Fuel check valve

[tim]

The limiting factors on the amount of time to purge vapor is the vent rate on the vapor condensation tank, and the distance to which the fuel traveled back down the line. I suppose if you parked uphill, that could be as much as 10 feet of fuel line (1/2 my estimate of the loop). Or do I need another lesson?

[SRR2]

Are you talking about the vapor recovery canister? That shouldn't come into contact with liquid fuel. The fuel/vapor separator routes evaporated fuel from the tank to the canister, and when the engine is running the canister purge valve opens to vent the canister to the engine intake manifold. Looking at the E39 Bentley, most engines (except for the M62/TU) have straightforward plumbing. Fuel pump -> filter -> rail -> regulator -> return line -> tank. The V8s are simpler where the regulator is built into the filter and the return line runs from the filter back to the tank. There's only a single line to the rail on the engine. If there's vapor there, it's either goign to recondense when the pump runs, or it's going to be blown through the injectors as the fuel fills the rail.

I found a spec on volume delivery for the E30. It's .5 GPM at full pressure, measured from the regulator return line with the engine off. Delilvery at reduced pressures, like an empty line is going to be higher, but by how much I don't know. For sure, the delivery of E34 and E39 fuel pumps are going to be greater than that.

Just for purposes of discussion, let's assume that fuel line has 1/4" ID and there's, say, 15' of it. And the rail is 3/8" ID and 2'. And the fuel filter accounts for 3oz. That amounts to 8.8 in3, 2.6 in3, and 5.4 in3 respectively. .5 GPM is about 115 in3 /per minute, so the total volume to charge is 16.8 in3. At roughly 2 in3 per second, that's about 8 or so seconds to charge a completely empty system. Now, I realize that these aren't actual numbers, but I'm just looking for a good engineering estimate. In reality, the E34 and E39 pump outputs are going to be higher, and the system volume will probably be roughly the same, so the charge time will probably be less than this estimate.

[SRR2]

Oh, by the way, you're right about the car stalling even after it was running. It happened once while sitting in traffic on a really hot day. No a/c in that car either. That was the straw that broke the proverbial camel's back. It had the electric pump fitted the next day. It was surprising how often that pump actually did suck vapor on hot days even while driving. It was noisy and you could hear it buzzing fairly often when sitting at lights in town. The ambient temperature had to be below about 70 for it not to occasionally pull vapor.

No two ways about it, a pump at one end of the car trying to suck gas from the tank at the other end just isn't a good idea.

[Javier]

3 bar counterpressure, and only pushes fuel for a couple seconds at key turn before cranking, so if the check valve is bad, and fuel line dries back to the fuel tank and keep fuel vapor only, you have a nice time starting the engine.

Javier

[2fast]

Ok I have not ordered the part yet.
Here are my symptoms.
when cold car starts BANG!1 second.
When warm or hot may take 3-4 seconds embarrassing.........But not always
Sometimes it start fine when hot.

What do I do feller's.

[Bill R.]

number that shogun gave you will work if you pull the fuel pump out and replace the original check valve... It can also indicate a couple of other things such as leaking injectors which would also allow the fuel pressure to bleed down and would tend to make a hot engine flood so that it would take a little more cranking to start... If you hold the gas pedal all the way to the floor on a hot start does it start easier than if you give it no gas, If yes then that tends to indicate that its a leaking injector (1 or more) causing excess fuel in the manifold , causing a flooding condition which you have to crank until it clears, by holding the pedal to the floor it shuts the injectors off while cranking... this is the clear flood mode.... If holding the pedal to the floor doesn't help then its a bad check valve or a bad pressure regulator.., you can test to get a basic idea first by putting a fuel pressure gauge on it and cranking it to see how high the pressure goes and then letting it sit and see how quickly the pressure bleeds down... It should hold with virtually no leakdown for at least 1/2 hour min. IF it does leak down then you can pinch off the return line coming from the fuel pressure regulator back to the fuel tank and check again to see if it bleeds down, also remove the vacum line to the pressure regulator and see if any gas comes out of there. If these things make no difference then it narrows it down to fuel injectors leaking or check valve leaking.

Ok I have not ordered the part yet.
Here are my symptoms.
when cold car starts BANG!1 second.
When warm or hot may take 3-4 seconds embarrassing.........But not always
Sometimes it start fine when hot.

What do I do feller's.

[Alexlind123]

My car starts the same every time, that is it takes about 2-3 seconds to start no matter if it is cold warm or hot. Any idea what this could be caused by? Its not a real problem, its just that it seems as if it is putting a bit more strain on the starter than normal.

[2fast]

Having foot on the gas makes no difference.
So if I got this part and had to pull the fuel pump out, how easy would it be
to do?

[Javier]

should be a piece of cake.

Check valve

Javier