Modern injectors, new fuel rail - no heat soak problem

[Zed Head]

I might as well post this up. I just got back from a long drive, with several stops, and not a sign of the heat soak problem. I've made several changes but I think this would be easy for anyone to do, with an adjustable fuel pressure regulator as backup for any tuning, rich or lean, that needs to be done. Since it's only me for now though, the risk is there that I just got lucky. Hopefully it's real, I don't want to cause anyone to waste time or money.

I’ve been running more modern injectors (1989) for five days now, and they seem to be immune to the heat soak problem. Or the overall modified fuel system is. I’m using 14 mm injectors, Bosch 280 150 901, with the injector o-ring as a seal to the intake manifold, bypassed resistors (just link all of the wires from the harness together on each plug) since they’re high impedance, a straight through aluminum fuel rail (the typical type), and no injector mounts (the rail holds the injectors down and the fuel pressure presses the o-ring against the manifold for the vacuum seal). I have an adjustable FPR but it is set to 36.5 psi. I also have the potentiometer on the coolant temperature circuit but it is set to zero. Previously, with my old original 1978 injectors, I had a very small amount of added resistance. So these may run a hair rich. Maybe they run the way the ECU expects them to run.

I tested them three times right after installing with a drive then a 15 minute wait and restart, another drive and 15 minutes, then a long drive and a 40 minute wait, and since then just normal daily driving. They haven’t missed a beat, not even a hint of the typical heat soak signs. I didn’t put my cooling fan hose back on just to make sure I wouldn’t turn it on by accident and screw up results.

I’ve copied below the links I used to choose the injectors and a few more to show the typical rail installation. Of course, with so many changes it’s hard to say exactly what made the difference.

Here’s a link to flow rates and other variables. There is a variety to choose from with ~188cc/min. I bought one injector from the wrecking yard and compared the flow rate to stock BWD replacement injectors that I already had mounted up on my testing device (a stock rail, six injectors wired in series, a fuel pump, filter, and some switches). Just ran them wide open for a certain time in to a Coke bottle and eyeballed final levels. They were identical. Crude, but so is the EFI system. Note that the flow rates don’t work out if you use the typical flow rate versus pressure calculator. But they did in the head-to-head test. I had planned to drop fuel pressure if necessary, but haven’t had to do that.

Stan Weiss' - Electronic Fuel Injector (EFI) Flow Data Table

Here’s a selection of Bosch injectors, with pictures, that I used to find one that would fit physically. I chose the 901’s for the nozzle and o-ring configuration. I got a set at the wrecking yard, with about 150k miles on them (it’s an experiment!).

Bosch Fuel Injector Catalog Wholesale Prices No Charge

Specific –

Remanufactured Bosch Fuel Injector 0280150901 25531465

Here’s a link to the type of rail I am using. I made my own but it’s generally the same, except for the mounting fixtures. If I had less free time I probably would have just bought one of his. But it was fun to build something new.

PALLNET FUEL RAILS - Vendor's Forum - HybridZ

The system might be bolt-on no-tuning required, or it might require a minor fuel pressure adjustment. I have not seen any changes in driveablity, they might actually be smoother than the old setup. The idle definitely feels smoother, maybe due to better atomization. The engine still runs great, in general.

It might be that something simple like just a straight-shot aluminum rail will do the trick (superlen might have been on the right track with his thoughts on the fuel flow getting side-tracked to one side of the stock rail). siteunseen is using a straight rail with stock injectors and hose clamps and does not have the problem. But he also has headers. My cooling fan experience led me to the injector bodies though, and the fuel rail was necessary to get them installed. I had considered making six adapters to attach hoses on to the 14mm injectors so that they could be used on the stock rail, but couldn't find the materials at the time. I do have materials located now though and may make some up just for a future experiment. That would be the one variable experiment.

Anyway, that’s the story. The car behaves like a normal car now. Not even a burp or bobble on hot restart. I’ll come back after these next few hot days (supposed to hit 80), or at the first sign of heat soak problems. If you're reading this and tempted. you should probably wait before buying anything. I've been wrong before. You can always put a plan together though.

Edit - the site software or my browser seems to be highlighting phrases like "Bosch injector" to lead people to eBay. Those aren't my links. Don't know how to get rid of it either.

Edited April 29, 2014 by Zed Head

[siteunseen]

Edit - the site software or my browser seems to be highlighting phrases like "Bosch injector" to lead people to eBay. Those aren't my links. Don't know how to get rid of it either.

Donate to the club, those are skimlinks I believe. After I got the gold star they went away, worth every penny! When your motors hot that aluminium rail feels cool while idling doesn't it? I made my rail too for 50 bucks and still have the measurements if anybody wants them, thanks again Willoughby. http://www.classiczcars.com/forums/fuel-injection-s30/43897-make-fuel-rail.html, #21. My old injectors had one small hole in the pintle, new ones are the hole thing with a spray hole in the center, Standard FJ707Ts. I'm glad things are better on your Z.

Edited April 29, 2014 by siteunseen

[Zed Head]

Thanks, I'm glad too, very glad.

I didn't know the Standard brand had a different injector outlet. My BWD's apparently came from the same location, in South Carolina (another guess based on maps from their web sites), but have the typical single hole with a pin sticking out. Also, the end is covered with a plastic pintle cap. I wonder if Standard didn't incorporate new technology to produce to an old spec. with the FJ707T.

What would be weird though, if the T is better than regular FJ707 for heat soak, is that the T series is the low budget line, according to Standard's description (no offense, I have some T series ignition modules myself, waiting as spares). That would be something if that was the case. Cure for heat-soak = low budget eBay 707T injectors.

Edited April 30, 2014 by Zed Head

[superlen]

Great info Zed!

[FastWoman]

Zed, this is exciting! To be clear, are you using the types of injectors that mount to the rail with an O-ring? I'm wondering two things, but I don't know enough about the o-ring type injectors to know whether these are good questions:

1. Is the opening from the fuel rail to the body of the injector fatter and shorter, so that fuel can dribble down more freely from the fuel rail to the interior of the injector? Put another way, is fuel vapor better able to bubble up into the fuel rail?

2. If I understand correctly, what physically holds the injector into place is the rail itself? That is, it doesn't have the same clamp and insulator as the OEM injector? I ask, because if the injector is getting soaked from intake manifold heat (heated by the exhaust manifold below it), as I believe, then perhaps the OEM injector mount is keeping the injector from dissipating heat to the air around.

Do you have a photo?

Oh, one more question: Are you running the same fuel you were using on the old injectors that gave you hot-restart issues? Same tank of gas from the same station? I ask because I wonder about winter-blended gasoline as a possible contributor to the issue.

Edited April 30, 2014 by FastWoman

[Zed Head]

Yes, these have the 14mm o-ring seal and the top of the injector is about 6 mm (a guess) from the stream of fuel flowing past. No long rubber hose.

That's an interesting question about what holds the injectors in place. The aftermarket aluminum fuel rails that everyone is using typically rely on the injector rail itself as a long rigid clamp on the tops of the injectors. As I was working on mine I was thinking about dangerous the whole setup is, with six large holes just waiting to spew fuel on a hot engine if the mounting brackets come loose.

To your point - I didn't use the mounting seats but may reinstall them in the future. I spent extra time making sure my rail was secure. So the injector is exposed completely, just sitting in the intake manifold hole. Who knows, it could be a factor in heat transfer. If I use the mounts again I'll have to make sure the seal to the manifold gets enough compression.

I'll take a picture and post it later.

Here's a closeup of 5 and 6. The overall setup is very industrial. My hood generally stays closed. That's the fuel return line in front of the injector clips.

Edited April 30, 2014 by Zed Head

[Zed Head]

I wonder if Standard didn't incorporate new technology to produce to an old spec. with the FJ707T.

Quoting myself. I found an old thread about the 707T's - http://www.classiczcars.com/forums/fuel-injection-s30/45474-fuel-injectors-fj3-fj707t.html

[FastWoman]

Interesting! Thanks!

Here are my thoughts: IF liquid fuel can dribble from the rail, down into the injector body, while at the same time fuel vapor can bubble up to the rail, then two things would happen. First, the injector rail system would act as a heat pipe, such that the injectors would be cooled by the rail itself, with fuel being the working fluid. Cooling would continue until all the working fluid is gone (vaporized, blowing past the pressure regulator). (So the larger the bore of the fuel rail, the greater its cooling capacity.) Second, when you go to fire up the engine, any fuel vapor will be free to rise into the rail, where it would either condense or be carried away in the return line. Liquid fuel would dribble past rising vapor to cool the injector very quickly, so that it would not be necessary to work through the injection of a vapor pocket (whose size could be enormous if fresh fuel is flashed to vapor inside a hot injector).

FAIW, I doubt the O-ring system is dangerous, provided the fuel rail is well bracketed (perhaps including a bracket in the middle). I've never heard of a fuel rail popping apart and spilling fuel. I think for that to happen, the engine would have to suffer such damage as to become deformed. At that point you've got more serious issues.

[Zed Head]

The heat pipe theory is a good one. It should work for the standard fuel rail also though, but without the surface area and conductivity of the aluminum rail. Vapors are free to rise in the stock system also, up through the rubber hose to the metal rail. Maybe the aluminum rail is enough to keep the injector bodies below the threshold. Could be why siteunseen's rubber hose/aluminum rail system works. Or, as you suggest, there's just more fuel available to keep the cooling cycle going. If siteunseen didn't have headers, he would have the fuel rail as the single variable experiment. Except for the 707T injectors.

There has to be more people out there with the barbed fuel rails, running stock injectors. Maybe another survey is in order. The problem with the problem is that the people who don't have it, don't really know what we're talking about. Little reason to get involved.

Maybe the accumulator theory is right, and the accumulator is a just a cooling fluid reservoir. Eventually the minimum work necessary or a set of factors that can control it will be clear, I hope.

I think that the o-ring system is only more dangerous because the safety built in to it by the designers has been removed. In a factory stock system, each injector has a clip holding the injector in to the rail. You can pressurize the rial without it being bolted down. If it comes unbolted, no fuel escapes. If pressure is applied to these aftermarket rails, unbolted, the injectors will just pop out.

Edited April 30, 2014 by Zed Head

[FastWoman]

Well, my thought about the stock system is that there might be narrow enough passages, perhaps even internal to the injector, that a fuel vapor bubble might block off the passage, so that liquid fuel would not dribble down into the injector. If fluid movement is blocked, then the assembly will no longer function as a heat pipe. Then if the injector becomes superheated, for lack of heat transfer upwards to the rail, it could flash liquid fuel inside the injector before the liquid can even reach the pintle. What is left, then, is a system that injects fuel vapor -- undoubtedly more volume, but much less fuel to burn. The vapor pocket is eliminated only when a mass of fuel vapor is injected whose total heat of vaporization is sufficient to reduce the temperature to a level where the fuel vapor pressure is less than the fuel rail pressure. (Phew!) So to achieve proper fuel flow, the volume of vapor that must be injected could be much larger than the lumen of the injector and feed hose.

I didn't know about the clips on stock o-ring designs. Would it be difficult to construct clips on a DIY rail?

[Zed Head]

I've pondered the heat pipe heat removal process. I figured that it was happening but apparently not removing enough heat. It's a viable explanation though. Maybe Nissan knew that and that's why they describe their cooling fan's purpose as to remove heat from the fuel system, and that's why it blows on the rail. Could also be why several of the manufacturers use some pretty fancy aluminum rails, and some of them are even finned (one side benefit of prowling the wrecking yards is you see a lot of stuff you would never see otherwise). Which I had though would draw heat in from the engine bay, but it's all about differential so engine off maybe fins are good, to dissipate heat to the engine bay surroundings.

It works for me, taking heat from the injector body, and fits the two cases so far. Mine and siteunseens. pallnet, the Hybtridz link I referenced above, sells rails with barbs. It could be that simple (Occam and Einstein and all those guys, you know).

On the clips - the factory clips usually fit around a round projection (the manufacturers typically use a stamped pipe type hole for the injector). You'd have to design your own but I'm sure it could be figured out.

Edited May 1, 2014 by Zed Head

[mjr45]

Zed just as an FYI, I took the Z out today with several stops after some running on the Interstate and up and down the mountain no hot restart issues. Stock 79 fuel rail, stock 75 pump with new check valve, nothing special. Outside temp was only 62°.

Edited May 1, 2014 by mjr45