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

[EuroDat]

My 280Z 5/77 has the problem occasionally. Not enough to drive me crazy, not yet anyways.

Its running a stock N47 exhaust, non webbed N47 inlet, JECS green injectors with standard fuel rail, ERG and the heat shield are still intacked and functioning.

I don't think a ECU fix with solve the problem completly. Sarah's theory (in the other thread) makes sense to me. The ECU will attempt to fix a symptom and not the cause, which seems to be vapour down around the injector tip.

Datsun seems to have attempted to fix the problem over the years

1; By using heat shields, removing the webbing in the inlet manifold to reduce metal which stores heat and

2; The later ZX had the fan blowing cool air from the other side of the engine over the inlet manifold to reduce the heat.

I think Siteunseen's set-up with the fuel rail would help cure the problem. The single rail means less amount of fuel above the manifold and it would be refreshed faster. Its why people are covering the fuel manifold to protect it from heat.

I wonder if a N42 head would improve the heat problem. The exhaust ports from the N47 and P79 have emmision liners which generate extra heat. The N42 head doesn't have them and may not generate so much heat. You would need the change the valve seats to steel and get the corresponding exhaust manifold. If anyone has this setup, it would be nice to hear their view on this combination.

Its just a theory. Of course its not based on any research and I don't have any plans on buying a N42 head to test it out.

Chas

[TheCrazySwede]

To be clear, Swede, the stock configuration is with a cast iron exhaust manifold, not headers. If you have headers and hot-restart issues, then that would put a dent in the heat-soak theory.

Where are you in the US? And is your hot restart problem a summertime problem, or is it year-round?

Aye, you are correct. I'm running with the factory exhaust manifold. I live in Commiefornia (CA) and I've had this issue occurring since around October of last year. The issue might have been present prior to that, but because the car wasn't my daily driver, I never noticed it. It is my daily now, so I've come to realize this issue. The car will run great otherwise. Even under hot weather conditions, the car will run strong and idle perfectly. Let it sit for 15-20 min (having it sit for 5 min does nothing) and it will act as if it's running on 5 cylinders. Capt. O suggested that I check my fuel pressure, so I did, and it gets proper pressure constantly, and maintains higher pressure when the car has been turned off as it should.

I spoke to a Nissan mechanic last week or so about the issue and he thinks it could have something to do with the ethanol in the fuel and the mixture in winter fuel. He said that a lot of his customers that otherwise had no issues with their cars start to come in around winter time for this exact problem. I live in San Jose, and there's a great Z Specialty shop nearby (Z Car Garage) that I hope might figure something out. They are pretty popular, so I have to wait for my appointment date...which is almost 3 months from now :/

[siteunseen]

Hello, my name is Mike, and I have a hot restart problem :disappoin:

Hello Mike! How many Z mechanics does it take to screw in a spark plug? 1, he holds the plug in place and the world spins around him.

Heard that a court ordered AA meeting but it was how many alcoholics does it take to screw in a light bulb.

Keep coming back!

[TheCrazySwede]

Hello Mike! How many Z mechanics does it take to screw in a spark plug? 1, he holds the plug in place and the world spins around him.

Heard that a court ordered AA meeting but it was how many alcoholics does it take to screw in a light bulb.

Keep coming back!

Haha, haven't heard that one before.

I hope to get to the bottom of this whole issue....

Were you able to "cure" the problem with your setup? I'm not as car-literate as most of you here, so you'll have to be patient with me. I'm no stranger to cars, I grew up taking part in motorsport and I still do, but I was always more interested being behind the wheel than under the hood.

[siteunseen]

Yes I was able to cure it but at a greater expense than a injector cooling fan from the ZXs. I did all of it while rebuilding my motor, you know the old "as long as I'm here I might as well go there too" adage. Getting rid of all the emission stuff and spaghetti pile of hoses that were there were my main goal, we don't have the inspections in good old Alabama. If you could find one of those fans that would be the easiest fix until you're ready to go a lot further, headers and a straight through fuel supply. I love what Zed Head said, "For the sake of the passengers in these embarrassing situations, please."

[TheCrazySwede]

Yes I was able to cure it but at a greater expense than a injector cooling fan from the ZXs. I did all of it while rebuilding my motor, you know the old "as long as I'm here I might as well go there too" adage. Getting rid of all the emission stuff and spaghetti pile of hoses that were there were my main goal, we don't have the inspections in good old Alabama. If you could find one of those fans that would be the easiest fix until you're ready to go a lot further, headers and a straight through fuel supply. I love what Zed Head said, "For the sake of the passengers in these embarrassing situations, please."

I hear ya. Yeah, unfortunately, good ol' Commiefornia won't let us pass on by in our classic Z's...unless mine was 2 years older, in which it would do just fine. I've read about the ZX's cooling fan setup and how it has managed to relieve a lot of issues regarding heating issues with these older Z's, but I've also read cases that object with quite contrary results. I don't remember specific threads or posts, but I've seen a few Z owners who have tried the ZX's cooling and still faced the same problem. Could this possibly be because of variable factors taking part in the issue? I don't see how a ZX's cooling fan could cure a leaky injector, for example. Given that cooling is the sole issue, would a ZX cooling system be the solution?

[hr369]

here was bosch' solution to the problem on vw's years ago.

A fuel accumulator to keep pressure in the system a little longer.

https://www.partsplaceinc.com/catalog/vw-fuelinjection-fuelpressure-accumulators-gaugekits48.shtml

There is a patent out there that combines a pressure release valve with

an accumulator. its a good read. What i find interesting is this ---> "The pressure from the vaporized fuel, in turn, may push any liquid fuel remaining

in the fuel lines back into the fuel tank" I hadn't noticed a rise in fuel

pressure after turning off the engine. Has anyone else noticed this?

It's possible that just an accumulator will fix the problem. Has anyone here

tried one?

Patent US7267108 - Fuel system pressure relief valve with integral accumulator - Google Patents

It appears the optimal location for the accumulator is right next to the fuel pump.

this is a mercedes setup.

Edited March 29, 2014 by hr369

[FastWoman]

HR369, yes, I've noticed that after shutoff, the fuel pressure will slowly rise from its normal operating pressure to a plateau at the FPR's bleed-off pressure. One can only presume fuel is bleeding off into the return line at that point. This could be confirmed, of course, by removing the return line and watching what comes out (and when).

It's worth noting that I've observed this on a warm (but not blistering hot) day in the shade with the hood standing open. This is one reason I believe the problem is heat passing directly from the cylinder head to the injectors.

The accumulator sounds interesting, but I would think it might create a performance changes. When the throttle is suddenly opened up, the intake manifold pressure rises (vacuum decreases), and then the fuel pressure must be dropped by the FPR to compensate. There would be a lag created by the accumulator, as more fuel would have to be bled off for the pressure to drop. And then as the throttle is closed, fuel pressure would have to increase accordingly. It would take time to fill the accumulator back up. I wonder if the accumulator is used in a constant pressure scenario (not regulated in relation to intake vacuum).

[hr369]

The only affect the accumulator has on fuel pressure while the pump is running, is that

it keeps the pressure more steady because of the reservoir of fuel it has. The magic happens

when the car is shut off and the spring and diaphram take over and supply residual fuel pressure.

Fuel pressure coming into the fpr is "always" constant and its the regulators job to raise or lower pressure. with the addition of an accumulator, its job has not changed. the only difference now is that pressure supplied to the fpr is more stable.

the accumulator is kind of like a surge tank to prevent starvation on the race track.

in our stock cars heat soak is the "race track"

[FastWoman]

HR369, if you were to install a pressure gauge anywhere in the system from the outlet of the fuel pump, to the injectors, to the inlet of the FPR, you would find that the pressure jumps up and down right along with intake manifold pressure. The FPR bottles up a 36 psi pressure differential between the fuel rail and the interior of the intake manifold, but because engine vacuum jumps up and down, so must fuel pressure. Any attempt to stabilize fuel pressure (with respect to atmospheric pressure) is going to make the system less responsive.

BTW, I mucked up my description of the fuel pressure compensation in my prior post. Throttle open -> vacuum drops -> fuel pressure increases (relative to atmospheric pressure). Throttle closed -> vacuum intensifies -> fuel pressure decreases (relative to atmospheric pressure).

Edited March 30, 2014 by FastWoman

[rossiz]

ok, so i'm a little confusticated here...

if the accumulator "stores pressure" between the fuel pump and the rail, wouldn't a drop in pressure due to throttle opening/closing simply pull a little of the "stored" pressure, which would be continually replaced by the pump? i'm not sure how the accumulator would make the system any less responsive, as the pressure would always be there - either from the accumulator or the pump itself, right?

[EuroDat]

I understand the benifits of an accumulator, but I thought they are used on static pressure systems. Wont an accumulator mess up the effectivness of the FPR, making it less responsive because of the extra volume. The orifice in the FPR is rated to the capacity of the fuel pump.