BMW 750il no start

[David85713]

Hello , I need some help guys ,I’m having trouble with my e38 ,it will not start it cranks but no start I took the batteries out an then charged they are low maybe alt prob but I dnt think that’s a problem due it not starting !? What could have happened ? Engine is all stock no mods ,my buddy did try to install a cold air intake in it an it started up fine the after a while it began to shake an I turned it off .an now it won’t start ..we put the stick air box back in an still no start !!! Idk !?!? Help what happened
Thank guys !

[shogun]

moved to E38 forum

[CPHES]

What year ( Batteries makes me think 99-01 ). What is the overall condition? There are 2 air boxes. Did you check all MAF connections? Which side did you take apart?

[SilverIris]

As CPHES noted, I will assume this is a 99-01 as well.

Crank but no start under these conditions sounds like Safety start mode was triggered. That happens when your Main Battery (top 55AH smaller one) is weak, so the car lets it borrow power from the Starter/EKAT battery (bottom 110AH bigger one). Generally speaking, if one battery is weak, it will drag the other one down.

Alternator is connected to the Main Battery (terminal NEAR driver's strut tower under the hood). Jumpstart terminal is connected to the Starter/EKAT battery.

This may sound dumb, but have you tried a "battery nap"? Undo both batteries negative terminals for 30 minutes, then reconnect. Sometimes, these cars freak out for no reason and this tends to knock some sense back into them.

Beyond a battery nap, it would be wise to check for excessive parasitic draw and ensure you have communication on the Canbus lines. A quick/dirty way is to turn the key to the position before Start (Position II), wait a few seconds and look at your temperature gauge with the engine being stone dead cold. A properly working system will stay on full cold. A panicking Canbus system will peg the needle to Full Hot because it can't send/receive information from the DMEs. It will also make the tachometer unresponsive too.

My 750IL had an issue where one battery kept draining the other while the Canbus system was panicking. Went through the Canbus system one module at a timewhile reading the Canbus line voltage as I disabled each one. ~2.5v is normal, I was getting 9v+ and climbing. Ultimately led me to the EKAT Control Module which was underwater (sunroof drain tubes, common issue) which had disintegrated and was backfeeding into the Canbus lines constantly due to no fuse by design.

Details are on page 3:
https://www.bimmerforums.com/forum/s...IL-with-issues

Solution was to relocate the EKAT Control Module to the trunk and reroute its power feeds through an empty 50A fuse slot (normally used for diesel E38s).

[David85713]

The smaller battery was low and both sides air boxes

[David85713]

Yes it’s a 99(05 of 99)
All connections are good
I have not tried battery nap ...I shall try it
Interesting silver I’ll have to look into that but I’ll try what i can to get started