Problem still exists!!

[dapinky]

I was aware from an earlier conversation with Trevor that they had changed the VSS - hence my thoughts that a swap of the entire instrument cluster may help to establish if the issue is within the wiring loom between the dash and the ECU, or in the unit itself (which may or may not be the actual VSS unit).

Unfortunately, I am no sort of guru with Elanscan or vehicle electronics in general, but am happy to swap bits round to see if anything improves!

[RonR]

Just had a look at the ECU code, there's an interesting comment:

Code: Select all

        ;----------------------------------------------------
        ; VSS ERROR 24 PEND (VSS Failure) EVALUATION
        ;  If any qual is not met, the counter is reset and starts over
        ;  --VSS <= 6 KPH
        ;  --MAP < 20 kPa
        ;  --RPM is in window 4000-6000 RPM
        ;  --VSS_FAIL_TIMER > 10 (10 seconds according to lotus docs)
        ;----------------------------------------------------

So after 10 seconds of receiving no data from the VSS (+ other conditions including RPM > 4000), the ECU sets Flag 52 Bit 5, which has the label 'VSS Error Pending'.
Once this flag is set it seems the ECU disregards anything coming from the VSS, which explains what we saw in Elanscan:

Merlot VSS+Flag.jpg

So there is a link in the code between the VSS and changed behaviour at 4000RPM.
From what I can tell switching the ignition off & on again should clear the flag and resume normal operation...... until the next time!

[TrevorB]

Just had a look at the ECU code, there's an interesting comment:

So after 10 seconds of receiving no data from the VSS (+ other conditions including RPM > 4000), the ECU sets Flag 52 Bit 5, which has the label 'VSS Error Pending'.
Once this flag is set it seems the ECU disregards anything coming from the VSS, which explains what we saw in Elanscan:

Merlot VSS+Flag.jpg

So there is a link in the code between the VSS and changed behaviour at 4000RPM.
From what I can tell switching the ignition off & on again should clear the flag and resume normal operation...... until the next time!

Ron, do you think then that this definitely points to the VSS being the problem?

If what Dave is saying about the instrument panel needs to be removed to get access to the VSS then I need to speak to MSC to find out exactly what they
did when they replaced it.



Trevor

[alan e]

Could it be the ECU that is faulty ?.

[RonR]

Ron, do you think then that this definitely points to the VSS being the problem?

If what Dave is saying about the instrument panel needs to be removed to get access to the VSS then I need to speak to MSC to find out exactly what they
did when they replaced it.

Could it be the ECU that is faulty ?.

From what I've seen it looks like the VSS, or the VSS wiring, or possibly the VSS circuit in the ECU is to blame (Thanks Alan). I've never changed one, but looking at the Engine Management Manual page EMK.3-G it looks like it's do-able with a right-angled cross-head screwdriver, as long as you have experience as a keyhole surgeon or an amateur gynaecologist.
There's a flexible circuit board which is clipped to the top of the VSS which would be my first guess for a bad connection. If that's OK there's a procedure on page EMK.4 pages 42 & 43 to test the wiring.

[Rambo]

So today Merlot came out of the garage with the plan to do a 'paper clip' test and see what codes were showing.
I was surprised that Code 24 came up as MSC had told me that they had changed the VSS module. So I'm assuming that the code
was still in the ECU. I disconnected the battery to clear the code and did the test again. Code 24 still showing?!

Am I correct in disconnecting battery to clear codes?

Yes.

But it sounds like you still have a stored error code 24.? Try disconnecting the battery for longer, then check no codes are stored, then go for a run and see if the problem at 4000 rpm still occurs. If it doesn't you have fixed it (maybe the ECU sees stored code 24 and automatically goes into limp home mode?). If it does you are still looking at the VSS

[TrevorB]

Trevor,

The VSS is a £20 part at SJ's (there is another thread about them at the moment!)..... but it is a simple Vauxhall part. Changing it is an instrument panel out job as it is held with a small screw and the 3 legs are soldered in.... so with labour costs, it probably isn't worth trying to save a fiver with a Vauxhall part.....

.... that said, what *may* be worth a thought is to borrow a complete instrument panel to fit temporarily to see if it cures the problem, and prevents the fault code.....

I'd just do a temporary fit of another one (as long as the bits plug in it doesn't have to be fully fitted for the test) and see what happens.

I don't know if a spare instrument panel is something which MSC would have lying around, but it is a Vauxhall Astra F/Vectra A/Calibra/Cavalier part.

(If they don't have one laying around, but it is something you fancy having a go at, then give me a shout before buying one on eBay - I can send my nurse out into the garage to see what she can find, and post it to you)

Dave, if only I was a hands on person, it would make life so much easier!

From what I've seen it looks like the VSS, or the VSS wiring, or possibly the VSS circuit in the ECU is to blame (Thanks Alan). I've never changed one, but looking at the Engine Management Manual page EMK.3-G it looks like it's do-able with a right-angled cross-head screwdriver, as long as you have experience as a keyhole surgeon or an amateur gynaecologist.
There's a flexible circuit board which is clipped to the top of the VSS which would be my first guess for a bad connection. If that's OK there's a procedure on page EMK.4 pages 42 & 43 to test the wiring.

Some great research Ron. This will certainly help MSC with some further checks. Thanks again.

Yes.

But it sounds like you still have a stored error code 24.? Try disconnecting the battery for longer, then check no codes are stored, then go for a run and see if the problem at 4000 rpm still occurs. If it doesn't you have fixed it (maybe the ECU sees stored code 24 and automatically goes into limp home mode?). If it does you are still looking at the VSS

Thanks Mark, I will try this next time I have the car out. Could it be the cheapest of fixes?!


I have spoken with Will at MSC today and he confirmed that they have changed the VSS. I suggested they look at this post for some useful suggestions.
As stated before Merlot not due for an MOT and service for a couple of months so that is the next opportunity to investigate the problem, if it's not
fixed before hand of course.

THANKS EVERYONE



Trevor

[dapinky]

Trevor,

The obvious solution is to put yourself on the list for Castle Combe.......

...... we could have the ECU swapped in half an hour to see if that is at fault, swap the complete instrument panel in another half an hour, check the continuity of the wiring between the two, and then sort out what needs doing, and have it fixed by lunch time parade lap!

[TrevorB]

Trevor,

The obvious solution is to put yourself on the list for Castle Combe.......

...... we could have the ECU swapped in half an hour to see if that is at fault, swap the complete instrument panel in another half an hour, check the continuity of the wiring between the two, and then sort out what needs doing, and have it fixed by lunch time parade lap!

I have witnessed how you work out in the field in person so I have no fear that this is possible. Although I do already have my name
down for Castle Coombe I would ideally like this sorted before that date. It doesn't mean that it won't be considered though.



Trevor

[alan e]

Trevor i have a new ECU in the garage your welcome to fit it to see fault is still there.

[dapinky]

Trevor i have a new ECU in the garage your welcome to fit it to see fault is still there.

Bring it to CC - I'll take my spare instrument panel and we'll have it sorted in no time (unless it gets done before then).

[Simon_P]

Trevor i have a new ECU in the garage your welcome to fit it to see fault is still there.

Bring it to CC - I'll take my spare instrument panel and we'll have it sorted in no time (unless it gets done before then).

Do we need a list? ..bring a bit to fix Merlot

[Simon_P]

Looking at the scan

The engine temp was 30c when you started it - always helps to have a scan at idle form cold until the fans come on so that you or someone else can check if the basic sensor data is somewhere around right.
If you have an error code clear it before you do a scan from cold at idle. otherwise you can't tell if it is a stored code or or when it was set.

The IAC reading is nonsense - Cant tell if it is duff IAC, vac leak or electrical... fault (need to do a scan from cold at idle) or just any time at idle you didn't stop long! Just read that the VSS is used to control the IAC so maybe linked.

The hesitation at 4000RPM is a fuel cut so likely a limp mode rev limit commanded by the ECU.

[Simon_P]

I was aware from an earlier conversation with Trevor that they had changed the VSS - hence my thoughts that a swap of the entire instrument cluster may help to establish if the issue is within the wiring loom between the dash and the ECU, or in the unit itself (which may or may not be the actual VSS unit).

Unfortunately, I am no sort of guru with Elanscan or vehicle electronics in general, but am happy to swap bits round to see if anything improves!

That could be a good offer - The VSS is only half of the game. It is an optical signal generator, so it is looking at something (a disc with markings?) in the back of the speedo if the disc/markings are faulty or there's a dead spider in the way it isn't going to generate a good signal.

Just had a look at the ECU code, there's an interesting comment:
CODE: SELECT ALL
        ;----------------------------------------------------
        ; VSS ERROR 24 PEND (VSS Failure) EVALUATION
        ;  If any qual is not met, the counter is reset and starts over
        ;  --VSS <= 6 KPH
        ;  --MAP < 20 kPa
        ;  --RPM is in window 4000-6000 RPM
        ;  --VSS_FAIL_TIMER > 10 (10 seconds according to lotus docs)
        ;----------------------------------------------------

So after 10 seconds of receiving no data from the VSS (+ other conditions including RPM > 4000), the ECU sets Flag 52 Bit 5, which has the label 'VSS Error Pending'.
Once this flag is set it seems the ECU disregards anything coming from the VSS, which explains what we saw in Elanscan:

yes but like a biblical quote it needs context, analysis and lots contemplation. I think that you are right but the conditions aren't met - RPM has been out of range for 15s

[Simon_P]

RonR - looking at the scan again I think you have identified the intermittent nature of the fault - the fuel cut at 4000rpm only happens after flag 5 is set. Hopefully that's the symptom identified.

[RonR]

Thanks Simon,

Good to have an expert on the case!

In the engine management manual the RPM range is stated at 2400-4400.
I've found a few errors in the disassembly comments so far, so I'll check the actual code vs the comments.

[TrevorB]

Looking at the scan

The engine temp was 30c when you started it - always helps to have a scan at idle form cold until the fans come on so that you or someone else can check if the basic sensor data is somewhere around right.
If you have an error code clear it before you do a scan from cold at idle. otherwise you can't tell if it is a stored code or or when it was set.

The IAC reading is nonsense - Cant tell if it is duff IAC, vac leak or electrical... fault (need to do a scan from cold at idle) or just any time at idle you didn't stop long! Just read that the VSS is used to control the IAC so maybe linked.

The hesitation at 4000RPM is a fuel cut so likely a limp mode rev limit commanded by the ECU.

Ron, Simon says that 'the engine temp was 30c when you started it'. I don't understand that as the engine was cold when we started the run?
Do we need to do another run?

RonR - looking at the scan again I think you have identified the intermittent nature of the fault - the fuel cut at 4000rpm only happens after flag 5 is set. Hopefully that's the symptom identified.

Simon, can you explain with laymans language. Or is that to do with the fault code still being present?

ALL this is great information and I have heard from MSC who are monitoring this post and they are going to get behind (literally) the problem by taking out
the instrument panel and investigating the VSS ribbon and electrics. Obviously if there is anything else for them to check out please add to the post.



Trevor

[Simon_P]

Simon, can you explain with laymans language.

I'll try!
You experience an intermittent apparently random "fault" - This is better described as a symptom - the symptom is a misfire at 4000rpm
Ron has identified the ECU code for a VSS error that sets Flag 52 bit 5 which we can see in elanscan (this may or may not be the VSS fault code)
As we can see the flag in elanscan we can look at points where you reached 4000 RPM before and after the flag was set
we can see that before the flag was set it was ok and after the flag was set, when the revs reach 4000rpm the injectors are switched off momentarily causing a misfire (injector pulse width =0)
We can now say that it is probable that the symptom that you experience is caused by a VSS error that sets flag 52
we can see that the VSS signal is bad

That's the good news!

The bad news is that we don't know what is causing the VSS signal error - loose wire? poor earth? dead spider? or the USB charger that you plug in to the cigarette lighter...

[Simon_P]

Good to have an expert on the case!

Haha! from the comfort of my armchair - lets wait and see!

In the engine management manual the RPM range is stated at 2400-4400.
I've found a few errors in the disassembly comments so far, so I'll check the actual code vs the comments.

20 kPa is very low - never got mine lower than 23 doing brake testing so Merlot getting down to 17 is probably due to the IAC being closed.

Ron, Simon says that 'the engine temp was 30c when you started it'. I don't understand that as the engine was cold when we started the run?

Cold is left overnight cold which should be about ambient temperature.

Do we need to do another run?

more useful would be to let it get cold over night, then do a scan from start-up don't drive anywhere - let it idle until the fans come on.

[RonR]

Trevor,

When I arrived the car was in the driveway, did you reverse it out of the garage? With a bit of heat soak that could have raised the temperature to 30 Degrees.

As far as the RPM range goes it's complicated - there are several different RPM measures used, all derived from pulse counts. The constants 4000 and 6000 are used, but I'm not sure if the field compared to has been 'scaled' or not. My 68HC11 assembler isn't good enough to quickly work out what's going on in the code (yet).