engine wont idle after awhile wont turn over

[Brezzi]

K so I was at a traffic light and as I go to put it in gear and accelerate my car chugs forward a bit then dies in the middle of the intersection. When I try to turn it over it wont catch. I moved it in to this parking lot and tried to jump it, no luck. I leave and come back in an hour to try again. It turns over but when it does the idle is very faint (comes in and out), also the gas econ. meter is going wacky while its running. (from 40 mpg to 0 mpg very quickly). If i try to engage the reverse or first it wont move and dies. After letting it idle it dies. After a few trys it wont even turn over. Any ideas to what could be wrong? I drive a 88' 325is if that helps.

Thanks,
-Brent

[hotballs]

My guess would be fuel pump.

[DmcL]

pump, pump relay or main relay would be the usual suspects id think.

[Jay87]

I would go ahead and pull the fuel pump relay (orange one underneath the cover on the driver side fender well). Then, use a spare piece of wire to jump the front and left terminals (labeled from your perspective as you sit in the car). I believe the numbers are 30 and 87 as labeled on the bottom of the relay, but could be mistaken.

This will run the fuel pumps. You can then feel the fuel return line coming from the regulator at the front of the fuel rail. If the flow feels intermittent, you can suspect your fuel pump of FPR. A better indicator would be to pop the return line off the regulator and catch the fuel in a cup to get a better idea of how much flow there is or isnt.

After this I'd look at the main relay and then start hunting for vac leaks. Good luck!

[Brezzi]

Thanks for all the help so far.. recent development: I let it sit over night and when I went to turn it over this morning it started up without any weird nose or rough idle and was able to drive it back to my garage (only 5 mins away). Does this help anyone? Was the motor just flooded or something?

Thanks.

[Brezzi]

havent fixed it yet bump

[Brezzi]

finally got some time and tools so i ran some tests today and Im still not sure what to do. Did the stomp test and code 1444 came back which means there are no current fault codes. So i tested the pump by jumping it from where the relay goes. I heard it turn on so thats not it. Then i poped the return line off the regulator and nothing came out of it when I ran the pump. Does this mean its the regulator? What should I do?

[Brezzi]

tired of not having a daily bump

[jlevie]

Then i poped the return line off the regulator and nothing came out of it when I ran the pump. Does this mean its the regulator? What should I do?

That could mean that:

The fuel is clogged
The FPR has failed
The pump is failing and can't produce sufficient pressure

Your choice is to diagnose the problem, or replace all of the suspect parts. To properly diagnose this you need to know what the rail pressure is after replacing the fuel filter. That means tee'ing in a gauge to the supply line to the fuel rail and jumpering the fuel pump relay. Pressure there should be 3.0bar with gas flowing out of the FPR. If the pressure is lower than that, the pump needs to be replaced. If higher, the FPR needs to be replaced.