Unique and confusing as heck - BMW Forum

terry717 · 02-26-2011, 12:52 PM

Okay have a 90 325i, just picked it up a couple weeks ago. Other than needing a tune up it was driving fine. I noticed when I bought it that it needed an oil filler cap as the old one was pretty busted up. Here's the quandary I'm having since I replaced the oil cap. It drove fine after putting it on going to pick up my son and a couple in town runs..we get home, and 2 hours later it acts like its run out of gas. You all know the sound of running out of gas the more you try to start it it basically drains the fuel out of the line and stops even trying to fire. So the next day I go out and it starts right up. Ran up town just fine again, get home and about 4 hrs later, the same thing. But today no firing. Are there relays I should be checking? Could the oil cap have changed vacuum on something? I know yesterday when I started it, I pulled the cap when running, and it acts likes it's going to stall, is this normal? Any ideas on where I should start? I know there is fuel in it. Thanks in advance!

terry717 · 03-01-2011, 11:16 AM

Quote:

Originally Posted by terry717

Okay have a 90 325i, just picked it up a couple weeks ago. Other than needing a tune up it was driving fine. I noticed when I bought it that it needed an oil filler cap as the old one was pretty busted up. Here's the quandary I'm having since I replaced the oil cap. It drove fine after putting it on going to pick up my son and a couple in town runs..we get home, and 2 hours later it acts like its run out of gas. You all know the sound of running out of gas the more you try to start it it basically drains the fuel out of the line and stops even trying to fire. So the next day I go out and it starts right up. Ran up town just fine again, get home and about 4 hrs later, the same thing. But today no firing. Are there relays I should be checking? Could the oil cap have changed vacuum on something? I know yesterday when I started it, I pulled the cap when running, and it acts likes it's going to stall, is this normal? Any ideas on where I should start? I know there is fuel in it. Thanks in advance!

Update: Okay since this post I have figured out that it is going through FP relays. I can put a good one in, drive it maybe 5 min shut it off, and the relay doesn't want to work again. I can get it back home by bypassing the relay with a wire in corresponding relay pin plugs..pump comes right on but of course runs continually. 1) The wire doesn't seem to get hot, so is this going to hurt anything? 2) All of this started happening after changing the OIL CAP...how does this make sense...anyone? 3) everything I have researched only shows me I have the one pump in the tank..do I have the one outside the tank as well on my 325i? Is the new cap supposed to be vented, as the other one I replaced was broken up, obviously creating a huge vent.

The only conclusion I am coming to, if it's feasible as I read it on another post is maybe there is too much vacuum in the tank for the pump to draw and the relay runs enough to stop working?

I'm pretty mechanically inclined as far as cars, but this is baffling me. Any suggestions would be welcomed.

k.sidlosky · 03-01-2011, 01:21 PM

Maybe a bad pcv. The cap was busted to help with the vacuum and now its running shitty. I would look into that.

Also look into getting a new relay.

terry717 · 03-01-2011, 02:02 PM

don't want to keep sticking 7-8 bucks into relays if they only last one 5 - 10 minute trip. Is it going to hurt anything to put the jumper wire in the place where the relay sits just to keep the pump on all the time when driving, until I narrow it down more? I really need the car for work, and don't get funds to fix it until the weekend.

k.sidlosky · 03-01-2011, 05:49 PM

The only thing I see it hurting is the fuel pump itself, if you keep the pump constantly running it could burn up. I would say go for it.