Diagnose brake problem. Booster? Jet pump?

[GAH111]

I have a 2004 M3. I had just finished rebuilding the Vanos at a shop I have about 200 miles from my home when the brake pedal became hard and I lost most braking power. I cannot hear any signs of vacuum leak and the rubber connections that I can see look good. I am surprised there is little on Youtube on either diagnosing the problem or even a good video on removing the booster. I reviewed the post "how does the brake booster solenoid work" I can't determine if the problem is the "sucking jet pump (where did that name come from), the valve or booster is not discussed. there is also mention of the electrical connection to the DME.

Basically how do I determine what has failed and how do I remove the jet pump or the booster if necessary. Sapote had a very good explanation on how the valve works and that the DME closes the air into it. If I'm looking in the wrong place please point me to a direction. Is the process of removing the booster the same for a non-M car. Most videos address the 3 series.

Thanks in advance.

[sapote]

the brake pedal became hard and I lost most braking power.

Do the brakes still work as a normal car with the engine off -- no power assist but it work with leg muscles? we want to know the issue is the booster or the master/brake-hoses/calipers.

Why the booster not working:
- jet pump hose clogged. Never seen this happened
- booster diaphragm ruptured. This should cause engine running lean code. Use OBD to log the data to see all the 4 fuel trims to verify
- The solenoid valve should not cause this problem.

I had changed a booster without disconnecting the master cylinder brake pipes and the ABS module, but it's a hard job.
It's easy to disconnect the brake pipes, remove the master, then the booster (disconnect the connecting rod from the pedal first). But you have to do the bleeding on the system, including the ABS

[GAH111]

It sounds like a booster problem then. After the Vanos rebuild the car is idling a little rough but I have no other information on the rough idle. I have been using a VeePeak obd but I am having trouble getting a reliable connection, can you recommend a replacement.

To answer your first question, brakes feel the same engine on or off, as for the stopping power engine off I don't know. With the engine on the brakes will engage with leg muscles, One side locked up when pushed hard but it was on a gravely surface.

[sapote]

It sounds like a booster problem then. After the Vanos rebuild the car is idling a little rough but I have no other information on the rough idle. I have been using a VeePeak obd but I am having trouble getting a reliable connection, can you recommend a replacement.

To answer your first question, brakes feel the same engine on or off, as for the stopping power engine off I don't know. With the engine on the brakes will engage with leg muscles, One side locked up when pushed hard but it was on a gravely surface.

I use this one: https://www.amazon.com/Veepeak-OBDCh...ef_=ast_sto_dp

It sounds like the rest of the brake system works fine. To verify the bad booster, log the fuel trims and precat O2 sensor and MAF in g/s

[jayjaya29]

The rough idle is a big tell.

[GAH111]

When i get to the car I'll log the trims and see what they say. I've no cats but I assume that makes no difference. Are there any decent "how tos" on removing the booster and is the removal process the same for a 3 as an M3?

g.H.

[sapote]

When i get to the car I'll log the trims and see what they say. I've no cats but I assume that makes no difference. Are there any decent "how tos" on removing the booster and is the removal process the same for a 3 as an M3?

g.H.

Basically the same; just clear out the parts for room in front of the master and around.

[GAH111]

I read the fuel trims. Again no cats but they have been tuned out for many years. As stated before the idle was rough but just before taking the initial readings (using VeePeak) the car wouldn't idle at all. The readings with me keeping the car running were: ST % bank 1: -2.34 to +1.56. LT 1 steady -9.38. ST 2: -.7 to -15 up to -22. ST 2 -10.6
After several restarts the car began to idle, the readings then are as follows: ST1: 1.56 to -6.25. LT 1: -21.09: ST 2: +1.56, +5, -3.91. LT 2 steady -23.44

I did not get the MAF readings, can tomorrow but going by the description above it seems to point to a booster. Please give me your thoughts.

G.H.

[sapote]

After several restarts the car began to idle, the readings then are as follows: ST1: 1.56 to -6.25. LT 1: -21.09: ST 2: +1.56, +5, -3.91. LT 2 steady -23.44

I did not get the MAF readings, can tomorrow but going by the description above it seems to point to a booster. Please give me your thoughts.

G.H.

It's best to log the whole 3 minutes of data with hot engine and not just a few samples as you did. The data says the mixture is very rich in contrast with a leaking booster which should cause a very lean mixture.

[GAH111]

Here are the logs I captured, as mentioned at first the car was not idling without me applying gas, then after it died it began to idle again. The engine was warm during the minutes noted above but I did not take any data from the MAF. To review from my previous posts I had just finished rebuilding the Vanos unit. The car ran well after the fix but a slight rough idle was present. This car has no catalytic converters. I read Archbid post on Fanatics regarding fuel trims which filled in some blanks but not enough to pin down my problem.

I removed the brake fluid reservoir yesterday but stopped there, if I need to get data from MAF I will reassemble. I did unhook the battery so the adaptations are lost for now. Since what I have sent indicates a rich rather than lean mixture, where do I go from here. What other possible issues may I have. By Archbid's post it points more towards a fuel problem. Please let me know as soon as possible. I will need to leave here (where the car is) this weekend.

Regards,

G.H;

[sapote]

Here are the logs I captured, as mentioned at first the car was not idling without me applying gas, then after it died it began to idle again. The engine was warm during the minutes noted above but I did not take any data from the MAF. To review from my previous posts I had just finished rebuilding the Vanos unit. The car ran well after the fix but a slight rough idle was present. This car has no catalytic converters. I read Archbid post on Fanatics regarding fuel trims which filled in some blanks but not enough to pin down my problem.

I removed the brake fluid reservoir yesterday but stopped there, if I need to get data from MAF I will reassemble. I did unhook the battery so the adaptations are lost for now. Since what I have sent indicates a rich rather than lean mixture, where do I go from here. What other possible issues may I have. By Archbid's post it points more towards a fuel problem. Please let me know as soon as possible. I will need to leave here (where the car is) this weekend.

Regards,

G.H;

If you are serious about troubleshooting it, then do as I suggested: Log the parameters with a hot engine (85C or higher) idling with these PIDs, in a .csv file format: RPM, MAF in g/s, all O2 sensors it has, all 4 fuel trims, intake air Temp, engine Temp, then upload the csv file to Datazap.me for it to graph the data, then post the link here for us to check it.

[GAH111]

Since I have never had to log information I did not know the parameters you required. As i stated before I will be leaving where the car is stored so it will take probably 2 weeks to learn how to get and retrieve the information you list above. Something you have not ventured is what possible issues could I have based on the relatively meager information that I have sent.

Of course I am serious about getting my car fixed.

[sapote]

Since I have never had to log information I did not know the parameters you required. As i stated before I will be leaving where the car is stored so it will take probably 2 weeks to learn how to get and retrieve the information you list above. Something you have not ventured is what possible issues could I have based on the relatively meager information that I have sent.

Of course I am serious about getting my car fixed.

Your brake and the rich fuel trim are not related. I think the rich mixture is either by too high fuel pressure or a bad MAF reports too high value which causes the rich mix.

[GAH111]

I put everything back together to get the information charted. Let me know if you have trouble getting it from Datazip. I had to covert the MAF from Lb/min to g/s

https://datazap.me/u/2004m3/logs/cmnc7a6es000ljp06qnv6ebcp?channels=6&sizes=100&sc=2-3-4-5-6-7-8-9-10-11

[sapote]

I had to covert the MAF from Lb/min to g/s

The log still show data in lbs/min. This makes all readers to convert the data to g/s. You should be able to select g/s unit in VeePeak's Setting/Preferences/Units/Airflow. Temperature also should be in C and not F.

My read: MAF = 1.47 lbs/min = 11g/s. Too high, it should be around 4.8 g/s at idling. The log data confirms my previous guess on the cause of rich mixture. Should try with a known working MAF is the next thing to do.

Edited: I see the g/s converted now.
No need to include those fuel trims related with (bank_n sensor_m) in the log to save bandwidth. The log should include O2 sensors (all installed).