Bew power issue with cold weather only

Bought car and it always has had a low power issue when the outside temp is around 15 or colder. It can be plugged in and in a heated garage and after a few miles power is lost. Above that temp no issues. Lots of power. Fuel mileage not noticeably different. Boost can still be ramped up with no difference in power. Struggling to get past 60 on the interstate once car is on for a few miles. Unplugging the MAF and all is good again. I have replaced the MAF with new and another working used from another car I own. Same results. My 1981 rabbit had more power when this happens.

Car had a rocket chip tune and now kerma stage 1. Stock everything. Fuel filter also replaced. Only solves have been unplugged MAF below 15 degrees or not drive below that temp. Can a MAF function go good/bad with the temp. Is there something else I can look at? Could a previous owner hardwired something to possibly jack up the power by tricking the temp only to make it bad when cold? Nothing blocking the intake. Has cold weather grill blocks in the front and full metal jacket for the belly pan.

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What about gelling fuel and a weak lift pump?
Look at the temperature in vcds to see what's happening there also.

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I agree, check for lift pump problems and check all the temp values in the engine controller (intake air, fuel, coolant) to see if any of those is "off" after a cold start.

Also, is the EGR intact and working or is it disabled altogether? If it is present, but electronically disabled, you may want to verify it is actually physically closed and not leaking.

Egr is deleted. Forgot to include that. Lift pump no issue. This morning it was cold enough where I hit the interstate doing 80 after plugged in all night at work. By 2 miles down the interstate it slowed down to 70 as it lost power. Pulled into a rest stop and unplugged the MAF and all speed and power back to where it hit speeds I won't say online as a test to it.

Oilhammer- are all of those temps found under the engine part of the vcds right? Will have to play around to find. I can live with the MAF unplugged-just bugs the heck out of me that it is an issue I haven't been able to solve and the random temps in this state makes it hard to line up to do the troubleshooting.

Thank you both. I will look at the different temp settings. The scan gauge shows 168-173 on the coolant temp. The intake air temp shows the correct range depending on the boost. Boost with cruise on is around 5 but it can go to 15 psi without any power increase on the Mcnally gauge.

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Temps are in the engine fields, look around..

Fuel pump coming on doesn't mean it's working well, or that it's getting proper voltage.

Did I read that last post correctly and power returns when you unplug the maf? If so then I would replace it with a known good one if I could. Either way that would make this my first part to consider replacing.

If you have a weak fuel pump the fuel getting thicker can slow delivery causing power issues. Also on the BEW there's a pressure regulator after the fuel pump that could be effected by temperature. Not sure if it's common, but it is possible.

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I would scan for codes after you feel the power loss and before shutting the engine off.

Also, then the temperatures 1st thing in the AM before starting the car.
All should be close to the outside air temp.
If it's plugged in all night the coolant temp may be higher.
Maybe a weekend test w/o the heater?

From https://www.ross-tech.com/
Here's one group in VCDS for temperatures.
Group 000 measuring blocks
From left to right
Engine idle speed: range 42 - 45 = 870-950
Start of injection: range 12 - 75 = 2 degrees ATDC - 3 degress BTDC
Throttle position: 0 = 0 %
Injection quantity: 11 - 45 = 2.2 - 9.0 mg/stroke
Manifold Absolute Pressure
Atmospheric pressure
Engine coolant temperature: 80 - 35 = 80 - 110 degrees C
Intake Manifold Temperature: 182 - 50 = 10 - 110 degrees C
Fuel Temperature: 91 - 201 = 20 - 80 degrees C
Air mass: 69 - 111 = 230 - 370 mg/H

First picture is start up MAF plugged in a fault codes cleared before starting up. There was an over boost and glow plug faults. Glow plugs are a different story as it seems to eat up 3 and 4 plugs. Only codes to return where the glow plug faults. 2nd picture is after driving which it was at low power and temp around 17 dF outside. 3rd picture is after I unplugged the car about a minute after the 2nd picture.

Fuel, intake and coolant seem to be changing correctly to me.

I question the fuel pump or other delivery parts being an issue because power returns after MAF unplugged. I question the MAF being bad as I have already replaced that a few winters ago and the results where the same. I can only dive into this when there is the time to do it - last year I was moving - and cold enough temps. Is there another measuring block that could be checked? Only is an issue when cold and maf plugged in. I have several BEW engine cars and this is the only odd duck that came like this when I bought.

The temps where of the car parked outside fyi and no plugged in.

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Temp values look OK. Can you log the MAF actual vs. requested when the issue occurs?

Also, you say EGR is deleted.... but is it still there? I have seen rusted out EGR coolers and/or pipes and valves that did not stay shut properly, and that leak messed with the MAF values to the point that the ECU had no idea what was going on. When you delete EGRs via software alone but leave all the components intact, that can happen. No EGR flow through the cooler means it slowly will rot out from the inside due to moisture hanging around.

Is the MAF under the same measuring blocks? Going to get cold yet this week so I can measure.

Hoping this is how
Air system part I: MAF

Go into Engine measuring block 003

Start Logging data

In a high gear (4th/5th), give full throttle from 2500 rpm up to 3500rpm.

Find and Open the Log file in Windows Explorer

Graph MAF actual -vs- rpm in Excel

The MAF is OK if the actual value is at least 850-900 mg/h at 3000 rpm.



Yes the egr hardware is removed. It was in place but the pipe cracked few years ago. Blank plates with cleaned intake now.

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And before the issue occurs, does it flag a MAF implausible DTC (P0101 I think)?

Often times, the beginnings of a charge air leak, especially on BEWs and BHWs for some reason, manifest themselves as a P0101 first, long before an actual P0299 low boost DTC will be flagged. And they will run fine otherwise until it sees that, then puts the engine in limp mode with no boost control. Disconnecting the MAF simply places it in sort of a fixed limited boost control, but depending on the software modifications you have, may or may not totally use the MAF reading anyway (that would be a question for your tuner... many EGR delete tunes will also delete the MAF since one of the MAF's primary functions is for EGR control anyway). The ECU can fairly accurately "guess" the value of incoming air if no EGR is present simply by looking at the RPM and IAT, which is exactly what engines that do not use a MAF do, along with MAP input.

If your MAF data never moves, and is stuck at say '500 mg/st', it has a MAF delete tune. If it changes as the RPM increases, it is still in use. Then you'll need to figure out if its input drops out or changes for some reason.

I would also add that many (most) non-OEM MAFs are junk. I cannot begin to count how many non-Bosch MAFs I have taken off of VAG products over the years that were not working properly. Pierburgs seem to do OK too, but I would prefer a new Bosch on a BEW, and I would want to be 100% certain it is in fact the correct one... there are several Bosch MAFs that are interchangeable but are not the same part. BHW and BEW MAFs for instance are NOT the same (same goes for the MAP), and these are often the ones that cause lots of problems since evidently Autozone thinks they are the same.

Is the EGR valve removed? They can leak through the top.

Another way to graph is going to Malonetuning.com and drop the log into the browser. It'll graph it for you. Then you can take the address from the bar and put it in a post so others can view it.
It's much easier than using excelband graphing it.

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