New Guy Needs Help
 

Just picked up a 280-Z for $500 and so far I love it, it's my old 1968 MGB-GT (my first car long ago) only better and, well, this one runs

Ok everyone, let's put up with a silly question first

IF my production date is April of '76, what's the model year? 76 or 77?

Here's the most pressing problem I am currently having, bear in mind vehicle has been sitting awhile.

Once the vehicle gets warm (temps around mid range on the dash gauge) the vehicle begins to mis-fire, sputter, lose rpm when applying gas under a load. Vehicle idles pretty much ok, every now and then dropping a little low, but nothing chronic.

Here's what I've done already.
New Cap and Rotor
New plug wires.

I've been advised that it is anything from timing, to bad fuel filter, to the "O" rings around the injectors.

Any other ideas? Or do one, all, of those sound correct?

I believe that would definately be 76, April is only the 4th month!

I realize that, was wondering how the model years ran since they tend to run different than calender years, so the production year and the model year aren't always the same.

When I bought my '77280Z a year ago it had bad gas from sitting. Try draining the tank or using premium gas with a cleaner(carb or injector) and a bottle of something that displaces water. Also change the fule filter a couple of times. This worked on mine and was doing the same thing as yours :cool:

Congratulations on your purchase! Sounds like it's in pretty good shape, too (esp for $500).
There are a lot of possible causes for the behavior you're seeing, including the stuff you wisely fixed already. You mentioned the car sat for awhile. Things you want to go ahead and do as they're cheap, easy to do, and fairly likely to fix the problem:
- drain the gas tank and put in new gas, preferably with some injector cleaner
- put in a new fuel filter
- open up and clean out the air filter box and replace the filter element. It's a favorite nest building spot for rodents and insects. Seriously. Driving it after sitting may loosen some of the debris and block the air flow.
- test for spark while a friend gives it some gas (maybe the coil's not keeping up at higher revs)
- check that the advance mechanism moves pretty freely. A lot of the older ones are in bad shape.
- check the vacuum lines for cracks or leaks
- Check the rubber boot between the AFM and the intake manifold for cracks, especially in the creases of the flexible part.

If it's still having problems, try to test the fuel pressure (you'll need to use an in-line gauge capable of at least 35 to 40 psi for this)
Anyway, that should be a pretty good start to getting it figured out.
good luck!
Dave

First, many thanks for your advice. Some more information has come to light...

1) This problem, apparently, pre dates the stationary period. I've talked with the previous owner and he suggested that I need to replace "the sending unit" that control the firing order.

I've been unable to locate any such device by that specific term.

2) I've replaced not one, but TWO fuel filters. Somewhere along the line someone added an additional external filter just outside the fuel pump, as well as the OE filter under the bonnet.

3) My gas cap isn't venting, should it? Tonight, while I was bouncing back and forth, I stopped and popped the cap and heard the vacuum pulling in air. Appears unrelated, left cap off and still had problems. Should I replace with a vented cap?

4) Oil pressure appears very low, if I can trust the gauge. Could this be an issue of low oil in the crank case and therefore too much heat building up and causing pre-ignition?

5) Lastly, it's going in the shop tomorrow to have some wiring repaired. The wiring harness that screws onto the left side (as facing) burned up somewhere alone the line and will be repaired, unknown if bad grounding will effect operation.

Regarding changing gas, etc. I've run about 100 miles on it so far, ran some dry gas through it tonight and will continue to do so.

True or False (other suspects)
Fuel Pump?
Coil?
Main Control unit (that "box" located between air filter and engine)?
Air Filters has been replaced.

Mind you with each succesive step, there is noticible improvement to the engine, however, the main problem still exists.

I shall keep up all posted.

And, yeah, it's not in bad shape, needs some cosmetics (rust, and a paint job) after the mechanics are squared away.

The PO probably meant the ECU (black box by driver's left foot), which controls the injector timing and duration.
Gas cap shouldn't be venting, that should all go through the vapor lines, tank, vapor tank, and charcoal canister. Your test confirms that wasn't the issue though (too bad, that would've been a nice easy fix).
Most likely, the oil pressure sending unit (right side of the block) is bad. Datsun/Nissan was never able to make one of those that worked worth a darn. Funny, considering what a great job they did with about everything else on the car.
Wow, that wiring damage sure sounds like potentially a big part of the issue(s), glad you're getting that fixed.
The fuel pump is pretty easy to check. On the car, you can unplug it, wire it to 12 volts and make sure it runs. Ideally use a pressure gauge while you're doing this and make sure the pressure is getting up to spec.
Though I've never had a Z coil failure, I have seen quite a few posts here that others have had problems very similar to yours that were fixed with a new coil.
The box between the air filter and the intake manifold is your Air Flow Meter (AFM, MAF sensor, depending what source you're reading). Easy to test against the specs in the manual with a multimeter. Can go bad, but I'd think it would be more likely to cause problems for you throughout the rpm range. Can't hurt to test it, though.
Glad it's coming along!
Dave

Ok, some more updates....

Car ran great on the 22 mile ride home. Got a pro working it now, he's an old 300 Z and M/Benz guy.

Good idea on the oil sending unit. Will check. Also going to check the distributor itself for broken missing teeth. Pretty sure the timing chain itself is good to go.

Beginning to look like the over all key is going to be keeping the oil level full, and repairing whatever is wrong there.

We also found some bad, dry rotted, cracked, vacuum hosing, all repaired.

I'll keep you all posted, this is a GREAT help to have.

Back to the other question.

Considering model years tend to run different from calender years, is my April 1976 (production date on door plate) make my Z a '76 or a '77? there seems to be a debate with the previous paperwork. It seems more like a 260 than a later 280, and it's a 4 speed, so I'm thinking it's a 76 model year?

Differences between 76 & 77
 

April 76, would most likely be the early 76 model car. The 77 & 78 were available with 5 speed manual transmissions. American market 76 cars came with the four speed transmissions. Some of the Fairladies Z's (Japanese - market) had an earlier style five speed transmission.

Also, the 260 Z, had two side draft carburators. If yours has fuel injection, it would be a 75 or later car. The 280 Z actually started in 75. The 260 Z last year was 74 in the U.S.

If your hood has funky vent cowl opening towards the rear of the hood, you may have a 77 or 78 car, or a 77 or 78 hood on a 76 car body. The hoods on the 75 & 76 280 Z's were steel, with no hood cowl opening or louvers for heat dissipation.

Speed :)

We've nailed down the most probably culprit, the distributer is just flat wore out! So that's what we're going to replace. Overall the performance of the vehicle is vastly improved with the minor work alread completed.

Onto the model year.

I do have two vents in the hood. Appearing like small louvers facing the windscreen. It is also a 4 speed, fuel injected drive train.

However it looks very much like a 260 (although runs better ; ) so I'm thinking it's a very late 1976 or a very early 1977. Probably a mid year, i.e. 76 1/2, with a little bit of the year prior and after within it. I found the same to be the case with my 68 MGB-GT.

As a post script we came upon the oil pressure problem, it's only pumping at 13 psi (verified with extrernal equipment). So we'll be looking into changing out the oil pump next.