LH 2.4 raised idle speed after high rev, ok after restart

Hi,

I have a setup with the LH 2.4 and EZK 116 on my B21ET in my Amazon.
Everything runs fine and hot/cold idle is about 800-900 rpm.


But when I once rev over ~5000-6000 idle speed raises to 1500 rpm afterwards.
When I turn the ignition off and on (less than a sec. off) idle speed is at 800-900 again.


All parts are cleanly rebuilt. And I checked for air leaks multiple times.
Signals from throttle flap are correct.


I did not have the speed input of the LH connected yet. (pin 17)
But now I simulate this input using an arduino, giving it 8 signals per drive shaft turn.
I thought this missing input was the reason but I still see raised idle speed after a short high rev.


Do I perhaps reach some kind of limit of the fuel map ?

Any ideas ?

Thank you in advance,
Bart

Speed sensor is why it does that

el-barto said:

I did not have the speed input of the LH connected yet. (pin 17)
But now I simulate this input using an arduino, giving it 8 signals per drive shaft turn.
I thought this missing input was the reason but I still see raised idle speed after a short high rev.

Click to expand...

First thought is wonder at why you chose 8/per instead of 12. Second thought is to ask if your LH2.4 fuel computer raised a 311, confirming the signal isn't recognized.

Thanks for the answer,

but then I should see error 3-1-1 oder 1-3-1 at least ... but I get no error codes at all ...

(the pin is 34 not 17. looked it up wrongly on the lh 2.2 table ...)

I do have an engine speed signal and see it on the oscilloscope ...

Do you mean the speed signal from the speedometer is missing or the count is wrong ?

I do get 8/per turn because this was easier to build and I did not know the original ration.
But I could raise it to 12 by software. But wonder if that helps ...

el-barto said:

Do you mean the speed signal from the speedometer is missing or the count is wrong ?

I do get 8/per turn because this was easier to build and I did not know the original ration.
But I could raise it to 12 by software. But wonder if that helps ...

Click to expand...

I figured whether it is considered missing or not would be shown by raising the 311. You could disable the simulated input to verify that does indeed report it missing. As to the 8 vs 12 -- I have no idea. I'd think it wouldn't matter... like going 40 instead of 60 kph. Your simulated signal is open collector and about 1mS long?



(from http://cleanflametrap.com/speedo.html)

Thank you for the answer and the link. This is indeed very interesting and helpful!

I trigger the input with a AQY212 photomos against car voltage so open collector should be met.

But by now I simply pipe through the signal I get from the drive shaft to the ECU.
So I'll next fiddle around with the timing.

Strangely I did not get 311 even while not triggering/simulating the input.

I have a 984 ECU which I downgraded to 962 because I couldn't work around the immobilizer.
But all wiring plans starting from '89 do have the speedo signal connected.

So thanks for pointing in a useful direction!

I have no idea whether the duty cycle could be important to the fuel computer, but I think it does take some time (and driving) to elicit the 311 when the VSS is missing. Doesn't seem like enough time passed between your posts to do a test drive.

When you get it sorted, please post your technique, as I often read here where folks are wanting to get LH2.4 working with rear axles having no speed sensor.

My speed sensor is all messed up from my latest G80 install WITHOUT the correct diff cover. My needle jumps around sometimes, but otherwise is completely dead. NO CODES! High idle is frequent. Point is, don't expect LH to toss a speed code. I had the cluster completely pulled out before and it still didn't even toss a code.

Thanks, this is interesting.

So I will experiment with the output signal ... and come back with something ... perhaps a solution suitable for everyone with the same problem.