Potentiometer

[Dave WM]

since talk about fuel pressure and starting difficulties often comes up I made this. I am not saying pressure is never an issue but I wanted to make this just so its not considered the only issue.

Its been colder here in florida lately in the 30-40's, and it does take maybe a full second after sitting overnite, but still not an issue. Now if the fuel in the rails completely drains out, I can see how it may take a couple seconds for the lines to refill, but that is not the same as no pressure (gas in line just the rubber hoses not expanded) think about it, you cant compress a liquid so any pressure readings static (pump off) will only be the tiny bit of expansion in the rubber hose. a few drops of bleed off and you are at Zero pressure, but still have fuel in the lines. perhaps a better test is to do as in the video, when you disconnect the line from the fuel filter does gas come out? if so you prob have fuel in the line all the way back to the injector so startup should not require a full charge of fuel going into the lines. you will see in the video I dump out some fuel (there was no evidence of pressure when I disconnect the line).

Guess I should qualify this with it being a 75 so maybe some of the talk about how to setup the test may not work for later models that have different circuitry for operating the fuel pump.

I just tried the same thing again this time with the temps in the upper 40's. disconnected fuel line, no pressure, drained same as in the video, reconnect. The engine turned over a tiny bit slower (batt temp and oil viscosity I presume) but still started in about the same time (less than a second). I did notice my AAR may be acting up will look into that, it has not been starting fast and then slowing down at idle, rather is seems to just sit at about 1k idle from startup to fully warm. I suspect its stuck at some middle air bleed amount.

Edited January 19, 2018 by Dave WM

[rcb280z]

20 minutes ago, Dave WM said:

a few drops of bleed off and you are at Zero pressure, but still have fuel in the lines.

This is what I was thinking earlier. I need to look at a few things.

Just feel if it was working before and not now I need to fix it.

[Dave WM]

I can see an issue if all the fuel is gone from the rail, as in dry, that's why I wanted to conduct the test again, to see if temps had anything to do with my ease of starting, this colder morning did not slow its starting at all. Try the disconnect from the line that goes to the fuel rail like in the video, see if you have gas in that rubber line. should be able to get a few teaspoons out of it when dumped over (it was exactly the same this morning for me, did not do the video thing though). I shot that video weeks ago when another z owner was having some questions about fuel pressure. Seems to come up a lot. Nearly drove me batty trying to find the exact cause of the drop in mine (very inconsistent) which is why I gave up chasing it and decide to look elsewhere for the intermittent starting issue.

I chased it for 2 years in fact when I bought the car the guy would break out the starting fluid (some times), helped me get a better price I think, anyway the eventual fix was indeed the switch, it has NEVER been intermittent since that, whereas before it would be fine one day and a problem the next. The only real issue I have now is the hot start in the summer, so when I go to get gas, I just pop the hood  (check oil anyway) leave it up while filling up, and it will start perfect. If I don't do that it will still start but not as easy and stumbles a bit. pretty sure this is an issue of the gas litteraly boiling out of the rail from the heat perhaps the later cars with the vents and power driven cooling fans don't have the issue. But come to think of it I have not tried testing it since the switch replacement, and while I know the hot start issue is well documented, I think I will test again (drive hard, shut down, restart after waiting a few minutes) when its summer time.

Edited January 19, 2018 by Dave WM