Fuel Delivery Problem

[stargazer_61]

Help!

My '95 540i is having a hard time running. This morning I put about half a tank of gas in it. When I went to restart it, it would crank, occasionally turn over, then die. It finally started and I went about my way going to work. During the drive with the cruise control set to about 70mph, the tach would occasionally drop 300-400 rpm, then it would surge up again. I was thinking speed sensor, so cut off the cruise. Engine rpm would still randomly fall off, then pick up again, then it steadied out for the remainder of my commute.

Upon arriving at my exit and stopping, then punching the gas to accelerate, it died. I tried several times to get it to start to no avail. Another motorist, in an E39 no less, offered to help me push it out of the road. When I went to unlock the steering and put it into neutral, I gave it one more try and it started, but it was difficult to keep running.

So, my questions are, what is causing this? Do fuel pumps just die, or do they function intermittently before death? Could the fuel pressure regulator be malfunctioning? Or is it merely dirty fuel filters or bad gas? It did this once before a couple of nights ago when coming to a stop after a long run on the freeway, but didn't die, just hesitated, with gas in the tank from a different brand and location.

[stargazer_61]

A bump.

I disconnected the fuel line and cranked the engine. I get flow out of the line, and there was fuel pressure in the rail. The car will idle when I can get it to start, but when put under load, it will stall. Anyone have any ideas?

[araine901]

Can you check for vacum leaks? ie: carb spray etc

[Bill R.]

flowing out of the line and feel some pressure but it may not be enough. If it idles but as soon as you put it in gear and try to take off it dies thats frequently an indicator of a bad fuel pump not providing enough pressure, I would check the pressure regulator and the pump both. Thats the first thing i would check.

A bump.

I disconnected the fuel line and cranked the engine. I get flow out of the line, and there was fuel pressure in the rail. The car will idle when I can get it to start, but when put under load, it will stall. Anyone have any ideas?

[stargazer_61]

It was the fuel pump. I was just hoping against hope that it was something simpler.

There is some debate amongst the mechanics around here whether or not they die slowly or suddenly. Most thought fuel pump death was sudden, whereas mine would run fine for quite a while, but did get progressively worse, leading me to believe that it was the pressure regulator.

Anyhow, it has been replaced, good for another 150k, I hope. MPG is up by 2 on the highway according to OBC.

[Bill R.]

than the drawn out process but at least you have it fixed now.

It was the fuel pump. I was just hoping against hope that it was something simpler.

There is some debate amongst the mechanics around here whether or not they die slowly or suddenly. Most thought fuel pump death was sudden, whereas mine would run fine for quite a while, but did get progressively worse, leading me to believe that it was the pressure regulator.

Anyhow, it has been replaced, good for another 150k, I hope. MPG is up by 2 on the highway according to OBC.