Heat Soak (Vapor Lock) Problem

[misterZ]

So, I've read heat soak, or as I like to call it, 'vapor lock' (carb talk), is an inherent problem w/ the L6 EFI; what can I do to alleviate this problem? It's frustrating to drive 10 mins to lunch only to come out and the car is very hard to start and keep running... spittin' & sputtering until I can get in gear and move a bit (getting airflow thru the grill to cool things off) before it clears up and dissapates the heat.

 

I plan to order the vented inspection lids from MSA, more for looks than the claimed functionality of helping with this problem.

 

Thanks in advance,

mister

[Cobra_Tim]

Anything you do to keep your fuel from getting warm should help.

[Tony D]

It's only a problem during that 5-10 minute period after a hot shutdown.

 

Later cars use a priming pulse of the fuel pump to restore fuel pressure to the rail and prevent this hot restart problem.

 

But this should NEVER happen after a 10 minute drive, even in 130+ heat.

 

If yours is doing this after that short of a run, you have OTHER issues not related to heat soak. A leaking injector, a leaking pump check valve, an obstructed fuel pump inlet, or running very hot to begin with...

 

Normally, this will occur after a highway run in heat (like I10 driving to phoenix in July pullinga small trailer) and then only in the 5-10 minutes after shutdown. Leat it rest for a 30 minute lunch, and it restarts FINE, try a restart after a 5 minute 'gas and go' and FINE. It takes time for the rail to heat soak, and then time for it to properly dissipate.

 

One thing I found that helped quite a bit was running a 160 degree thermostat (save the comments guys, it does not kill my mileage, nor does it cause any adverse issues in real world applications on the early S30 EFI!) the underhood temperatures really stayed lower than when running a 190, and it works really nicely.

 

But like I said, if yours is doing this after a 10 minute run to lunch, something is BIG wrong. That should NOT be happening.

[misterZ]

But like I said, if yours is doing this after a 10 minute run to lunch, something is BIG wrong. That should NOT be happening.

 

 

My fuel mileage is 20 but I drive hard (14 mi one-way to work); no visible leaks or discoloration and the car appears and drives mechanically sound. I've only owned it about 5 mos but when I drove home from purchase and stopped 1/2 way (75 mi trip, mostly highway) to pee and have a smoke, I experienced the heat soak for the first time but thought it was bad gas or something else, i.e., poor fuel delivery or bad plugs. Of course, it cleared up once I got moving but I immediately called the seller and he indicated he never experienced such a thing.

 

You are correct about gas `n go; no issues, and yes, if allowed 30 min< it's fine... but sometimes I don't have the extra/needed time to cool off.

 

The car has never ran/got hot under my ownership but the seller said he had problems overheating bringing it back from CA (Apr 08) but a new fan clutch resolved that problem--he claims it never got red. When I had the car up on the rack for tire rotation I got a good look at the underside and it appears there had been some engine work at some point as the freeze plugs on the driver/injector side appeared newer/cleaner (as in replaced) than the opposite side of the block.

 

The injectors look good but come to think of it, I did notice today some heat discoloration on the fuel rail between 3-4 (like you see on chrome headers sometimes) but likely from age(?). I might try a colder thermostat and see if that helps.

 

I'm also going to try to make this year's DNI so I can have others take a look, discuss mods and offer suggestions--I wouldn't hesitate driving this car anywhere but GA is so close.

 

Thanks for all the good info!

[neotech84]

Sounds like you need to get a Taurus fan with a timer...... if you are really worried about heat. Not a bad upgrade, use the search and check it out.

[cygnusx1]

Nissan added vented hoods, heat shields, fuel rail/injector blower, I think they might have even wrapped a few rails with insulation.

 

On another note. As per TonyD, make SURE that your fuel rail pressure stays up for at least an hour after you shut off the car. Bad check valves in the fuel pump are common. Mine failed at about 110K miles. The valve can be replaced and the pressure will keep the fuel from boiling easily.

[HowlerMonkey]

I'm actually working on using the nissan dual feed injectors on the L engine by cutting up two stock fuel rails and using the Z31 pressure regulator.

 

They are designed to accept fuel from the side feed and then the top feed is where fuel exits the injector once the regulator starts returning fuel to the tank.

 

In a strictly top feed system, fuel does not flow through the injector to cool it until it is injected.........which might take a while.

[misterZ]

Later cars use a priming pulse of the fuel pump to restore fuel pressure to the rail and prevent this hot restart problem.

 

But this should NEVER happen after a 10 minute drive, even in 130+ heat.

 

 

 

Is there a good after-market fuel pump or swap for the S30? I've suspected this for some time only b/c it takes 2-3 tries to start the (cold) engine and keep running on it's own w/o pumping the pedal. Once running, it's smooth w/ good idle... purrs like a kitten.

[cygnusx1]

I have an aftermarket billet rail, a high performance Walbro 255lph pump, and I wrapped the fuel rail in two layers of foil backed fiberglass. I still get vapor lock. After I wrapped the rail, I delayed the vaporlock from about 15 minutes to about 25 minutes on average (NY Spring temperatures). I suspect that the exposed injector bodies are the culprit. My next project, today, is to wrap the injector bodies with little foil/glass sleeves. I wil let you know how that goes.

 

Before you change anything else. T in a fuel pressure gauge, run the car, shut it off and make absolutely sure that the pressure stays in the fuel system for at least 30 minutes++

[woldson]

I had a similar situation.

Esp. on a short drive. Ended up being (dang it can't remember, map, maf, the stupid trap door thingy).

Adjusting that and cleaning the chts solved this.

Do you have the injection fan?

I knew it was not a heat soak problem, cuse the car was not hot enough to have this as an issue.

It seemed that under the right conditions, with the car already running rich, the cold start injector would fire and cause a super rich condition.

You could smell the gas.

[srbigbutt]

This is the one problem I hate with my car. Atleast i'm glad to know i'm not the only one!!

 

I partly blame my problem on not having a heat shield between the intake and exhaust manifold. Is anyone else missing this heat shield as well?

[woldson]

Not yet;)

[DuoWing]

Back in the Summer Tony and I had a discussion on this over on Zcar. Basically his method was to put a little bypass toggle switch in the car so he could keep the fuel pump running for about 10 seconds or without the starter turning to cool the rail.

 

For one thing I know my check valve in my pump is bad so that's part of the problem as most of the time over night my fuel pressure would be pretty much depleted in the lines. Anyway along with the discussion we had I had ran around for a while with a fuel pressure gauge constantly hooked up under the hood of my car. I started monitoring it I'd take not even a freeway drive, but a long drive on some 45mph back roads pull into a lot and stop the car. After just a minute or two the gauge pressure started rising a good bit. Indicating that the rail was soaking in heat and the fuel was expanding. Basically the best thing to do other than a little bypass to keep the pump running would be to just do the 3-second prime, then do it a couple more times to help cool the rail.

 

Eventually I need to replace the little check valve in my pump and see if that helps to any degree.

 

As for the heatshield I still have that heatshield between my exhaust manifold and intake manifold and the problem still occurs. It was really bad the one day, but that was after about 1.5-2 hours on the freeway and then I shut the car off right at the rest stop. I should have let it idle for a bit to just help bring temps down.

[Pyro]

mine does that a little also.

 

I plan to install an injector blower motor and a momentary switch for the fuel pump.

 

Not sure how I'm going to control the blower yet, but will make some sort of timer that activates after the ignition is shut off. (rc circuit, ic timer, transistor, and relay)

 

and will plan to run the fuel pump for 10 or 20 seconds before start up with the momentary switch.

 

I'll most likely try the momentary switch first because that will be the easiest.

[Tony D]

Yep, that little "S Terminal Bypass Switch" is a quick and easy way to never have to get that irritation ever again.

Curiously, has anybody ever noticed moder cars with returnless fuel systems now have a start relay that controls cranking of the car---it's not a direct action from the ignition switch...it has interplay through the ECU. My Dodge Truck only needed a 'tick' from the ignition via key, and the car cranked itself till it started. The rental Altima I has a couple of weeks ago with the 'pushbotton start' was similar...

 

Ever wonder why they do that? Perhaps there is some fuel pump modulation that is occurring that pre-runs the fuel pump to prime a deadheaded fuel rail and compress the gasseous fuel bubbles back into solution before the engine actually cranks???

 

Hmmmm, could be! The more things change, the more they stay the same!

[DuoWing]

They're just figuring out ways to solve problems that still exist and just making it less noticeable to the operator? That's pretty interesting that they do that.

 

Is there really any reason for a returnless fuel system? Or would it be so there's less fuel lines to run? I mean is there any advantage or disadvantage?

[HowlerMonkey]

Yep tony......I tested that at lexus and found that they will crank for 10 seconds by itself when I unplugged the coils.

 

They needed this get this step tried and true before evolving to the start button.

[Tony D]

What it involves is that similar problems return when they change the systems. The government mandated lower EVAP standards, one way to DRAMATICALLY reduce evap is to keep the fuel cooler. Not running a return line accomplishes this.

 

Go measure your fuel tank temperature when you have 1/4 tank! You will see what I mean (and also why people who are perpetually broke have more problems with their EFI---that hot fuel has a tendency to get vaporized in the rail more often than the guy running around with a full tank!)

 

So the solution in the late 70's was to pre-run the fuel pump for 3 or so seconds whenever you turn the key on, and keep the fuel flushed and pressurized.

 

And this worked FINE for DECADES (80's, 90's) but then came returnless fuel systems.

 

Deadheaded cooler fuel in an engine bay that now is running 215F instead of 180F... all those covers, tight engine bays, lots of sound insulation keeping everything toasty...

 

So they have to figure out how to keep it from doing what it did in the 70's. And that answer was to go to a cranking relay. The SOLUTION WORKS! The problem WILL ALWAYS EXIST! It will not go away. You can not change the laws of physics.

 

The thing is, people driving cars today are even more ignorant than they were about their vehicles than they were in the 70's. So it becomes automatic. It reduces warranty incidences, customer complaints, etc etc etc...

 

I mean, my dad killed the battery in his Ford LTD one cold day because he was out of habit flooring the pedal before cranking the car. "Flood Clear"---no fuel goes to the engine. Of course second recrank, he really floors it to 'set the choke' and exacerbates it. So then he cranks it again with the throttle held open to clear out the gas that it wasn't injecting...

 

Repeat until battery is totally dead. It was so common amongst older car owners Ford was letting distribution know to MAKE SURE they instructed their customers that they DIDN'T TOUCH THE GAS PEDAL AT ALL before the engine started!

 

Now, they don't have to do that, either. You just touch the contacts on the ignition switch, and the car auto-cranks and auto starts. In many now, with throttle by wire nothing you do to it will affect the T/B position until after it get's a 'run acknowledgement' from the ECU check cycles.

 

I digress...

[misterZ]

mine does that a little also.

 

I plan to install an injector blower motor and a momentary switch for the fuel pump.

 

 

 

I purchased one of these blowers last night off eBay for $30. shipped; I never knew about them but understand they were installed on 82-83 S130s. There are a couple left for sale... search "280ZX intake cooling fan".

 

We'll see if it was worth the investment but I'm concerned my strut bar will be in the way of installation. The new hood vents I installed (http://forums.hybridz.org/showthread.php?t=148739) seem to help disipate the heat better and helped a little but I still have the heat soak problem.

[cygnusx1]

I have wrapped the injector bodies with silicone foam rubber, and the fuel rail with two layers of foil backed fiberglass liner. It will still vapor lock if I park it hot with the hood shut in about 15 minutes. My hood is the early non-vented style, my turbo gets really hot, and I run a dead head setup. I have the worse case scenario. What seems to help is cycling the power on and off to megasquirt two or three times when it's a hot start. Each powerup runs the purge cycle, flushing some of the vapor out through the injectors. I am going to try increasing the PW for hot starts next. I may make some vented inspection lids too. Anyone have lids for sale?