Zed Head

I have an MSA AFM and it works fine. But for a while I thought that it ran rich. But after tuning and cleaning and fixing a variety of odds and ends I put it back on (I had switched to a junk yard AFM that was leaner), I found that it works great now. No flat spots. I would make sure that everything is to spec. first. And I would use an adjustable FPR to lower fuel supply before I messed with the AFM. I think that when you move the preload on that spring you change the position of the air flow - enrichment curve differently than using fuel pressure or a potentiometer. The starting and ending points move, since it's preloaded (low RPM) and it goes full enrichment before maximum air flow is achieved (WOT high RPM). And it's a weird load on the spring with the air acting on a lever, the vane. I'm not sure that changing spring preload simply makes things richer or leaner everywhere. When you use the potentiometer (richer) or fuel pressure (richer or leaner) you keep the shape but move the whole thing up or down. My logic could be off, but there are other ways to get to where you want to be.

The thing about the EFI system is that you can be at the limits of in-range and if they all add up the wrong way, you'll be rich or lean. A few ohms, a psi or two, a vacuum leak, a mis-adjusted AFM. They can add up. The best place to measure coolant sensor resistance is at the ECU connector. It's what the ECU sees. Plus, the ECU connector itself can get corroded, adding resistance. The ECU is not really in a good spot, a lot of water leaks pass by its location.

You didn't mention ignition timing or adjusting valve lash. Those are two basic tuneup procedures. Very important too. Also, the CSV only gets voltage during starting. So, unless it is leaking, it will have no effect on MPG. The idle drop when you press the clutch is kind of typical of running rich. My car does that if I have it tuned rich (potentiometer). Timing affects that also. 40 psi is 10% too high on fuel pressure. But the gauges available today are often inaccurate. Might try another gauge. The first two things that I would do is to check and set the timing, confirming that it does advance when RPM increase, like it should, and check and set valve lash. Also check your cam timing when you have the valve cover off. And, in the future, the actual numbers are nice to see. "Within range" doesn't mean as much.

I don't know what 72 used but my 76 spray bar had a paper gasket between each spray bar block and its cam tower. Looked stock, by the shape and the cut edges. I was just looking at it the other day. I think that it might also show up on the carpartsmanual site. But any sealing method would probably work. It's not a tight tolerance piece, any way you look at it.

Then the hose with no home probably goes to the charcoal canister. But if it's open the distributor advance won't get its vacuum and you'll have a vacuum leak at the throttle body while driving. Your 76 might also have the vacuum advance solenoid, which only allows vacuum advance in top gear. Complicating hose routing. That's why taking notes is good. If you're not familiar with how all the various devices work it's easy to misplace something or leave it disconnected. The diagrams and descriptions are in the Emissions, and Engine Electrical, chapters.

The vacuum comes from the throttle body. It's called ported vacuum and only sees vacuum when the throttle is off-idle. Throttle closed, there's no vacuum. And there are no hoses connected to the alternator. Great that you're digging in to doing your own work, but you should take notes when you take things apart and/or use the diagrams in the FSM when you put them back together. Based on the hoses to the dashpot and the alternator. there may be other things connected not-quite-right. That could be part of your problem. Off the bat, I'd say that your vacuum advance hose to the distributor does not have a vacuum source. Just a guess. Every hose and wire has a specific purpose and needs to be properly attached. You said that you checked the firing order, but did you check the rotation direction?

Sometimes the tachometer will give a clue. If you're in gear, engine turning, and power disappears but the tachometer still shows the engine turning that would mean you still have spark. If the tachometer drops to zero immediately but you're still coasting in gear with a dead motor, no spark, maybe the module, or the coil, or power to either/both. If the tachometer starts jumping around or reads abnormally high or low, it might be the module. Not a 100% clue about the module, but might tell something. Forgot one thing, that I just recently figured out on my car. One of the PO's of my car had jumped the two pickup coil wires together at the junction box. I never really figured out why until the other day when I was testing old parts to see if they were any good. One of the two pickup coils from that distributor, long since swapped for a better one, was bad. The jumper wire allowed the ignition module to see both pickup coils and use the one that provided a good signal. Short story - maybe one of your pickup coils is bad. If so, the engine would only run when cold.

Doesn't the rear main seal ride on the end of the crankshaft itself? Not a bearing? Just wondering. That's why they make those Speedi-sleeves for the end of the crankshaft. Unless you mean that it was pressed in until it touched the bearing. (Aside - Monroe puts the seal on the crankshaft before installing the shaft.) Might help the process to list all of the problems you were hoping to find causes for. The oil leak, high oil pressure, oily cylinders, etc. And, for your own future pondering, take a good look at the rear main seal area just to see how it's wide open to the crankcase. No oil pressure on the seal. And did you check all of the bearing orientations and locations before removing to make sure that there were no blockages? Don't forget to check the crankshaft passages themselves for blockage. Just living vicariously...

You just need reliable, not powerful. The cam and the transmission don't mean anything as far as the fuel pump goes. Get a stock pump, or try the Mazda pump (search around the internet for model). If your mechanic did all of that work just to find a weak fuel pump, you might still need a new mechanic. By now, using this forum and the internet, you should know more about your car than any of the mechanics you've used. And spark plugs don't get damaged from back-firing.

I circled it for him. That little Sorry game piece shouldn't have a hose attached. The other end of that hose either needs vacuum or supplies it to somewhere.

I broke a center bolt also when I finally took my head off. May be best to use the torque wrench for loosening also. If you can't get it loose at some set percentage (10%, 20%) above the desired torque setting, maybe leave it and try something else. Once you break one you're committed to removal. Better plan some down time just in case.

That's a good catch. So take the plug off, clean it up so it's an open circuit, then leave the plug off and try to start the engine. Much easier than shorting the relay. You've uncomplicated things. I've actually cut the FSM section out on that before but forgot about it.

What was it? A part came loose or there was a vacuum leak?

I forgot to ask what year car also. And if it was stock before you modified. If you browse a few threads you'll see that the more details you provide the faster things happen. Every year of car has subtle differences. When cold, the fuel/air mix is extra rich. After warmup it's leaner. If you have a vacuum leak from the disabled EGR or CSV port, you might be too lean to start. Let it cool and see if it starts. confirm that it's getting spark. Check everything that you worked on to make sure nothing came loose (that's the most likely cause, actually).

The BCDD system is designed to clean up the exhaust from excess HC (unburned fuel) under certain conditions. there's actually a little gizmo on the speedometer that measures road speed, and engine speed is involved too. Has anything else malfunctioned or have you modified some things?

How did it run before you "improved" it? What did you remove, exactly?

Maybe your firing order is off. I can't tell from the picture, but it doesn't look right. 1-5-3-6-2-4, counterclockwise. The engine will start and run with the plug wires backward, clockwise. These engines will also run on three cylinders, maybe even two. OR, maybe you have a vacuum leak that is letting air past the AFM vane. There's a switch in the AFM that opens, cutting power to the fuel pump relay, if air flow drops too low. You might have left a fitting on the intake manifold open. All air must pass through the AFM, except for a very tiny amount for the AFM idle bypass, and the charcoal canister.

Things are only going to move a tiny fraction of a millimeter so the other attached parts won't be affected. Interested to see if it works. I tried on mine, but it was too far gone. Good luck.

What year is the car? They changed a few things over the years. The post on the door jam is adjustable. Maybe yours is loose and has moved inward, or somebody moved it in the past. I re-adjusted mine and found that you can get a variety of closing actions depending on where that post is set.

FastWoman described the pressure switch and alternator pump control. Those are both bypassed during starting though, powering the pump directly. On my 76 when the AFM contact stopped working, the engine would start, run for about three seconds, then die. It would do that over and over. With a low battery the alternator powered relay may not be getting enough juice to keep the fuel pump operating. And a dry engine may not be generating pressure right away even with the switch intact. Collecting all of the facts, if it were mine, I would get a good, charged battery in there, pull the small vacuum line that feeds the AC control bottle (the tiny nipple on top of the intake manifold), and squirt some starting fluid in to the manifold. Ideally, you would have a friend either running the can of fluid or the key, and just keep the engine running long enough to get things moving. If that didn't work, I would probably short the fuel pump relay to keep the fuel pump on. Actually I would probably do that first, just to take the fuel pump control out of the picture. That's a little more involved though. This leaving and coming back to the problem really kills the flow, just on the internet. Must be way worse trying to do it on the car.

I think that his muffler shop created the abomination in the first post. Some of his other posts imply that he doesn't have many good shops to go to. He's in a tough spot.

Actually, I've done a lot of driveshaft (propeller shaft) Googling and not seen that. There is an early short propeller shaft, used with the forward mounted diff. Then the longer 240Z shaft, same length as the 280Z shaft, with replaceable u-joints. Then the 280Z shaft with staked in, non-replaceable u-joints. There is a problem with the side "drive shafts" (not the center propeller shaft) being too long on one side, if you convert to an R200 diff. That problem is described here and there. And the diffs themselves have an annoying growling noise, independent of u-joints or wheel bearings. Could be the bearings though, but they can be checked. How long have you had the car and what have you done to it? BUT, back to your direct question - if you have the forward mounted rear diff, then you have to use the short propeller shaft or remount the diff to the later rearward position to use the 280Z length shaft. Do you have the early diff position? You did not give the year of your car.

I've never heard this at all. Can you give a source for that information? Wheel bearings and u-joints don't really make the same noise when they fail. U-joints get clunky during gear shifts, and can cause a vibration. Wheel bearings, at least the rear ones with big ball bearings, tend to get loose before making lots of noise, allowing the wheel to move side-to-side and up and down and clunk a little bit, I believe. You can jack the back up and lift and tug on the wheel to test the wheel bearings. Crawl underneath and visually examine and pry on the u-joints. There should be zero play.

Disconnect the muffler entirely and see what happens. It will be loud but you should be able to tell if it's down on power.

After seeing some pictures of filter insides, there is a lot of room to pack the same filter media are in to a smaller volume. You'd have to cut one open and look though, to know if that's what WIX did. Seems like a good idea if they did it right.