NewZed

What happens to resistance on the tach line with power and ground connected to the distributor, but nothing on the tach line. If it's a switch like the HEI module it will go from low to high. The FSM says it's a pulse,which may or may not be a voltage. Maybe you just need a bigger pullup resistor. More guesses. At the bottom of Moby's writeup he says that a 2K resistor is for 12 volts and the 1K is for 5 volts. From the writeup: ____________________________________________________________ *Pullup/Pulldown resistor quick course You use a pullup resistor to get your line(or pin,connection) to some voltage (5,12, etc). Suppose you want a pin to have 5volts. If you just add a wire to 5 volts there is nothing to limit the current and if the pin happens to be an input to a transistor that is switched to ground then you have a short to ground from 5 volts and you burn stuff up. So instead you add a resistor to the 5 volts and the resistor will limit the current according to ohms law. Current is voltage divided by resistance. If you put a 1k ohm resistor to 5 volts then if the pin is switch to ground by internal electronics it can only draw 5 milliamps max(the resistor current-limits the path). A pulldown is similar except that you want a pin/wire connected to ground and you want the path to be current limited. To size the pullup or pulldown correctly you should know what the circuit is that you are adding the resistor to. But as a general rule you can use a 1k resistor for 5volts and a 2k resistor for 12volts. That limits the current to a few milliamps which is conservative. Sometimes the circuit may require more current to operate properly.

What happens if you just measure voltage at the tach signal to ground, with power and ground to the main distributor wires? I'm just curious as to how the tach is designed to work. The FSM implies that it outputs a voltage on the two output wires, zero or something (1982 EFEC-61). I think that the pullup resistor might be for the Megasquirt side, not the distributor side. Maybe. I thought I understood the pullup resistor for the HEI module because it pulls up one circuit (G and W) so that it can control the other (B and C). Normally G and W would have negative and positive voltage from the VR pickup. I don't get the purpose for the distributor tach line, since the "control" is from the other side. Unless it's completing a circuit to ground through the tach line and somewhere, like the distributor body. Just thinking in writing. Is your distributor body well-grounded? Maybe you're missing a ground circuit somewhere. Don't place too much value in any of this. Basically, I'm just bumping your thread until someone who knows speaks up.

Edit - I don't know enough about electronics to guess anymore. I would certainly try to isolate the distributor from the other components though. Don't test with everything connected together. Interesting problem. Good luck.

It's easy to mis-visualize the parts.

The simplest test for you would be to view fuel pressure when the problem happens. Get the vacuum number from your dash gauge and the fuel pressure number from another and you'll have numbers that tell you something. The standard practice is to T in a service gauge and run the hose out of the partially open hood to where you can see it while driving. Your idle numbers don't show anything wrong. But, more to the point - does the engine run differently above 4000 RPM? You never really said. Or are you doing all of this work because your AEM gauge shows a number? You might just have an exhaust leak.

Do you have a good ground on the tach's ground wire and on the pullup resistor? I'm more curious now just to see what you're doing. The details aren't clear, no way to tell what you really have wired and how.

Where is this Aeromotive filter? Before the pump or after? The stock Nissan pump is huge so that it can pass enough fuel to support the engine while still filtering. You might have the wrong filter. The high impedance injectors won't hurt anything but if you left the resistors in place you're running less current through the system, including the ECU, than designed. Your pressure and intake vacuum numbers don't add up but 38 psi would be sufficient pressure to make things work right. 19 inches of vacuum is 9.3 psi. 38 - 9.3 = 28.7. Your picture of the gauge at idle shows 25. Probably just two bad gauges, combined, or the camera caught a bounce. Who knows. If the lean-out happens even when you work up to 4000 at part-throttle then the TPS probably isn't a factor.

No, the suspension systems changed in mid-1974.

The small market may lower the value of time spent returning e-mails and responding to queries. I didn't get any replies either. Maybe one of those "here if you want it but we don't have time to support it" deals.

About halfway down the first page in this link there's a diagram (little yellow box) showing the distributor wiring. Connect power and ground to a battery and measure voltage on the "tach signal" from the distributor while you spin it. If you get the zero and five, then your problem probably isn't the distributor. You might need the pullup resistor to get a consistent signal. http://forums.hybridz.org/topic/23244-megasquirtnspark-mssmsns-installation-guide/

Your 25 psi at idle implies 22 inches of intake vacuum, which is very high for the 280Z, I believe. And you should have seen 36-37 psi when blipping the throttle. Disconnect the starter solenoid wire and turn the key to Start. The fuel pump will run but the engine won't turn over. Or disconnect the vacuum hose to the FPR while the engine is running. You'll get full pressure on the gauge, it should be 36-37 psi for a stock regulator. Why not use the FSM or the Electronic Fuel Injection Guide to know that the TPS is right? The early one was written for your car. Test at the ECU connector. http://www.xenons130.com/reference.html Those Ford injectors are one lb/hr higher rate than stock. You should be running rich. Are they low or high impedance? If they're high, did you bypass the stock resistors in the power circuit? Maybe the injectors aren't opening correctly. Just some possibilities.

Compare your diagram picture in Post #2 to diagram in Post #1 here - http://forums.hybridz.org/topic/23244-megasquirtnspark-mssmsns-installation-guide/ Here's a followup thread to that one with more information - http://forums.hybridz.org/topic/56329-megasquirt-overview-for-newbies/

Megamanual? You haven't described the ignition module, igniter, coil driver, IGBT.... What is supposed to be controlling your coil?

No gauge, it's all guessing.

If you grease the steering rack bushings well they will squirm around to fill the gaps when driving. I had about a quarter inch gap I couldn't close but just torqued bolts and drove. They're elastic. They fit perfectly now.

http://www.nicoclub.com/archives/use-nicoclub-coms-factory-service-manual-database.html

Considering the MS document, doesn't that just mean you were looking at the plug upside down. Or something like that. The order is the same for each. The line drawn on the LS2 picture implies that it also grounds the A pin through the coil body. Maybe a resistance check of the four pins to the coil body (mounting points) would be the easy way to find the A pin, as a reference point. For future wirers.

Teach a man to fish or hand him a fish, plus several more. Are you sure that the curves are the same? I can't find the full curve for 1976 (or 1973) but the FSM says that 116 ohms = 50 C (BE-46, testing the gauge with a resistor). Plotting 1995 Pathfinder data, (EL-41) gives ~96 ohms at 50 C. It's on the low temperature end so less relevant, but still not the same.

The 3.7 is going to make your odometer readings high unless you changed the speedo gear in the transmission. Same with low profile tires, it's diameter that matters, not width. so your calculations may be off a little bit. My 76 essentially stock 280Z gets about 20 mpg, mostly city with some highway and it runs great, with plenty of power,and very little gassy smell. I've seen a variety of "surveys" on forums and it seems like most people are around 20 to low 20's on mileage, on the pre-O2 sensor cars. I also have a potentiometer on my cooling temperature circuit and can "trim" the circuit while driving, from lean to rich (I have an adjustable FPR so start a little bit lean). The engine is much more responsive on the rich side. Probably because there is no acceleration enrichment until WOT on the early EFI system. So I run on the rich side, for fun. The higher gas mileage people may be leaving some engine response on the table to get their high numbers. It's not obvious either, unless you can play with enrichment while driving. Mileage is also worse in the winter than in the summer, possibly because the air temperature compensation is not quite right in the stock Nissan ECU algorithm. Just a guess on why, but I get 1-2 mpg higher every summer when it's nice and hot out. The 20 is a summertime number. The starting then dying with the angry noises isn't normal. You haven't mentioned your timing specs. either. "Fine" at idle may not be fine while driving. Ignition timing can have a big impact on gas mileage, and performance. The distributor advance mechanisms have to work properly, they're often corroded on the old distributors and don't.do what they're supposed to do. Have you given the engine a good tune-up, including valve lash adjustment? It sounds a little noisy in the video and your vacuum readings are on the low side. By the way, those $15 JEGS gauges aren't very good, I had one that hid a fuel pressure problem from me for quite a while, a few years ago.

Compare resistance values between the two sensors. Use a meter or check the FSM's. My 95 Pathfinder FSM has resistance values listed, just like my 76 280Z FSM. They call it the "thermal transmitter" in 1995.

Get a voltmeter and start probing. Eventually you'll find a spot that has no voltage when it should. Once you try it you'll never go back.

A lot of the P79/F54 ZX engines have the K cam. It seems to have been neglected when someone put the specs. out on the internet (specs. which may or may not be totally correct anyway). It's the standard NA cam for the ZX engines. The specs. in the FSM are probably as close to right as you'll get.

Total rookie on head work, but would new valves be an option? If you can't find pads, or they're very expensive. Maybe the valve tips were dressed to equalize lash and it was overdone. New valves might get you back to where you need to be. Page 80 of the Honsowetz Modify book says that Nissan Motorpsorts has up to .330" stock lash pads. Of course, that was in the year 2000. They might be out there somewhere. Feel free to ignore...

Save the thing you want to paste as an image (.jpg or whatever), click More Reply Options on the Hybridz page, and attach the image. A great tool for saving images is the Snipping Tool in Windows 7 and beyond. It's in the Accessories folder. It saves files with a .png extension.

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