The V8 Owners Forum -

Just on a slightly different topic but shows just how frustrating this all is in relation to what RPI supplied. Whilst watching videos on Rovergauge I came across a mention of a grounding plug for the diagnostics port which is there to prevent ECU interference. I had no idea this was supposed to be present as its missing from my loom, looking closely I can see where the black ground line has been cut.

Not sure how much difference this makes but its obviously there for a reason.

I believe the plug grounds from the black wire to the white with pink stripe. Can anyone confirm this please.

scudderfish wrote: ↑Tue Oct 28, 2025 6:40 am Can you attach the complete log? If not, email it to me at dave.g.smith@gmail.com

Regards,
David

Same here, PM me if you have to do it via e-mail. I have an Excel file with a macro in it which may be able to make some sense of it, may just need to tweak the macro to get something meaningful from your trim data.

heli_madken wrote: ↑Tue Oct 28, 2025 3:22 pm Just on a slightly different topic but shows just how frustrating this all is in relation to what RPI supplied. Whilst watching videos on Rovergauge I came across a mention of a grounding plug for the diagnostics port which is there to prevent ECU interference. I had no idea this was supposed to be present as its missing from my loom, looking closely I can see where the black ground line has been cut.

Not sure how much difference this makes but its obviously there for a reason.

I believe the plug grounds from the black wire to the white with pink stripe. Can anyone confirm this please.

Grounding can be very important for your sensors - not just for shielding:

I know you don't have megasquirt ECU - but this is interesting on the theory for grounding:
helped me solve some weird issues I was getting.
https://www.msextra.com/doc/pdf/html/MS ... .4-12.html

SuperV8 wrote: ↑Wed Oct 29, 2025 1:21 pm Grounding can be very important for your sensors - not just for shielding:

I know you don't have megasquirt ECU - but this is interesting on the theory for grounding:
helped me solve some weird issues I was getting.
https://www.msextra.com/doc/pdf/html/MS ... .4-12.html

Thanks for your help I will take a look at the link, I will also add the ground loop.

Trying to get to grip with the log files. if I am formatting and interpreting the data correctly the MAF seems to be very 'lazy'. I was taking it easy on the test drive but did hit 76% throttle at one point. The MAF read just under 43%, looking at videos on line (havent been able to find any logs to compare) this level of throttle results in much higher values closer to 80>90%. As a result its only selecting fuel map row 6.

I think this is why the Lambdas are mostly adding fuel, again most videos show subtracting fuel.

The other strange thing is the idle bypass valve appears to be constantly 50% open, but not sure if I am misreading the figures.

I am probably completely wrong but do I have a faulty MAF, its the only thing I havent replaced. Surely with the number of failures I have had this isnt yet another one.

Hi Heli
Only managed to get a quick look at your data so far this evening as it was a late finish for me today but I'll add my initial thoughts to the comments on your last post.

heli_madken wrote: ↑Wed Oct 29, 2025 2:22 pm
Trying to get to grip with the log files. if I am formatting and interpreting the data correctly the MAF seems to be very 'lazy'. I was taking it easy on the test drive but did hit 76% throttle at one point. The MAF read just under 43%, looking at videos on line (havent been able to find any logs to compare) this level of throttle results in much higher values closer to 80>90%. As a result its only selecting fuel map row 6.

I think the TPS results you are reading are absolute rather than uncorrected, my spreadsheet massages this back to corrected and this results in a maximum throttle opening of 68.3%.
The maximum row you get to is 6.13 which was done with a TPS of 66.2 I'd say that is not too bad, in fact I think that may even be high as there are only 8 rows and IIRC they are counted 0-7 - I need to check this though. Either way I don't think that is an issue.
To check this properly I'd try and find an uphill stretch, going slow in high gear (if it's a manual) and floor the throttle, this should make the engine breath as deep as possible. This will test your maximum row value.

For future sessions I suggest you set your throttle reading type to Corrected and MAF reading type to direct.

heli_madken wrote: ↑Wed Oct 29, 2025 2:22 pm
I think this is why the Lambdas are mostly adding fuel, again most videos show subtracting fuel.

I need to spend a but more time with the Lambda readings as this is uncharted territory for me but I don't think the MAF reading will upset this.
As above I don't think your MAF is necessarily a problem.

heli_madken wrote: ↑Wed Oct 29, 2025 2:22 pm The other strange thing is the idle bypass valve appears to be constantly 50% open, but not sure if I am misreading the figures.

That does seem a bit strange. it seems that whenever you have an open throttle the IACV gets pegged to a value of 50.5556%
I need to compare this to how mine behaves but I seem to recall from when I looked at the code that the IACV is wound closed once the TPS is away from zero.

Apart from at the very start of the readings the roadspeed doesn't seem to drop low enough to go to low speed idle and looking at the RPM the engine appears to be driven by the vehicle motion hence IACV not being actively used so can't really glean any information from that.
You could probably take a log on a run where the vehicle is doing a bit of stopping and starting.

BTW, the logs seem to indicate you only got up to about 18MPH, is that correct?

heli_madken wrote: ↑Wed Oct 29, 2025 2:22 pm I am probably completely wrong but do I have a faulty MAF, its the only thing I havent replaced. Surely with the number of failures I have had this isnt yet another one.

Hang on, lets not be firing the parts cannon just yet, I don't see anything here to indicate a MAF issue. Let's get some more data first and ideally do the test I mentioned earlier and make sure you record with the "Linear" setting for MAF


Only had a quick look at the lambda's but I don't think these look good. I'm seeing values between +255/-256 on the Odd bank, I'm assuming the maximum should be +/-255 which would indicate that this bank is going to the extreme limit in each direction, can't believe that is right. Surprised this didn't cause an error to be thrown.
The Even bank is better but only slightly, +227/-249. Hopefully someone with more experience with closed loop can chime in but to me that seems wrong.
These are just the min and max readings so my be only for brief periods, I hope to look in more depth tomorrow.


Edit
Meant to mention your coolant temp reading looks a little low, maxing at 78, mine typically runs at 87. I don't know when this will cause enrichment and may be quite normal depending on thermostat.

Thanks for your detailed response, I will set the logging to what you suggest.

I am on a steep learning curve with this and was also confused by the road speed. The software has a multiplier I discovered and worked it out that I need to set a value of around 3.7 as I was mostly doing around 60 mph on a rural road, not many start stops around here.

ZF4 HP22 Automatic gearbox is fitted, supplied by Ashcrofts and uprated with a larger torque converter and other HP24 components. it too also gives me problems as it has a sticking governor valve. For anyone doing a full rebuild try to be careful when you order major items like engines and gearboxes. I ordered the gearbox too early so the warranty had already run out by the time I got the car on the road. This makes the lack of torque from the engine appear even worse as the box doesnt shift down very well to match engine speed and road conditions.

I replaced the lambdas recently and didnt see any change in performance so whatever is causing them to behave in the way they are its not related to component failure unless the new ones are also duff.

After the engine running hot issue in August I refitted the RPI supplied 72'C Thermostat in 'panic mode' which together with the very large Alisport radiator make the engine run far too cool in the cold weather we are having at the moment so I need to calm down and refit at least the 82'C thermostat.

In late July I had an issue with damp getting into the RPI Power Amplifier, when I eventually got the engine to start I had quite a large induction side backfire. Is it possible this damaged the 'hotwire' of the MAF. It is after this point only that I started getting the white sparkplugs and running hot issue. I know your reading of the data doesnt support this.

Again its is really appreciated how much effort you have put into this thank you.

The fact that both lambda readings (or is it trim value?) show similar response indicate the issue (if indeed it is one) is not related to a single sensor, it would be odd for two sensors to fail in the same way at the same time (unless from a common cause) and as you have changed them anyhow I'd say it is more likely that the cause is elsewhere either airflow is varying but not being monitored or fuel flow is.

This is a graph of Odd & Even lambda for comment. In RG it looks like you can only log short OR long term trims not both at the same time, it may be worth getting a log for each and noting which is which.
I'm not sure if the values logged are the lambda readings or the trim which 14CUX puts in place based on these, before I reach out to anyone else on this it makes sense to know what values were being logged.

I had a look at the mapping values and plotted them out,
normal The horizontal axis is RPM, vertical is 'load'. They look typical and as there are no sudden changes I don't think they will be contributing to the trim movements.


IACV activity.
I had to search back to some of my initial logs for this as more recently I've only logged the parameters important to me but it does look like you log is typical. Maybe I misunderstood the code (I wasn't particularly interested in this area) and that when not running idle strategy the IACV is driven to a mid value from where it starts adjusting once idle control is called for. Looking at the data it would appear that the system 'learns' a value to use as this starting point so when you come off the throttle the IACV is already more or less where it needs to be to give the idle RPM required.

I may not have the logic completely covered there but the bottom line is there is nothing unusual in your readings.

I was logging short term trims on the Lambdas, assuming the logs follow what you have selected on the screen of RG.

This thread is quite long now so just thought I would do a brief recap on the engine in case this has any bearing on whats happening. The two main differences from normal are the cylinder heads which are Merlin F85 large valve and the intake plenum which is an ACT triple throttle body (Jenvey 3 x 48mm) breathing though a foam cone type filter. Camshaft is a Piper 270i.

Induction noise is quite loud so the engine is taking in a lot of air.

Any further update on resolving the issues?

Not yet, I have had an enormous amount of help from GDCobra which I am really thankful for.

Currently looking at fuel supply making sure that fuel pressure whilst driving is adequate. Not been able to complete the tasks I want to get done on this due to awful weather.

There are a couple of interesting segments in the RoverGauge manual which may also give an answer to two of my issues. The first is how the 14CUX sets its long term trim values which according to the manual only happens when the engine runs over 90'c for a period of at least 3 minutes. After I had the issue in the summer I went back to the RPI supplied 72'c thermostat and fitted a programmable fan switch that I set to 88'c. Whilst doing this work I will have had the battery disconnected which reset the ECU. 88'c I think is definitely too cold so my engine has not since set its long term trim as I dont think its ever been as high as 90'c as the twin Spall fans and radiator are very effective. I think Land Rover intended this engine to run very hot for emissions purposes.

If I undertand whats happening I think this may be responsible for the wild short term trims as the engine has not got its 'baseline' values. I am hopeful that this may also be the reason for the lean mix.

The second interesting statement in the manual relates to the TPS, apparently once the TPS reads above 84% the ECU widens the injector pulse to give an extra amount of fuel to boost performance. The ACT Throttle bodies on my car have a custom throttle linkage that I found early on did not match the throw of an RRC accelerator pedal only achieveing around 60% throw. Also did not have provision for the autobox kickdown linkage.

So I made an adapter which gave more throw and accomodated kickdown - This used part of the original system and a longer lever to acutuate the ACT throttle butterflies. But I didnt get the length of the lever quite right so currently getting only 81% throttle which until recently I thought this was enough but plainly it isnt so it will be interesting to see how much more performance I will get when I have this corrected.

Thanks again to GDCobra and please put me right if I didnt understand the long term trimming issue correctly.

heli_madken wrote: ↑Tue Nov 11, 2025 3:39 pm Thanks again to GDCobra and please put me right if I didnt understand the long term trimming issue correctly.

That's as I understand that although I've never debugged the code for closed loop as I only run open loop so didn't need to know that but that is what those in the know indicate. 90C seems a bit high to me, the normal value I've seen in RG logs for my own car is 87 although I may have seen slightly higher on occasion, obviously not an issue as no trims on my setup.
I'll drop you a mail later as I have a few more things to share, just been a bit busy this week.