FastWoman

Thanks, Sparrow, but wrong dashpot. I don't mean the one on the distributor for the vacuum advance, but the one on the throttle to ease its closing. I'm afraid you're over my head with timing tweaks. I do just stick with stock on that one, because I'm afraid of getting myself in trouble. Perhaps with my new digital advance timing light I might get a bit fancier. (My trusty old Sun light -- late '70's era -- finally bit the dust. ) Tomo, an oil-filled dashpot would probably work better! Those OEM air-filled dashpots are horrible, ill-conceived things! I think I'll just need to wander through a wrecking yard someday.

Sparrow, I think it's extraordinary you're calling people stupid and silly after only 12 posts (not that other posts of yours aren't helpful). This isn't that sort of forum. We're a bit kinder and gentler here. People here almost always offer constructive suggestions and solutions here without getting insulting about it. We have people here of all knowledge and skill levels, from rank beginners to Z restoration professionals. Argneist's problem, BTW, has already been solved. It was a hole that eroded between the EGR inlet on the intake manifold and the main body of the manifold, resulting in LOTS of exhaust gas bypassing the EGR valve and flooding/killing the #4-#6 cylinders. IMO, that's a bit less than obvious. In fact I've never heard of that happening on a car before. I have to give this beginner a whole lot of kudos for diagnosing this weird problem (with a bit of help from his friends on this forum), when a few professional mechanics thought there was nothing wrong. (Note: every other cylinder was missing in the firing sequence, so the exhaust beat was steady.) I mean, we're talking about a guy who at one time was terrified to turn a screw, for fear of hopelessly destroying his car. (Sorry, Argneist! ) And here he/we accomplished something the pros in his area didn't, because they didn't have faith in his car, dismissing it as one of those bumbly old antiques that "just runs like that." I think that's what this forum is all about.

I LIKE the timer idea, darom! I suppose the downside is that you pull up to a light, your engine dies, you go to restart it, and you have your switch in the wrong position. The horn blows for 10 sec, and you royally wizz off the guy in front of you! Leonard, this relay doens't look too bad, although I have no idea how reliable the company is that's marketing it: http://www.wolstentech.com/products/timedelayrelay/timedelayrelay.php You'd want the positive trigger relay TDR-P. You'd send +12 to the trigger input from the ignition key. You can set your delay for whatever you wish. This unit has both on and off delays, so it's very versatile and could be used on other projects. The price is fair, IMO. It can switch a load up to 10A. As the OEM horn is fused at 10A (at least per my '78 FSM), it would be fine to use it to provide power even directly to the horn. However, I would use it to power the horn relay instead.

Here's one I've thought about trying: Hook up a switch between the key switch and the starter. In one position, it sends current to the starter solenoid when the key is turned. In the other position, it sends current to the HORN when the key is turned.

One more little gremlin dead! Now that you know each of your cylinders is pulling its weight with a dry engine compartment, maybe see what happens after you've hosed everything down. I'm guessing you might have some badly sealed ignition parts that might need a touch of dielectric grease.

Hey, you! Get back to work! :ogre:

If I were you, I'd replace all 6. You don't have to mortgage your house to buy the OEM injectors. Lots of people pay to have them cleaned up and flow-tested, but if yours is leaking, it's no good anymore. The BEST solution, imo, is to replace with (cheap) Sorensen or Standard Ignition injectors.

To make certain all your cylinders are pulling their weight, you can unplug injectors one-by-one. When you unplug an injector to a working cylinder, the RPM should drop. If the cylinder's not working, the RPM won't be affected. This could rule out issues like clogged injectors and faulty ignition wires/plugs.

Twist, solder, and tape is good, but only if the tape is then taped up (and stabilized) inside tape wrapping around the entire bundle of wires. (Heat shrink tubing is better, BTW.) Nissan constructed some of the harness this way -- well, with crimping instead of soldering. Check to see if your insulation came loose somewhere on your CTS wiring. If you have a short, that could create an extreme lean condition. The best way to troubleshoot all of your wiring, BTW, is to do the electrical tests described in the FSM at the level of the ECU's large connector. If you have a short or open circuit somewhere, you'll be able to locate/measure it there. Yogurt cup test: Dunno.... Search around your kitchen for a cup, bottle, jar, or whatever will stuff inside the mouth of the boot and seal it. I only joke about the Yotastic yogurt cup, but it's not something essential. Just find something that will stuff up the hole. Keep looking! There's a gremlin or three hiding in there SOMEWHERE!

Dunno... Maybe if it were an Auburn or Duesenberg... or even a Toyota GT2000... But going through such heroic efforts to restore a Z would seem silly.

Sort of late to the conversation, but I inserted this midpipe muffler on my MSA premium exhaust: http://www.summitracing.com/parts/MPE-10436/ The fit was fine. My installer was a bit worried about the size, but he had no trouble doing it, and it looks great. No clearance issues.

2.5 is plenty large. I have MSA's premium 2.5 exhaust with a midpipe muffler to tame it a bit. It's mellow, somewhat louder than I'd really like, and it almost has a tiny hint of ricer-car crackle to it. I sure as heck wouldn't want anything larger. Remember that the original exhaust was just under 2". If you go too small, you get back pressure. If you go too large, you get too low exhaust velocity and don't benefit from exhaust scavanging. There's a "just right" middle zone that's probably right around 2". But try to find a 2" aftermarket exhaust!

... or alternatively, maybe you could give both of your carbs a shot of starter fluid when this happens, and see if the engine will fire briefly.

It's a completely analog ECU! You might have air in the lines. The Z can be a bugger to start when there's air in the lines!

Zed, "intake/crankcase leakdown test" it is -- best performed with a yogurt cup. Yeah, KD, that will tell you whether you have any issues with the PCV hose. The test will instantly rule out quite a lot. And indeed, we're talking about the miniature christmas light bulbs. Just pull one out of its socket, and plug into your injector connector. It's a similar resistance and will flash when you get voltage to the connector. I'm glad you've got some new connectors on your injectors. Although you apparently didn't do your thermotime switch and cold start injector connectors, those wouldn't really be a problem while the engine is running. There's a drop resistor assembly beneath your master cylinders that's in series with your injectors. You might check those connectors. Also, how were all the bullet connectors inside your engine harness when you peeled it apart? And how did you make your new connections? (Some people just twist wires together, so I guess one has to ask.) Tell me about the connection between your AFM and throttle body. You've rigged something there besides the stock boot. Is it completely air tight? If you've got unmetered air leaking into there, you're going to have a lean-running issue. You can still buy a stock boot for roughly $50 from a Nissan dealer. Regarding the vacuum: Your engine won't run badly because of a low vacuum. Rather, you'll have a low vacuum because your engine is running badly. You've reversed the cause and effect. Ignition: You might try spraying down your engine compartment at night (with a cool engine, please!) and seeing if you can replicate your poor running. Then with the lights off, watch your engine for any stray sparks. You could easily have a tiny break in your insulation or a carbon trace somewhere, resulting in an ignition short. No more ideas tonight!

VERY NICE! FAIW, you can also compound and polish plastic just the same way as paint (and with the same products). If you think about it, paint nowadays IS plastic.

PS your vacuum of 14.5 reflects an inefficiency somewhere. It always does -- any engine, anywhere. (Well, maybe not with Model T engines. Dunno.) You should be pulling 17 or 18. So when your engine was running fine before with 14.5" vacuum, it really wasn't. You just didn't realize it. Thus my point, almost all old engines have multiple problems of which their owners are absolutely unaware.

Looking at your video, I see some bare wires beneath that loom material, and I see a crumbled rubber boot on your cold start valve. I'm guessing those are your original connectors. If so, the ones on the front of the engine and on your injectors are probably crumbly. I'd replace that stuff. I'd also wrap up your wiring harness with electrical tape, rather than the plastic loom material. That will keep the water out if you wrap it well. Oh, and just because you have electrical issues doesn't mean you don't have other issues too. In my experience, any car older than 10 years, maintained in a typical manner (or even fairly well) has at least a few engine problems, if not many of them. Even my own engine has one problem -- a faulty air regulator (Grrrrrr.... Just replaced it. Might have to break down an order a NEW one.) So if I were you, I'd go on a general search for other issues, including vacuum leaks. You should contemplate this issue while enjoying a refreshing cup of Yotastic yogurt.

KD, considering your carwash experience, I would now be astonished if your problem isn't electrical. Pull the cover off of your throttle position sensor when that happens to see if you have water between the contacts. If so, just blow it out. That's a common car-wash-related problem. Obviously ignition is the other, as you've alluded. I'd replace every ignition service-related item that has any age on it at all -- cap, rotor, wires, plugs. I suppose it's possible your ECU got a blast of water, based on what you're writing. However, it has a pretty tight box and sits behind that plastic kick panel (or is yours removed?). Just have a look: Pull the big connector (WITH THE IGNITION OFF). Is there moisture inside? Open up the box. Is there moisture inside there? There's your answer. Your ECU triggers off of the (-) terminal of the ignition coil, so you might have an issue there. Just another thing to check. My best guess is that you've got some bad connectors in the engine compartment -- crumbly, leaky, corroded. How would you describe their condition? I'd pay special attention to the sensor connections -- TPS, CTS, AFM. I'd say you got 1/4 mi down the road before current passage started corroding one of your connections, to the extent that electrical contact was lost. All of those Bosch connectors have water seals. I'm guessing yours have lost their integrity. (Am I right?) Replacement 2-conductor connectors are available on Ebay very cheaply. A seller named "forest" (something like that) sells them. Search "280Z injector connectors" to find them. It's the same connector for the injector, cold start valve, thermotime switch, water sensor, and air valve. You can snip the 3-wire TPS connector off of a more modern junkyard car or pay an outrageous price for a used one off of Ebay. Your AFM connector should be in good condition with a bit of cleaning. Use dielectric grease to improve all of your connections and seal out water.

Well, a low CTS resistance is going to result in a bit leaner running; however, I don't know whether that small error is going to have that large an effect (stumbling, bucking, backfiring -- through intake, I presume). If the problem occurred suddenly, I'd probably still look for an electrical contact or part that's bad. Do the full round of electrical tests in the EF section of the FSM. It doesn't take all that long. If you don't find anything there, then you should probably just go on a hunt to look for anything out of whack. Sorry, but there's a lot of stuff: HERE'S A ROADMAP FOR YOU, in no particular order. Others may have some additional ideas: Yes, do the yogurt cup test to make certain your system is tight. It's very quick and easy, and the results are unambiguous. Then while the AFM is out of the car (for the yogurt cup test), open it up, and check the tension of the clock spring, using the method outlined on the Atlantic Z website -- tech tips -- beer can and water method. Clean all the contacts, and do the electrical tests in the FSM. Reinstall, but don't seal back up the access cover yet. Pull your distributor cap to see whether the breaker plate is stuck or whether it rotates freely. Those go bad and jam up. Then check your timing to see if it's within specs. Read your plugs. Better still, show us pictures. One list member had a goofy problem where his EGR leaked and fouled out his #4-#6 cylinders, so that he was running on only 3 cylinders. Ya' never know what you'll find, but we definitely knew something was up when he showed us his plugs. (Note: I couldn't talk him into doing the yogurt cup test. He would have retained much more hair on his head if he had done it in the first place! ) Put your multimeter on your plug wires to make sure they test good. (See the FSM for resistance per meter.) Also run your engine at night in the dark to see if there are any stray sparks. This would be a good time, in general, to replace any old ignition components -- cap, rotor, plugs, wires. Use NGK spiral wound blue wires and NGK plugs -- probably B6ES-11 on yours, but check your manual. Pull your valve cover and adjust your valve lash. Put your transmission in 5th gear, and push it to rotate the engine to TDC. Check the alignment marks on the cam sprocket. You'll be looking for wear in the chain that would cause your valves to be late in their timing. (Note: This is not a "suddenly bad" sort of thing, but it should be checked.) Check your compression. Now if your compression is good, valves are right, timing is right, ignition is good, fuel components are good, FUEL PUMP AND FPR ARE GOOD (WOOHOO! ), AFM is to spec, and there is no EFI component you can find that is failing, it's probably the ECU that's gone wonky. ECUs can go suddenly bad via a fractured solder joint. ZTrain had this happen, and he fixed it by opening it up and re-flowing all the solder connections. They can also just drift out of spec over time, as their semiconductors get tired (see above). This happened to Cozye and me. In both our cases, the ECU drifted towards shorter and shorter pulse widths, and we corrected by adding resistance to the coolant temp sensor circuit. To check whether you're running rich or lean, you can tweak the vane of the AFM with the engine running, to open it up or close it off a bit. My guess is that your engine will pick up rpms when you open the vane a bit, indicating that it's running lean. Anyway, it's a lot of stuff to check through, but if you're methodical about it, you'll come out the other end with a nicely running engine, probably after finding at least a half dozen little problems that added up to a bigger problem.

Very interesting... although I looked at the diagram of the damper in the FSM, and it would appear to operate differently from how the little writeup indicated. In the Datsun damper, it's not necessary for the diaphram to be moved by fuel pressure in order for fuel to flow. Maybe a different' design?

Looking at your pics, I see your EFI retrofit. Is that a MegaSquirt system? Please share all your experiences with it. A few of us have been talking about making the conversion. Oh.... And welcome!

Wait a minute, there! There's nothing humble about a 280. No need to make apologetic sounds. Some people prefer the 280 to the 240. You've got fuel injection, which is a wonderful thing when it works right. In fact your '75 has the very FIRST fuel injection in the Datsun lineage, and although it's not the BEST fuel injection, I personally believe the intake system on that year is the prettiest. Also, while the 240 may be a better sportscar, the 280 is a better GT. If you're actually going to drive the thing on a daily basis, as I do, that's a very good thing. Both models (and also the transitional 260) are good machines and good examples of what they are. So be proud! Don't think of your 280 wistfully as a 240 look-alike with different bumpers. Think of it as a 280!

Well, I fall on the side of "rip the crusty old junk out," but it's a matter of preference. If you keep your fusible links, I'd replace with new. You can still get the little things. You can also buy fusible link material to roll your own. In my case it made sense to replace with MaxiFuses because my fusible link assemblies were broken (fractured bases) and just hanging on the end of the wiring harness. I have to say I love my MaxiFuses, but if my fusible link assemblies had started off in good condition, I'd have probably kept them. Darom, do fuel dampers actually get clogged up? I thought that was a pretty trouble-free part. FAIW, I've read on this list where one person had a plugged up metal fuel line and had to replace it. When I was diagnosing my own system, I simply opened it up past the fuel filter and ran the pump. I got plenty of volume, so I was satisfied I didn't have any restriction of flow anywhere.

Yay! You can do it, honest! We'll be here for you.