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BMW and MINI, Power Brakes Weak, Hard Pedal, at Cold Start, Stop and Go Driving

Feb 23 17

Dear Otto,

I have a 2003 530i.  The power brakes don’t seem to work well when I start the engine in the morning or after work.  The pedal is harder than normal and I have to press it harder to get the brakes to stop well.  I have to drive it a bit and then the power assist seems to come back and all works normal for the most part.  Sometimes this also happens in stop and go driving, but once I get moving again the brakes are fine.  The shop has replaced the brake pads and the vacuum booster (wow $$$) and bled the brake fluid multiple times, but the issue has not changed.  Do you have any suggestions?


The symptoms that you’ve described would fit perfectly into a faulty vacuum check valve or “sucking jet pump” for the vacuum power booster.  The power brakes on your E39 5-series (97-03), as well as many other BMW and MINI models, are operated by a vacuum  booster that amplifies the pressure that is applied to the brake master cylinder when you press on the brake pedal.  A key exception to this is some of the early 6-cylinder and V12 models up through the early ’90s.  These models use a hydraulic fluid boost system.

Typical Sucking Jet Pump:

Typical Check Valve:

The vacuum for the vacuum assisted power brake system comes from the engine’s intake manifold.  While the engine is running, the intake manifold is normally under a vacuum (internally) and this vacuum is applied to the brake booster.  There are engine operating conditions when the vacuum may be low, such as cold-start, acceleration and stop & go driving.  When the vacuum is low, the power brakes may not be adequately boosted through the vacuum booster.  To help eliminate this issue, there is a one-way check valve in the hose that connects the engine (intake manifold) to the vacuum booster.  Additionally, some models also have a device known as a sucking jet pump.  This is nothing more than a vacuum divider, but it does incorporate internal check valves for the vacuum to the brake booster.  The check valve (and the valves in the sucking jet pump) allows vacuum to be applied to the booster when the engine is producing higher vacuum, but does not allow the vacuum to be dissipated out of the booster when the engine’s vacuum is low.  This keeps the power brake assist available through the conditions when there is not enough engine vacuum to properly operate the vacuum booster.

Without having your car here to diagnose in-person, we can’t be certain exactly what the fault is.  However, we would not have suggested the repairs that have already been performed.  For a “virtual” diagnosis, we would suggest that you replace the vacuum check valve as your described symptoms certainly can be attributed to a faulty check valve.  If the check valve does not cure the issue, the sucking jet pump may be at fault.  On some models, the check valve is a disc-like plastic unit in-line in the vacuum hose from the engine to the vacuum booster.  Your 530i incorporates the check valve into the 90-degree elbow that connects the vacuum hose to the booster.  Models that incorporate the sucking jet pump (such as your 530i) have the unit installed in-line in the vacuum hoses between the intake manifold and the vacuum booster.

Power Brake Vacuum Check Valve for E39 5-series (except M5):

Click HERE to search for Power Brake Vacuum Check Valves and sucking jet pumps for all BMW or MINI models.

If you do not find the parts for your BMW or MINI, just give our Advisors a call at 800-535-2002, for assistance.


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BMW and MINI Fuel System Rust and Corrosion, Lines and Tank, Gas and Diesel

Feb 21 17


* Frienemy – (Urban Dictionary):
Friend/Enemy – A “toxic” person who poses as a friend but subconsciously or consciously wishes you harm.

This is exactly what the gasoline or diesel fuel is to your BMW or MINI.  It’s the friend that makes all things work ….. and the enemy that can destroy your fuel system and even the engine itself.

Moisture in gasoline and diesel fuel has always been an issue due to contamination in storage and transport, as well as condensation within the storage vessel (such as the vehicle fuel tank).  Additionally, today’s gasoline, that commonly has ethanol added, tends to separate the water molecules from the fuel, rather than suspend the molecules within the fuel.

Why should we care about moisture (water) in our gasoline & diesel?

There are two basic issues that make water contaminated fuel a bad thing for our BMWs and MINIs.

1) Water contaminated fuel does not burn well in the engine’s combustion chambers.  This can cause minor misfires that may or may not be felt, very rough engine running – all the way to the engine refusing to run at all.

2) Water in the fuel system will promote corrosion and rust within the metal parts of the system (tank, lines, pump, injectors).  This corrosion can actually eat through a tank or fuel line, but also damages the pump and the fuel injectors, causing these expensive assemblies to need replacement.

By the time you notice the problem, it is often too late.”
The chemists at Liqui Moly recently performed a telling test.  An accelerated corrosion test was performed with a steel rod inserted into a solution of naptha (a safer and inert replacement for gasoline) with  just 10% water.  After just 24 hours the steel rod was rusted.  In the same test, with Liqui Moly fuel system additives, the steel rod shows not rust at all.

How do we prevent fuel system corrosion and rust damage?

1) Keeping the fuel tank fuller, rather than lower, will help to keep condensation in the tank to a minimum.  This is also much better for the longevity of the in-tank fuel pump.  Click HERE for an article on this subject.

2) Regular use of a moisture barrier product will help to keep the interior metal surfaces of the fuel system protected from the corrosion and rust formation.  The Liqui Moly Jectron fuel system cleaner and Super Diesel Additive not only clean the system of deposits and corrosion, but add the molecular protective coating to the fuel system’s metal surfaces.

Click image below for Liqui Moly Jectron fuel system cleaner:

 Click image below for Liqui-Moly Super Diesel Additive:


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How to Properly (Fastest) Defrost, Defog, Your BMW or MINI windshield

Feb 2 17

We all know the scenario (well, at least those of us in the northern climates); you head outside to the car for your morning commute and the windshield is covered with ice and snow.  Do you know how to properly set your climate control for the fastest windshield clearing?

*  Of course, if you do need to get going right away, you’ll have to manually clear the heaviest ice and/or snow

* Set the climate control to the defrost setting (direct all of the air at the windshield).

* Set the heat to full hot.

* Set the blower fan to high

* Be sure the fresh/recirculate control is set to fresh air

* Here’s the kicker …. if there is moisture on the inside of the windows, turn the air conditioning button on.

Once the windows are clear enough to start driving, if you are having trouble with the insides of the windows fogging (windshield or side windows), make sure the blower is on high speed and the recirculating air control is NOT turned on.  Recirculating the air will keep all of the interior moisture … in the interior, and on the windows.  If the windows are still fogging, turn the air conditioning on (in addition to the heat) and run the blower at high speed.  The air conditioning will help to dry the air.  Removing the excess moisture from the interior will help to keep the windows from fogging up.

If it’s quite cold out and snowing heavily enough (or freezing rain) to be accumulating on the windshield while the vehicle is driving, running the climate control on full defrost (as outlined above) may not keep ice or icy snow from freezing to the windshield, due to the windchill while the vehicle is moving.  In this case, fold the driver and passenger sun visors down to about 90-degrees or a bit more (make sure you can still see under them), while running the blower on high and the heat on full hot, in the defrost function.  The visors will help to keep the heat that is blowing up across the windshield from just blowing past and to the rear of the interior, and will keep the windshield itself warmer.  If you start to overheat, crack open a side window to allow excess heat to escape.

*  You can greatly improve the performance of the vehicle’s windshield and glass in wintery or rainy conditions through the use of Aqupel windshield treatment. This will help rain and snow to “bounce off” the windshield and even the side and rear glass, greatly improving the clarity and vision.

Click HERE for article on Aquapel glass treatment

Click HERE for Otto’s Aquapel DIY video

Don’t want to scrape frozen ice or snow from your windshield?  Keep the ice and snow completely away, while your car is parked, with the BAVauto® Windshield SnowShade!

Click below for Windshield SnowShade (click image, enter your vehicle info and search “snowshade”):



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