Hot-start issue with EFI - who has it, who doesn't

[Zed Head]

Like a NOS setup except the pssst, psssst is for cooling, not clearing the NOS lines?  All the kids would think you want to race.

 

The scary thing about rapid cooling of hot parts is that they tend to distort and sometimes break.  I had a cooling air setup on my injectors for a while, with a hose with holes in it to direct air on to each injector.  It worked great but I had to twist a timer dial every time I stopped the engine.  Keeping them cool, instead of cooling them after they got hot.  A turbo timer would probably work.  It was a lot of complexity though.  The aluminum fuel rail and the insulation of the injectors seems simpler.

 

A timer on the fuel pump do the trick.  Keep the cool fuel running through the rail.  I had pondered that but never tried it.  Leaving the fuel pump running with the car unattended bothered me, plus heating the fuel in the tank.

 

I also thought about running a line from the coolant system over the injectors with an electric  water pump, but air was easier.  The situation is just aggravating, overall.

Edited June 12, 2015 by Zed Head

[Chickenman]

Pouring some cold water over the fuel lines and Injectors worked for me. It's a pretty standard fix for Vapor Lock.

 

Edit: Autocrossers  often carry a small pressurized Garden sprayer.  They spray the Intake manifold and Carb down between rounds, particularly if they have Multiple drivers and are making back to back runs or " Re-runs ".

 

I used one when I Hillclimbed. Sometimes a car would crash when you were next in line and the event would be put on hold for a while. Everything would heat soak in the engine bay. Crew would pop the hood and then spray the Carb and Intake Manifold down with the water sprayer. If this wasn't done car would bog off the line and you would lose time.

 

Also worked for cooling off the driver who was slowly baking, sitting in a 100+ degree car and covered in a triple layer Firesuit

Edited June 12, 2015 by Chickenman

[Chickenman]

Chicken, I have a priming switch on my Z, and I can tell you it doesn't really help to resolve the hot restart issue.  I think the problem is that the cool fuel won't dribble into the injectors just with gravity and therefore won't cool them.  Instead, you have a stubborn pocket of fuel vapor inside each injector that doesn't really budge from where it is.  The only way to get rid of that pocket is to inject vapor into the intake.  Then fresh/cool fuel enters the injector, flashes, and must be injected as a vapor.  Eventually this happens enough that the fuel vaporization, combined with cool air rushing through the intake (perhaps a more significant factor), carry away enough heat that the fuel no longer flashes inside the injector.  And that's when the engine evens out.

OK..thanks for that. One less thing I have to do.

 

I think part of my problem was that the Battery was low due to a weak Alternator. I couldn't crank the engine long enough to clear the Vapor Lock. Never mind evening out... I couldn't even get the danged car started before the Battery gave up.

 

New alternator soon to be installed.

[FastWoman]

So I was thinking a while ago about a modification to the fuel rail.  The old style of injector insulator has a plastic bottom and metal top, or so I think.  What if a different metal top were machined that would have a cooling tube running through it to cool the injector body?  The cooling tubes could be plumbed in series with each other.  Then return fuel from the FPR could return through the cooling tubes before going back to the tank.  If it were put together that way, then priming the pump for a minute or so would actually cool the injectors, so that starting would be possible.

[Chickenman]

Re-visiting the Primer button. My idea was to use it for a bit different purpose than what Fastwoman may had noted.

 

My idea was to use the Primer button to get Fuel running through the Fuel Rail and back to the Fuel tank via the return line. This to purge any vapors in Fuel Rail. Not overly concerned about the small amount of Vapors in the Injectors, Those will readily clear in fairly short order. It's when you get Vapor Lock in the Fuel Lines that really causes the big problem. That takes a lot of cranking to clear.

 

With the Primer button, you can purge the fuel lines without running down the battery cranking the engine. Then when you do use the starter, the big vapor lock in the lines should be gone. The Injectors will clear relatively fast.

 

The rough running issue is secondary to the " No Start "  issue for me.

[FastWoman]

Well, it MIGHT get you over the hump, but there's a lot more heat in those injectors than in the fuel rail!  In my experience, the vapor in the lines clears pretty fast anyway, judging from the sound of the pump -- maybe 3-4 seconds.  And FWIW, I believe someone else tried a priming switch too -- didn't help them either.

Edited June 13, 2015 by FastWoman

[Captain Obvious]

And to test the possibility of a primer button helping your hot-start, you could just pull the starter solenoid wire and run the pump for some time with the key in the START position. Then after you're convinced that the fuel lines have been purged, you can reconnect that wire and then try to start the engine.

 

Of course, it's kind of a negative test... If it doesn't start, you know priming didn't help. But if it DOES start, you won't know for sure if it would have started even if you DIDN'T purge. But it's an easy way to mess around with it anyway.

[Chickenman]

Or maybe I'll just pop the hood if I'm stopping at a Rest Stop for a Coffee or something. Might be the easiest  " temporary " solution. It may not even happen again once I replace the alternator.

 

Going to be a Hot summer in the PNW...so I guess I'll find out soon.

Edited June 14, 2015 by Chickenman

[Zed Head]

I have a book that compiles all of the Road & Track tests of the Z cars over the years.  Found an interesting comment in a test of the 1979 280ZX from April 1979, compared to three other sports cars.

 

"And we found that after a brisk workout, it would sputter and spit back through the injection on restart."  

 

Think they meant intake, not injection.  So it looks like the hot-start problem has always been there, even with ethanol-free fuel.  Just a consequence of placing the injectors next to the hot exhaust manifold.  The R&T guys probably got things pretty hot so there would be a lot of excess heat in the block and manifolds.

[siteunseen]

Did the '79 ZX have the fan for the injectors?

[Zed Head]

I looked for it in the FSM but didn't see it referenced anywhere.  From what I've read, most people that have the fan have never actually heard it run.  The switch is set for 210 degrees or somewhere close to that, apparently, and it's mounted in the thermostat housing.  I mounted a ZX fan on my car, with a manual switch, and they're pretty noisy so you'd know if it was on.

[Patcon]

Zed,

Did the fan help?