Are more 280 owners noticing difficult restart when engine is hot?

[deadflo]

I just started noticing this condition in my 79 ZX. It only happens when you try to start the car after is has already run and been sitting for about fifteen minutes or so. Sputtering, missing, backfiring. Seems like a "hot soak" issue. I found this link on Zcar.com. Note two other long time 280 Z owners have had the issue recently, for the first time. I just celebrated 20 years with this car, and it's never happened before. Wonder if it's related to ethanol in gas these days? There is a great discussion of it at this link:

http://www.zcar.com/forums/883144/vapor-lock-heat-soak-voodoo-whatever-you-wanna-call-it

Note the discussion includes references to the check valve on the fuel pump, and fuel pressure issues, but I still wonder about the alcohol fuel, given that it seems to be cropping up more in cars that have never had problems. I'm not even sure where to get non alcohol gas, since all pumps in Washington state say the gas "may contain up to 10 percent ethanol".

[Z train]

Sounds like leaking fuel.Obvious targets are the Cold start injector and the 6 main ones.Cap the CS injector and see if it happens.If it still does,after you've cranked it for a bit,pull the plugs and see if any are wet.

[deadflo]

I've had my cold start valve disconnected for about eight years now...

on the other hand, I havent checked to see if it is leaking.

[RT Hunter]

I have a 280z, and have the same issue. Rough idle after the car is hot, and turned off for 15mins. But starts up in the cold perfect!

[deadflo]

Did you check out that link? Seems like more folks are encountering this all of a sudden, on cars that have never done it since new. Could be that fuel pressure issue, but Im wondering if it's related to gas with ethanol??

[deadflo]

Oh yeah, I will check leaking cold start injector, but it's only happening in that 20 minute window or so after it has run. I can get it to clear out after it runs bad for a few seconds,it does not RUN bad when hot, just RESTARTS rough.

[Z train]

Oh yeah, I will check leaking cold start injector, but it's only happening in that 20 minute window or so after it has run. I can get it to clear out after it runs bad for a few seconds,it does not RUN bad when hot, just RESTARTS rough.

And when you get it started,it runs but is shaking all over and after a minute or two it smooths out and all is normal-right?

[RT Hunter]

Did you check out that link? Seems like more folks are encountering this all of a sudden, on cars that have never done it since new. Could be that fuel pressure issue, but Im wondering if it's related to gas with ethanol??

Yea, I checked the link out, but no solution

I don't think it's fuel pressure issue related. (if you're meaning that it loses pressure after sitting) Because then, it would also have hard cold startups. My 280z has perfect cold start ups. Hot start ups are fine too, but not when it has sat 15-20mins. But if it sat for an hour or longer, then it starts up fine.

[deadflo]

Ztrain, yes, it dies but if I give it some gas as I crank, I can get it to "clear out" after about 20 seconds or so, then runs fine.

I will look at rhe cold start injector first. The reason I disconnected it years ago, was, it was wet with gas on the TOP of the connector.So it was leaking to an extent then, but stopped when I disconnected the wire to the thermotime switch.

I found that link real interesting . Tony's info was very good, but I want to see if any of WashingtonZmans ideas work. I'm driving home from work soon, I'm gonna leave the hood open after I shut her down, and then try to restart in about fifteen minutes. We'll see if that changes anything. It has done that stumbling the last two times Ive gotten home and tried to restart.

It isnt really hot enough for the fuel line blower to come on, so i cant tell if that helps anything. it would nice to wire that upto a switch somehow..

[Z train]

My 810 does the same thing.I've been toying with the idea of getting the injectors cleaned but hav not gotten off my arse to so it.

[Powerglide]

It's the alcohol in the fuel. It may also be a loss of residual fuel pressure. But that usually makes itself apparent by a hard start/extended crank/die out first thing in the morning. You might alleviate the problem somewhat by using gas with less alcohol. Install a second check valve between the fuel filter and the fuel rail. Sometimes a piece of crud from the tank will cause the check valve on the pump to hang open a bit and cause a loss in residual fuel pressure. But again---this usually will not cause a HOT restart problem---only cold start, first thing in the am. Short of removing the check valve on the pump to clean it---you might try tapping on it with the car running to dislodge any crud that might be present between the check ball and the seat. Your injectors may also be leaking a little causing a RICH hot-restart condition. The car will stumble till it clears the excess fuel. But that shouldn't last more than 15 or 20 seconds. I wouldn't worry about it. An EFI Z is NOT a perfect system. Relaible by 1970s standards and FAR superior to poor running, carburated domestic junk of that era. Believe me. I lived it.

[deadflo]

I'm thinking alcohol too, Powerglide. Results of my non scientific test of: run car hard, park in sun with hood closed. Try to restart 15 minutes later.Stumbled and ran crappy both times I tried that.

Then run hard, park in the shade with hood open. Try restart 15 minutes later. Ran fine both times!

I'd like to hook up my auxillary cooling fan(that the ZX's have on the fuel rail) to run every time I shut her off. I need to figure out how...

OH and again, this car has never had this issue in 20 years. And it now appears alcohol is in all the gas in Washington state, that I can figure out..

Edited June 3, 2010 by deadflo