After running smoothly since a new HPFP, I recently developed fairly severe hesitation at low RPMs and a significant decrease in fuel mileage. Strange thing was the car wasn't throwing any codes so it had me thinking carbon buildup.

I had been running the Manic Stage 1 map B so I decided to set it back to stock. Shortly after I got a P129D code (as well as P2188, too rich at idle). The car seems way down on power (less than stock).

After reading t0ad's thread, his symptoms are very similar to mine so I decided to order a new MAP sensor.

While I wait for it to come, I was wondering if anyone knows what the "plausible" range of pressure is for the intake manifold? The freeze frame data was showing 43.7 inHg but I have no idea if this is really high or within normal ranges. I've noticed in the stock map that the pressure rarely goes above 35 inHg...

 

Update:

After replacing the MAP sensor, I started having P129E errors.

I ran out of knowledge and time to troubleshoot this so I took it to a BMW/MINI repair shop.

Today I got the results of the diagnostics and they are saying the ECU is outputting 5.7 volts on pin 1 and 5 volts on pin 3 of the MAP wiring. This is happening with the ignition on and the engine off and with the engine running. They said one of the pins should be a 5 volt reference and the other is the actual value from the sensor. They checked the ground at it appears to be fine.

Since it is coming from the ECU they are warning me it could take a while to trace down what is happening.

I reached out to Way who did my Manic tune but wanted to see if anyone else had thoughts on this situation?

 

I'm curious --- what are you using to measure manifold pressure --- (freeze frame data?) My boost gauge reads vacuum as inHg, and boost pressure as PSI. Are you asking about vacuum or boost readings? Note that nobody else has responded in the 10 - 11 days since your original post. Maybe your question isn't using common terminology? My gauge has 30 inHg for max vacuum (on one end of the gauge). The dial goes thru zero and ends at 30PSI. The scale is different, with vacuum occupying about ⅓ of the dial readings. The most vacuum I've noticed is about 24 inHg (idling) and I've pegged the pressure readings, but my usual driving is in the vacuum side.

Also, there are two MAP sensors --- one on the intake manifold and the other near the passenger-side fender, on the "plastic" air intake pipe (which also measures air temp). Was it the manifold unit you replaced?

Any time I have low RPM problems, I usually find it's caused by a loose air hose, however, that's probably unique to my mods.

There is often a difference between chassis ground and ECU logic ground. If the repair shop tech measured voltage with respect to chassis ground, this could account for the unusual readings. And the ECU only OUTPUTS reference power and ground. The sensor INPUTS a voltage proportional to manifold pressure --- somewhere between the reference power and zero. It's been a few years since I connected my Boost / Fuel Cut Defenders, and I don't remember the actual reference voltage or pin numbers, but I'm pretty darn sure about the sensor operation --- sensor voltage increases with manifold pressure and cannot be less than zero or more than reference voltage. I'm pretty sure my sensor read about 2.2 VDC at 20PSI. Probably never at zero or more than 3 or 4 VDC (all this with ignition on and sensor connected to the ECU).

 

Thanks for the response and for trying to help me!

When I first posted about the issue, I was pulling the freeze frame data using a OBDLink LX which was connected to OBD Auto Doctor on my phone. I didn't understand the complexity involved with the manifold pressure, engine load and timing so I thought the MAP sensor should be outputting values between X and Y. After reading your post and some other material on the interwebs, I now see how my question didn't make much sense.

I replaced the MAP sensor on the intake, not the sensor on the plastic air intake pipe.

The repair shop has told me the same thing you are saying, the ECU should output reference power and ground. In my case, they are seeing the ECU put out >5 volts on the pin that it should be receiving voltage from the MAP sensor. They are seeing this at the MAP wiring harness and at the harness connector on the ECU (eliminating bad wiring as the cause).

I asked them about the ground and they are confident they are measuring it correctly. At this point I don't have reason to doubt them.

About 3 weeks before this issue started, I replaced the original battery with an Autocraft Gold. At the time I was fairly confident that my car didn't have IBS, but I was wrong. So I put about a thousand miles on the car without registering the new battery. Today they are going to put a known good OEM battery in the car, register it and do a full charging cycle to make sure everything is OK. They said having an unregistered battery that is overcharging could cause all sorts of strange electrical issues but they aren't confident that will resolve the MAP voltage issue.

At this point they think there is a chance the ECU has gone bad, but I'm really hoping its just the battery.

 

As my name implies, I'm old school --- gauges and hard-wired connections, minimal wifi / internet use. AccessPort is used for monitoring and data logging as required. Too bad it's not supported any more. No clue what your OBDLink LX is. I also don't have a mobile phone --- stone age!

When the battery is replaced but not registered, the ECU doesn't know about it, so it continues to deliver a higher than required charging current. There's a high probability this charging current messed up the ECU. Hopefully, it just caused the battery to have excess voltage, and the ECU has over-voltage protection. I have no experience with our ECU. Knowledge comes from the Bentley manual and discussions with dealer service techs.

If your Autocraft battery is the correct size and rating, it should be acceptable, unless it was ruined by overcharging. I've read where others have used after market batteries and had no issues.

Again, when measuring the map sensor voltages, it's important to have the sensor connected, so there's no "open circuit" voltage errors --- both ECU and sensor are under normal load. Not easy to do without a "breakout box" to allow access to the conductors. I used "pigtails" on each wire when adjusting my FCD's.

Anyhow, I wish you luck --- keep us posted about your final fix --- it might help someone.

 

I'm having that issue and I might be in contact if dealership gives me the run around. Glad you get good service, mine sucks.

 

There is something to be said about old school approaches to cars. It's situations like this that make me dislike modern computer controlled engines...

Here is the update now that I have the car back. The Autocraft battery was replaced with an OEM battery and was registered with the ECU. Everything on the charging system checked out fine.

The issue with the Autocraft battery wasn't that it was aftermarket, it was that Autozone couldn't provide some of the battery specs needed to register it. It seemed like a simple question, but the guys at my local shop kept providing the cold cranking amps (which is printed on the side so that wasn't very helpful).

The car is still throwing P129E, P1255 and P0107 codes on start. The repair shop says they don't have the equipment necessary to bench test the ECU to rule it out as the source of the issue.

Here is exactly what their report says:

"Checked wiring between sensor and ECM-OK. Values at sensor-sensor appears to be getting 2 reference voltages 5.7V on pin 1 and 5.0V at pin 3. MAP sensor voltage should not exceed 5.0V and should not be coming out of the ECU to the sensor."

I'm also going to study the wiring diagram in the Bentley manual so I can become more familiar with the system because this sure seems like a wiring issue, not the ECU.

I should mention that the MAP sensor I installed is aftermarket so I'm going to swap it over to a new OEM sensor to make sure that I don't have a defective part. The repair shop was willing to try this but I didn't want to pay their labor fees for a simple DIY job.

If the OEM MAP doesn't fix it, I'll probably start reaching out to some of the vendors on the board to see who is able to test ECUs (assuming that is something that can be done).

 

Yeah, if it came up with a code right after replacing with non oem part then go back to that step, install OEM sensor.

I've never had any luck with anything but MINI Battery. Even the optima lasted but 3 years. OEM one lasted 7 and never left me stranded.


GL!

 

Probably learned that lesson the hard way.

While ordering the OEM sensors, I found this article from Pelican Parts. This is one of the most straightforward explanations of how the MAP sensor and ECU work together to adjust the fuel/air mixture. The Pelican articles are a great source of information!

 

Quick update on my P129D/E codes:

Replaced the aftermarket MAP with an OEM MAP. Also replaced the TMAP with an OEM sensor. The o-ring on the original TMAP may have been my problem. It was smaller than the new one and was covered in dirt. The sensor tip itself also had a little bit of dirt. The port where the TMAP plugs into the air intake was also dirty, possibly showing signs of sucking in air where it shouldn't be coming in.

After finding this, I'm kicking myself for replacing the MAP and not checking the TMAP when oldbrokenwind asked me about it. Lesson learned...

I reset the codes and on first start the difference was very noticeable. Smooth idle with no stumbling or roughness. I drove about 40 miles today with several stop/starts and the codes haven't returned. I'll update the post in a few days in case others are watching.

 

It's been almost 3 weeks and I'm still issue free. Even set the tune back to map B and the car is running great. Hopefully this thread is useful for someone else struggling with these codes.

 

HI,i have exactly the same issue on mini cooper r55 2013 . Checked everything and battery is like oem and registered . Map sensor is new and oem but still have 5.7v on pin 2 when sensor connected (4 pins sensor)