V12 limp mode

[bigv12]

What are the quick checks that are easiest to do first when car goes into limp mode.

my batteries drained and then when car started again. Gone into limp mode

[shogun]

your E32 750iL V12? your profile shows: My Cars 850 3.0CSL 750iL M635csi
or an 850? With M70, or M73? If you post a question, details please.

too weak batteries can often cause limp mode. stomp codes? BMW Stomp Test Procedure 840i, 750il, others) https://www.youtube.com/watch?v=9V30TVY-Ltg
codes explained https://www.bimmerforums.com/forum/s...e-pedal-faults
All 1989–94 BMW vehicles equipped with a self diagnostic system have the ability to retrieve engine fault codes by counting MIL flashes. These are four-digit fault codes (pedal faults) and have different code numbers than those retrieved by the scan tool. Pedal fault codes can be retrieved with the ignition on, engine off, and with the gas pedal rapidly depressed to the floor five times without interruption.
Important Tips for Reading Pedal Fault Codes
• Blink codes cannot be retrieved if the scan tool is communicating with the vehicle. • Blink code retrieval can be used for comparison and backup to the scan tool.
• V12 engines have two ECMs, one for each engine bank. Codes need to be retrieved from each bank separately. The left engine bank is on the driver's side of the vehicle, which is
Bank 2. The right passenger side is Bank 1. Be aware that each bank's induction system (MAF sensor and intake runners) are physically located on the opposite bank. To access
the second ECM, depress the gas pedal to the floor six times. All cylinder 7–12 codes begin with a two.

[bigv12]

thanks for your info shogun very helpful
car is M70 850i E31 6 speed manual

[shogun]

I will never forget the comment in 2004 from a 20 year BMW master with PhD, quote: Mismatched tires will set EML light if vehicle has traction since it reads all 4 wheel speed sensors and gets an "implausable" reading. Low voltage will set EML only if it drop below 11v for more than 90seconds. Low voltage will also cause problems with the IKHA (heater/ac), memory for seats/steering and transmission will go into limp mode. Just for clarification: I am a 20 year BMW Master with 3 PhD's from Germany in Engineering and I know these systems better than almost anyone. I did 12 years of R&D on these system for a manufacturer in Germany, so I am not some "Key Board" mechanic or read some crap on the internet. Ronald Trochelmann unquote

Ron is as far as I know now CEO of Noelle Performance Group

[bigv12]

very impressive. And yes I understand perfectly I have read your pages before over the years very helpful much respect for guys like you. So many who don’t understand out there!
I am wondering as my gearbox is mechanical (manual) what could cause the engine to do this.

[rjjablo]

Limp Mode is rarely transmission related. It is typicaly ignition or fueling related. Low battery voltage, plug wires, plugs, distributors and rotors, coils, cam doughnuts, crank sensor etc etc etc

[shogun]

yes, and you mentioned in your first post the possible problem >>>> "my batteries drained and then when car started again. Gone into limp mode"
That is the first thing you have to check, get a cheap battery load tester from HF, that will tell you exactly about the battery condition. To test with a multimeter a battery does not help much, use a load tester.
Then make a stomp test
Please use the reply button instead of reply with quote, I always have to delete your unnecessary quotes of the post before.

[henryc]

Hello, Shogun - PM sent.
/Henry

[EEDegreeToDrive]

It's also important to note there's no such thing as "Limp Mode" -- There are two/three distinct conditions that folks refer to as limp mode (most applicable to automatic transmission cars).
--For the V12, ignition problems can cause "Catalyst Protection Mode" which shuts down the injectors of one bank if it doesn't get positive confirmation of spark in the cylinder ID probe. This often happens from bad plug wires, trying to use 'fancy' spark plugs, or a bad cylinder ID probe (aka donut). (This is because most cars would otherwise die/stall and end up on the side of the road; but for the V12 BMW, the engine keeps running on half and they didn't want to keep dumping unburnt fuel from the other half into the exhaust, so shuts it down the injectors)
--The second issue is "Transmission Falisafe Mode" aka Trans Fail Prog-- If the transmission module detects a failure (it doesn't shift when it should, or the output shaft speed doesn't increase properly, transmission slips, etc) it'll slam into 3rd or 4th gear. This also happens with low batteries, when folks think it's OK to just 'jump start and go' without letting the batteries charge up enough.
--A third issue is that there's a discrete signal between the transmission module and the engine computer... Think back to the E32 days with the 3.5L.. If the transmission senses a problem and drops into "Trans Fail Prog" mode, it sends a "I'm having trouble, be nice to me" signal to the engine computer (DME) which artificially limits the maximum RPM to 'protect' the "failing" transmission from further damage..

Two common scenarios arise from the combination of these three things...
1) Bad ignition component (coil, plug, plug wire cylinder ID probe) module causes Catalyst Protection Mode; Engine drops to 6 cylinders. Driver compensates by pushing harder on throttle; Transmission expects output speed to be increasing in response to 80-100% throttle, maybe after downshifting a gear or two.. Transmission doesn't know the engine is having trouble and throws "Trans Failsafe" code,drops to 3rd or 4th, and then, to add insult to injury, sends signal to engine (already running on half) which further limits the output power... Kind of a poor compounding of conditions.

2) Bad General Module or other condition kills batter; Driver jump starts car, starts driving, but two dead 85-100Ah batteries are such a load that the 100A alternator can't provide enough voltage for all systems, transmission, and charging the dead batteries, so about a minute or two down the road, transmission goes into failsafe mode due to low voltage. Of course, limiting engine output to ~3000 RPM also means the engine can't quite run the alternator fast enough to keep charging the batteries.

All that said, if one has ignition problems on a road trip, far away from home, etc, if you shift the transmission manually and resist the urge to push the throttle more than about halfway, you can often avoid the transmission failsafe program, and running or 6 cylinders without the RPM limit will get you home. You can also 'reset' transfailsafe by leaving the car in gear and cycling the key 2-3 times, then putting it in park, and properly restarting the engine. (I drove a few hours from Indiana to Maryland one time on only 6 cylinders, though I did have to stop a time or two to 'reset' the transmission module)

Also remember not to jump start and go, but if you have to, try to conserve electricity for a little while until the voltage picks up (blower motor, lights, etc)

Limp Mode is rarely transmission related. It is typicaly ignition or fueling related. Low battery voltage, plug wires, plugs, distributors and rotors, coils, cam doughnuts, crank sensor etc etc etc