Zed Head

Hook everything back up, remove a vacuum line from the top of the intake manifold and squirt some in that way. The easiest is the tiny one that supplies the heater valve control bottle. That way you'll have fluid in the intake manifold plenum so any air passing by will have to pick some up. Be aware also, that all openings to the engine have to be sealed. Oil filler cap, dip stick tube, all vacuum hoses, valve cover bolted down, etc. The intake system is connected to the PCV system so any leaks in to the engine will be a leak in to the air intake.

How did the spark look? Blue or orange and weak? And when you say starter fluid do you actually mean starter fluid or something similar like WD-40 or brake cleaner (people do things...)? Read the Engine Fuel chapter in the FSM. Those overgrown o-rings and other stuff will make more sense. It should run with starter fluid if you have spark and nothing major went wrong. How did the plug that you pulled look? You might have just re-fouled it with bad gas when you re-installed it.

Size comparison. Edit - Normalized in the post, resized to original when clicked. Handy.

I think that he wants to go directly to electronic with the least amount of fuss. The MSD option would be great if the tachometer problem didn't exist. No load on the points to wear them out, reliable points trigger with a reliable electronic ignition. Pertronix modules have their own issues, like burning out if you leave the key on. If he switches to an electronic distributor then he has to get in to advance curves. It's surprising that MSD doesn't put a little effort in to clearing up the tach issue. I'd guess though, that people that developed the product are long gone and those that are thee now just repeat what the instructions say. What's wrong with your tach operation that you need to develop a circuit board?

The reading on the vacuum gauge tells about the state of the various engine components - valve timing, valve condition, ignition timing, valve seals, rings, power balance between cylinders, etc. If the engine is running, it doesn't tell you anything about vacuum leaks in to the manifold. With a vacuum leak, the engine RPM can increase, actually increasing the intake vacuum or keeping it the same.

To siteunseen's point on the EGR- there have been cases where the internal passages of the EGR have rotted out. If the tube at the intake manifold from the exhaust manifold is open, and the EGR passage in the manifold is rotten, it would be a vacuum leak, even if the vacuum nipple is blocked or even if the top of the EGR has a plate sealing it. In the same vein but a bigger stretch, the internal-hex head nuts in to the EGR passage could be loose. Very unlikely though since they're really hard to loosen.

I saw the word "booster" earlier in the thread and assumed it had been covered, but does the problem happen when your foot is on the brake pedal? A bad booster diaphragm will cause a vacuum leak. Foot-on-brake might be coincidental with high RPM.

Throttle blade hanging due to PCV gunk was an issue documented by Nissan. Addressed with a factory published remedy in a Nissan Technical Bulletin. Just to more clearly restate what I posted before. Easy to test. Stick toe under throttle pedal and pull up when RPM are hanging high. Takes a little finesse but you can actually get skilled at it while diagnosing. If RPM drop the problem is between your toe and the throttle blade/throttle bore interface.

Do you still have the throttle linkage dash-pot? They get worn and sticky. The throttle blades get sticky in the bore also due to PCV backwash. Carb cleaner around the blade will clean it up.

It seems like the tests show that the injectors are okay but the connections aren't. There are two sides to the connection - power supply, and grounding at the ECU. You can check the connector pins with a voltmeter. We just had a big discussion about in another thread. You really need to switch from a phone to a computer to get the good direction on what to do. It's all in the Engine Fuel chapter of the FSM. http://www.classiczcars.com/forums/fuel-injection-s30/52066-no-start-fuel-injectors-not-firing-1978-280z.html Datsun Service Manuals - NICOclub

What were the results of your tests? And where is ZUPPAN?

What year was it? The early S30's (up to mid-74) are known to be more flexible than later.

Beware that outside of the relay may not represent the condition of the inside. They're easy to take apart, just bend the little metal tabs.

What is the idle speed before it starts to stall?

You should consider your skills, relative to what the car needs. Everyone has their own specialties and areas that they like to work in. Some people do body work, some paint, motor-heads, electrical, etc. Do you know much about small block chevys? Cold start behavior is way down the list of things to worry about. It's a 77 so you might need to pass emissions standards. Find out what's allowed in your area. Make sure the title is clear and correct. Since summer in your state is only about 3 weeks, you should have lots of time to fix any problems. Make sure the problems are ones you'll enjoy working on.

beerman, since you know the Mastech, can't he just get the probes where he wants to measure and turn the knob until he gets an in-range reading? Then re-zero, if he needs to. I've been spoiled by my auto-ranging meter which also reads negative. But I bought it because my old Micronta meter wouldn't calibrate to zero anymore.

I don't think that you want a coil with a ballast resistor. With the MSD you can use one of their high performance coils, with no ballast. The points are only used to trigger the MSD so the ballast isn't needed anymore, if you get a better coil. Many people have problems with getting the tach to work. I looked at the instructions though and see something I haven't seen before that might explain why some get it to work and some don't. Copied it below, from Page 7 of the 6201 PDF file. I think that the original ballast should work, I don't know why you'd need the Chrysler dual ballast. If I understand what they're trying to say, that reducing current through the points will keep the tach working. As I read the instructions I realized that they're not very well-written, and give poor explanations of why the wires are connected where they are. Good luck. BALLAST RESISTOR If you have a current trigger tach (originally coil positive) and use the White wire of the MSD, you can purchase a Chrysler Dual Ballast Resistor (used from 1973 - 1976) and wire it as shown in Figure 5.

Not sure that you understand what resistance is. When you disconnect the gauges you wouldn't get rid of resistance, you would create infinite resistance (ignoring the conductivity of air). "No resistance" would be a very very small number or a zero on your meter. High resistance, or "some" resistance would be a number from typically 60 to 1,000's of ohms for most of the tings you'll measure on your car. Infinite resistance would be what you get with the meter probes touching nothing at all, just air. You really need a meter that you understand to get good measurements. The cheaper, or older, meters have an adjustment knob on the face. After you pick the range, you touch the probes together and move the knob until it shows zero. Then you know what "no resistance" looks like. If you have a small light bulb, like a dash bulb, handy you can take a measurement on it to see what "some" resistance looks like on your meter, with one probe on the center electrode on the bottom and the other probe on the shiny metal side of the bulb. A typical bulb will measure about 4 ohms. You need to get good resistance numbers, and know what the proper range of resistance is for what you're measuring. Some resistance is good, it's how things work.

The Nissan "goop" might be for anti-rattle, or -buzz.

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.