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Old 09-11-2020, 02:16 PM
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andrewwynn andrewwynn is offline
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Join Date: Jun 2015
Location: Racine, WI
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I'm about to replace my MAF. It's perfectly functional I'm just consistently running lean with no known leaks and at 190,000 miles on the clock on the original "it's time".

If the eBox heat isn't the problem I would def be willing to send a working ok MAF to use as a tester once I get my replacement.

I'm 80-90% confident on the eBox heat, and I'll add to my theory: after you rest and allow the eBox to heat up from the heat soak, you drive away which starts to cool off the eBox but with little to no internal air flow it takes a while. By the time you drive a few minutes it will have cooled down but that initial start threw something off like when your get a cylinder misfire.

The eBox cools off just enough that the start up sequence throws no flags and the engine more or less magically runs normally.

Were it my or wife's X doing this I would drill a hole for a thermometer probe and drive the car enough to bring to temp but also heat up the engine bay. Then measure eBox temp. (I have a Bluetooth thermometer so I would cheat a bit here and monitor temp on a graph on my phone).

Then see how hot the eBox gets on a short drive like under 10-15 minutes when it's 90 ambient and during the parking phase.

Then do the same meausurement after a long drive and park. It should go higher and if the temp gets over 160 it's almost for sure the cause.

It is likely still not a for sure thing because breeze and sun will affect tge parking phase so once you have some baseline numbers you can with relative safety heat the eBox parked in the sun hood opened monitoring the temp.

Then say you get baseline of 140. 150 let it heat to 155, 160, 165 and maybe 170 to see if you can reproduce the problem.

More on the theory: I'm thinking the circuit affected is the O2 feedback loop and it could read high or low or open when it goes to hell. So maybe watch on a scanner the live reading (wifi obd dongle and smart phone great for this).

I would not go over 170 for testing even if it gets that high just introduce some cooling and see what the improvement is. (fyi the numbers could be much lower, but it's very rare for temp below 130 to mess with Electronics and usually it's over 160 where problems come in.

Over 180 can damage some Electronics permanently so I would keep at least 10° safety margin. It might be a combination of heat plus time (almost certainly is in fact ) so 150-155 for ten minutes for example so sun heat to 160 but shade it on/off to keep it from climbing but stay 160 for ten minutes as example.

There is one common element to almost every part that's been replaced: they are all connected to the DME that is almost certainly the root of the symptoms. More than likely some part that usedtacould handle 160f fails at 150 for example. And if adding a fan means not replacing DME that's for sure the way to go.

I have SMD soldering skill I would actually try to find the part if possible and swap it. It's likely a tiny simple three legged transistor. 40¢ part
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2011 E70 • N55 (me)
2012 E70 • N63 (wife)
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