DBW dc out & throttle closure

Hopefully someone can help me out with this issue I’m having with my Bosch DBW throttle body.

The ECU starts to close the throttle at high rpm approx 7600rpm, this happens in tandem with the increase in DC out %.

The target throttle position and actual throttle position overlay perfectly into this point, where as expected the target remains as expected but the actual starts to fall.

I have double checked all wiring and no issues, have also fitted a new throttle body and redone the calibration yet the issue persists.

Incredibly frustrating, if any one has any suggestions then please do let me know.

I have a log I can share which I assume will be required to see if there is an issue I am missing

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I’ve seen your post on the facebook group, have you posted a log file and calibration?

Could be so many things, what size Bosch throttle body?

It’s a Bosch 68mm (part number 0 280 750 156).

I tried to post the log file here but it won’t allow it as it’s an emublog.

Log file attached below that shows the issue.

What does your DBW - Characteristic#1 table look like? is the Map targeting a lower Throttle Position at higher RPMs? Also, has your TPS been calibrated properly for the voltage it actually see’s? You can check under sensor setup/TPS.

I had a similar issue on a car where the Voltages were not set correctly so the throttle when pushed to the floor only actually reached 89% Throttle…so when the characteristics table got higher in the revs the throttle wanted to close down slightly.

providing a base map with your log may help as well but that is where I would start looking.

I can’t see how that would be the issue as the car has ran and worked perfectly for months now.

This is a new issue and no aspect of the map has been altered.

Fitted new throttle body and carried out a recalibration via the wizard, yet the issue remains.

Make sure all power grounds are connected to emu

Didn’t see in the original post where you stated it had been running perfectly for months. disregard my statement.

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All grounds to the ECU and chassis are as they should be and have been continuity checked.

I’m at a loss as to what the issue is, also seems odd that it only happens at high rpm under full throttle.

I had a similar problem with a customers car. The car was running for months without any issue and suddenly the same problem as yours appeared.
It was a ground problem! The customer didn’t wire the DBW ground to sensors ground, instead he just used the car body.

A few people have suggested it may be a ground issue, but I have double checked and checked again.

All grounds including the sensor grounds are good.

If it was a ground issue chances are the DBW closing fault would occur anywhere in the rev range at random not just at high rpm under WOT

Log file is super interesting, it just starts closing at roughly the same RPM and its very repeatable.

PID is doing its thing, target error causes more DC but still starts closing.
Battery voltage is kinda erractic but its not falling off with rpm or anything.
No protections or errors present until above 7600 rpm, TPS value stays the same.
There’s random dips in the DBW error aside from above 7600 rpm, but seems to be of no consequence to the PID. This is most interesting because it looks like a drop out but its only shown in that channel, not the TPS 1 or 2 inputs (analog 1 & 2)

While I don’t have your cal file to see if there’s some other setting that somehow hasn’t been an issue up until now, and since you’ve tried replacing the DBW unit, that kinda just leaves wiring.
I have installed a bunch without issues but I know the connectors can be super finnicky.
My theory is that the engine is vibrating in such a way above 7600 rpm that the connector is loosing proper contact with one of the motor pins. This could explain the DBW error dips if its logging error’s at a faster rate then the position sensors are shown in the data logs (i think its 25hz in the graph logs)
What engine? is it solid engine mounts? How is the dbw motor attached to the engine?

Curious what pedal are you using? I see analog #3 and TPS are identical, and I’m assuming the plausible check is into analog #3

@FloorItGarage very helpful reply, appreciated.

Pedal box and PPS potentiometer are from OBP motorsport.

I have checked the plug at the DBW and all seems good but I will check again.

Engine is a K24, not solidly mounted.

I can attach the emu project file of it would be helpful.

Attach project file and we’ll see.

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my next idea would also have been engine vibration.

I personally think there’s a problem with the electrical harness, and that’s causing the issue with the throttle.

I’m noticing a strange correlation between the closing of the throttle and the RPMs, especially with the DC injectors at the RPMs that are at 100%. It seems like the power ground wires are just too thin in diameter.

I’ve encountered similar cases where wires that were too thin were used. The throttle worked when the engine wasn’t running, but as soon as the engine started and the power ends began to work, the current simply didn’t flow properly.

Thanks for the input, I have continuity checked the harness time and time again and all is good.

In terms of ground wire size I believe they are sized appropriately at 0.75mm2, 1mm2, 1.5mm2 for, sensors, injectors, coils, DBW etc.

I have made a new harness to go direct from ecu to DBW throttle body to see if that helps the issue but i am not holding out much hope in all honesty.

I will post my EMU project file shortly, I do not think the issue is with the project file given the car ran perfectly for months before this issue started causing troubles.

EMU Black project file in link below

Look at the battery voltage:

It looks like something is wrong with the voltage regulator.

Does DBW behave the same when the engine is not running ?
If it works ok, then try to disconnect alternator and check what happens.


Thanks for the input, I will certainly give it a try but as it only has a small race battery it can’t be a permanent solution.