Why does my fuel pump shut itself off?

[vegaskyle]

It first happen a couple of weeks ago. I was driving home from work on a hot day after a couple miles my car (91 318is) died. It started back up and went a few more miles then died, I came back later that night to change the fuel filter but it ran fine. I replaced the fuel filter and 1 week later it did the same thing. I left it for a few hours and then it ran fine. Sunday I replaced the fuel pump, it ran fen untill today. Driving home from work its 107* and it dies.

With the back seat out I can start the car, hear the fuel pump run then it shuts off after a few seconds 10-60 and the car dies.

Anyone have a clue why? Is the heat a factor?

[vegaskyle]

I made a video of the old pump, it would make aloud whirling noise right before it shut off. The new one doesnt. I'll try and upload them to YouTube if it would help.

[Fusion]

Fuel pump relay?
You can jump the relay to test if its bad or not, search around on how to do that.

[vegaskyle]

Does anyone know where the fuel pump relay is on a 91 318is? I can't seem to get a straight answer. The only Bentley I have is for an e36 (only one that covers the m42) and is of no help.

[pharow]

It looks like you need a new pump. How old is the one that is in there now?

[fredn]

Fuel pump relay is the middle relay on the bracket in front of left hand side shock tower in the bay... if its the same as my 88. I'm trying to research how to "jump your relay" to see if it works... Let me know if you find anything or know how to do this? =)

[vegaskyle]

It looks like you need a new pump. How old is the one that is in there now?

It's exactly 5 days old, the filter is 12 days old.

[Ceeker]

First check the relay. Also check the pump filter on the old one to see if it is clogged with sediment. You might have a dirty tank and the pick up is getting blocked. What happens is that it works for a while and soon as it begins to restrict flow it may shut down as a safety feature.

[vegaskyle]

First check the relay. Also check the pump filter on the old one to see if it is clogged with sediment. You might have a dirty tank and the pick up is getting blocked. What happens is that it works for a while and soon as it begins to restrict flow it may shut down as a safety feature.

I gave the old one a once over and it looked ok but i'll take a closer look at it now. I figured the fuel pump was the culprit when i took the old one out so I didn't look too closely at it.

[vegaskyle]

I just went and got the car and drove it the rest of the way home (about 5mi), this was also the case the other 2 times it did this. Is there any reason why it only has this problem after it's been sitting outside all day and then driven home on days it's hotter than 105*?

[416stroker]

Could vaper lock cause the pump to kick off?

[Ryann]

Your crank position sensor could be taking a shit. The system would shut down your fuel pump if it lost the CPS signal.

[vegaskyle]

Vapor lock was the first thing I checked.

I think (and hope) you are right Ryan. I'm going to test the relay and if that isn't it replace the crank sensor.

Would the heat cause it to fail? I only have this problem in hot, hot weather. The water pump, thermostat, and coolant are all less than a year old and the car shows no signs of overheating.

[jlevie]

It is almost impossible to have vapor lock on an engine with electronic fuel injection. Fuel flows through the rail and back to the tank the whole time the pump is running. So any vapor in the lines would be flushed back to the tank.

If the pump stops running while the engine is running, either the DME turning off the fuel pump relay (bad CPS, bad DME, bad main relay, or a DME power/ground problem), or the fuel pump relay is dropping out. You can eliminate the relay from the equation by jumpering pins 30 & 87 of the relay socket. If the engine still dies, I'd look to the CPS, DME, main relay, or the DME power/ground.

[vegaskyle]

**7/5 Update**

I drove the car around a little hoping it would die so I could test the fuel pump relay and see if it would run when I jumped it. The car ran fine and I never got the chance to test it out. I decided to move on and try some other potential causes. I un-hooked the crank position sensor and tested the resistance on terminals #1 and #2. The Bentley calls for 1200 +/- 10% ohms but I was getting a reading of 560-580.

So I think I found the problem. I'm going to order up a new CPS and hope that fixes it. I guess I'll chalk the new fuel pump up to experience and preventive maintenance.