QR25DE Tuning

[jaf]

Ha Ha! Opposite problem here - best to wait till winter to do garage stuff.
It wasn't hard to find 2 other X-Trails in the work carpark when I was working with 350 other people. I had to set their timing and idle for the privilege of dumping their ROMs though (and diagnose a blown head gasket in the process).
The AFR table rethink is purely due to error codes and limp mode that indicate something else is at play here. Unfortunately almost everything affects AFR so it is easy to be fooled - I just ignored the seemingly backwards load axis to make it look right in my head. A bit of wishful thinking too that Nissan had decided to use bigger tables - not that they are really needed. When I have time, I might edit the 6E25 table as if it is a throttle closure on decel map and see what happens. Wouldn't it be great to have no throttle hang and some degree of engine braking?

[fenugrec]

Some success today : I dumped the 128 first bytes of my Sentra's ECU ! They're the same as the XTrail ROM (reset vector @ 0x000000) so I believe I'm getting valid data.
But the process is slooooow.... it takes ~ 375ms per byte. It would take 54 hours to dump 512k !!! Let's just say I'll have to tweak my method a bit before I try to dump the whole
thing...

[fenugrec]

I slightly increased the download speed, ~ 40 ms/byte now (~6h for the full 512kB). In theory I should be blazing at 10-15ms/byte but I'm getting huge delays somewhere, I need to investigate. In the meantime I dumped the first 4K. No tables in there, but there's some reset code that's very similar to the XTrail's.

[EDIT: updated download speed]

[fenugrec]

Boom ! 11ms/byte. Now we're cooking... it took ~90 minutes for a full dump. I still find that terribly long but it's better than 54 hours, and I think I've pretty much maxed out the capabilities of the 10.4kbps link with the service ID I found. Here's the complete dump. I'll start digging in the code to see how identical (or totally unrelated) this is to the XTrail.

[jaf]

Congrats!! Another first.
I will take a long hard look at your ROM and let you know what is of interest.
70 mins is about how long it takes for me so there is a bit more speed to be had.
Seems there is more interest in the QR25DE than the 350GT - must be related to the tuning potential

[jaf]

Here's a quick look into your ROM.
Tuning is vastly different from the X-Trail but not necessarily for the better. Many maps are identical (as also found in the 350GT ROM) I am tempted to flash this into my car to see what happens.......what could possibly go wrong?
Can you give a bit more detail about your car i.e. complies with what States? What octane fuel does it have to run on? Any idea if the cam advance mechanism does 30 deg or 40 deg?
X-Trails 02 and 03 have 30 deg, 04 to 07 have 40 deg advance. I think the Sentras changed later? Is your ECU the later shaped one (not the same as 02-03)?

[jaf]

Hi fenugrec,
Can you match up some rpm and load axis to the timing, AFR and Cam maps on your ROM?

I guessed that the middle ign timing map on the X-Trail is the Low Det map as in the Sentra ROM and this is holding up as correct so far.
I have increased the high load timing to be more like the Sentra ROM and that seems to be a good thing.
I assume the 1st map is the hi det fallback map. Why the third ign map has less advance than the low det map only on the 400rpm row is a mystery?

See how the cam timing looks when resolved (assuming a 30 degree vvt cog). Compare that to my current map which is a very good all-round performer.

[fenugrec]

Hi, here's a bit more info :

04 Sentra SE-R Spec-V M/T non-ABS QR25DE Canada

Octane: Regular (lowest common north american octane, I always forget if it's 87 RON, PON, or (R+P)/2. Owner's manual recommends Premium (91) but says Regular 87 is ok.

Intake valve advancer range : there's no way of knowing without taking off the cover and measuring it, right?

Emissions: good question, I would guess it complies with US federal regulations, but probably not the California supplemental requirements. So I have the evap canister, catalytic converter (except the pre-cat, probably removed by the previous owner after the engine rebuild), 1 or 2 (I forget) O2 sensors on the exhaust.

General notes : this engine is from the "cursed" years of Spec V's; Nissan had that huge recall because of pre-cat ceramic debris being sucked back in the cylinders under certain operating conditions. My own engine has a "Nissan remanufactured 2006" tag on it so it must have been done under warranty at the time. I hear they would also reflash the ECU; I'm not sure what that changed, and if mine was reflashed or not. Could it be the peculiar dip at 62% load and low RPM we can see from your cam timing comparison ?

**
"tempted to flash this and see what happens"
Haha... if the NATS garbage is compatible it might start...
**

Tables: here are the axes I confirmed from the code : (db = 8bit, dw=16bit). I haven't determined their units though. (sorry for the ugly formatting, these are straight from my rough RE notes)

6611, 6711, 6811 16x16db: axs 8052 + 8062 (db); ign ?
6921 8x8db ax 855c 8822 db
6a51 8x8db ax 89aa 89b2 db
6AD1 16x16db: ax 7f44 + 7f88 (db)
6CA1 8x8db: ax 7F2C + 7E23 db; AFR ?
6D11 8x8db ax 87b6 87be db
6d51 8x8db ax 87b6 87be db
6D91 8x8db ax 855c 8822 db
6DD1 8x8db ax 8956 + 896a db; cam?
6E11 8x8db ax 894e + 897a db; cam?
6e71,6f71, 7071 16x16db: ax 7e77 + 7e9b (db)
71dc, 73dc: 16x16dw ax 8ac2 + 8ae2 (dw)
75dc 16x16dw: ax 7F5C db(?) + 8B16 dw often; sometimess 8B16 + dynamically selected axis???
79dc 8x8dw ax 8d36 + 8d46 dw
9488,9688: 16x16dw: ax 9b1c + 9b3c (dw),
9888: 16x16dw: ax 9acc db + 9b5c dw

[jaf]

Thanks for that info. Any idea if the compression ratio is 10:1 or 9.5:1?
What you have said makes more sense of the ROM.
The AFR table has been comparatively leaned out to stop the cat disintegrating again - that also helps performance but it looks like they pull a lot of cam timing under load so you don't see any benefit.
The peak in the cam timing should coincide with cruise conditions to give a bit of EGR function and decompression to reduce pumping losses. When you put your foot down, it should arc around the back side of that peak. If the engine is pushed too hard, the cam timing rolls off to reduce power output to safe limits. Your map rolls back way too quick. You would feel very disappointed going from partial throttle to WOT???
If you look at the raw cam map in 3D form, it doesn't represent reality since it has to be interpolated (along the load axis only). That is why I drop it into a spreadsheet to do the maths.
I caught the cat problem just before it affected the engine luckily. Removing the cat looses power if no retune to go with it and will loose even more if running a gutted stock manifold. If it needs to look stock, cut the top off the manifold, insert a 3 inch pipe and weld it back together so the exhaust flow doesn't tumble in the big pot.
Any SpecV forums mention when the changeover to 40 degree cam advance happened? I think it was 05 but could be wrong. 30 degree VVT is better by the way....

Edit.... see attached spreadsheet version 2 with the axis around the right way this time + AFR calculations. Pay attention to the load and rpm axis when comparing Sentra to X-Trail. The AFR formula differs from Tom's 350GT calculation - my one is based on wideband O2 sensor data collected some time ago and I like to think it is more accurate.

[fenugrec]

I thought all QR25DE's had 9.5 compression ratio ? Owner's manual says nothing, service manual says 9.5... The only other authoritative answer I can find is
http://web.archive.org/web/200802061853 ... pecs.shtml

I looked around for some info about the 40deg cam sprocket but found nothing. I could remove the IVT cover and check but I don't have the liquid gasket stuff handy.

Re your graphical map comparison : did you take map 6AD1 (16x16) from the sentra (which has a similar dip), or 6E11 (8x8) and extrapolated to 16x16? And since the axis data in the ROM isn't evenly spaced out, won't that change substantially the aspect of the map (is that what you meant when saying the 3D view wouldn't be accurate)?
I tried loading the correct axis info with WinOLS but I'm not quite doing it properly yet, until I know for sure which axis is which (X vs Y). I'm working on that; I had analyzed a lot of table reading functions of the Xtrail ROM so now I just need to find the Sentra equivalents. One thing is for sure, the two ROMs certainly weren't compiled the same day by the same guy. Check out this ridiculously convoluted code to access ram FFFF F500 (TCNT6 registers, i.e. the one used for PWM-ing the throttle motor - assuming the Sentra uses the same IC pins for this):
***
mov 0xFFFFFFF5, r2
shll8 r2 ; now r2=FFFFF500 !!!
mov 0, r0
mov.w r0, @(0x10,r2) ; clear FFFF F510 (BFR6A)
***
No wonder I couldn't find any references to F500, let alone F510!! I'm inclined to believe this was done on purpose; what kind of insane B-grade retarded compiler would generate such code ?? But then, why would they obfuscate this and not everything else ? None of this makes sense to me.

Re my Sentra's high load response - I haven't driven it a lot (got it only a few months ago), and most times it was in snow so I wasn't mashing the gas pedal anyway. But I'm putting on summer tires this weekend and the last of my suspension parts monday-tuesday so I should be rolling again shortly.