628 ECU for 850's

[mercuric]

Indeed there seems to be very little, if any real difference, simply from changing the ECU -- The timing difference is indeed quite minor, a slight increase in midrange torque under full load might be noticed, depending on how much boost you're running in that RPM range -- If you're developing a lot of midrange boost due to running an MBC, the T5 map is probably more appropriate, as these motors don't seem to like a lot of midrange timing advance under boost. The fuel maps are even more similar between the T5 and T5R, both are pretty lax under 4k... Even the boost map is almost exactly the same, spare a slightly less aggressive ramp-down past 5100RPM.

You can view the maps with Motronic Suite, the package includes the majority of stock binaries, including the -072 (T5) and -628 (R) ones, is free, and doesn't require any hardware to work, unless you actually want to flash an ECU. Then it's a ~$10 investment in an FTDI VAG-COM cable and some time spent soldering up some wire leads to get power to the ECU and cable, and connect the serial data pin to the ECU -- Trivial if you're handy with an iron and understand basic electronics.

The load unit is milliseconds. Stange huh, load in time? Well, it's not so much load as it is theoretical injection time -- From what I understand Bosch decided, on M4.x, to measure load using what's essentially the uncorrected injection time. Of course, actual injection time is modified by the fuel map and other corrections, but that's just what they used for the load unit in M4.x. There's probably more to it, but unfortunately nobody's leaked the engineering-level docs like has been leaked for some of the M7.x variants. The load units in milliseconds are in .048ms increments, of course being an 8-bit value, the maximum load is 12.24ms, aka .048*255. The stock maps go up to 8.5ms, which is sufficient for the stock application and a bit, but it's pretty easy to go over 8.5ms even with a completely stock car and an MBC/EBC -- Or just by modifying the boost control valve duty cycle map in M4.3. Once you exceed the highest load on the map, it just runs off the highest value, of course until it hits the MAF limit, then it fuel cuts.

In short, it's a lot more bang for your buck getting a $10 VAG-COM cable and setting up the -072 ECU how you like it, versus buying a factory -628 R ECU, which seem to net a good penny just being a rare and "special" thing.

The performance difference on the R comes from a few factors:
1) The wastegate actuator setting from the factory is slightly higher, which results in a slightly more aggressive spool-up and peak turbo response pattern
2) The ECU allows an "overboost" condition for a short period in the higher RPM band -- IIRC it allows about 1.5psi of additional boost, in a fairly narrow RPM band for a limited timeframe.
3) Slightly more aggressive midrange timing at full load
4) The -628 "R" boost map doesn't fall off as quickly after 5100RPM, resulting in slightly more top-RPM boost

All 4 of these differences are quite minor, but are differences none-the-less. The extra pound or two of boost allowed by the time-limited overboost condition is likely the sole source of the +18HP factory rating, but is also both time and RPM-range limited. The powertrain hardware is the same. So while it does allow for an upgrade on paper, the actual performance improvement, especially in daily-driving conditions, is pretty limited.

The real difference in the R cars is the lowered suspension and upgraded interior. Yes, on paper they have a few more ponies, but nothing that isn't achievable on the T5 with minor tweaks to the ECU maps. It wasn't until 99+ when R cars actually went to larger turbos (and followed up with larger-displacement 2.5L engines and AWD systems) that the R cars really got a serious advantage. The difference between the S60/V70 T5 and R is much more notable -- Over 50HP IIRC, plus AWD, which is key, as I'm sure we've all experienced just how little traction there is in 1st/2nd when the turbo spools up.

[KllewT5]

Nice post!

[mercuric]

Cheers, little update for those who might want to look at Motronic Suite -- The gentleman who did that project has moved on to other things, and his site is no longer. However his work, mostly on Saabs, didn't disappear completely: http://socalsaab.com/suites/suites.htm has Motronic Suite, plus his other Saab-related projects.

[northernlights]

Here are two 1/4 mile runs with this ECU in my otherwise stock 1994 850 Turbo sedan. I believe this is in the ballpack of what the magazines published many years ago.



Fortunately they do not count reaction times for us amateurs!

[goofy2]

I have installed the 628 ECU in my 1996 T5 Wagon and I am now getting a DTC Fault 444 which wasn't there before.

[mecheng]

Can you use the 628 ECU in a LPT (ie 97 GLT)?

[erikv11]

As long as they are both 4.4, sure. I tihk they will be, but check the VINs. You will also want to pay attention to whether or not the ECU has SAS. And put a 15g on the LPT!

[phils94850]

Im still currently selling a chip for the 94-97 850 turbo models, a lot safer than just a grainger valve and im cheaper than anyone else. Message me if interested, we are currently working on getting the website back up and going soon..