After some opinions about a little 'gremlin' that's popped up in my 9-3.........
So I've not long had this car (bought just before xmas as potential engine donor for volvo project but decided to drive it for a while so I can get to know it) and one of my first priorities was an unlocked ECU so I have the option of running the engine standalone in another vehicle down the line and I happened to find one of 'Nige's' stg2 units on ebay for a very reasonable £80, also benefiting from the T7 APC upgrade. This was perfect for my purposes and I went ahead and bought it along with a T7 APC valve. Bear in mind that the car was not boosting properly when I bought it, it just had base boost and thus I cannot compare what I am about to describe to its stock 185hp tune, I guess really it was behaving like a LPT model and giving about the same sort of power, consequently placing MUCH lower demands on fuel and ignition hardware than it is now with a fully functional T7 APC and stg2 tune. The reason for me mentioning this should become apparent shortly as I describe my symptoms and pose some possible answers...
When accelerating at WOT right through a gear, sometimes but not every time, it hesitates right around 5k. The hesitation is in no way violent, there's no drop in boost pressure and if I keep my foot down, after a second or two it carries right on through to about 6.5k (not the supposed 7k limit on the ECU, another interesting point to note. I have no reason to believe that the rpm limit is not as advertised, everything else about it is great, no immo, plugged and played, T7 valve working well, tune seems very good, car is very driveable, huge increase in power from effectively a LPT and engine absolutely happy under all other conditions than the ones described). At around 6.5k it just tops out on rpm, in this lies my first question; what is the normal behaviour of the rev limiter on T5? Does it 'bounce' or is it like a diesel (ie just held steady at max rpm)? I didn't want to hold WOT while 'stuck' (like a diesel) at 6.5k for too long to find out if it would rev any further and so quickly backed off for the sake of the engine. I am curious whether it hit its rev limit or whether I was experiencing something like what happened at around 5k.
Initially I wondered whether the ECU might be detecting knock and backing off (it does boost well and pulls hard) but from what I've read, the knock detect 'back off' is quite a violent affair and this doesn't seem like that (if my understanding of knock protection on this engine is correct) and there's certainly no audible problem with the engine running when it does hesitate occasionally, it just holds steady for a second and then goes like the clappers again. I have read about the installation of a knock LED which is something I would like to do anyway but it would also help me confirm or disprove my theory that it is not knock related. Again, any experience on how these engines behave under knocking conditions would be gratefully received and may instantly tell me if this is a knock related problem or not.
As already mentioned, I think not, which brings us onto the big question, what could it be? It is not boost pressure related, that's for sure, the needle stays firmly in the red (another reason I'm steering away from knock as I understand the ECU will pull back on boost in these conditions?). I do believe the APC to be working correctly, boost limit in 1st is very apparent and it doesn't boost silly high like with 'W' hose disconnected, just in the lower 1/3ish of the red portion of the gauge, plus only base boost is available with valve disconnected and hoses left alone. This obviously leaves fuel or ignition as potential sources of the problem. When I got the car I gave it a full service, the old plugs were very worn although the engine was running ok (but without the tune remember), I fitted a set of genuine Saab plugs that came with it (which was nice, and turned out highly necessary!) and the DI cassette looked to be in good order (insofar as one can see, ie no cracks, oil leaks etc). I later found out that the DI was a genuine replacement a little while ago and has covered around 60k so I guess I can't rule it out but it seems unlikely as the problem is in no way like a misfire.
This leaves fuelling and this is what I'm leaning towards. To me it seems like it could be that the injectors are struggling to deliver enough fuel for some reason. Maybe they are dirty and not spraying correctly, maybe there is a problem with fuel pressure regulation? The engine did not hesitate through the upper rpm range with its old ecu and low boost but I think I shouldn't straight away point the finger at my new ECU setup as the hardware on the engine would never have had such high demands placed on it and thus its capability at higher performance levels is unknown. I'm thinking maybe to start by checking/servicing/cleaning the fuel system and then going from there, I guess cleaner injectors and a new fuel filter aren't going to hurt right? Any thoughts on whether this seems a reasonable course of action based on the symptoms I have described (hopefully in helpful enough detail, thanks for taking the time to read if you got this far!) would be ace. Cheers.