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Check the color and shape of the fuel pump relay and compare it to the horn relay. Not sure on the E53, but on the E46 the horn and fuel pump relay are the same and you can just swap them. The horn relay rarely is used while the fuel pump relay is used every time the vehicle is started and is energized the entire time the engine is running.

I would doubt the horn relay on most 10 year old vehicles has seen more a few dozen cycles.

It looks more and more like a faulty pump relay to me, although you've already changed the relay recently.

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Quote:

Originally Posted by Juggernaunt911 (Post 1059134)

So here is an update..

We are seeing spark, but zero pressure at rail. Upon further investigation we found that fuel pump does not appear to be priming or turning on when key is in "on" position. Checked fuel pump relay again and fuse and we are seeing power there and relay appears to be switching ok.

On spec I changed out ignition switch but still no change. Out next step would be to try to change out crank sensor, but I just don't want to be changing out parts just because. My mechanic also scanned multiple times and not seeing any error codes, we also re synced EWS and DME but it did not seem to help.

My question is, is there a "main" relay or ignition relay somewhere in the dept under the hood we can try? Would the CPS still be an issue if we have spark? Anything else we can try??

Thanks!

Point of Order
Does the pump come on with the key in Position I (ON) or Position II (RUN)? ON runs accessories such as the radio and windows, RUN is the position that powers the pump. RUN is the key position before START, where the key returns to after the engine starts.

If one was sitting in a parked car with the radio on, they would not be wanting the fuel pump to be running. This is what prompts my question about the key position. You said that you are testing for power with the key in a position where power would not be present.

Have you check the ignition switch?

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I have already swapped out the K92 relay, but can try a new one just for kicks.

I think I would 2nd the ignition switch if another relay does not help.

So when the key is in position 2 (Run) we don't here the pump, but we do have power to the connector into the pump.

So the main problem is that we can't get the pump to come on, which in turn means no rule pressure and no start. However, sometimes when the vehicle has been parked somewhere warm, the pump comes on just fine and there are no issue with starting???? It seems to only happen during cold starts when outside temps are low.

Parts changed already:

Ignition Switch
Fuel Pump Relay
Fuel Pump
Battery
Temperature Sensor

Quote:

Originally Posted by Juggernaunt911 (Post 1059297)

If the engine is not running when the key is in the run position the DME will not command the fuel pump to run. If you have 12 volt at the pump the pump should run, not unless that 12 volt is the fuel gauge voltage.

Sorry, I am confused. Key position 2 is the run position (just before start) shouldn't we see the pump come on before we start engine (in position 2)??? Or does the pump only come on during the start process????

I am pretty sure that when key is in position 2 the pump should come up and prime correct?

The fuel pump comes on briefly in the run position, but if the engine is not running power to the pump is turned off. If you have a fuel gauge you can connect it to the fuel rail and turn the key on to the run position. The fuel pump will run briefly, but if the engine does not start the DME will not continue to send power to the fuel pump.

Here's a video on testing for fuel at the fuel rail.

https://www.youtube.com/watch?v=axxl98lToN8