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I'm trying to identify a fuel leak on my 1986 944 Turbo.
It's around injector one.
Fuel starts to appear when you turn on the car, but it seems that it continues (and perhaps even increases) in the few seconds after you turn off the car.
My current thinking is that it is not the injector itself like I first thought, but rather the rail in that area. Reason for this is that I visually identified areas of 'weeping'/'welling' on the rail and not directly on the injector. All injectors have brand new, fresh seals. The injectors sit as they should. All fuel lines are new. Fuel rail is the original one from 1986 as far as I can tell.
Here are some photo's that show the leak(s) location(s):
This is the area that seems to have a sort of 'fuel well', fuel keeps appearing there, slowly This is the back of the 'well area' but it also seems to have its own problem. Fuel also appears here it seems. This is the area where fuel pools.
Inspect your short fuel line connection at the rail, next to your arrows.
Good chance it's loose or was over tightened and the rail has cracked.
The fuel rail remains under pressure after the car is shut down. This is by design and should maintain pressure for a minimum of 20 minutes.
With the injectors no longer accepting fuel I could see the leak increasing, path of least resistance.
These vehicles have a history of engine fires. I would find and fix the issue before driving it again.
Repeating mj951....
The factory fuel rail is prone to fracture / leaks and has burned many a 944 to the ground. Many more damaged to a lesser extent by these same fires. I wish there were a GOOD replacement fuel rail.
MM
Thank you for your insights.
I've decided to buy a new OEM fuel rail as opposed to a second hand one or a new, modern aftermarket kit. I need to get this car moving in the next two weeks, so I don't have time to figure out how to install an aftermarket kit.
Unfortunately, the OEM fuel rail is as expected quite costly, paid 800 EUR for it. I'll try to torque it to spec, but I probably need a set of crows feet wrenches.
I replaced my fuel lines many years ago and will admit I did not torque these lines down. I built two new SS fuel lines with AN fittings but replaced the short line with an OEM one.
If you're comfortable with it and used to wrenching on things, you should be able to tighten them down with a shorty wrench (don't want to much leverage) until they are just snug and feel about right.
Check for leaks before driving and check again after the first few times out.
You could also use a little high temp thread sealant. I've used Loctite 567 and Permatex 59214 on the end nut mainly because I have that off at least once every spring checking / adjusting fuel pressure.
I don't like keeping the fuel pressure gauge attached throughout the year so I put it on, check the pressure and remove the gauge. And since I don't want to over tighten the cap nut I use a little thread sealant on it.
Also note, there's a ball bearing sitting inside the cap nut at the end of the rail, don't loose track of it.
(Edit) Equally important are the smaller bolts (M6?) that hold the fuel rail down to the head and cam cover. Do not over tighten those as they can easily strip.
As a general FYI, thread sealant is only necessary with tapered/pipe threads where the interference between the male and female threads provide the seal. I prefer the high-temp liquid type versus plumber's tape.
The 944 fuel rail uses straight threads, with ball-end flare fittings providing the seal, similar to those used in the gas lines in your home. This is why there is the ball bearing between the fuel rail test port and its cap. The JIC or "AN" fittings also use a 37 degree flare with straight threads, sealant won't do much.
The key with the factory fuel rail or any other such combination of swivel and fixed fittings is to always counter-hold against whatever you are cracking loose or torquing back down---the square part of the 944 fuel rail is either 19mm or 22mm, I cannot remember right now. I am not even suggesting to use a torque wrench, too much opportunity for an inexperienced user over-torquing a fitting---just nice and snug while counter-holding. An open-end wrench is often a loose fit, so I prefer these pliers wrenches from Knipex. I use them all the time at work in applications where an open-end or flare nut wrench doesn't work (even for camshaft timing of Porsche V6 and V8 engines in Macan/Cayenne/Panamera) and at home for random projects when I don't have access to all my wrenches:
Thanks for all the tips!
I'll do the snug method with wrenches then.
Unfortunately, the PO did strip one bolt out of the four holding the rail to the head. I have to helicoil that or get someone to do it as I've never done it before.
The aluminium head is pretty easy when inserting helicoils. I replaced all (and I do mean all) threads with helicoils when I had the intake on the workbench. It is not hard to strip a thread in aluminium.
Take a close look at the short fuel line connection near the rail, right where your arrows are pointing. There's a good possibility that it's either not tight enough or was tightened too much, causing the rail to crack. If you're not confident in fixing it yourself, consider reaching out to an affordable plumber in Vaughan, as they often have the expertise to handle such issues.
Remember, the fuel rail is designed to stay pressurized even after you turn off the car. Ideally, it should hold this pressure for at least 20 minutes. Since the injectors stop taking in fuel once the car is off, the leak might actually get worse as the fuel finds the easiest way out.
It's important to note that these vehicles are known for engine fires. So, I strongly recommend locating and resolving this issue before you consider driving the car again. For a reliable and affordable fix, a plumber in Vaughan might be your best bet. Safety first!
The weld from rail to mount tend to crack. Be careful when replacing it make sure it’s positioned carefully before tightening it down to avoid breaking weld marks and leak again, I’ve done this before 🤦♂️
My rail was cracked as other posts suggest. New rails are approx £600 in the UK so I had a local guy rebraze or maybe silver solder mine. I think he said all the fittings inc the injector cups were electro brazed or welded at the same time originally using a single fixture? If you look at the base of the injector cups they have dimples which promote conduction during the process. I think he said the part was electrically heated whilst sitting in a braze or weld powder, which then melts over the heated interface. Anyways he did an old school repair with a gas welding torch. The risk was local repairs melting adjacent joints but it seems to have been fine since. No more leaks. I would echo what other posters say about counter holding when removing the end cap and making sure mountings are not bent and that injectors are helped into the fittings at each end rather than exerting transitional pressure on the rail
We've been through at least 2 stock rails on our enduro car. They are just at the end of their life now. We replaced ours with the Lindsey one, which was a bit tricky to get installed and sealed, but now works quite well.
The new rail I bought had a sticker that said made in 2008 I believe. So yeah they are pretty old. But no leaks anymore! I didn't want to mess with an aftermarket rail.
11-11-2023, 04:10 PM
Fuel leak - rail side
