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Old 08-13-2019, 08:09 PM   #1
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Leak detection pump

Hopefully someone can give me some insight on this, I have a 2003 BMW 325i with the M56 engine (please don't make fun of me...lol). I think my leak detection pump which pressurizes the emissions system to I believe 21psi has gone south on me. My question is if this goes out, does it cause a shutdown of the whole fuel system? My problem is I am not getting fuel to the fuel rail. I want to exhaust all other possibilities before I submit and say it's the fuel pump. If I turn the key to the on position I can feel the pump running. I understand that I may be getting a soft fail of the fuel pump, but wouldn't I get some fuel at the fuel rain on a soft fail. Hopefully someone can give me a little insight on this.
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Old 08-13-2019, 09:27 PM   #2
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DM-TL pulls vacuum to test Evap, it does not pressurize tank. It is only for Evap test purposes, engine will run fine without it.
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Old 08-13-2019, 09:38 PM   #3
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Ok, thank you. I'm guessing the cut vacuum hose I found may be why the leak detection pump isn't coming on. I guess I should start looking at buying a new gas tank. I found one at a salvage yard in Dallas which is about 6 hours from me for $100. I'm just afraid of buying it and the fuel pump die out on me 6 months down the road.
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Old 08-13-2019, 09:48 PM   #4
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Wait, are we talking about the same thing because although I got the pressure wrong, this is what is said about the pump.

Hobbies Cars & Motorcycles
What Does the Leak Detection Pump Do?
LDP Detects Fuel Vapor Leaks and Triggers Check Engine Warnings
muffler under car
Table of Contents
Vincent Ciulla
Updated May 24, 2019
The leak detection pump is the component that often triggers those "Check Engine" warning lights when it detects small leaks that would be hard to see. It is required under federal law as it ensures your evaporative emission system (EVAP) is functioning correctly.

Your car may still be covered under the five year/50,000 mile emissions warranty.If so, you should not have had to pay a penny for that repair since the leak detection pump (LDP) is an emission control device, as is the charcoal canister (also called the vapor canister). If they are bad, there should be no charge for repair or replacement. Challenge them with your receipts for a refund and further repair of the canister. If they give you an argument about it, call Chrysler, and they will take care of it.

Now, are you ready to learn more about the leak detection pump then you will ever need to know?

Leak Detection Pump (LDP) Operation and Diagnosis
The evaporative emission system is designed to prevent the escape of fuel vapors from the fuel system. Leaks in the system, even small ones, can allow fuel vapors to escape into the atmosphere. Government regulations require onboard testing to make sure that the evaporative (EVAP) system is functioning properly. The leak detection system tests for EVAP system leaks and blockage. It also performs self-diagnostics.

During self-diagnostics, the Powertrain Control Module (PCM) first checks the Leak Detection Pump (LDP) for electrical and mechanical faults. If the first checks pass, the PCM then uses the LDP to seal the vent valve and pump air into the system to pressurize it.

If a leak is present, the PCM will continue pumping the LDP to replace the air that leaks out. The PCM determines the size of the leak based on how fast/long it must pump the LDP as it tries to maintain pressure in the system.

EVAP Leak Detection System Components
Service Port: Used with special tools like the Miller Evaporative Emissions Leak Detector (EELD) to test for leaks in the system.
EVAP Purge Solenoid: The PCM uses the EVAP purge solenoid to control purging of excess fuel vapors stored in the EVAP canister. It remains closed during leak testing to prevent loss of pressure.
EVAP Canister The EVAP canister stores fuel vapors from the fuel tank for purging. EVAP Purge Orifice: Limits purge volume.
EVAP System Air Filter: Provides air to the LDP for pressurizing the system. It filters out dirt while allowing a vent to atmosphere for the EVAP system.
Leak Detection Pump (LDP) Components
The main purpose of the LDP is to pressurize the fuel system for leak checking. It closes the EVAP system vent to atmospheric pressure so the system can be pressurized for leak testing. The diaphragm is powered by engine vacuum. It pumps air into the EVAP system to develop a pressure of about 7.5' H20(1/4) psi. A reed switch in the LDP allows the PCM to monitor the position of the LDP diaphragm. The PCM uses the reed switch input to monitor how fast the LDP is pumping air into the EVAP system. This allows detection of leaks and blockage."
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Old 08-13-2019, 10:42 PM   #5
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M56 had a 15yr/150k emissions warranty, I don't get the relevance of the quoted Chrysler info.
BMW calls the leak detection pump a Diagnostic Module - Tank Leak.
Yes, it sounds like you have a fuel pump problem. $100 is a steal for a M56 tank, I'd buy it and be done.

If you don't live in a state where the M56 was sold you could swap to the standard tank/Evap system. It all bolts in except you'll have to adapt the fuel lines to connect to M56 engine and some easy wiring.
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Old 08-14-2019, 12:42 AM   #6
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Why do you think the DM-TL pump is bad?
Are there evap trouble codes in the DME (engine control module)?
What are the EKP (fuel pump control module) trouble codes?
Which "cut vacuum line"? Post a realoem.com link to said part.
How did you check for fuel pressure at the rail?

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