'83 280ZX has me puzzled

[hall.nathan89]

I recently bought a this car and to be perfectly frank, it has me stumped. I bought it from a dealership who had aquired it as part of a trade-in for a truck. It's obvious that the person that last worked on it knew what he was doing, but I'm starting to think that he either gave up or died prior to finishing the project; certain things about the car are beautiful! Other things (such as the vacuum system and the in-dash electrical) are nothing short of a nightmare.

The car wouldn't pass emmisions just days after I bought it, so I took it back to the dealer to have them fix that issue. Their mechanic claims to have tuned it and replaced the catalytic convertor. They then gave it back to me and told me to drive it for a few days. My suspicion is that they didn't actually tune it, and if they did, they didn't do it well. There was a lot of backfiring and sputtering. It ran... Not well... but it ran. Which brings us to Saturday.

The engine has been replaced fairly recently but when it was done, the vacuum lines weren't connected right. After contacting some folks in the local club and spending the better part of last Saturday on it, I was able to get most of my vacuum system sorted out by comparing it to an '82. Following this great adventure, I proceeded to check the plugs, wires, coil, distrubutor, etc... and then I adjusted the timing (8 @ 700 if memory serves). I can tell that it's a much happier car! It runs wonderfully... sometimes...

My problem now is that it doesn't want to stay running. Sometimes it won't start without giving it gas, sometimes it stalls if I'm not giving it gas. It stalled in the middle of an intersection yesterday and on my way to work this morning. It almost stalled on the freeway when I let off the gas a few minutes ago. It seems to idle well most of the time, right around 700-750 but when it decides it's going to quit it'll drop down to about 500, then come back up to 700 momentarily and then just die.

I've looked all over the forums to figure this out, but I'm not finding much. Any suggestions? Thanks in advance!

[hall.nathan89]

Update: After some troubleshooting, I think it may be the fuel regulator valve... Any input?

[Zed Head]

I think that you mean the fuel pressure regulator (FPR). Easy to check with a fuel pressure gauge. ~36 - 38 psi with the vacuum line off, or engine not running, and in the 28 - 32 psi range at idle, engine running, with everything connected. Insert it between the fuel filter and the fuel rail.

You could also have a clogged fuel filter or crud in the gas tank or a bad fuel pump. But the fuel pressure measurement will tell you whether or not to keep looking. Since you're problem is kind of intermittent, you might want to strap the gauge in the engine bay for a few days so that you can check it when the problem happens.

[hall.nathan89]

YES! That's exactly what I meant. My apologies for the incorrect terminology; I was a bit flustered at the time that I wrote that update. I have a fuel pressure gauge that I can leave in line for a few days. I'm relatively certain that it's not the filter, given the on-and-off nature of the problem. Am I wrong for thinking that? Thanks for the suggestion.

It leaves me with a question, though. Once I determine that it is a fuel pressure problem, how do I go about determining the cause? I would think that the FPR would be the easiest place to start, given the ease of access, but is there any way to bench-test one of those?

Obviously from there I'll start looking at the tail end, and if I'm going to spend an afternoon under the rear of my car, I'll check the tank and the pump all in one shot.

Thanks!

[hall.nathan89]

Checked my FPR. Seems to be operating fine, but my fuel pressure seems a little low; sits at around 30 until I pull the vacuum line on the FPR, then spikes to 40. Question NOW is, would the low pressure be caused by anything other than a failing fuel pump?

[hall.nathan89]

I got it! I figured out the problem! I have an '83 car with the engine/manifold from an '81. So my vacuum lines were still all wrong, even though I thought they were right.

Are there any other problems I should watch out for with the difference in the engine? How will the ECU handle a different engine?

[Zed Head]

The engine long-blocks (block, pistons, head, etc. no manifolds) should be essentially identical, with P79 heads and flat-top pistons, if they are both NA, not turbo, engines. But the various valves and gizmos on the intake manifold, and the distributor, and the AFM, might be different enough to use a different ECU. You might try to find the part numbers for the ECU and the AFM out on the internet world and see if they are different. Or you could look through the Engine Fuel and Emissions sections of the FSMs and see if the functions of the ECUs are different. I would look at the Electrical section also and see about any timing changes in the distributor. The early 80s distributors ran a ton of vacuum advance to go along with the EGR, and somewhere in there they started using a temperature and vacuum switched, dual timing control for the advance.

The 80s were the age of emissions control so there are all kinds of interacting devices on the engine. If you're lucky, they stabilized for a little while on one ECU and AFM setup for your two engines and the changes were elsewhere.

Probably sounds more complicated than it is, a look at the FSMs will tell a lot. XenonS130 - S130 Reference

[DC871F]

I had an 81 do the same thing a few years back. For kicks I went to junk yard (when there were alot of ZX's there) and replaced the airflow meter, everything ran smooth as silk after replacing.

[Zed Head]

Coincidentally, this thread came up on another site -

ECU question - HybridZ

Referencing this page -

XenonS130 - ECU Information

[Wade Nelson]

Did you get your problem figured out? How about posting a follow-up so others who might have a similar problem in the future can benefit from your experience.

[hall.nathan89]

I appologize for the delay here. I haven't been on in a few weeks.

So far I've just been running it as-is and it seems to be fine. I do still have a problem with it running a little rough for the first minute or two, but after that it smooths out and purrs like a kitten.

I also have a problem with my battery dying after 10hrs of the car not running, but I have yet to determine if that's related to the engine swap or not.

As of right now, I'd say that the '81 guts are working great with the '83 brain