Engine won't rev and hunts

[ANDTWENTY]

So just thought I would update anyone thats been following this, I haven't put anything up recently mainly due to work taking up all my time. I have been trying to diagnose any issues with the ECU with the help of Laird Scooby. We haven't found anything but I'm still fairly confident its the ECU at fault as I've been over and checked parts again and other bits and bobs that may cause issues and still nothing. I read a post from someone with identical issues as mine and his was solved with a second hand ECU. I have tried a second hand one which turned out to not work at all and haven't been able to find another one other than from Sweden.
This brings me to where I am now, my ECU is now in the hands of Royal Mail on its was to a company that will test the ECU and give me the clarity I need on it. If they find an issue they will fix it and send it back with a lifetime warranty, if they find nothing then I have an ECU I know works and I'm back to square 1 but at least I know its not that. Anyway I shall update you all on the return of the ECU!

Fingers crossed!!

[ANDTWENTY]

Another little update for anyone interested!
The ECU arrived yesterday and they tested it, they then called me and said that they have indeed found issues with the ECU. They wouldn't say what the issues were until they go ahead with the work. I said they can go ahead and fix it so in a few days I should have a working ECU and hopefully a working 940!!

[mocambique-amazone]

The ECU won't recognise the open TPS.
Not the first ECU that did fail with this symptom....
Ask them if a sensor or something else did a short-cut and dud destroy the ECU.
We will see, the result will be there soon, in front of "Boris Exit"
Good luck, Kay

[Laird Scooby]

Originally Posted by mocambique-amazone

The ECU won't recognise the open TPS.
Not the first ECU that did fail with this symptom....
Ask them if a sensor or something else did a short-cut and dud destroy the ECU.
We will see, the result will be there soon, in front of "Boris Exit"
Good luck, Kay

That's a possibility Kay. My money is on dry joints, a capacitor gone down or a firmware problem - or a combination of those.

As firmware could also cause the ECU to not recognise the opening of the TPS idle switch, we could both be right!

Apparently it's 3-4 days to repair and test the ECU so maybe we'll all know come friday!

That will still be before Brexit - if it happens! I'm heartily sick of all the "remoaners" trying to disrupt and delay it happening, if a general election happens and one of those parties were voted in, can you imagine the fuss they'd create if everyone else saidthey shouldn't be allowed to take power without a second vote?

But i digress! Not the right place for that kind of talk really, there's a Brexit thread i used to watch (and contributed to a few times) but even that seemed to become a place for back-biting so no longer subscribe to it.

Now it's fingers crossed on the ECU and that there aren't any other faults!

[Ian21401]

Good idea. My brother and I have both used “ ECU Testing” in the past. One required repair and worked thereafter, the other “no fault found” so that eliminated one cause.

[ANDTWENTY]

Originally Posted by mocambique-amazone

The ECU won't recognise the open TPS.
Not the first ECU that did fail with this symptom....
Ask them if a sensor or something else did a short-cut and dud destroy the ECU.
We will see, the result will be there soon, in front of "Boris Exit"
Good luck, Kay

Are you thinking that the sensor could have caused the issue or it's just the ECU that failed resulting in the failure to read the TPS signal? I'll ask them when they call me up what it was that caused the issue if its failing to read the TPS

[Laird Scooby]

Originally Posted by ANDTWENTY

Are you thinking that the sensor could have caused the issue or it's just the ECU that failed resulting in the failure to read the TPS signal? I'll ask them when they call me up what it was that caused the issue if its failing to read the TPS

I've got my "fussy head" on so bear with the pedantry, the TPS is only a switch - well two switches, one for idle and the other for WOT (Wide Open Throttle) and these select maps inside the ECU, one for idle and the other, extra enrichment for WOT running.

Everything in between is set for cruising and/or medium acceleration. This is influenced by the MAF, if it's flowing much more air than the engine is burning (and the Lambda is telling the ECU that the engine is burning the fuel efficiently) in ratio to the fuel being injected, it adds fuel. However, there's a limit to how much fuel it will add when the idle switch is selected so even if the switch falls off the end of the throttle spindle, it will still rev but only with limited power - i.e. not on load. I think this is what Kay is referring to.

Conversely, if the ECU doesn't recognise the idle switch is made, it will still idle passably well but won't select the idle map so if revved, will throw a lot more fuel into the engine. Also above (i think it's 1200rpm) there's a fuel cut if the throttle is closed so it will rev but then "think" the throttle is closed so cut the fuel but then sense the extra air flow and try to rev again once it drops below the threshold of 1200rpm.

Bear in mind, if the AICV opens sufficiently, it's entirely possible for the idle speed to hit 15-1600rpm, again this is with the throttle closed (and hence the idle switch) but it stays idling at that speed (until it warms up at least) without a problem. This is because the ECU is sensing a cold engine so allows more enrichment and/or ignores the idle switch.

There isn't really a straight answer to your question because of all these factors, as your ECU was giving symptoms as if it was always reading a closed idle switch in the TPS but ignoring the temperature inputs it's highly possible a firmware fault caused it.
However it's also possible there's nothing wrong with this part of the ECU and it's purely down to the injector signal on the output transistor.

We won't know until you get the report back of what the fault was and even then might still be somewhat in the dark if they've put something like "Txxx not getting signal due to <whatever other problem denoting another failed component>".

We'll all just have to be patient until you get the report back sadly!

[ANDTWENTY]

Originally Posted by Laird Scooby

I've got my "fussy head" on so bear with the pedantry, the TPS is only a switch - well two switches, one for idle and the other for WOT (Wide Open Throttle) and these select maps inside the ECU, one for idle and the other, extra enrichment for WOT running.

Everything in between is set for cruising and/or medium acceleration. This is influenced by the MAF, if it's flowing much more air than the engine is burning (and the Lambda is telling the ECU that the engine is burning the fuel efficiently) in ratio to the fuel being injected, it adds fuel. However, there's a limit to how much fuel it will add when the idle switch is selected so even if the switch falls off the end of the throttle spindle, it will still rev but only with limited power - i.e. not on load. I think this is what Kay is referring to.

Conversely, if the ECU doesn't recognise the idle switch is made, it will still idle passably well but won't select the idle map so if revved, will throw a lot more fuel into the engine. Also above (i think it's 1200rpm) there's a fuel cut if the throttle is closed so it will rev but then "think" the throttle is closed so cut the fuel but then sense the extra air flow and try to rev again once it drops below the threshold of 1200rpm.

Bear in mind, if the AICV opens sufficiently, it's entirely possible for the idle speed to hit 15-1600rpm, again this is with the throttle closed (and hence the idle switch) but it stays idling at that speed (until it warms up at least) without a problem. This is because the ECU is sensing a cold engine so allows more enrichment and/or ignores the idle switch.

There isn't really a straight answer to your question because of all these factors, as your ECU was giving symptoms as if it was always reading a closed idle switch in the TPS but ignoring the temperature inputs it's highly possible a firmware fault caused it.
However it's also possible there's nothing wrong with this part of the ECU and it's purely down to the injector signal on the output transistor.

We won't know until you get the report back of what the fault was and even then might still be somewhat in the dark if they've put something like "Txxx not getting signal due to <whatever other problem denoting another failed component>".

We'll all just have to be patient until you get the report back sadly!

My only concern is that was it the TPS that caused the failure of the ECU and could it do it again? but being a switch I'm not sure this could be possible, unless perhaps it allowed too much current or voltage through and damaged a circuit?

It seems as though there must be something a little more than just that to cause the problem but as you say were just speculating. Hopefully ill here something from them soon.

[Laird Scooby]

Originally Posted by ANDTWENTY

My only concern is that was it the TPS that caused the failure of the ECU and could it do it again? but being a switch I'm not sure this could be possible, unless perhaps it allowed too much current or voltage through and damaged a circuit?

It seems as though there must be something a little more than just that to cause the problem but as you say were just speculating. Hopefully ill here something from them soon.

No, no and no. The TPS wouldn't cause the failure (unless someone deicded to feed it with +12V but even then, unlikely), it's an earth switch so the current is already going through (and almost certainly limited by) the ECU so damage to the circuit isn't possible in that respect.

[ANDTWENTY]

Originally Posted by Laird Scooby

No, no and no. The TPS wouldn't cause the failure (unless someone deicded to feed it with +12V but even then, unlikely), it's an earth switch so the current is already going through (and almost certainly limited by) the ECU so damage to the circuit isn't possible in that respect.

So that's a no then? I just wanted to make sure that I won't be setting it up to fail