girvan

My GS400 has a problem where it is rev limited to exactly 4200 rpm. I don’t know when this happened and I can only cause the problem in two ways:

A) Revving the engine on Neutral
B) Going max in 2 using E-shift.

I cannot test the 1-2 change as E-shift does not control that but it appears to happen at 4200 and the higher change points like 3-4 at are at 120MPH and above so it not easy top test. I use the POWER setting.

Since A is on almost no throttle and B is on full throttle, I don’t see how a fuel or ignition problem can cause such a consistent rev limit. There are no error codes set.

In every other way the cars performs perfectly. It’s almost as though I have a 4200 rev limit set.

Anyone with any ideas? Are there any conditions where the engine is limited to 4200 by the ECU? Is see none in the service manuals.

girvan

Well I guess I missed the obvious - the rev counter under-reads exactly 50% so the rev limit is really 6,300 which I think is right.

Now I need to find the cause and/or replace the rev counter as it apears to be calibrated for a 12 cylinder engine.

girvan

Still need some help here...

I isolated the problem to the gauge ECU board behind the gauges. The rev counter meter movement itself is fine. I need to change that board.

Does any one know where the Odometer data is stored? Is it in the main engine ECU so I don't need to deal with changing or explaining things?

Or is it in the display ECU? There is also a sub board with the mileage LCD display.

Also anyone else seen this problem? There was a post with identical symptoms down to the identical amount of error a few years back but no resolution stated.

jcat_350

are you sure it's revving past 4200rpm? Almost sounds like a kind of valet mode now that i reread it.

girvan

Thanks I checked with scan tool and oscilloscope. Both show the same 50% higher reading so I am 100% sure engine is working fine and rev limiting at 6300.

As I mentioned there was a post with exactly the same issues on the same car in 2004...

jcat_350

i would think that since everything is working fine but just not displaying correctly that the Display ECU is to blame. If it was within the main engine ecu it wouldn't be reading the sensors right and would probably cause other problems. The fact that it's just displaying wrong, i'd just try a different display ecu, maybe even disconnect it from power to try and reset it.

Parker Gen

...I'm going to ask a question a lot of people might be thinking... how could you not know it was revving at it's peak, and not mid range?

girvan

"Thanks I checked with scan tool and oscilloscope. Both show the same 50% higher reading so I am 100% sure engine is working fine and rev limiting at 6300."