Engine cutout at high rpms

  #1  
Old 03-20-2016, 03:23 PM
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Angry Engine cutout at high rpms

My daughter's 2003 L300 starts and runs fine, but if you try to accelerate hard (why else do you have a V-6?), the engine cuts out. If you drive like a grandma, it works normally. When the engine cuts out, the "check engine" light comes on, but goes off after a few seconds. If you ease off the gas, the car returns to normal.
I don't know what would cause this--any ideas?
I have an adapter to connect a laptop to the ODBC2 connector to read codes and sensors--when the cutout occurs, the interface stops sending data making me think that the ECM is affected by the cutout.
I've made this occur multiple times, and the car still runs fine if I drive like a grandma--this makes me think that the ECM is working OK.
 
  #2  
Old 03-20-2016, 11:22 PM
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Do the speedometer and tach work correctly?
Does it start to cut out at the same rpm range? If so, what range?

Normally I would suspect something simple, like a rich or lean condition code
due to worn out front O2 sensors sending bad info and wrecking the air:fuel mix.
But that sets a hard code and is easy to track down.

So, in absence of that code and the strange data stream behavior, I'll go out on a limb and GUESS that there is an issue with the vehicle speed sensor. The problem is such that the VSS is providing normal output at lower rpms, but for some reason, when the rpms increase past a certain level, the VSS signal goes to 0 mph.

When this happens the ECM thinks the car is not moving and imposes a 0 mph rev limiter mode to prevent overrevving of the engine while sitting still, even though the car really is in motion. If you continue to try to increase the RPM, once you hit the pre-programmed limit I THINK the fuel is reduced , causing it NOT to increase RPMs and to cut out. I'm guessing around 4K rpm as the rev limiter point, but that is based on the S Series 1.9 DOHC engines. The V6 in the L300 is a different animal entirely.

As far as ECM behavior , I don't think that the data stream should ever "hitch" like that under normal operating conditions or abnormal ones either.

Does your laptop software have the ability to retrieve "historical" OBDII codes?
If so, I believe the event turning on the SES light should be recorded as a historical code.

Can you reproduce this behavior at idle in Park?
 
  #3  
Old 03-21-2016, 09:32 PM
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Speedometer and Tach work correctly.
Cutout does happen sitting in the driveway in park (approx. 3500 RPM).
Stream of sensor data through ODBC2 stops when cutout occurs.
While driving, cutout happens at around 2200 RPM.
After repeated cutouts, Check Engine light stayed on.
Codes are P0700 (Transmission Control System MIL request) and U2105.
 
  #4  
Old 03-22-2016, 05:04 AM
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P0700 is how the TCM (Transmission Control Module) lets the ECM (Engine Control Module) know that it has at least 1 stored code. It must be read directly from the TCM.


U2105 Means that either the one or more of the TCM, ECM, BCM lost communications with the other two (fell off the CAN (network)).


Read this, follow troubleshooting and let us know what you find


A code means...SAE U2105...car will not start..ran codes only one that


It may be a loose connection, burned pin, etc or something more serious.


But the TCM should be investigated regardless


I was sorta close on the 0 mph speed sensor angle; it cuts out as designed at 3500 when not in motion, but ECM stored speed READS 0 if the ECM is not communicating properly.


The fact that the diag data cuts out leads me to believe either this is normal behavior for a vehicle going from running to not running, or it signifies a problem with ECM communications.


So I am guessing it is an ECM TCM issue, but I could be wrong. I am far from a CANbus vehicle expert so you will want to get confirmation of my educated GUESS.
 
  #5  
Old 03-24-2016, 09:27 PM
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Thanks so much for the diagnostic advice. Problem is fixed--all the ECM bolts were loose! Once I tightened them up, the engine was smooth up to 6000 RPM!
I had disassembled this several months ago to replace the thermostat (wow--what a job compared to a "normal" car) -- I guess they vibrated loose?!?
So, bad grounding of the ECM led to the symptoms I reported.
 
  #6  
Old 03-25-2016, 02:56 AM
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Glad to hear you're all good to go!

And thank you for stopping back in to give us the resolution.
 
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