testing fuel pumps/relay

[Philo]

I'm thinking CPS. It could intermittently be going bad, not giving a reading for the pump to send fuel.

Mine did a similar thing on start up. The sensor would not read for a bit, then all of a sudden it would kick on.

[dystynkt]

You need to understand that the fuel pump is controlled by the DME and is only enabled when the DME sees timing data from a rotating engine. The pump does not run just because the ignition is on. So what you saw is normal. Check rail fuel pressure.

Ok great thanks jlevie. I will pick up a pressure gauge to test the pressure. Just to understand, when should I get pressure? Will it be while the engine is cranking trying to start? Just want to make sure I am looking at the right time. Good learning experience.

[jlevie]

You need to understand that the fuel pump is controlled by the DME and is only enabled when the DME sees timing data from a rotating engine. The pump does not run just because the ignition is on. So what you saw is normal. Check rail fuel pressure.

[dystynkt]

Ok so I just pulled the line going into the fuel rail and did a couple tests with it. When I turn the key to the 'on' position (which I think should start the fuel flowing) there is no fuel going to the rail which is why the car isn't starting. Next what I did was pull out the fuel pump relay, and with a wire jump from pin 30 to 87 which should kick in the fuel pumps. When I do this, the fuel starts flowing to the fuel rail. I don't think the relay is at fault because I switched it with the relay to the right of it (main relay?) which had the same part number and still nothing. When I bypassed the fuel pump relay I can hear the main fuel pump going loud, but (without taking the cover off and only taking the rear seat out) I can barely make out the sound of the transfer pump. Could this indicate that the transfer pump is bad? Also, with the key in the 'on' position, should I be able to hear the fuel pumps going? (because i don't).

Thanks in advance for any wisdom you can bestow upon me!

[dystynkt]

1. Check line at rail.
2. Check for clogged fuel filter.
3. Check for functioning fuel pump/transfer pump.
4. Check for leaks in the lines.
5. Check CPS.
6. Check for gas in the tank.
. . . And above all else, listen to jlevie.

*list in no particular order.

fuel filter is new, both fuel pump and transfer pump seem to be working, and I know the car has a full tank of gas. as for the rest, I will check it out along with the fuel pressure at the rail like jlevie said. thanks for your help it is much appreciated.

[Philo]

1. Check line at rail.
2. Check for clogged fuel filter.
3. Check for functioning fuel pump/transfer pump.
4. Check for leaks in the lines.
5. Check CPS.
6. Check for gas in the tank.
. . . And above all else, listen to jlevie.

*list in no particular order.

[dystynkt]

When faced with a no start situation, the first check is to see if spark is present when cranking the engine. If it is the next check is to measure fuel pressure at the rail by tee'ing in a pressure gauge at the rail inlet. The results of those two tests tell you where next to focus diagnostic efforts.

I know there is spark I have already checked that along with all the air hoses for cracks. I have narrowed it down to fuel. 2 times now in the last couple days I have gotten the car started, been driving, and all of a sudden the engine cuts out and it is fuel starved. Now it wont start at all just cranks. I will have to get a pressure gauge to check at the rail inlet. Thanks for the suggestion.

[jlevie]

When faced with a no start situation, the first check is to see if spark is present when cranking the engine. If it is the next check is to measure fuel pressure at the rail by tee'ing in a pressure gauge at the rail inlet. The results of those two tests tell you where next to focus diagnostic efforts.

[dystynkt]

Lately I have been having some trouble getting my 85 325e to start right, and now it just won't start. I know the problem is related to fuel. For the last couple weeks I have had to let the fuel pumps run for a bit (leaving key in 'on' position) before trying to start the car and it would start. Yesterday the car started and right when I started driving it died. So, I pulled the fuel pump relay and jumped it as described in repair manual to make sure both fuel pumps were running. By listening to them they both seem to be working. However, I don't seem to be getting any fuel to the engine because it won't start. Is there a better way to test the fuel pumps and/or the relay? I don't want to just start guess buying all new parts for it. Thanks in advance for any assistance.

This is the current situation: Ok so I just pulled the line going into the fuel rail and did a couple tests with it. When I turn the key to the 'on' position (which I think should start the fuel flowing) there is no fuel going to the rail which is why the car isn't starting. Next what I did was pull out the fuel pump relay, and with a wire jump from pin 30 to 87 which should kick in the fuel pumps. When I do this, the fuel starts flowing to the fuel rail. I don't think the relay is at fault because I switched it with the relay to the right of it (main relay?) which had the same part number and still nothing. When I bypassed the fuel pump relay I can hear the main fuel pump going loud, but (without taking the cover off and only taking the rear seat out) I can barely make out the sound of the transfer pump. Could this indicate that the transfer pump is bad? Also, with the key in the 'on' position, should I be able to hear the fuel pumps going? (because i don't).