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This is the start to what I hope becomes another great build thread.  I picture it ending with a photograph of my Z, shining in the beams of Texas sunlight coming through a massive cloud of burnt rubber. There I am in the driver seat… old, broke and happy!


I am an engineer, not a mechanic. I hope by the end of this project and after a few more years at my job, the gap between the two will meet somewhere in the middle. I do not have unlimited time and I have a baby on the way, so I apologize in advance for any long periods without updates or if at some point this becomes another sad part-out page. So far, I have only vicariously enjoyed your successes and turmoil. I’m going out on the same limb now, thanks for having me.


Before I forget, many tanks to Matt (if you’re out there) for selling me the car…sorry I couldn’t offer more.


Please post as much as you want with input, critiques, questions or moral support!


For a little back-story here is my new member post.




Starting line:


Price: Every bit I could spare for…$2500!!



75 280z L28et (seller said ‘83… wiring harness and sensors are 81?) 5speed. It has strong metal everywhere except driver floorboard that has small patch and potentially lower section of deck lid. Battery tray, fenders and all towers are in great shape.


Running condition:

Fires right up, runs terrible. Not highway safe!


Good Mods from previous owner:

Very surprising bunch of aftermarket parts for a car that runs terrible! No details on what had been done so far… so it’s back tracking and investigation for everything but the obvious below.


It has a “Recent†engine rebuild, no details, in a pretty clean engine bay. JSK fuel rail and FPR and an unknown newer style pump, MSD ignition coil with new distributor and wires, HKS BOV, new intercooler (~10x24x3â€), SS intake piping, KN filter set, oil cooler mounted behind intercooler, filter to cooler oil bypass, single small electric radiator fan, Interior has all new carpet, headliner and dash pad, doors open well and have decent liners.


If that’s not enough, 4 brand new xxr wheels and tires!


post-14240-084706400 1331568356_thumb.jpg


post-14240-063053700 1331568299_thumb.jpg


Downsides: Fuel management is no good and frustration with this is why he sold it. I think injectors are almost full open all the time. It spits un-burnt fuel straight out of downpipe onto my garage and starts burning your eyes within a few seconds. Under medium throttle at standstill engine can die from flooding. Oil has heavy fuel contamination after only a few hours of tinkering.


Rear-end CLUNK when you shift quickly under load… I have ideas but I am not sure yet.


Owner before me could not get hood latch open when he bought it… so he DRILL cut a hole in the hood above the latch to get it opened.


No chassis light/electrical works, all HVAC controls removed, gauges don’t work.


Status of diagnostics:


I fixed an early issue with battery drain coming from a short in the rear-defrost (by fix I mean I removed the fuse)


I then moved on with the “ecm connector test†and found almost everything reads open circuit or the wrong resistance. I have determined that the coolant temp and head temp sensor have no/broken connectors, wiring for them is bundled and zip tied. The TPS wiring was cut and then wrapped in elec tape so it only LOOKs like its plugged in. AFM was broken into and now doesn’t read the correct resistance throughout the range. But hey, Intake air temp reads great!


Drawing board:


I picture having the drive train and ride at 100% and spending as little money as possible to get the look to 75%.


Right now I am considering removing all of the original engine controls and going with Megasquirt and maybe even 3.0 with spark control. My reasoning for this is that after adding up just a replacement AFM, harness repairs/connectors and OE sensors I am already almost to the cost of the MS system. I also think it is the coolest thing EVER to have that kind of system in a 40 year old car. So instead of asking the question “do you think I should Msquirt?†I am going over all the other answers to that question and the final product and decide for myself.


I may go with just toggle switches for all chassis stuff besides brake lights and have a space for a small laptop to sit where the HVAC and radio used to be to show the extra gauges from MS.


*Suspension to be addressed*


After all that, its new seats… cheap paint job… and open road.

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Hello OilKiller and welcome!


Having started with a non-running Z project myself a few years back, I'm actually a little jealous that you have so much troubleshooting in front of you.  Maybe I'm a bit off, but I really like fixing things and you appear to have an excellent platform to begin with.  HybridZ is a spectacular resource and you will find answers, tips, hints and theories on almost everything related to Z engines.


If I were in your shoes I would make my first objective to get the engine to start and run in a reliable fashion.  Megasquirt is an excellent aftermarket EMS (I use it) though several other brands are available.  While MS1 or MS2 could serve your needs, buying a preassembled MS3 unit is probably your best value.  That way you can grow into new features such as sequential injection.  In the short term, I'd run a fuel only MS install saving EDIS or another ignition system for down the road.  Getting you car to start and run, if only around the block because you have no lights, is a tangible and rewarding first goal.


As you have probably already learned, the '75 Z ignition is controlled by the ICU; Fuel management by the ECU.  Adding Megasquirt replaces the ECU, but you should look into the '81-'83 ZA dizzy (HEI module) or MSD6 to replace the ICU.  Factory service manuals and electrical schematics can be found at xenons30.com (among other places).


As you describe it, your engine may have issues.  Gas could only get into the engine oil if unburnt fuel is passing the piston rings into the block.  And this would only happen if (1) you have an injector that is stuck open and/or (2) you have a cylinder that is not firing.  Maybe you have coolant in the oil from a leaky head gasket?


As far as the electrical system, since you are an engineer, let's hope you're an EE.  IMO, the '75 Z electrical system was designed by the devil herself.  Thoroughly over-engineered.  Part of the fun of installing Megasquirt is ripping out ~50 yards of wire from the original EFI system that you'll never need again.  You'll simply have to address the electrical bugs as you go.  I ended up buying a trickle charger/starter because I got so tired of swapping batteries and jump starting my car until I got the electrical system debugged.  Works great now, but boy howdy it was a pain in the ass.


Good luck and keep us apprised of you progress.

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