poor acceleration in heat and cold

[02stu]

My motor has become very picky about the temperature it operates in. It pulls strong in weather between 60-75 but out side of that it falls on its face. The oxygen is new so I doubt that is the problem, could it be the mass airflow sensor?

[Mike B.]

Check your intake air temp sensor. I've experienced similar symptoms on another car (non-BMW) and it was this sensor.

To do this:

1. Check that reference voltage is reaching the IAT sensor > disconnect IAT sensor connector > turn ignition key on > check for 5V between supply voltage wire (gray) and ground > check for 5V at DME pin 77

2. Check IAT sensor resistance across sensor terminals > at 68 degrees F you should be seeing around 2.1-2.9 k ohms. The sensor response should be linear as the engine warms up and the resistance at 176 degrees F (80C) will be 0.27-0.40 k ohms.

If the sensor fails #2 it is faulty and should be replaced. If it fails #1 there is a wiring/DME issue.

[aeryk7]

How well is your intake shielded from heat ?

This can usually be felt when you first start your car in the morning feels real peppy then after some hard driving and then it feels piggish.

Inner headlight removal helps to get cooler air in there as well

[static]

My motor has become very picky about the temperature it operates in. It pulls strong in weather between 60-75 but out side of that it falls on its face. The oxygen is new so I doubt that is the problem, could it be the mass airflow sensor?

i've had that and it was exactly the reason i said "f#@$% the motronic" and went with megasquirt instead.
At least i can see, datalog, understand and relate everything that's happening inside the ECU

[aeryk7]

I bet when it gets in the 40-50's you wont be complaining

[Mike B.]

i've had that and it was exactly the reason i said "f#@$% the motronic" and went with megasquirt instead.
At least i can see, datalog, understand and relate everything that's happening inside the ECU

Instead of diagnosing the problem, you just chucked the DME and went with megasquirt??? Now that is the way to figure out what's wrong... Just switch ECU's that will fix everything.

Almost all of these heat related issues can be fixed by installing a cold air intake or a diagnosing a bad IAT.

[static]

Instead of diagnosing the problem, you just chucked the DME and went with megasquirt??? Now that is the way to figure out what's wrong... Just switch ECU's that will fix everything.

Almost all of these heat related issues can be fixed by installing a cold air intake or a diagnosing a bad IAT.

trust me, i am not the kind that gives up easily. I love diagnosing (i write linux drivers for living if that tells you anything) but i just got frustrated when after a lot of searching i realized how little knowledge there is about motronic in the public domain. I wanted to write my own diagnostic software, for instance, that would talk to motronic over the serial link and extract and datalog all kinds of data - but, according to my lengthy research, there is absolutely no info on how to do that (docs on protocols, etc)
I realize people figured out how to tune it pretty well, but it's only half (or less) of what a standalone has to offer.


Alex