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Mike's Accord CTDi - The Sleeper!

28K views 156 replies 11 participants last post by  Mike_Mac 
#1 ·
Well, I suppose I've modified my car a lot and it's an ongoing project I might as well knock up a quick thread in the 'Modification Projects' section. :)

This won't be massive on external mods and details etc, as the plan was always to keep the car looking totally standard. It's my daily driver and primarily used for commuting (I have a fun car that's meant to be the one I play with - it just never turns out that way), so any mods beyond keeping it serviceable are just because I can't leave any car I own alone... that said I can't seem to keep things concise, so it'll probably be longer than I thought by the time I'm done (if I ever am...).

As most of the work is already done, this is more of a look back at what's already finished and then tracking the final bits of getting the Hybrid in and mapped (famous last words).

A long time ago in an area of the South West Far, Far Away...

... what started as a boggo Accord 2.2 CTDi EX saloon, bought in Mar 2011 was first tweaked with Accord Type-R front Calipers, adjustable rear camber arms and lots of other electronic stuff I wired in (i-Pod connectivity, Rear View Camera and a Dash Cam amongst other things). More recently I also had to shell out when a tree branch fell on the roof and dented it badly:



Although the cost was also bumped up because I had both bumpers and the bonnet done at the same time (having put over 100K on it in less than 3 years it was a bit battered). I also had the alloys refurbed in shadow chrome, from originally being diamond-cut, as it still looks great, but isn't as fragile:



(looks great in direct sunlight - that was a dark day).

The main tweak, though, was to get it mapped as soon as I'd upgraded the brakes. A Stage 1 map (started with Elite S1, then Celtic S1, then back to Elite S1) quickly turned into an EGR-off map (one of the first Accords to get it - I was a test-mule for Faddy at the time :D!) and then, in a roundabout way it ended up as a Premier Stage 2 EGR off map (~183 bhp):



Just a quick plug - throughout my Accord ownership, Fahad has been constantly in the background, be it advice on maps, assistance on sorting out the same, plus other issues and events - a really top bloke in all respects! :)

Having the software and Galletto OBD tool to install and remove Maps didn't help, as I was always tinkering. All of this necessitated installing a Honda 325 clutch when my original one went west and that was pretty much as far as I thought I could take it...
 
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#2 ·
… until I got a bit bored and started digging into how I could get more power! (I should just call this Project Clarkson :D). Trevor’s threads on his CRV caught my eye on this site, which was when I first started lurking…

For a long time I avoided upping things, because I wasn't keen on a paddle-clutch in a daily driver. However, when CG Motorsport started producing their twin-plate clutch, removing all the potential failure points, it wasn't long before a parcel arrived on the doorstep:





This coincided with the first talk of a ‘Hybrid’ Turbo for the i-CTDi. Having previously had a Supra I was happy with the concept of Hybrids, so started watching with interest. Then, when I saw the group buy on here I thought I might as well add the first Accord to the list!

(plus I like spannering and this was a nice challenge to get stuck into)

To do the Hybrid, I needed a Clutch (had!), a FMIC (hmm!) and a Hybrid (No Accord ones done yet!), so I started looking into what would be needed. As far as I know only one other Accord owner has done this (Brodziu on Type-Accord) and there isn't any FMIC packages for the Accord. I started reading up on twin-pass, vs single pass and tried to work out the routing.

Just then, as if by fate, a FMIC group buy materialised, so I stuck my name down on the list, thinking – I’ll just get any additional pipework fabricated – should be fine!!

Also, while, not strictly necessary, an Accord CTDi A-Spec kit was sourced, after a looong wait, and is ready to go on:

Sports Supension Kit Part #: 08W60-SEF-601 - ordered from HH.



Soon, all the bits were in place and it was time to get stuck in to the hard part…
 
#3 · (Edited)
Installation Begins…

I handed the car over to a mechanic I’ve known for a long time and trust. The plan was to install the clutch and FMIC, along with a few other things, with me helping when I could. That would allow me to make sure the FMIC and Clutch were working correctly before I moved to the next stage and get the Hybrid installed.

The FMIC was installed along with a new condenser and some mesh where the old grille was, as the Accord's front bumper provides NO protection from stones and I don't want my IC going the same way as the late lamented A/C Condenser! It took a while, but eventually it was done.





The routing was slightly more 'roundabout' then I had hoped, the bumper needed a fair bit taken out, and the fog lights interrupted the pipes, which meant a lot of trimming and adjusting, plus grinding down the NSF fog light multi-plug so it could be rotated 90 degrees. It does the job and avoided having to seriously hack about with the PAS cooling pipes.

Basically, the only way to bring the left side hose (as you look at it) to where it needs to go was to bring it back on itself across the top of the FMIC and then back down to follow the original routing. A local firm fabricated a lot of the pipework running across the top (where the red line is on the picture below):



So, all in all, it went ok, and the routing should keep the flow rate decent. A 'Twin-Pass' IC would basically have meant a 180 degree switch internally, so i prefer this option TBH.

All back together and on the drive (quite stealth - which i like!):



Back on the road I got used to both a bit more induction noise and the new Clutch which, although it's heavier than stock, didn’t take long to adjust to, is perfectly fine in traffic and is bedding in nicely - there's still a bit of judder in 1st, but that is quickly receding and only surfaces when taking off quickly, or uphill. All in all - quite happy with it and I know it'll take the power, and torque!

The Turbo

After some research I ordered my Turbo and decided not to get the exhaust vanes 'clipped', as I don't like the sound of it (or the cost!). Will be interesting to see the differences between the two when more people get them installed.

Overall, this has been the major ache of the whole thing (which is entirely down to me!) - Turbo Clinic (specifically Paul) have been absolutely superb throughout my various muck-ups!

As there were no Accord Turbo Hybrids available, and I didn't have a spare to send for conversion, I ordered a Civic one, anticipating that there would be minimal differences. I did subsequently buy a used OEM Accord Turbo, just as a spare, and am sodding glad I did!

On arrival the first differences between the Civic Hybrid and the Accord OEM Turbo became obvious (Hybrid Left - OEM Accord Right):





The angle of the outlet from the compressor wasn't a problem - the compressor housing can be rotated easily to the correct angle, but the inlet is totally different. Despite being the same engine the Civic's engine bay has the turbo lower than the Accord, so there's all sorts of pipe-work to bring the air flow down to it - hence the mount point with the two stud holes. The Accord's turbo is mounted much higher, so the pipe can just go straight on. On the plus side, it makes DIY removal and fitting possible (but not fun).

I therefore sent off my spare Accord compressor housing back to Turbo Clinic to be bored out to accommodate the larger compressor wheel, and the results can be seen below:



At that point I ordered the Gaskets from HH (which took a while to come through) and then got on with some spannering to remove my Turbo.

However, when I came to fit the hybrid, it all went wrong! Although the main body of the two look identical, the Accord Turbo's mounting points are about 10 degrees further 'round than the Civic's - meaning that the exhaust downpipe now fouls on one of the cross-members - it took me ages to get the thing in place (lying on my back in the driveway with the car on axle stands and ramps) and then there was the moment of realisation!

A quick back-to-back confirmed it with my spare Accord turbo, so things hit a slight pause, while the hybrid went back off to Turbo Clinic, again, to transfer the Turbo cartridge into my exchange unit and then marry it up with the already machined Accord compressor housing…
 
#4 · (Edited)
What followed was an interesting few days!

The Turbo arrived back on Thu, having been subjected to a near overnight turn-around (again massive chuck-up to Paul and Turbo Clinic on this one), so on Wed I put the Stock Map back on and cleaned, re-oiled and installed a Pipercross filter I'd had sitting around for ages now.

Once I had the Turbo back I managed to get it in without too much fuss (it's getting easier having had to do it a few times now, and the mounting points were a lot easier to line up now that I had the correct Turbo). No photos as I was under the car and fighting to get it done ahead of the rain - which I managed, just!

Once on it drove OK - even on the Stock Map with the hybrid fitted - a result. This means that I can run any of the maps I have on the Hybrid without issues or having to swap back to the old turbo.

Then, on Fri, I drove to Celtic Tuning to get the mapping done. The plan was to install their Stage 3 map, which has already been used by a few on here...

On the way I noticed the stock map seemed gutless, but assumed I was used to various stages of map. Plus I know the EGR valve is not good, so assumed that it was robbing a bit of power.

On arrival the car went in and I watched the initial runs and the mapped runs on the dyno. Immediately it became apparent that things were not right. The stock map (blue on the plot below) was underpowered and had a massive dip in both power and torque. Again I assumed it was the EGR, but, when it was blanked off and the Stage 3 installed it didn't look too much better (Orange Plot below):



As you can see, not too impressive. I spoke with the bloke behind the desk who said the mapper had put it down to Air/Fuel issues, but I had only put a new MAF sensor on a few years back and it had run the previous Stage 2 EGR off map fine... until I had installed the Turbo - so that was where my suspicions were firmly set. The thought of taking it off again and trying to get to the bottom of it all was NOT filling me with joy - I thought about jacking it all in and moving on to the next project (been doing some reading up already... :D) and was generally a bit teed off. Especially compared to what it should have been roughly getting (taken from Celtic's website):



At home, I compared the plot with the one when I had a Celtic Stage 1 installed, as it was the same company and Dyno:



As you can see then my stock plot was really good, and the Stage 1 was excellent, with a really smooth curve and good power/torque.

I then produced a comparative trace comparing both power and torque on:

Original Map - Light Blue
Original Map with Hybrid - Orange
Celtic S1 Map - Grey
Celtic S3 with Hybrid - Yellow
Celtic S3 Example Map - Dark Blue



As you can see, my two Hybrid plots were horrific - significantly outperformed by my old Stage 1 map on the stock turbo and light-years behind the example Stage 3. Note the slight lag in all the Hybrid maps from stock, though - you can see it just takes a bit longer to get into its stride and shifts the power quite high into the rev range... Completely what was expected, but interesting to see the differences in how the remaps differ from stock.

By now I was sure the turbo was at fault (probably from me cocking up the install or something similar) so decided to go back to Celtic, get a refund, refit the spare turbo and dig into the Hybrid fitment etc a lot more before deciding what to do next. This was compounded by the car going into limp mode three times before I could get it back to them. Just in case I stripped out the Pipercross filter, as it was the only other change I'd made, but there was no improvement.

So! On Sat just gone I returned to Celtic and showed the actual guy who mapped my car the plots above. We then had a long chat where he said that during mapping the turbo had barely broken a sweat, so he didn't think that was the issue (phew! :D). Likewise AFR stayed fine, if a bit lean, so it wasn't a fuelling or airflow issue (likewise :D).

He then went into more detail about the Mass Air Flow issues he had been fighting on the day and again said that he thought it was MAF sensor related. I'd done a bit of reading on this the night before, so asked whether the filter oil could have contaminated the MAF? Although Pipercross refute that this is an issue there is lot of results on it when you look online. He agreed this could be it, and that they don't generally oil PC filters for exactly this reason. I therefore decided to swap out the MAF sensor before committing to getting a refund.

Before I left, Celtic checked the codes for why it had gone into limp mode and found fuel rail pressure had been fluctuating. Basically, Stage 1 and 2 maps generally don't need more fuel (apparently), whereas Stage 3 does - turns out my fuel pump is tired and therefore straining a bit to deliver what's asked of it now. The map's top fuelling was tweaked to remove this issue, losing a bit of power at the top end, until I get a new fuel pump fitted. Overall, I was happy with the service given and the guy I spoke to (Cameron IIRC?) was a top bloke.

On the way home I bought a used MAF on eBay, which will arrive next week, but before then, decided to clean the MAF (had some sensor specific cleaner handy anyway). There was a noticeable deposit of 'stuff' on it and the cleaner only got some of it off. I then (carefully) rubbed the rest off with tissue and it proved to be a grey oily substance... hmmm!

I finished by thoroughly cleaning and wiping the MAF housing and Air Pipes, re-installed it, reset the map and took it out for a drive...

All I can say is that it's definitely putting out a LOT more power and has only got better when I took it out today for the 0-60 comparisons:



Around 7-8 seconds to 60 ain't bad - especially with the need to change gear again just before 60mph!! I suspect if I spent a bit of time working out the shift points I could get that a bit lower, but I was trying not to rev it to the max, avoiding the power drop later in the rev range...

While I will get a dyno test done early next week to check, I suspect it's putting out more than the old S2 map at the least - performance on the motorway when on the move is very good! :)

More to follow...
 
#5 · (Edited)
PS - Mods, feel free to shift this into the Accord section if preferred.

ETA: I've also found out the best way to finish bedding in a CG Twin Plate - repeated 0-60s with slam changes :VroumVroum01:

(seriously - I went to fill up later in the day (looking at the OBC you can see why! :D) and it was like stock!

(Still wouldn't recommend it, though...)
 
#7 ·
Fantastic stuff! And great to see all this being done to an Accord... I'm so damn jealous!

Hopefully the new fuel pump will allow rail pressures to satisfy the full map requirements. If not, then there maybe other reasons why the rail pressure is iffy, but I'll not waste time explaining until you know you still have a problem.
 
#8 ·
Cheers Jon, I'm assuming you're going to talk about injectors primarily?

Having seen a new pump for over £2K on Lings I will be looking at a second-hand low-miles pump - once that's on, and the other MAF issue is confirmed as being sorted, I plan to go back to Celtic and get them to tweak as much as they can to get the optimum performance out of it.

Plus I want to discuss just how much they've throttled boost in 1st, 2nd and 3rd gears, which I understand is common on remaps, to keep things under control.
 
#9 ·
Wow Mike, what an epic journey. A very impressive journey at that.

I'm so glad that you shared your story, it's great to hear.

I'm so relieved that you are still on track. All credit to you for taking your Accord into the relative unknown.

Will be looking forward to future updates.
 
#11 ·
didn't understand most of it BUT enjoyed reading it, I am always impressed when people can do these sort of things to a car when I struggle to even locate the jacking point - credit to you mate
 
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#15 ·
Correct - I'm not after a massive difference, just slightly tighter than stock.

The alloys I'm really happy with - much more durable than diamond cut and still give a real contrast between high/low points - especially in the light. Even Mrs Mac approves :D

A-Spec kit will be installed on Friday if all goes to plan, so I'll get some more pictures up then - probably after a quick clean...
 
#16 ·
Two steps forward...

Well it appears I spoke too soon...

Drove in to work today fine, thinking - feels nice and pokey! :D

Booked it in to Alan Jeffreys in Plymouth for a Dyno and waited...



I was hoping for at least over 200 hp - I was wrong! It produced a good power and torque curve, so I think the MAF clean has worked, but topped out at 185hp! Gutted! You can compare it here (blue is the latest run):



Speaking to the dyno bloke, he said that all looked fine except for boost - it was only at around 15-16 psi - should be around 22-23. So, armed with that info I called Celtic. Basically they confirmed the map was set to 22-23 psi, so, in their opinion, it was the MAF (told them this was very unlikely to be the case), or the N75 valve (or the EVR valve in Honda speak). As it controls the level of boost via the Wastegate it is a prime candidate. Therefore, when I got home I swapped it with the other similar valve in the engine bay and went out for a drive.

I wasn't expecting much, because I know what finicky little sods these valves can be, whether it's VSVs, IMRC or EVR they can be proper little sods to troubleshoot as they tend to fail intermittently. TBH, I didn't feel much difference, except for one or two times when it really seemed to 'Go', but then went back to normal. As I am now very suspicious of my butt Dyno I will probably suck it up and replace both EVR valves and see where I go from there, after trying the spare MAF, which should arrive tomorrow, just in case!!

PS - Celtic really don't like MAFs! The bloke on the desk I spoke to initially was adamant that you couldn't clean them - you HAD to get a new one, and seemed Hell-bent on laying my issues on its doorstep! I get what he was saying, sort-of, but I'm sure companies like CRC etc wouldn't market 'MAF' specific cleaning spray if it didn't work! Plus the dyno plot was miles better than previously!

PPS - On a positive note, if it felt that good just back on the performance I'd had before, then it's going to be awesome when I finally resolve these issues and break 200hp! :popcorn2:
 
#18 ·
They may have a point but there's one bloke there who's very dogmatic about it :D

I've got a spare MAF arriving tomorrow anyway, so it's not really necessary now, plus I don't think it's an issue anymore after I cleaned it - the Turbo control valve seems more likely a culprit. If it's not that then it's back to sq 1!
 
#22 ·
I'm keeping an open mind, but really don't think it's the issue now - but you never know.

Just wincing a bit at the thought of replacing the EVR valves - especially if it turns out they're not the problem either!

Not sure what else it could be though?
 
#25 · (Edited)
Replaced my MAF (Improvement) & MAP (No change) sensors due to similar issues. Haven't had it back on the RR yet. Feels strong up to 5,000 RPM. Running 24 psi constant, brief spikes to 26 psi.
Interesting point you made - Celtic said despite boost pressure set @ 22/23 psi yours was only reading around 14 psi!
Haven't manually checked my boost, just taken readings from the ECU data on Elites RR.

MAP sensor Saab 9-3 9-5 1.9 TiD Honda Accord CRV Civic FRV 2.2 CTDI | eBay

A thought, could the constant boost pressure be affected by the Hybrid's efficiency? Should we be checking boost off the throttle body values and seeing if there is any discrepancies with the ECU readings? Will have a chat with Elite and see what Dave thinks.
 
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#26 · (Edited)
I'll be very interested in what you find out Trev :)

On my own side, I've knocked up a quick flow chart (no pun intended!) tracking what I think is all the possible areas that impact boost:



(Note: I am not an Engineer, so this is Johnny, Age 5, level drawing ;) )

If there's any area or factor missing, please let me know, as I intend to use this to track my progress in each area to definitely eliminate them step by step from the possible causes.

From that diagram the current hit list (with priority (1-4) in brackets)is:

Map
Celtic Stage 3 (4) - Checked - Unlikely to be cause.

Turbo
Hybrid Turbo (4) - Not Checked - Unlikely to be cause.

Sensors:
MAF (2) - Checked - New one ordered anyway - probably a waste of money, but it'll shut Celtic up! :D.
EVR (2) - Swapped with other EVR - no difference - May replace with new one once leak check complete.
MAP (2) - Not Checked - New one ordered.
FSV (4) - Not Checked - Not likely to impact.

Air Flow:
Airbox to Compressor (3) - Not Checked - Unlikely to be cause.
Compressor to FMIC (1) - Not Checked - Possible leak may cause loss of boost - Test Kit Ordered for Friday.
FMIC to IMRC (1) - Not Checked - Possible leak may cause loss of boost - Test Kit Ordered for Friday.
Cat #1 (3) - Not Checked - Could stock exhaust be strangling boost?
Cat #2 (3) - Not Checked - Could stock exhaust be strangling boost?

So, currently I have, or am about to, order some new sensors and will investigate either leak testing the various pipe-work, or getting it replaced with steel pipes (focused on the FMIC - currently a prime candidate!). That should eliminate the obvious factors...

(What would be really useful is if I had a boost gauge that I could tee in at various points of the pipe-work!!! :( ).

ETA - Just ordered an intercooler pressure test kit - will arrive Fri. Until that's done I'll delay ordering the EVRs as a swap of the two had no effect.
 

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#28 · (Edited)
Are the ends of all your IC pipes swaged?

Your diagram actually looks pretty useful, nice one.
The IC is, but some pipes were custom made. I believe they were, but will check.

When it was first fitted there was a leak, which was eliminated, but the higher pressure may still be causing some leak-through - I certainly find it suspicious that it's near mirroring my old S2 map's boost - it may be that 15 psi is just where a join gives way... The IC pipework does also have quite a few bends in it too...

Therefore I've ordered a pressure test kit as a first action - no point spending £00's if it's just a loose pipe!!
 
#31 ·
#32 · (Edited)
The ELM327 OBD2 reader arrived toady, so I got it connected to Dashcommand and went for a drive...

MAF and MAP look fine (to me), which isn't too much of a surprise. Boost on the other hand... I feel a bit better now, as my Butt Dyno wasn't as off as I thought.

The boost was fluctuating quite a lot; at time it was putting out 20 psi (max of 20.8 overall), but a lot of the times it was around 15-17 psi and quite often dropped from 18-20psi down to 13-15psi. If I was gentle on the throttle initially, then kept a steady increase to WOT, it would generally reach 20 psi. WOT from the off - generally not.

So! My thoughts are still that there may be a boost leak in the FMIC piping, but other culprits could be a weak EVR valve (maybe), or, something else...

The plan remains to check IC pipework and then the EVR valves...
 
#35 · (Edited)
The ELM327 OBD2 reader arrived toady, so I got it connected to Dashcommand and went for a drive...

MAF and MAP look fine (to me), which isn't too much of a surprise. Boost on the other hand... I feel a bit better now, as my Butt Dyno wasn't as off as I thought.

The boost was fluctuating quite a lot; at time it was putting out 20 psi (max of 20.8 overall), but a lot of the times it was around 15-17 psi and quite often dropped from 18-20psi down to 13-15psi. If I was gentle on the throttle initially, then kept a steady increase to WOT, it would generally reach 20 psi. WOT from the off - generally not.

So! My thoughts are still that there may be a boost leak in the FMIC piping, but other culprits could be a weak EVR valve (maybe), or, something that occurred last night, the Wastegate might not be keeping up with the demands on it.

I don't know if TC alters it when they turn it into a hybrid, but I suspect probably not and my turbo had done 160K miles before being hybridised. In my mind is the possibility that it's just not keeping control of the boost well, hence the full load of WOT might be causing it to open a bit (boost loss), whereas if you increase throttle gradually it can maintain the pressure.

Happy to be told wrong and that the WG is fine (crosses something else off the list), but the plan is the check IC pipework, then WG (not sure how though) and then the EVR valves...

If you don't find any pressure leaks it's likely to be in the mapping. The performance differences in the Hybrid custom V1, V2, V3 I'm comparing is noticeable.
(Fuelling, Injector timing, Turbo Pressure mapping tweaking.)

Part throttle flow rates can be tricky to optimize on Hybrids.
The variable actuator will have no problem reacting to vacuum imputs. It's worth re installing the map, need a Galetto and laptop.
 
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#39 ·
My experience so far... is that the VNT actuator needs to be set exactly right or it won't produce boost properly. Best way to check that is to log the Turbo VNT duty cycle. (I do that with the HDS I have...) Ideally, on a data logging run from 1.5k to 5k in 3rd/4th, the duty cycle should go below 30% at 5k RPM, but it should be as close to 20% as possible.

If the actuator is too long, the duty cycle rapidly drops to +/-20% and then climbs back up to 30%+ causing the boost to spike around 2-3k RPM then drop to down around 13-14PSI.

If the actuator is too short, the duty cycle never gets below 30% and you'll find you get "boost too low errors" logged because the turbo isn't producing boost effectively in the lower RPM ranges.
 
#92 ·
If the actuator is too short, the duty cycle never gets below 30% and you'll find you get "boost too low errors" logged because the turbo isn't producing boost effectively in the lower RPM ranges.
Allan - I was just reading up on what to log before starting to fiddle with my HDS and this seems to describe exactly what is going on - I'll still get my HDS up and running correctly first, just so I am adjusting based on fact, not supposition, but that quote gives me hope it'll be sortable! :)

Hopefully my VNT Duty cycle will read quite high...
 
#40 · (Edited)
I should also say, that I'm talking from experience with the Civic turbo. The Civic VNT actuator pulls on the VNT lever and it looks like the Accord does the same. If the VNT actuator was on the other side, it would work similar to the VAG setups since they have the actuator pushing instead of pulling.

On the Civic, the duty cycle starts high (about 60%) and goes lower. On the VAG setups, the duty cycle starts lower and goes higher, so they aim for as close to 80% as possible at peak RPM.
 
#41 · (Edited)


Just a little datalog example showing what it looks like when the actuator is too long.

EDIT: Since the colours aren't too clear in the picture, it's worth noting that the lowest line at the timing point (the vertical dashed line) is the Turbo duty cycle. On that run the duty cycle was getting from 60% to 23% too quickly and then the ECU compensated after the timing point by raising the duty cycle. It's also worth noting that the boost and IQ dropped when the duty cycle went up and that is the point where the car lost power.
 
#42 · (Edited)
Thanks for that! Very informative and hopefully when I can extract the datalogs I've just recorded from my iPhone (sodding Apple!!) I can get to work looking at them on ScanXL.

TBH I don't think it could be the actuator arm - my boost (after looking at the live data) seems to vary. At times its up at 20-22, others it's 15-16 - in the same gear and engine speed). I'd have thought a dodgy arm would have given a consistent fault? As said I'll try and post the log up here when I've got it exported.
 
#44 ·
Thanks for that! Very informative and hopefully when I can extract the datalogs I've just recorded from my iPhone (sodding Apple!!) I can get to work looking at them on ScanXL.

TBH I don't think it could be the actuator arm - my boost (after looking at the live data) seems to vary. At times its up at 20-22, others it's 15-16. Is have thought a dodgy arm would have given a consistent fault? As said I'll try and post the log up here when I've got it exported.
It all depends on the starting point for the run... ;P My boost was fluctuating quite a bit depending on where I was in the rev range and what gear I was in. It was only "consistent" when I was doing datalogging runs in 3rd from 1.5k RPM... If I started the run at a lower or higher RPM, the boost profile would be different.

So for example, I would find that at 4k RPM I could have 14psi, lift off the throttle and floor it again and I'd have 24/25psi...

It's not technically a "dodgy arm", it's just not the length the ECU is expecting it to be. It's all to do the N75 maps in the ECU (which basically controls it all and determines what the duty cycle should be) but trying to retune those maps are near on impossible (unless you want to spend a couple of days on a dyno). The ECU is programmed to have the arm at a particular length, if it's wrong it'll cause the VNT vanes to move more/less than the ECU is expecting and the ECU compensates (badly, because it's trying to protect things).
 
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