Solution for BMW E46 misfires

Question: BMW E46 misfire

I have so random issues with my e46 a multiple of misfires, open and closed loop fueling while driving and I’m guessing a vac leak but it looks rich to me with short term fuel trims at 28.3 and no readings on long term fuel trims, also I bought one INPA from , could I ask which lead I need to use INPA, I have standard obd2 cable is this efficient, also post 02s are stuck solid at 1.275 v is this normal?
Need to see Freeze Frame and warm idle Fuel Trim values.

Go on read the following parts.
If you are chasing an illusive rough idle and/or Lean codes at idle that you have not been able to find, beware the power brake booster is one more problem area. We have been seeing power brake boosters leaking vacuum but still functional and no obvious lose of braking effort. Most of these booster failures are happening after year 10, usually around year 11-12 on most of the cars that have had booster problems.

Often power brake boosters leaking vacuum will cause the STFT to by very high, +20 to +27% and often LTFT may or may not be over +10%. One problem that makes booster failures hard to find during a smoke test is the input check valve for the booster blocks smoke from entering the booster and even if there was not an input check, many might fail to think to look under the dash for smoke from booster leaks.

Symptoms of booster leaks are higher than expected Fuel Trims, cold start and rough idle issues. Additionally if you know what to listen for, you can actually hear the booster leaking vacuum from under the dash. It may sound like a fan running under the dash and may change in volume as you apply the brakes while stopped or the hissing noise may diminish when accelerating normally from a stop. Keep in mind that some DME boxes may have a fan in it so do not confuse a DME box fan as a booster leak.

In order to hear a leaking booster, you will have to turn off the main HVAC fan by running the fan speed all the way down manually, have the windows up and radio off. While stopped and idling listen for a hiss or fan sound from under the driver side dash. The lower hush panel will muffle the sound and may need to be removed to easily hear booster leaks. When the boosters first start to leak, you can apply the brakes and the hissing will drop in intensity and may even stop while the brake is applied. If you have an OBDII scan tool connected to watch Fuel Trims, you may find that the Fuel Trims drop back toward 0% when the brake pedal is applied and when the brake pedal is released you will probably see the STFT rise first.

To confirm if the brake booster is a problem the booster hose can be removed and plugged or the booster hose might be able to be pinched off for a test. The booster vacuum hose is molded and pretty stiff so it may be hard to pinch off.

As for a solution, you could consider a used booster, but in my opinion you do not know how long the used booster will last and the amount of work to replace the booster is probably not worth risking on a used booster? But as they say, you either have time or money, if you had both you would not be here on this forum working on a 10+ year old car.

A new ATE power brake booster with a 2 year warranty for around $177 shipped. These boosters appear identical to what was installed at the factory, so I assume ATE may have been the OE supplier? You could also consider a re-manufactured booster as well. I did not spend much time looking in re-manufactured booster pricing and availability because I thought the $177 figure was pretty reasonable for a new booster. The dealer booster pricing was too high and the OEMbimmerparts booster came with the same warranty as the dealer booster.

Replacing the booster is not too hard, it is just time consuming. Expect to spend about 4 hours replacing the booster. On cars with the ABS controller in the passenger side drug bit it will be a bit easier. On later cars with the ABS controller under the booster and master cylinder it will be a bit more difficult.

Under the dash is not too bad, not sure all cars have the safety loop to keep the push rod from falling off the brake pedal if the clip falls off, but I had to remove the brake pedal from the fire wall and twist and turn the pedal to get the booster push rod off the brake pedal.

Once the master cylinder and booster are loose, getting the booster out of the cavity and the new booster in is a bit tricky. It will require a bit of patience and you will have to twist, turn and pull on the booster but it will come out of the cavity where the booster is tightly tucked into.

Once the new booster is in and the master cylinder is reconnected, you will have to bleed the master cylinder and brakes. I connect everything up, made sure not to cross thread the master cylinder hydraulic lines, then leave them partially loose and fill the master cylinder with brake fluid and then let the system gravity bleed for a few minutes, this is usually just a fast drip of fluid from the connections. Once I have let the master cylinder gravity bleed for a while, I snug up the brake line connections on the master cylinder than then bleed the master cylinder using the 2 man method of pumping the pedal and then cracking the master cylinder connections just like a brake bleeder screw. Do half of the master cylinder, then move to the other half. I usually bleed the master cylinder with between 5-10 pumps for each half.

Some may worry about damage to the master cylinder due to over stroking it. A good master cylinder should not have problems with over stroking, but a 10+ year old master cylinder might. If you are worried, put some phone books under the brake pedal to limit the travel when manually bleeding the brakes. I have found that usually bleeding just at the master cylinder is sufficient, but you may want to fully bleed the braking system after the master cylinder has been bleed. If for some reason the master cylinder fails during bleeding to over stroking, it needed to be replaced anyway. Keep in mind the ABS controller will not be an issue as you will not introduce any air into the ABS controller when bleeding the brakes. So not get worried, just bleed the brakes as the car did not have ABS. You do not need special software or anything to activate the ABS controller.

Remember that brake fluid can damage paint and it is water soluble, so have a garden hose or lots of water available for rinsing any brake fluid that leaks into the engine compartment and also protect the exterior paint on the car from brake fluid.

I would like people to report in when they are finding bad power brake boosters on their cars and how old the cars are. We do not need mileage as the brake booster life is not significantly affected by mileage. But the build month and year along with how old the car is and where in the country the car is located would be helpful. Stating how old the car is based on the build date will save people from trying to do the math when the actual reply was made in the thread.

I can think of over a dozen cars on the forum here that I know have had failed brake boosters recently and I assume there are more out there that are leaking vacuum that have not been identified and there are more boosters that will be failing in the near future. There may be a lot more failed boosters that have not been documented here as well.

Again the initial data seems to support that most of the failed boosters are 10 years old and it seems the bulk if the failing boosters are 11+ years old, many are concurring in year 11 & 12, some boosters may last longer depending on where in the country the car has spent the main part if its life.

So please report in booster failures as this will be able to give owners an idea when they are typically failing and how common the failures are. Please post the build month and year, age of car and where in the country your car currently resides.

I had to replace the booster last year on a 2001 325xiT that had a 9/2001 build date and the booster failure was noticed around year 12, however, I think the booster had failed sometime in year 11.