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

[rcb280z]

And let me add that what I thought was a "hot restart" earlier this year was not. It is the oxygenated fuel we have to use during winter months. Makes the car seem like its running lean, leaner than it should.

[TheCrazySwede]

And let me add that what I thought was a "hot restart" earlier this year was not. It is the oxygenated fuel we have to use during winter months. Makes the car seem like its running lean, leaner than it should.

Same here!

[BackDoorz]

Vapor Lock, Heat Soak, VooDoo, whatever you wanna call it ...

________________________________________

I have read a lot about "heat soak" and "vapor lock" for quite a while now. I was always under the impression that those two "quirks" were not likely to happen on FI type engines. If you do a "Google" on the subject, you will find a vast number of folks that say it can't happen. After saying all that I will add my spin.

I have a 1976 280Z, automatic, A/C, with ~155,000 miles. I am the original owner. The car is all original under the hood. This car was my daily ride for about 10 years (1976-1986). I live in N.C. where it gets 90 to 100 degrees for most of the summer. From the first day I started driving this car, till I parked it, I never experienced any type of "heat soak" or "vapor lock". I could go anywhere, park, come back out in 15-20 minutes, and she would start right up with no problems.

For about 6 years (1986-1992) this car was parked in my garage. I did not drive it. I decided to start driving it again. I did some work getting her "road ready". I started to drive this car on a limited basis, still experiencing no "heat soak" or "vapor lock".

After about 4-5 years I noticed that on rare occasions the car would seem to, what I thought, flood for just a brief time after about 15-20 minutes with the engine off. As the years have gone by, I can tell that this problem has gotten progressively worse. Now it is like this everytime it is parked for 15-20 minutes.

I have changed several items in hope of correcting this problem. New fuel pump, new FPR, fuel injectors cleaned and tested, cleaned all electrical contacts, new AFM, cooler thermostat, new fuel filters (G3 & under hood), complete tuneup (including adj. valves), checked for air leaks, etc., etc., etc. I installed a switch underneath my dash to allow me to just run the fuel pump before I tried to start the engine, hoping to pump cooler gas around the fuel rail. I have seen very little improvement if any.

My conclusion about this problem ... gasoline. The gasoline that I was putting in this car in the 70's and 80's in nothing like the gasoline that I'm using today. Each area of the country seems to have their own blend for summer and winter.

I intend to try and burn ethanol free gasoline for awhile and see how that works. I also plan to take the fuel rail off and wrap it and the fuel injectors in some type of heat wrap. My thinking here is maybe insulating the fuel system from the heat as much as I can.

[Zed Head]

Welcome to the club and thanks for adding. Fuel quality has been discussed here and there. Unfortunately, most of us have to live with whatever is in the local station's tanks.

So far, people with Standard FJ707T injectors, aluminum fuel rails and headers, Standard FJ3 injectors with headers (Post #84), and me with Bosch 0280 150 901 injectors, aluminum fuel rail, and stock manifolds, seem to have eliminated our hot start problems. Although it's not clear if rcb's issue will come back in the winter-time.

Here's a really interesting presentation from Lawrence Livermore National Laboratory showing how ethanol affects vapor pressure, but also showing that gasoline can be different in different areas of the country. That's one more thing that gets the discussions messed up, one guy says I have these parts and no problem, another says I have the same parts and have the issue every day. But they're talking about different petroleum distillations, and different ethanol percentages. It's worse now than in the past because modern cars are designed to adjust for the variation.

http://www-erd.llnl.gov/ethanol/proceed/autoupd.pdf

[S30Driver]

I will be very interested to hear the outcome of BackDoorZ's ethanol free gas test.

My car has the stock green injectors, a Pallnet aluminum fuel rail, stock manifold & soon to install my chromex coated main heat shield.

[Quintillion977]

'77 280Z, stock injectors (recently cleaned and flow-matched, two were replaced) on stock fuel rail. MSA 6-1 header with stock heat shield. I drove it daily until I was out of the area for pretty much all of 2013 without a problem. Came back in November and went right back to it with no issue whatsoever. It sat parked since March and I just drove my truck but now that the weather is nice (and hot...) I decided to bring out the Z. Ran it for a while and took it around the block to make sure it was ready for the commute. Ate dinner and went out to start it back up and nothing. Hot weather? Maybe. I didn't try the usual starter disconnect/run the pump trick because I was... disappointed. That worked for me in the past (I feel your pain, rossiz, and I was also thinking about a toggle switch for this purpose). I will tinker with injector fans and see if that helps.

[FastWoman]

And the million dollar question: Did your car start up effortlessly after it cooled off? Don't get too heavy into the diagnostics yet. The classic hot-restart issue is that the car starts fine cold, you run it around, getting the engine and engine compartment good and toasty, you shut down, you return 10-15 later, and the engine won't fire up. Let it sit for another hour, and it will start up just fine. Your case is interesting because you have headers.

I assume you have fresh gas in the tank?

I, too, am interested to hear Backdoor report back. I tried running some ethanol-free gas here, and I didn't have a hot restart problem, but my hot restart issues are too seldom for me to conclude whether that was just by dumb luck. The fuel did make my engine run a bit too rich, though, which is why I went back to the ethanol blend. Remember, I have the potentiometer mod to richen the mixture. I could re-tune for the ethanol free gas, but I don't want to have to buy all of my fuel from one gas station.

[rossiz]

so i'm not sure i can offer anything conclusive here, as i've done quite a few things at once and can't tell for sure which one did the trick, but it's been hot as all get out here in seattle the past few weeks (hot for us at least, upper 80's) and the car has been starting just fine. when it's really hot it runs a little grumpy for a few seconds, but cleans right up with a rev or two on the pedal. i'm using the cheapest gas i find (as always) which typically has ethanol in it.

mods:

new n42 head

shaved/cleaned manifold

new ceramic coated 6-1 header

home made "ghetto-style" single run fuel rail (cut from oem)

all new injectors (nos oem)

Edited August 9, 2014 by rossiz
mis-labeled the head...

[Quintillion977]

I am inclined to blame the fuel rail after reading what rossiz said. I had never seen the fuel rail mod until I just Googled it... interesting. The gas in it it kinda old (April). I am about to run some errands in the Z and put some fresh gas in the tank. Wish me luck and I will report back.

[rossiz]

quick edit: the new head is an n42...

[Quintillion977]

Yesterday I drove around all day. Ran errands with lots of 15 minute stops, drove in traffic, and opened it up on some of my favorite lines. Ran like a champ and started right up every time.

[Quintillion977]

Update: I was out of town for five days and came back. Z is still running and starting perfectly. This is still the same not-so-fresh gas that I had when the hot start issue popped up the one time.