Is it true that a check valve in the fuel pump is supposed to keep gas from backflowing to the tank when the engine is turned off?

I changed my fuel pressure regulator the other day and was surprised to find no fuel present when I disconnected it. I was expecting a brief spray or at least a dribble but it was dry. The engine had been run probably an hour or so prior to this.

I wonder if this could be connected with a hard starting problem I've been having. Recently it's been taking four or five seconds, sometimes longer, before firing up, where it used to be almost immediate. I'm thinking maybe this check valve has gone bad and it's taking a few seconds for the gas to get pumped back up to the rail.

Does this sound plausible?

yes it does cuz when i changed my fuel injectors the engine had been off for a while and there was still fuel in the rail and a good amount came out when i took the injectors off

Yes, there is a check valve in the fuel pump to keep a slight pressure to prevent vapor lock when the engine is hot. Some of the earlier cars seem to have had a separate check valve installed and several people have reported using one of these valves in-place of the bad internal valve in the fuel pump. It's much cheaper then buying a whole new pump.

It is No. 1 in the picture below. Look around for it, maybe your car is early enough to have had one installed. Sometimes they are located in the inlet line in the engine bay or with the pump/filter assy in the wheel well.

http://bmwfans.info/original/images/1891_p.png (http://bmwfans.info/original/E24/Cou/633CSi-M30/USA/L/A/1984/03/mg-13/)

Thanks guys. Sounds like I might have a faulty check valve.

Bad weather today has kept me from looking under the wheel well, but under the hood I do have two little canisters in-line with the fuel line that look like part 1 in the drawing. I was thinking they were vibration dampeners but maybe one of them is a check valve.

Also, I'll mention here that when you're installing a fuel pressure regulator, the key is to lube the O-ring. Otherwise it grabs and wants to tear. I ruined two O-rings this way before getting smart and putting a dab of motor oil on both the ring and the bore it fits into.

Also, I had hoped that maybe the new regulator would solve my bad mpg problem (thinking maybe it was allowing too much pressure so too much fuel was flowing), but it didn't. I had also hoped it might improve a little stumble I have at about 3500 rpm but no such luck with that either.

I just recently changed my injector o-rings and fuel lines. Both of those canister's are vibration dampeners. You can see right through them. I was told that they were not needed and I left them out when I ran the new fuel line. This info is from an independent shop where the owner was a one time head mechanic at the local BMW dealer. He said they would leave them out when replacing the lines.

i just talked to a guy from roadfly about that. He removed them from his car, and hasnt felt any difference to speak of. Im removing mine when i replace the hoses on my car before SESF. I dont want a carbecue...

-Jeff