Lyttek

I'm leaning towards coolant: white = water/coolant blue = oil

Haven't had time to get stuff to check fuel pressure... but did manage to fix part of the problem... At some point in the past, someone "adjusted" the TPS so that as soon as the idle contacts opened, the full-throttle contacts closed... which may explain part of the poor mpg it was getting (I just figured it was an old car, ) Drove it quite a bit yesterday after getting the switch back to normal operation and it was nearly perfect. There is still a little stumbling when its warm, but the only way I could tell was a very faint sound that followed the same pattern as when it was missing badly. It may have poor fuel pressure to begin with, the the TPS "fix" may have been the previous owners solution, . Having said that, I don't know why unplugging the TPS previously had no effect, nor why this missing problem decided to appear now... I've had the car a couple of years now and it's never done it before.

More info: Have replaced the temp sensor with no change. With a little more testing I've found it starts missing: A) when it reaches the higher end of the normal operating range; when cold/cool/warm it runs just fine about 1500 rpm, load or no load C) under load, it starts a little under 1400rpm D) unplugging TPS has no effect

The FIRST THING I would do at this point is take it back to the shop that did the work. If THEY put it all together, then THEY should be looking at it. Don't get another head and swap and see if that fixes it... or really do ANYTHING else... the more YOU do to it, the more likely they'll be able to say it wasn't their problem, or YOU did something to it or whatever.

Any problems with the starter? I'm wondering if something's loose, worn, vibrating, etc.... since we can't exactly tell what the sound is like, it's hard to ponder.... Loose heat shield? If it happens at a specific rpm, I'm thinking of something that vibrates and is hitting a resonance frequency... if it were a constant but variable noise, I'd wonder about bearings, springs, etc...

I assume you or your neighbors haven't lost any pets recently? ;-) Does the sound have a pattern, or is it pretty solid? Does it happen at 2800 rpm sitting still?

I would think the grinding would be caused by the throw-out not letting the clutch fully release, so you're getting some residual spin, causing the grind. As for the third-gear whine... I don't think that would be related...

Here's a little more info to deepen the mystery... Drove 40 miles one way last night, no problems. Car sat for about 45 mins, then headed back home. Got about 20 miles and noticed it started again. Here's what's weird: driving in 5th gear at about 35mph, approx 1500-2000 rpm, I can really feel the missing. On a flat level stretch, I can push in the clutch and let off the accelerator ever so slightly to maintain the same rpm, and it's as smooth as silk. As soon as I start to let the clutch out, it starts missing again. When I parked the car, I was able to reproduce the same effect, and basically it starts missing when it gets any load whatsoever.

I assume there's only the one temp sensor? The temp gauge appears to be working fine... Not sure about fuel pressure, I'll have to look and see if I have the tools to test that.

1978 280z idles as smooth as could be, cold or hot. problem only occurs when warm, and seems to appear after stopping at a light. replaced plugs, wires, cap/rotor, have recently replaced injectors. Thought the TPS sensor connector looked corroded, so cleaned the contacts in both the plug and sensor. It *feels* like it disappears if I tromp the accelerator when it's happening, but not completely sure. The other day I drove it for about 35 minutes, no problem. Sat for about 10 mins, then drove back into town, another 30 minutes. Got almost home, stopped at a red light, as soon as I took off, it starts missing, intermittently, and feels like it's only one cylinder. Doesn't clear up until it's sat for awhile.

Just thought I'd post an update: the alternator was bad. Unsure why that would affect the fuel pump, but all's well on that front.

New problem just developed, haven't had time to anything but basic troubleshooting. Car has been running fine. Drove, parked, shut car off. Heard fuel pump running, gauge on dash shows a discharge (red light). Pulled negative cable from battery, pump stops. Put cable back on, I can hear the fuel pump relay click, but pump doesn't run. Turn key on, pump comes on for "priming" and never shuts off; have to pull battery cable again. One thing I tried but don't know if it holds true for this car like some others: started car, runs fine. Pulled battery cable while running, car dies. (should it not keep running if alternator is fine?) It's going to be a couple of days before I get a chance to delve into, so thought I'd start researching ahead of then. TIA