1976 280z Fuel Injection Issues

[superlen]

Zed,

I have you covered on the injectors. I can control all six separately, so if we know the offenders, we're good to go. I agree that it's a rabbit hole on figuring out who/what/how much.

Your idea on increasing pressure works too, from what I have read online. This makes sense as the higher pressure in the rail will require higher soak temperature to cause vaporization. I don't know if 45 psi will completely solve it, but it should definitely help. HellFire will run at 36, 45, 50psi, or whatever you want to set it at. I ordered an adjustable FPR for testing the stock injectors at different pressures. This may turn out to be the easier/better solution.

Another thing I thought of is that when we try to purge the fuel fail by running the pump for a bit of time, I'm not convinced that it is sweeping the entire rail. Looking at where the FPR is located and the circular nature of the rail, it may just be bypassing some/all the rail. If this is true, just re-plumping the rail such that the prime condition forces fresh fuel to completely replace the warm fuel should help as well.

I have to do some tuneup on my system before I can get some good numbers for HellFire testing, and one of the items is installing the FPR & building a new rail. I'll post back what I find.

Lenny

[Zed Head]

That's a good point about sweeping the full rail with new cool fuel. If I did not have air cooling on individual injectors solving my own problem, I'd probably go out and modify a rail to see what happened.

Interested in what you find with fuel pressure. If it works, there are several people making aluminum stock fuel rails that will take more modern injectors.

What brand of FPR did you order? The Aeromotive FPR's leak down rapidly (seconds) when the pump is off. Poor FPR for daily usage, their design is for high flow for high HP.

[EuroDat]

I think 45psi would improve the spray pattern and atomization. I noticed it as well when I was bench testing my injectors. They worked better at 3bar which is a little less than 45psi.

With the higher pressure you will probably reduce the return flow because you are approaching maximum pump pressure and the impeller will start to cavitate and loose efficiency. That will probably give you a little less cooling capacity when your not flushing as much fuel across the rail.

Would be fun to have a system that gave your the possiblity to play with some settings and experiment.

Chas

[superlen]

Chas,

Good points on the pump/cavitation possibility. Hopefully, the extra PSI should negate the need for the cooling flush cycle.

Zed,

I'll have to check on the FPR. It's just a cheap EBAY model. (I think it was around $50) I bought it and a piece of the AL fuel rail you spoke of to play with a few months back. I looked at the stock rail a little this morning. The way it is designed if the fuel diverts equally along the front & rear loop, the entire rail should get flushed with new cool fuel as desired. However, I wonder if possibly one of those loops doesn't get flushed very well. If the stock FPR was moved to the end of the rail then that possibility could be eliminated. I forget the link, but someone on here did relocate the stock unit to the end and cleaned up the rail looks tremendously. I need to find that again.

Lenny

[superlen]

This was the regulator I bought.

Universal Silver Adjustable Fuel Pressure Regulator Gauge JDM FPR EF EG EK D15 | eBay

We'll see how it holds up.

[siteunseen]

That's the universal FPR I bought only to find out it wouldn't keep the pressure. I almost bought a rising rate Bosch or MSD? like in the picture but tried the coolant temp tweak and it cured my problem. So I just bought a '78 model FPR and put it at the end close to the firewall.

EDIT:

My problem wasn't hard starting BTW, I had a mid range stumble around 2500 RPM. The higher fuel pressure made it better at the time I was trying to figure out the problem.

Edited January 14, 2014 by siteunseen

[Zed Head]

So you have a straight-shot fuel rail. Do you have the hot start/heat soak problem?

[EuroDat]

I have seen that set-up used before as well. The ZX FPR has 1 inlet and 1 outlet and works well at the end of a single rail system.

I was thinking of going this route as well by making one out of 3/4" and TIG welding the tie-ins for the injectors. Polished or water blasted it would look nice, simple and clean up that side of the engine.

It on my "to do list". So many thing, so little time;)

Chas

[racebird1]

When all is the way it is supposed to be it will run very well without adding extra cooling fans or higher fuel pressure. If it is running rough at restart something is wrong. Make sure the fuel pressure is correct and the fpr is letting the excess fuel return back to the fuel tank( and there should be fuel returning). If the fuel is vaporizing then it is running too hot because when everything is normal this will not happen. You can try pulling out the fuel rail with the injectors and placing the rail into a large pan and crank the engine untill full pressure is reached. While doing this make absolutely sure that there is no source of ignition or you will start a fire. Check the spray pattern while you are at it and then make sure the injectors are holding pressure and not leaking down. Just because they were replaced does not mean that they may still have an issue. I also noted that you put grease or oil on the orings be careful what you use because some greases will attack the rubber.

[siteunseen]

So you have a straight-shot fuel rail. Do you have the hot start/heat soak problem?

I've never had that problem before. Actually the fuel rail feels cool to the touch when it's idling, cost $50 to make.

[Zed Head]

Well, there's one data point for purging the fuel rail, maybe. What brand of injector are you using?

And, do you have the stock exhaust manifold or headers? I have another theory about where the heat comes from.

A good poll would probably shed some light on the heat soak problem.

[siteunseen]

New Standard FJ707T injectors, $30 at amazon.com, ceramic coated 6 into 1 header with OE heat shields. Horizontal shield and the vertical one too, had to trim it for the header runners. Also have a vented hood. 1/2" in and out of the rail, 5/16" to the injectors.