Zed Head

Here is Nissan's documentation from the 1980 EFI book. Since you're mostly looking at a warm engine, the resistance at 180 is probably the most relevant. I'd guess that their spec is 250 to 275 ohms, by eye (edit - probably more like 300 to 350 on the high end since the line is 500. Of course, they are just lines on a piece of paper [pixels on a video screen]). Seems to match what CO's plot shows. Yours all seem rich. Did you measure at the sensor pins or at the ECU? Might have resistance at your bullet connectors in the sub-harness oe at the EV1 connector itself.

I'm trying to get past the assumptions. The means to know are at hand...

Just curious but I had an exchange about this in the past and proposed that maybe the cap would still seat well without the gasket. Could you try yours and see? I think I was just being obstinate and that I probably actually had a gasket on my old cap. My memory was of looking at it and being surprised that Nissan used two hard flat surfaces to seal the oil filler area. But the car was gone so I couldn't check it.

It's actually a shaped gasket, by CO's picture, not an o-ring. The question is, does it still exist in the cap. The fact that oil is leaking from two places kind of suggests blowby pressure. Maybe a clogged PCV valve or hose.

Oil smoke has a distinctive smell, and so does gasoline vapor. Might be worthwhile to run through the cloud and see what it smells like, if your nose works. And water vapor dissipates pretty quickly. You could put a smooth cold surface at the exhaust pipe, a mirror or a piece of chromed metal, and see what condenses. If it's as bad as you describe you should get something.

Details might show something. "Did" is not enough. Valve seals can get damaged during installation. You might even see something just by removing the valve cover and taking a look. Is there blowby? Smoke from the oil filler cap? Wrong/poor rings and ring sealing should show up there also.

It has the same chamber volume as a P79 head. With flat top pistons it will have the same CR as a 280Zx engine, 8.8. One benefit is the lack of exhaust port liners.

Are those the solid rocker arm pivots? They look adjustable. Should be fun. What will you do with it when it's done? And, have to ask - what is all of that stuff?

Was the ECU replacement new or just a different old one? The symptoms do fit a bad ECU. But a bad ignition module is also a possibility. If the tachometer needle is showing high RPM when you know it's low that is a sign of a bad ignition module. The ECU opens the injectors for every third ignition pulse. So it's dumping too much fuel because the ignition module is creating too many sparks. SteveJ can do a module swap if appropriate. And, banging on the ECU is the old ECU testing method.

This seems most likely. I remember way back in my early car days spending a lot of time and effort trying to figure out a similar problem, only to find that it just needed a tuneup. Really, just new clean plugs. The carbon will absorb moisture while sitting and get more conductive. Then you get no spark. 40 psi is high on the fuel pressure. Many new aftermarket regulators seem to run high. 4/36.3 = 11%. That's a lot of extra fuel. Plus, if you have a new aftermarket AFM it might be running rich also. My MSA reman did, bought back in 2009/2010. And, I've also read that there is a lot of variability in the coolant temperature sensors. An adjustable FPR like Hussein Holland and I were talking about might help solve the running rich problem simply. Watch out for the shiny aluminum adjustable FPR's, they almost all leak pressure rapidly when the pump shuts off.

I'd pull injector plugs. Electronic ignition systems don't like it when their spark can't get to its intended destination. It will go somewhere though. I damaged an HEI module when I left two plug wires off.

Is it running bad rich or running bad lean? Bad lean would give you some intake popping and bucking. You might check the FPR vacuum reference hose for fuel. That is something that could go bad suddenly. Also, if you still have EGR might be worth checking that. Maybe a channel opened up in the EGR passage. And, of course, the old thrown rocker arm. Fairly common after an engine has been sitting. You can eyeball that under the valve cover.

Could you add some poorer pictures from farther away? Throw some more dirt and grime on also. Ha ha ha...

The print on the actual part says 0 - 5. But the eBay text does say 3 - 5. Who knows.

Mike replied to a Support request that I made. In case anyone else has concerns. Thanks Mike. Sorry to be a pain, but it's a big deal these days. There really are hackers out there, and many of them are pretty good at what they do. https://www.classiczcars.com/support/1485/

Think about plumbing.

The bike shops also sell the regulators. Can't find specs though, yet. Edit - Looks like they are three bar. (https://www.ebay.com/itm/222779941480) https://www.denniskirk.com/search/fuel+pressure+regulator.q https://www.amazon.com/Fuel-Pressure-Regulator-Davidson-1995-2001/dp/B07W7QM3SM

The other benefit of that first one is that it probably does not leak down when the pump is off. The shiny anodized aluminum adjustable FPR's all seem to leak down because they use a ball and seat for the valve. The holder that you linked for the Harleys seems to be a two exit port system like the 1978 and later regulators. Looks like it would probably plumb in nicely on a 78 or later factory fuel rail. It took my brain a while to figure out how they worked when I first saw that style. The valve is actually inside the FPR, probably the flat steel seat. https://www.denniskirk.com/v-twin-manufacturing/fuel-pressure-regulator-housing-63773.p1802126.prd/1802126.sku https://www.ebay.com/itm/111963132346

Have you measured the pressure coming out of the mechanical pump, between the pump and the carbs? Don't know if you mentioned it, this is page 11.

The first one looks very interesting because it's adjustable and has a vacuum reference port. Do you have some internet links or part numbers? I've found that many of the older parts that would be valuable for the Z's are not actually available anymore. I built a vacuum reference adjustable FPR for my engine but now you can't get the FPR that I started with. NLA.

Found a book. https://www.amazon.com/Carburettor-High-Performance-Manual-SpeedPro/dp/1787111687

I'll bet that SU's have problems with high performance cams due to the nature of how they work. One problem with cammy engines is that they tend to run poorly at the low RPM where they sound the coolest. Really, to smooth things out, idle PRM should be raised to give a more consistent intake vacuum. But then you lose the lope. That piston is probably jumping up and down with each intake pulse.

Once the pressure is set the gauge can come off. No real need for a permanent gauge.

These look decent. Holley has been collecting brands and rebuilding their reputation so quality is probably fair. A selection of psi ranges. You would want the second one, I think. https://www.summitracing.com/search/part-type/fuel-pressure-regulators/product-line/holley-fuel-pressure-regulators?SortBy=Default&SortOrder=Ascending

I wouldn't use it. A decent gauge, those hose clamps, and pieces of hose would cost over $25. It's universal because they can change the ad copy to fit any application. 140 psi. "adjusts oil flow"? "ideal weight"? Not good... Fuel Pressure Regulator Kit: Prevent stalling, flooding, and other drivability problems by making sure your carbs are getting the right amount of fuel pressure with MOJTBE products. Adjust Capacity: This Aluminum Fuel Pressure Regulator Kit is adjustable from 0 to 140 PSI maximum fuel pump capacity. Optimally adjusts oil flow to meet your car's fuel pressure requirements. Materials: Premium aluminum construction for ideal weight and superior durability. Package Includes: 1x Fuel Pressure Regulator, 2x Hoses, 1x Accessories. NOTE: Not Legal in the state of California & New York, Not complies with C.A.R.B. regulations, Not for sale in the states of CA and NY. No instruction or direction included in the package, Professional installation is highly recommended.