipe exhaust puffs hard against my palm in a blub-blub-blub-like pulse.

*sighs*

Edited December 20, 2010 by Jennys280Z

[cozye]

AC vacuum connnection is a small fitting right by the EGR valve on the intake. It's the smallest diameter fitting.

I would run the NGK/Nissan OEM plugs. MSA has them cheap.

The fuel enrichment test seems to confirm you are running lean, but probably not by much if your car was running bad at mid to upper rpm's. I can tell you that when I jumpered my TPS, it was running too rich at upper rpm and had a loss of pickup, but it was still very smooth.

I'm wondering if you have multiple issues going on here. Sounds like you have a miss or something that needs to be addressed before you mess around with fuel.

On the brake line fittings, a good flare nut wrench and a soaking of PB blaster should take care of it. Take your time and don't stress about it. It will be fine.

As far as replacing the distributor, put the motor at TDC and the rotor should be pointing to #1. That way you will be able to orient it correctly when putting back in.

To test mechanical advance, disconnect vacuum advance, rev motor up to 3-4000 rpm with timing light. You should see the timing mark advance. If not, your mechanical advance isn't working.

Advancing timing to 12-13 is probably a good idea, but it's not going to solve your problems.

Don't add the resistor to water temp sensor yet.

Have you not adjusted your valves? Do that hot, and pronto!!

timing chain stretch,, how many miles on car? I put my cam gear on #2 as my chain was stretched a little, but still within spec. It didn't help my situation. I would suspect that unless you have 200k miles, it's not it.

Did you thoroughly test AFM per FSM? Did you do the voltage output test by applying 12v power and measuring voltage output as the flap is moved?

hissing sound from thottle body is likely air flowing through the idle speed screw bypass. When you get your car running better, your idle screw will be turned down more and that will quieten up a bit.

valve cover gasket is reusable if its a newer one. I clean the oil off of it carefully, and clean the oil off the mating serfaces and reuse. The one I got from MSA has a rubbery feel to it and is holding up good after taking mine off a dozen times.

dipstick seal leak is a vacuum leak. make sure the oring is there.

stuck vavle? have you done a compression test? This would show up.

fuel injectors leaking, do you hold fuel pressure on the rail overnight? They could be clogged or dirty. If you are suspect, you can pull them off and send them for cleaning and flow testing. It's about $20 per injector. Not a bad idea but probably won't fix your issue. Have you done a balance test by pulling off each injector pig tail? When you richened up the car was it idling smooth then?

The AFM connector is easy to get off. Unbolt the three bolts on the bottom of the AFM, loosen the boots, lift the AFM about 4 inches to gain access to the connector, then take a small screwdriver to pop the retainer clip off. Trust me, when you have done this 30 times you will be able to pull that AFM off in 2 minutes.

I doubt your exhaust is clogged, but that test will show it.

vacuum readings and idle behavoir cold, ignore this for now. It's just going to throw you off. Do all test and troubleshooting with car at operating temp. low cold idle is probably air bypass not opening all the way, but thats low priority. Fix other issues first.

Just to confirm, have you put new plugs, wires, distributor cap, rotor, and checked your air gap on the pickup coil? Have you done the balance test by pulling a plug wire to each cylinder breifly while running ? dont shock yourself

To give yourself peace of mind on vacuum leak sources, disconnect all external vacuum from manifold including brake booster, leave the FPR hooked up, and plug all the holes with a short piece of hose with a screw in it.

Personally I think you may be trying to do too many tests at once and running in circles. Do one thing at a time, thoroughly, and double check, twice, then move on to the next. Rule it out and don't look back at it.

Save the resistor in the water temp circuit for last. This may fix the car, but if it's not the problem then you will only be covering up the real issue. You have to rule everything else out positively.

[FastWoman]

Whew! Quite a few things raised here! You've done quite a lot of work. (Kudos!) Coz has already addressed most of your questions. I'll add a couple of things:

Distributor: Perhaps the "capsule" is the timing pickup coil. It's the plastic part with wires coming out that you will see when you pull off the distributor cap. My AutoZone Duralast distributor came with that part included. It didn't come with the base plate, though. That had to be transplanted. Removal: Remove your distributor cap, and note the direction the rotor is pointed. Clean any debris off your engine around the base of the distributor. Completely remove the screw you loosen to adjust the timing, and just pull the distributor out. Transfer any needed parts from the old distributor to the new one (the base plate and possibly the pickup coil). Put the rotor on the new distributor, and point it in roughly the same direction as it was pointed before you pulled the distributor. Put the distributor down into the hole, and turn the rotor a little bit back and forth to seat it in the notch. Alignment isn't really a big issue. It will either go in well in the correct position or poorly 180 deg in the wrong direction. Once the shaft drops into the notch, just put the screw back in, put everything back together, and set your timing. Easy job -- really.

Valve cover: You might rip the gasket, or you might not. It might be good to have a valve cover gasket on hand anyway, just in case. Clean any debris from around the valve cover first. Loosen all the bolts just a bit at a time, to avoid bending or warping the valve cover (which would cause leaks). You'll eventually retighten the valve cover the same way. Lift the valve cover slowly, to make sure your gasket isn't about to get ripped. Once the valve cover is off, marvel at the beauty of a flat tappet inline-6 valve train. To me it's the prettiest part of the engine. ;-) You'll need a set of feeler gauges and a couple of wrenches to do the lash adjustments.

Oil filler cap: Mine has a hard plastic O-ring on it. I only discovered it when I made my own O-ring, and it stuck to the plastic O-ring, pulling it off of the cap. Prior to that I thought it was just part of the cap. If it seems tight, it's probably tight enough.

Vacuum line to air conditioning system: It actually controls much more than that. It controls all the air doors in your air handler under the dash, affecting both A/C and heating. There should be a small vacuum line going from your intake manifold, along the firewall, and around to your two magnet valves mounted near the wheel on the other side of the engine compartment. (Well, yours might be a bit different, being a '76. Check your FSM.)

I agree with Coz that it will be very important to pull off your AFM and check it out thoroughly. That's the heart of your EFI. It's got to be healthy. Remove the 3 bolts (being very careful not to drop them). A plastic bag tucked under the AFM might catch them if you drop them. Just loosen the bands on the air boots, shove the boots off of the AFM's lips, and pull the AFM up a bit. Then work the spring off the connector on the bottom, pull the plug off, and lift the AFM the rest of the way out. This will give you a chance to do the spring tension tests on Atlantic Z (with the beer can). I wouldn't adjust the spring to change your mix, though. Just get the tension to specs if it's out. Clean the thing up with carburetor cleaner, spray a bit of WD-40 where the flap hinges, etc. Be sure to shoot carb cleaner through the air bypass passage in the bottom.

Inspect your boots for any cracks -- particularly the one between the AFM and throttle body. Cracks and splits in these things will mess up your mixture.

Now do the yogurt cup test! It's really very easy.

Then do the electrical tests.

Once everything passes, clean up the connector, and put it all back together with some dielectric grease.

... and they +1 EVERYTHING that Cozye (Eric) said!

Edited December 20, 2010 by FastWoman

[Jennys280Z]

Wow thanks for the info. guys. Lots to take in and do here moving forward.

AC vacuum connnection is a small fitting right by the EGR valve on the intake. It's the smallest diameter fitting.

I don't have an EGR valve. You're directing me to the back end of the intake manifold, right? The only connection there is to the brake booster and that one is plugged. Unless there's some kind of vacuum line underneath the manifold I haven't seen, I can't find anything else connected to it.

This car has an after-market Nissan-dealer installed A/C system, so there is an external box with a temp control on/off knob under the dash just off the front edge of the center console. Not isolating the A/C as a source of vacuum leak is unacceptable if I'm going to be confident I don't have a vacuum leak...

Is it possible this particular A/C system doesn't need engine vacuum?

[FastWoman]

Jenny, my 1975 (from long ago) didn't have an EGR, and I guess the '76 is very similar. On my '78, the HVAC vacuum line fitting is very small diameter and is closer to the brake booster vacuum line than anything else. Look at my engine picture in post #41. The HVAC vacuum line is the small red line in the lower right of the picture. From there, the line travels along the firewall, across to the opposite side of the engine compartment, to a vacuum valve assembly. It's quite likely you don't have these magnet valves. One of them feeds a high idle acutator on the throttle assembly (that returning yellow line, next to the outgoing red one). Instead, I bet the vacuum line goes through your firewall through a grommet. It would feed to the heat/vent mode switch above your center console. I suppose it's possible it's not vacuum actuated. Check your FSM. Anyway, the vacuum would be used to open and close air handler doors to divert airflow here and there -- but that could also be done with cables and levers.

Try moving the mode selector back and forth without the engine running. If you hear/feel doors opening and closing, your air handler probably isn't vacuum controlled. If you don't feel/hear much of anything except the sliding/clicking of the switch mechanism, it's probably vacuum controlled.

Someone else here should be able to tell you whether you've got a vacuum controlled air handler. (Someone else????)

[Jennys280Z]

Yep where you have that little red line, I just have a metal bolt closing it off. I'm guessing your larger red line coming out of your manifold and heading to the right is your brake booster vac line. If it was that easy to find I would have seen it. I'm wondering if it's hiding in some hard to see place under a fuel injector wire or even on the underside of the manifold above that heat shield. I see thicker rubber hoses going into the firewall on the passenger side of the car that I know are for the A/C, but it seems likely that my A/C doesn't need engine vacuum. My 1976 FSM says that the A/C does use engine vacuum (and does a lousy job in not mentioning where it comes from too!), but that is the A/C that came from the factory, not the aftermarket A/C that I have. I don't have an A/C setting on my mode selector bar that the FSM illustrates, just that external console (plastic box with a knob) next to it under the dash.

My air handler! Woah that's another new vocabulary word for me hehe. When I move that selector slider back and forth, it always felt "heavy" and kinda hard to move, and I actually remember hearing/feeling doors opening and closing, just like you said.

[Jennys280Z]

The Remanufactured distributors are sold "without Module". I think I said "without Capsule" up above by mistake. Sorry! I suppose these distributors don't have modules because they're a "points" style.

Edited December 23, 2010 by Jennys280Z

[FastWoman]

I think for the dealer AC, the air handler would be of the heat-only variety, as shown in your FSM. I remember having the very same AC in my '75, and there are no vacuum controls necessary to blow cold air.

Be sure the distributor is for a '76!

[Jennys280Z]

I think for the dealer AC, the air handler would be of the heat-only variety, as shown in your FSM. I remember having the very same AC in my '75, and there are no vacuum controls necessary to blow cold air.

Be sure the distributor is for a '76!

Will do hunni and thank you!!! xx

[Jennys280Z]

Cleaned all my fuel injector connectors. Some of them were bad...thick green oxidation...but they're all nice and clean now. Installed a new PCV valve and fan belt. Vacuum at running temp is now a solid 15inHg and I noticed the variance in the vacuum needle has been cut in half from about +/- 0.4inHg to +/- 0.2inHg. When the vacuum gauge needle does move, it's intermittent, and slow, maybe a quarter inch fluctuation every 2-3 seconds or so. So the movement of the needle is far slower than the speed of the engine or the valve train.

I pulled my AFM off. It was difficult for me. Pushing my rubber boots out of the way I might have put a hairline crack on the lip of one, or it was there already, but it's outside of the clamp and not going to hurt anything.

It would appear my AFM was tampered with. I have a 2nd AFM here that I bought on Ebay that appears unmolested. The glue blob on the locking screw is pristine. The glue blob on mine however is mangly looking and while it's possible I suppose that the glue dried in this mangly shape, I doubt it. It appears that one of the teeth on the black wheel (on both AFMs) has a round notch carved out of it. You need good near-vision to see up close to even see it. It looks like a rounded notch carved out of one of the Vs between two of the teeth on the wheel. On the unmolested AFM, this rounded carved position is right at the 12-oclock position. On my AFM that I removed from my car, this notched tooth is about two teeth to the right, ie. about two (maybe 2.5) teeth clockwise from 12oclock. This explains the slightly lean condition I suppose. This would also coincide with Tom Thorman warning us when we picked the car up from getting a tuneup not to "mess with that thing" while pointing to my AFM. I suspect now that he installed hot plugs, adjusted the AFM wheel, and sealed the front cover with a red sealant. Why he did this, I don't know. The car ran awesome though, after that tuneup. Was he compensating for carbon buildup in the engine? Maybe he was ignoring something else wrong with the car and just covering up the problem by adjusting my AFM wheel instead, and all this cleaning of electrical connectors I've been doing has reintroduced the original state of the car (now with the leaner AFM setting)...anyway I wonder if anyone else has noticed that a tooth on the wheel seems to have been marked by the factory.

So I'm interested in moving my AFM wheel 2-3 teeth to the left, but I'm concerned how I'm supposed to hold the wheel from going "SPRONG* when I loosen the locking nut. For you guys who have adjusted your AFM wheels, should I just press the wheel with my thumb toward the back of the AFM housing, or what? This is probably a stupid question, but I don't want to break this beautiful contraption.

I did all the electrical tests per AtlanticZ and the AFM I got on Ebay has the same resistance values of 126 and 226 ohms (pins 6 to 8 and 8 to 9), though until I cleaned the one I bought its values lowered considerably on the other two resistance tests (from 88 to 73, and 216 to 200 ohms, making it exactly what my AFM tested at). Curiously, the fuel pump cutoff switch on the AFM I bought was defective (pins 36 to 39). I looked closely at why (physically) the switch was failing and after some gentle finger pressuring, the cutoff switch works now (ie. infinity to zero resistance upon moving the flap instead of the zero to zero I got initially).

I also did the soda can test on both AFMs to the midway point and they both tested right about in line with the results obtained on AtlanticZ.

I had a real scare cleaning the one I bought, though. Someone used a rubber sealant to seal the front cover. While I was spraying carb cleaner into the AFM body, I must have been spraying it on the outside too because suddenly there was a lot of thick black paint on my fingers (melted rubber sealant) from the carb cleaner. Luckily I caught it early and it didn't contaminate any of the sensitive things under the cover. Word to the wise: Be careful cleaning this thing! *phew*

My brake booster arrived so I'll be installing that soon. Wish me luck! Someone on this site said I should paint it before installing it or I'll be sorry (because of it rusting out?) Biggest challenge to me doing the job has been eliminated: I loosened my brake fittings under my master cylinder, but unfortunately they were already rounded by the mechanics who got there before me. The front fitting was tight and rounded enough that the flare nut wrench moved across the corners. I used a small vice grips insulated by a few layers of shop rag and tapped that with a mallet to loosen the fitting without any further damage to it. I'm still unclear on what a clevis pin is that connects the pedal to the booster but I'm hoping it's exactly like the pins that connect the parking brake to the rear brakes. It's so freaking uncomfortable bending my neck at an angle to work under the dash. Blech! I need a new boyfriend that's better with cars than I am (tall order ) !

I'm still waiting on a valve cover gasket...hopefully will have an update on my valve lash in a few weekends from now.

HappZ new year Classiczcars!

AFM readings listed below:

Pins 6-8 226 Ohms on both AFMs

Pins 8-9 126 Ohms on both AFMs

Pins 7-8 200 Ohms on both AFMs (after extensive cleaning of the bought AFM it lowered to match my AFM from 216 Ohms)

Pins 6-7 73 Ohms on both AFMs (after extensive cleaning of the bought AFM it lowered to match my AFM from 88 Ohms)

Pins 36-39 Originally defective on the bought AFM; operating normally on mine.

"Thermal sensor"? What the heck is that? The air temperature sensor? If so, it showed infinite resistance on both AFMs, not 2.5k Ohms.

Also some AFM trivia for you guys: The 1975-1976 AFMs don't have the mixture screw in the lower rear area of the AFM housing. I suspect this is a feature only on 1977 and later models. There's a little plug there where the "idle mixture" screw should be. I also don't have that air bypass that runs along the bottom of some AFMs, either. What I do have is a little circular flap in the middle of my square flap. The early '76 AFM being tested on AtlanticZ is exactly like mine.

Edited January 1, 2011 by Jennys280Z

[Jennys280Z]

Oh I meant to add...some test results from my last startup.

1. Exhaust isn't clogged (I was shocked about that too );

2. My distributor's centrifugal advance is working, just some light revving from the throttle linkage and it was obviously advancing to 25 degrees advanced and beyond.

3. Someone (Eric?) asked about fuel pressure retention in the rails. Well I installed a fuel pressure gauge between the fuel filter and fuel rails and viewed it periodically and recorded the numbers. My fuel pressure at the gauge held as follows:

Fuel pressure before engine shutoff: 31psi (with 15inHg manifold vacuum)

Fuel pressure immediately after engine shutoff: 28psi

Fuel pressure 5 minutes after engine shutoff: 33psi

Fuel pressure 15 minutes after shutoff: 34psi

Fuel pressure 30 minutes after shutoff: 32psi

Fuel pressure 60 minutes after shutoff: 9pis

Fuel pressure 90 minutes after shutoff: 0psi

Hope these numbers are normal, and indicative of my fuel pressure regulator not being faulty but I have no idea what I'm supposed to be looking at and if these numbers look okay. Can someone please advise? ty

Edited January 1, 2011 by Jennys280Z

[FastWoman]

Wow! You've made a lot of progress!

Corroded fuel injector connectors: I bet that made a BIG difference! You might also check the connectors on the cold start valve (top of intake manifold, near throttle), the three devices screwed into the thermostat housing (thermotime switch, EFI coolant temp sensor, temp gauge coolant sensor). I think you've already been into your TPS connections. When you put all these connectors back, don't forget to grease them a bit with silicone dielectric grease.

The minor vacuum flucturation you see is normal.

Old factory glue globs in the AFM would not have deteriorated at all. They should be very firmly stuck. Yours was probably adjusted by someone. (Just ask the guy who tuned the car. He should tell you.)

Why would the mechanic adjust the AFM wheel? It was to change the fuel/air mixture. Unfortunately he did this without fully troubleshooting the rest of the system, so his adjustments would have counteracted problems elsewhere that were not fixed (e.g. vacuum leaks). The problem with this, besides still having the problems, is that when you fix the problems, your mixture will become off kelter. Rather than to calibrate to the properties of broken equipment, it's better to fix the equipment and then make adjustments only if/when necessary.

IMO, contrary to Atlantic Z, it is not a good idea to adjust the mixture at the AFM spring. A much better approach is to adjust the AFM is to make sure it is mechanically correct. In other words, do the beer can thing to make sure the spring tension is right. You want the thing to peg out at a certain rate of air flow. Forget, for now, what this does to your fuel air mixture. Let's get everything right, and then we'll make the final adjustment to mixture electrically -- in a way that corrects the mixture the same way at every airflow rate.

My AFMs have no notches carved in the wheels that I am aware.

If you need to adjust the AFM wheel, you can just hold the wheel with your thumb (as you suggest) while loosening the set screw. The tension on the spring won't be any greater than the tension on the flap (which you can prejudge). Just mark it before you begin, and don't let go of it, and you'll be fine. No big surprises.

Air temp sensor: It's the thing that looks somewhat like a white pencil eraser, sticking out into the air path in the inlet of the AFM. There are two black wires coming off of it, attached to the connector at the bottom. I forget what sort of resistances you should expect, but you definitely shouldn't get an infinite resistance. You should double check your connections and measurements. I don't know where you would get a replacement sensor if both of yours have gone bad, but I'm sure there's a source. Having this sensor out of whack could affect your mixture quite a lot, albeit not as much as the coolant temp sensor.

You should check your fuel pressure with the vacuum line unplugged. You should get 36.3 psi. Right now you're getting 31 psi running at 15 in Hg engine vacuum (= 7.3 psi), so your total regulated fuel pressure seems to be 38.3 psi -- about 2 psi above spec. Although there's a small error, I doubt it amounts to a hill of beans. When experimenting with my own fuel pressure, I ran my rail pressure up to around 50 psi (differential between fuel rail and engine vacuum) and *almost* corrected my lean running condition by doing so. I think your fuel pressure is probably good enough.

Your fuel rail does lose pressure fairly fast, though. The FSM has service criteria for the max permissible rate of leakage before it's necessary to replace the check valve on the fuel pump. On the other hand, it would be premature to blame the check valve for leaking. Your (worn?) injectors could also be dribbling fuel into the intake manifold after engine shutdown. In any event, the check valve is NLA. You can get an aftermarket check valve to go in the fuel line if you need one. They're cheap and available on Ebay.

Brake booster: Yes! Good for you! Important fix!

Happy new year to ya'!

Edited January 1, 2011 by FastWoman