Mercedes W116 300SD "Planet Express" ownership/build log

I've got about five B5/S4 alternators in the shed. Not sure if they'll work in your application though. What's the criteria?

LKQ is replacing it at no cost to me. They're pulling it from a B5.5 TDI so I know it'll be the correct fitment. Thank you for the offer! 

Still awaiting alternator, let's check fault codes

I'm not worried about the glow plugs

The MAP and IAT and Baro are all related to the MAP sensor and could cause a limp mode condition. I think that's where I need to look. I'll need to check the wiring and the sensor. The wiring is new and supposedly tested. The sensor worked fine in the Passat when I drove it. Maybe it's just a ground? We'll find out

The 4 pins on the MAP connector. 

Ground            0ohms referenced to chassis ground

IAT output       4.92v

5v supply         4.96v

MAP output     5.65v

I don't understand how the MAP output could be more than the 5v supply. I wonder if I have the pins wrong, or if that's my problem. 

New alternator is in, puts out 14.6v and didn't overheat after 10 minutes of running! It came with a voltage regulator that was broken in shipping but thankfully my 07K alternator is also a Bosch so the regulator swapped. It's got less brush life but I don't exactly plan to put that many miles on this car. 

I ran checked the measuring blocks for the IAT and the MAP. The numbers are definitely not correct. Digging in to what that means. 

Gotta get it ready for Halloween 

Much more important than making it run right

I think we have figured out the issue. Not sure the solution yet. My tune is expecting a 2.5bar MAP sensor but my car has a 3.0bar MAP sensor. The scaling is wrong so the measured pressures are all wrong. 

I also dug into the brakes a little. I am getting all fluid, no air, out of the rear bleeders. I manually bled the brakes a bit and put the vacuum bleeder on them, but never got any air. Still though, it doesn't feel like it has rear brakes. I spun the rear tire while my wife hit the brake pedal. That's not great. 

I haven't memorized all the brake troubleshooting you've been doing but I would suggest taking the calipers off, putting a spare disc or something else in between and pressure bleeding them in various orientations. When I initially converted the E21 to rear discs I was getting fluid with zero bubbles but no pressure in the rear, just like you're experiencing. Once I moved the calipers around I was able to get them fully bled as there was air trapped *somewhere* inside the calipers themselves. 

Only other situation I've seen like that was my K1500, one of the master cylinder seals had failed. It would pump fluid but not build any pressure, so it bled fine but would bypass fluid once you actually tried to use them. 

Those trucks are so notorious for crappy brakes that I drove it that way for 25k miles before I realized something wasn't right because it had completely killed a brand new set of pretty decent front pads in that time.

Working on a car alone on a lift

I took the rear calipers off and bled them at many angles. Fantastic idea! Now I trust my brakes around town. 

Off to do some data logging. I'm getting way less boost than the car specifies, but the sensor is reading high. Very odd behavior methinks. The car is hella butt slow. Feels maybe as fast as the OM617 off boost but I'm not getting boost. Interesting that the sensor reads high at idle but as soon as I start driving it shows that I'm not getting nearly as much boost as requested. I cycled my N75(VNT actuator) and heard the exhaust note change. I'll check that it's getting full travel next I guess?

Fancy log

buzzboy said:

I took the rear calipers off and bled them at many angles. Fantastic idea! Now I trust my brakes around town. 

 Awesome!