P38A Cruise control...... Again!!

Yes it should be a "well tuned loop" . . . but this is LR & Hella. I doubt ECU is that smart, so it probably gives the vacuum a "bit extra", hence if the cable is too tight the engine will probably over accelerate.

These ECUs are very old. Maybe the refresh rate isn't great?

Interesting to read up on this...
My 2001 has the same issue - has the later cruise ECU - but it also seems to hunt a fair bit.. will speed up above the set speed, ease off, and go under target speed, speed up again etc..

I haven't tried the different tunes in mine, nor even really looked at it on diagnostics to see what options I have.

Might have a poke about on it tomorrow and see what options I have available...

Wazzajnr said:

W

Wammers, I was referring to the cruise control ecu values.

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I am not aware that the cruise control ECU has any values that can be changed before 1999.

wammers said:

I am not aware that the cruise control ECU has any values that can be changed before 1999.

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There are 5 available "tunes" (4.6 engine, P38 4.0, disco II 4.0, ECU default and unknown) of these, I can select the disco, the 4.6 and the default. The other two give "no data available" if you try to select them.
They DO change the parameters (prop gain, int gain, hysteresis etc etc) and it does make a marked difference how it behaves.
The 4.6 engine tune seems to be the best, the default ecu is way too sensitive and hunts massively, the disco setting is not sensitive enough, also causing it to hunt badly.
If only I could change the numbers directly, I could easily tune it but it appears you can only choose the tunes that are available in the ECU.
My guess is that the ECU has been replaced at some stage to try to get the cruise working and its not the right one, thus, does not have the data set that the P38 4.0 needs.
Not much I can do for now until I get back to blighty unfortunately.

Wazzajnr said:

There are 5 available "tunes" (4.6 engine, P38 4.0, disco II 4.0, ECU default and unknown) of these, I can select the disco, the 4.6 and the default. The other two give "no data available" if you try to select them.
They DO change the parameters (prop gain, int gain, hysteresis etc etc) and it does make a marked difference how it behaves.
The 4.6 engine tune seems to be the best, the default ecu is way too sensitive and hunts massively, the disco setting is not sensitive enough, also causing it to hunt badly.
If only I could change the numbers directly, I could easily tune it but it appears you can only choose the tunes that are available in the ECU.
My guess is that the ECU has been replaced at some stage to try to get the cruise working and its not the right one, thus, does not have the data set that the P38 4.0 needs.
Not much I can do for now until I get back to blighty unfortunately.

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So i take it your car is a MY 1999 or better. If you look at the Nanocom site it gives the setting numbers for each different car, what numbers you should see for each car selected. Have a read here. http://www.nanocom-diagnostics.com/downloads/preview/hella-cruise-control Cruise on the petrols is not something i am familiar with.

Yes, it's a 2000MY.
I think my ecu is not right. Reading that document, I don't have the option of a disco 4.6
New ecu beckons methinks.

Thanks for all the information gents, I'll update you on progress when I get home and have a play with it.

The Hella 5GA-006-310 is also used in other vehicle makes, so if yours doesn't have all the LR vehicle options, it could well be from the wrong vehicle. Why not order another online to be ready for you when you get home ?

Wazzajnr said:

Yes, it's a 2000MY.
I think my ecu is not right. Reading that document, I don't have the option of a disco 4.6
New ecu beckons methinks.

Thanks for all the information gents, I'll update you on progress when I get home and have a play with it.

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Do you have the correct engine selected in BECM options menu?

wammers said:

Do you have the correct engine selected in BECM options menu?

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Put simply, no idea!!! I didn't even know that was an option.
I'm guessing that as the BECM and engine ecu have to communicate to even start the car that if it were wrong I'd have bigger issues than cruise control!
However, I'll have a look and see what's selected.

Given that you have some miles to do, why not use the Nanocom data logging on the cruise ECU while driving. Bit of a long shot, but the Road Speed & Target Speed input values might hint on why it's surging ?

Wazzajnr said:

Put simply, no idea!!! I didn't even know that was an option.
I'm guessing that as the BECM and engine ecu have to communicate to even start the car that if it were wrong I'd have bigger issues than cruise control!
However, I'll have a look and see what's selected.

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You have a choice of Motronic, Gems or EDC. As you say if the wrong one is selected everything would maybe go tits up. Was just a loud thought rather than a suggested remedy.

Lost me on page one, ill stick to brick on peddle

I think if you can get the correct tune and cruise ECU for the engine it will work well. My cruise on my 4.6 Thor would overshoot once on resume if you resumed from a significantly lower speed that it was set at. Other than that it didn't hunt. So I think the factory PID loop is OK. I think there's something else going on with your setup.

wammers said:

You have a choice of Motronic, Gems or EDC. As you say if the wrong one is selected everything would maybe go tits up. Was just a loud thought rather than a suggested remedy.

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Yep, found it and it is set to motronic. Good thought though!
I think I have a plan now which is to get a new cruise ecu ordered up first and then see what it behaves like.
Worst of it is, when I replaced the vac pipe to the brake pedal, the new one wouldn't go through the old grommet as it was a bigger od so I just put the pipe through the hole for now thinking that when I get time, I'll silicone it in.
You wouldn't believe how much cold air comes through such a small gap at 80mph when it's - 15degC outside!
My knees were freezing last night!

albany said:

I think if you can get the correct tune and cruise ECU for the engine it will work well. My cruise on my 4.6 Thor would overshoot once on resume if you resumed from a significantly lower speed that it was set at. Other than that it didn't hunt. So I think the factory PID loop is OK. I think there's something else going on with your setup.

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A well tuned Pid controller should give one overshoot, one (smaller) undershoot then level off at setpoint.
Yes you can tune the overshoot out but it makes it respond very slowly.
I know it should be better than it is so I want to get the right ecu first, and if it still hunts then I can look at any other parts of the system that might throw it out of the range that the parameters can handle.

I would still double check the cable adjustment before changing ECU.

pwood999 said:

I would still double check the cable adjustment before changing ECU.

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Yep, I'll have a look at that next week in Czech. If it is just that then I'll be a happy bunny but sadly, my luck isn't normally that good!!
By the way, like the dash on yours! I'd like to do something with the sounds on mine at some stage. It's got an aftermarket head unit in it, but I think there's amps in the doors too so on volume 1 it's barely audible and volume 2 is too loud.
Also, radio reception is ****e.

In a perfect world I'd love to be able to have something that works with the wheel controls and was Bluetooth to my phone but I think I'm asking too much.

I'd also like a DAB receiver as the fm stations in Europe are crap!

If you're near Heathrow on your journey back to Chorley then message me. If I'm home then you can come have a look at the tablet install.

But better to start a "DAB Stereo" thread for this part.

O

pwood999 said:

If you're near Heathrow on your journey back to Chorley then message me. If I'm home then you can come have a look at the tablet install.

But better to start a "DAB Stereo" thread for this part.

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OK, might do that at some point. I'm quite often down that end.

As you may have noticed, I get sidetracked!