Fuel check valve

[2fast]

Ok Guys I have a hard start problem when warm or hot so I thought I would try the Fuel check valve,I have a few questions.

Were is the old check valve does it have one?
Can I get this part at my local store or do I have to get it at BMA?
I sent BMA a email for a price and shipping cost to New Zealand.
What does this check valve do.
I had a look at http://www.bmwe34.net/e34main/trouble/535ihot_start.asp

Thanks

[Blitzkrieg Bob]

The fix kit from BMA is an inline valve that goes on the fuel line, under the access panel in the trunk

The valve keeps the fuel system pressurized so starts are a snap.

[Bill R.]

when that one fails you can use the inline as a replacement. The check valve keeps the line pressurized all the way from the fuel pump up to the injectors, this prevents vapor lock from ocurring since the boiling point of the fuel is much higher when its under 35 psi than at atmospheric.. So it serves 2 purposes , 1 to ensure that fuel is right at the injectors when you first crank it, and 2. to prevent vapor lock from occurring in the fuel line

Ok Guys I have a hard start problem when warm or hot so I thought I would try the Fuel check valve,I have a few questions.

Were is the old check valve does it have one?
Can I get this part at my local store or do I have to get it at BMA?
I sent BMA a email for a price and shipping cost to New Zealand.
What does this check valve do.
I had a look at http://www.bmwe34.net/e34main/trouble/535ihot_start.asp

Thanks

[2fast]

Thanks for great replies

Can I get this Fuel check valve from my local parts store or will they look at me funny when I ask for it.

[SRR2]

A nitpicky point for my edification if you don't mind: my experience with vapor lock was on cars built in the 50s and 60s with mechanical fuel pumps mounted on the engine that relied on air pressure in the tank to suck the fuel all the way to the pump. I had one problematic car in particular (I think it was a 62 Lincoln) that refused to run once run and parked on hot summer days. The fuel line was routed over one of the resonators and presumably the fuel just evaporated there and that was that, the car was immobilized. It sometimes took a couple of hours, and once in a while a jump start due to all the cranking, to get it going. I finally got fed up with that BS and put in a primitive electric diaphragm pump to replace the mechanical pump and the problem was essentially solved, though it was pretty funny listening to that diaphragm pump buzzing like pulling vapor out of the line until the evaporating gas cooled the line enough to allow liquid to pass.

OK, so that bit of history said, how does a fuel system that uses a pusher pump in the tank ever get vapor locked? Doesn't seem possible to me. Check valve or not, once the pump runs and pressurizes the lines and rails to operating pressure, any vapor would immediately recondense, and 'locking' in the classic sense just can't happen.

[tim]

That 62 Lincoln had a one way system. All the pumped fuel was blown into the carbs, and any excess was held in the bowl. If the carbs flooded when warm, and the fuel line wasn't totally airtight, the fuel would back down into the pump and created a bubble in the line in front of the carb.. A check valve would fix that too.

On the BMW we have the recirculating type, where the pump goes to the rail and back again, so the whole line is pressurized. When you shut off the car and it's warm or you have leaky injectors, the fuel travels in both directions back to the tank, leaving a bubble of air on the fuel rail. As long as you can keep the gas up to the rail on the supply side of the system, it's fine. The return line is only a factor if it leaks.

So to answer your question, it's not vapor lock, and unlike the lincoln, if you keep cranking it will eventually start as long as the pump can get the system up to pressure.

[SRR2]

Tim, I understand the concept of vapor lock and know exactly how the fuel system in the Lincoln and the BMWs works. That wasn't the question, and for that matter, your diagnosis is wrong. Vaporization leading to "lock" occurs in areas of low pressure. Assuming that the fuel feed to the Lincoln's mechanical pump was normal, any bubble occuring between the fuel pump and the carb would simply have been pushed into the carb and vented into the intake the moment the float called for fuel. The vapor lock in the Lincoln was caused by 1) heating of the fuel line over the resonator, and 2) use of a suction type of fuel pump. Bad design combination.

The question, if you reread my post, was how come Bill R. calls the problem "vapor lock". The entire fuel system is pressurized, therefore I see no way for vapor to form in any part of the system that would 'lock' anything longer than a second or two that it takes for the pump to build full pressure. And in that case, I would hardly call it a lock. The Lincoln, when this problem occured, was "locked" in the sense that the engine was incapable of running. Now that's a LOCK, in my opinion.

As to "air on the fuel rail" Don't think so. There's no way for air to enter a properly working fuel system short of running out of gas. At most you'd have some fuel vapor, and that would recondense and/or recirculate back to the tank as soon as normal pressure is restored.

[tim]

Sorry, man. didn't mean to piss you off.

[DanDombrowski]

Im not sure if I'm pointing out the obvious here, but you can get vapor in the lines with the BMW system because the entire fuel system ISNT pressurized (at least when the fuel can drain back to the tank when the original check valve fails). Thats the whole point of the check valve, to keep it pressurized. I'm sorry if I'm misreading your question.

Now, would fuel vapor in the line lock it per say? I don't think so. Probably just people using the same terminology now as when they started using it.

[SRR2]

Right. We're in violent agreement. I wouldn't be a bit surprised to find vapor in the engine fuel rail if the check valve had failed. In fact, I'd be surprised if there weren't vapor there! My point, and I think we're on the same page, is that because the system is pressurized from the tank, it can't "lock" in the classic sense of the concept of "vapor lock" which is why I mentioned the Lincoln fiasco. Anyway, at worst, it will take a second or two to purge the vapor as the pump pushes enough fuel into the rail to recondense it and/or push it back into the tank.

I think this has been a productive argument. I bet there are at least one or two members who understand the role of the check valve a little better than they did before.