Zed Head

What are the RPM at the beginning? Before it drops to 500 then dies? You forgot to mention that you have a performance cam. You didn't say what kind of engine management it has either, with carbs or stock EFI.

Thanks superlen. I see pull-up references all the time on the Megasquirt threads. Forgot about them. I thought the purpose of the pull-up resistor was to hold the transistor in a certain logic state. Otherwise it floats erratically. Anyway, you've filled in another hole in my own logic state (pun stretch!!, p's and n's....never mind)...

I almost added a comment about a transistor's usage as a a switch or relay but that's a whole other forum, with lots of discussion possible about nomenclature and terminology and what's actually happening. Regardless, the two pins at the injector plug will always both show battery voltage against ground in the stock Nissan ECU setup with the key on. I just wanted clear that up to help the OP along in his quest. I even went out and measured, again, to be positive I was living in the same reality now as last time I did it, and just to see those comforting numbers on the meter.

Actually, both sides of the plug will measure battery voltage. The reason that its' possible, I believe, is that a transistor is a resistor. You'll be measuring voltage through very high resistance. You could short it to ground but no significant current will flow, until the other side of the transistor has been switched. They're kind of like relays but harder to diagnose. So, one side is battery voltage through the dropping resistors to the injectors - the power supply - the other is battery voltage from the transistor in the ECU. Waiting to switch states and let that current flow. Note - I could be WAAAYYY off and the reason why both sides have voltage. Maybe there's a branch circuit with high resistance to some other part of the ECU. But I am sure that both sides show equal voltage. I've confirmed it, been confused by it, and read about it on other forums.

It's the way transistors work. When the transistor switches states, the current flows, but when you're measuring at the pins the transistor isn't in the state that grounds the circuit. Transistors are weird things. Are you sure that you're getting a good strong spark? I had an ignition module that would give a spark outside the engine, but it was a weak orange spark and wasn't enough to kick things off unless I used starting fluid. Then it would run. With your 78 electronic ignition you should get a nice fat blue spark.

To add a little to FastWoman's suggestions. You want to test from the pins in the injector connectors to ground, with the key on, to measure voltage. You won't see any voltage measuring from pin to pin, they're at the same potential. They'll both show battery voltage to ground, it's a transistor thing. If you're getting good strong spark, and find that you do have power to the injectors with the key on, but no injector action, it could be an ECU problem. The ECU uses transistors like the ignition modules do, and they get flaky when they get hot, and/or old. If you don't have power to the injectors, then the fusible links, as FW says, would be the place to look. The fusible links for the FI harness are two green wires next to the battery, with white connectors. They look like two jumper wires. Check the contacts there, and also check the contacts for the EFI system ground wire, it's connected directly to the battery negative terminal. The ECU uses a wire that runs from the coil's negative post to Pin #1 at the ECU connector to count engine RPM. Every third spark, the transistors in the ECU ground the circuit to the coils, causing them to open and squirt some fuel. It's a batch-fire system, firing all six injectors at the same time.. If you find the problem and fix it, all of this agony will fade away pretty quickly.

As noted earlier, it doesn't really sound like the "heat-soak" problem. The fact you don't even get a pop sounds more like a spark issue. Are you still using the stock ignition module? With the ballast resistor? Next time, or right now, you might check for spark to be sure it's actually a fueling problem.

I think that I saw your post on another forum about the same issue. It will be much easier to just source a complete R200 differential. You have to take the whole thing out anyway to replace the ring and pinion. They're not like Fords or Chevys that can be serviced from underneath the car. The easiest direct replacement for you would be a 3.7 R200 from a 1979 280ZX. Everything will be the same as what you're using now (unless somebody swapped in a 1975 R200, which are unique in the driveshaft bolt pattern). Second easy is a Z31 R200. You'll need to swap the pinion flanges because the Z31's use a different bolt pattern (oddly, they use the 1975 280Z bolt pattern, apparently). If you want new there's always Nissan. Spendy. Here's the cost of a 3.54 ratio R200 - CARRIER-W/ :: Nissan Parts, NISMO and Nissan Accessories - Courtesyparts.com You'd have to ask around to get the part number for a 3.7. Good luck.

I'm thinking the same as EuroDat. The one that you saved is a switch that you won't use. Do you have the upper left item connected to anything? The lower right is for the temperature gauge in the car. Keep that one. It use's a yellow wire with a female bullet connector. Probably in that harness you had in your hand in Post #4. The one that you took off with the extra wire to ground is also a switch, I think it's the one for the second pickup in the distributor. Have you had the distributor cap off yet? You might not even have a second pickup. You don't really need that switch, the engine will run fine without it. It's a fine detail that Nissan added to perfect warm-up.

Can't really tell what this means - " replaced the sensors besides the one with the bullet connector" but you probably don't need the switch on the upper left, in the attached picture. Your 77 probably had a switched, two-pickup distributor, to control timing while warming up but it's not really necessary. You might remove it and see if the thread and hole size are correct. Thought that you were getting a different housing.

These last few posts are interesting (although painful to read in rossiz's case). ZXR616 has a header, as does siteunseen, the only two cases of "no problem" so far. ZXR616's case is a little bit confounded by the fans, but they probably don't run when the car is parked (do they?). I do things to my car that I wouldn't normally recommend to others, although the experiments are typically hidden so the car still looks good, but in this case I'll just describe my ugliness. If you get desperate to just know that the problem might have a solution, go to the wrecking yard and get 2 heat riser tubes from an 80s - 90s Chevy S10. It's a flexible fiber/foil tube that fits perfectly over the nose of the ZX fan. Get a one hour bathroom fan timer from Home Depot. GE brand. Get a ZX blower, or a marine bilge blower (Amazon). Mount the blower somewhere in the engine compartment, tape the tubes together to give the length to go from blower to injectors, punch sizable holes in them over the injectors, mount, attach and wire everything together. The purpose is clear so details aren't necessary. The tube will lay down right on top of the engine, the hardest part is squeezing it between the hood latch and the valve cove. But it's flexible. The timer is attached to the steering column. I reach down and turn it on whenever I park. I used a lot of zip ties for my experiment, which is still there because it works so well. I have noticed though, recently, that I get a little stumble sometimes, even with the fan on. I wouldn't be surprised if gasoline formulations are changing. But if I forget to turn the fan on, it's a guarantee that I'll have a serious heat-soak problem. On the stock ZX fan setup - apparently the ZX fans don't turn on much using the water temperature switch. Better to use a manual timer.

Different scene then. Before and after seems like where you're at. If it didn't make the noise before, but it does now, then you must have altered something when you were adjusting lash. Did you knock one of the anti-rattle (mouse-trap) springs off or bend it? Easy to do since they're right next to the locknuts. Their purpose is to keep the rocker arm tight on the pivot. So it doesn't make noise.

I have a noise from my #1 cylinder. It's been there for about 20,000 miles, no change. I also adjusted lash, and double-checked. And have excellent compression numbers, a smooth idle and otherwise great performance. I've kind of come to the conclusion that some rocker arms and their associated parts just move differently than others and are noisier. Or I have a loose part somewhere that is just noisy, but okay. I decided that noise is not a problem. I've also noticed that I hear odd noises more after I work on the engine.

Since it is a race car, I wonder if whoever started it cold didn't give it the old high rev warm up routine. It's hard to resist since you want to hear that race motor rev. I've seen many people do it over the years. I always cringe. Hard to see why the noise would appear after sitting for so long. On your compression numbers - 20/150 = .13. Cylinder #3 is 13% low. It runs better on 4-6, which fits the bad #3 theory.

Could be height on the two combined gauges - fuel/volt meter and oil/temperature. I noticed that the slot for the light to escape is tiny at the base of the tube the bulb sits in. The light path on the speedo and tach is different. It would be where the filament sits I would guess, and the MSA's sits higher. Still seems odd that you would get a big difference. In person, both of the lights looked the same. Bummer. Good luck.

Stuck timing chain tensioner? Just a WAG. Something that might stick while sitting, maybe. Didn't watch the video the first time.

I've messed with a few old stuck injectors and found that a rap with a light weight wrench or a screwdriver blade will break them free sometimes. Nothing to lose. Try to hit the solid metal base if you make an attempt. If you get to the point where you're considering replacing them, you might also jump the two pins at the injector with a full 12 volts. A quick jolt or two won't burn anything up but the higher current flow might create a stronger magnetic field to pop things free (although I'm not sure how much stronger). Don't short your wires, there's not much room in there. Connect the wires at the injector and make sure they're clear then tap the other end to the battery. Edit - apparently the magnetic field strength is proportional to current so a 12.6 volt jolt might have an affect. Edit 2 - just a note on why they might get stuck. It's a tight fit inside and the gasoline flows past the metal core of the solenoid plug and the pintle pin which seats in the pintle orifice. Dried or old fuel leaves gooey varnish behind, gluing things together. If you get it free, let it run for while and rev it up to get clean gas through to clean things up.

Bad gas? Today's fuel doesn't last very long.

Sounds like the injectors aren't opening. Try swapping injector plugs from a cylinder that works to one that doesn't. It's batch fire so it doesn't matter which is where. Also, try the long screwdriver stethosocope trick to hear the difference between an injector that's opening and one that's not.

I went out and compared Eiko to MSA and took the attached picture. Maybe you didn't get a good ground when you re-installed the gauges. Do those bulbs ground through the sides or do they have a dedicated wire? (I'll probably check myself right after I post this). They have their own wire. Weird that you get lower illumination. Maybe they popped out of their locations when you reinstalled the gauges. It's happened to me. Good luck. Eiko A72 on the right, MSA on the left.

The 116 injectors seem to be the common replacement from back when people knew how to work on these engines. There must be a list or document out there that the mechanics had. FastWoman said that she had a set on 1975 car in the past, and I've seen them on several salvage yard cars. I actually picked up a full set from a salvage yard from a ZX. They worked great for about a year until one sprung a leak at the pintle. I'm 99% sure that 105 - 116 are the same injector except for hose length, based on the flow data that's out on the interweb. I keep my eyes open so that I can get one more to replace the leaker. They're used on VW Super Beetles with fuel injection, a few old Volvos, some BMW's and some Fiats. In case my experiment with 90's era injectors doesn't work.

0 280 150 116 is the Bosch part number. I ran a set of those for a while. They seem to be the design that Nissan modeled their injectors on. They have a more vaporous injection pattern than the Nissan injectors, not that it seems to matter to performance. In your third picture isn't that an A46 - 00? I've not seen any over here that have JECS molded in to them, although I have seen a few ECU's and AFM's with JECS labels. I think that Nippon Denso was making most of these kinds of products for everybody in Japan back in the 70's. I've wondered if the JECS label goes on replacement parts or factory production parts.

If you blow up the injector picture you'll see the typical A46(I think) - 00000 number of the stock Nippon Denso or Denso injectors. They look like they were probably green when new. Pretty dirty now. Those are the older style two part insulators, with the aluminum upper half. Hard to tell if they are better or worse for heat absorption. There's an air gap in the middle which might let them transfer heat faster, but the metal piece might hold more heat. Nissan might have changed just because it's cheaper to make a one piece plastic insulator than a two-piece. And that 35 psi constant is an unknown. Kind of odd, as EuroDat noted. To hr369 - I picked up a ZX manifold, more just to have a complete ZX engine package than for the heat-soak problem, but have realized that you need a longer head pipe to fit the shorter manifold. You'd have to do some exhaust work, it won't swap straight in. Back to Post #37 though, I'm not sure that's the typical heat-soak problem. It doesn't usually wipe out all of the injectors, just a few. The engine starts but runs bad. Yours didn't start all. That seems more electronic or electrical. Then when it did start you said it ran rough for a moment. Heat-soak running seems like eternity although it's only 20-30 seconds. But, if you do have it, it will come back, and you'll get familiar.

How are you checking? Is there software available that checks, or a web site? Found some bewares on resetting passwords. Pitfalls everywhere. Here's one. http://www.tomsguide.com/us/heartbleed-password-phishing-scam,news-18595.html

Playing with the vane at idle only changes idle fuel mix. There's a screw adjustment on the side of the AFM to adjust idle mixture. It's described in the FSM. Have you checked coolant temperature sensor resistance at the ECU plug yet? That needs to be right before messing with the AFM. There's a chart in the FSM, Engine Fuel chapter, that will tell you if the ECU is seeing what it needs to see. Check at the ECU, if it's wrong then check at the sensor. If it's wrong at the ECU but right at the sensor, check the wiring in-between. Best to get each individual item correct before modifying any. They all interact, and the ECU expects them all to be right.