Boost and throttle position

[Martin Cockett]

I have had a 1998 2.3T Anniversary (225 bhp) for about 18 months and have never really been convinced that it is performing as it should. Most of the time it has only been possible to get it to boost into the broken red zone by pushing the throttle to the floor. Moderate throttle i.e. half to two third will get the boost gauge about half way into the yellow with associated modest acceration. No checks by my dealer or independent Saab mechanic have revealed any obvious fault (or indeed any acknowledgement that there is anything amiss with the performance).

However, very rarely (a handful of occasions since owning the car) it boosts easily into the broken red section without the need to resort to full throttle. And since having had some exhaust and suspension work done at Malbrad in Huddersfield last week the car has been absolutely flying. For four days running now it surges effortlessly to the top of the yellow and feels for once like a really swift car. I am anticipating a return to its more recalcitrant mood anytime now so would appreciate your expert opinions. I can provide the following additional info.

1) The performance appears unrelated to atmospheric conditions or to the weather in general.

2) I am pretty sure I have no leaks and that base boost is ok as it does do its stuff on occasion.

3) The APC solenoid does buzz.

4) The car has done 68000 miles.

5) I have been using Shell Optimax for a couple of months (and noticed no difference compared to Tesco unleaded) and have recently switched to BP ultimate.

Many thanks in advance for any insights!
Martin

[philcrombie]

hmm - all I can suggest is to carry out the following list of things to look at:

1) Check the thin (3mm) vaccum pipes running from the intake pipe and inlet manifold through the bulkhead. These can look OK, but can have a tiny leak which messes everything! - If they are dry and leave your hands black when you touch them, better to replace now. (about a fiver)
2) Disconnect the battery for 10mins to reset the ECU. Then go for an adaptation run - at least you know it's a clean slate.
3) Make sure your airfilter is nice and clean.
4) If you don't know the history, throw in a new set of NGK sparks, gapped correctly. Lubricate the DI with silicone grease when replacing.

If the problem has been intermittent, you might want to look to the DI pack as it can throw all sorts of varying faults. 68k is very young for that though.

[philcrombie]

oh - and you might want to get yourself a little boost gauge so you know exactly what the boost is. (just a temporary one on a long piece of 3mm silicon hose is fine for the job)

FYI - when I bought my Aero (same engine as yours), the boost wouldnt go past the hatched section. After doing the above list, it was transformed (along with change to Optimax)

[Martin Cockett]

Faero,
Thanks for your suggestions. As it happens, I flattened my battery a few weeks back and had to disconnect it to recharge. Did an adaptation run afterwards and my impression is that it has felt perkier since. I will check the hoses at the weekend as you suggest and have a look at the DI cartridge. I have also wandered whether the APC solenoid might be playing up but I do not know whether when they do start to go, they do so in subtle ways or just fail completely. I have had so much fun the past few days that I really want to get to the bottom of the problem.
Thanks again
Martin

[philcrombie]

Some info. here on checking out your solenoid

http://www.saabscene.co.uk/cgi-bin/ultimat...pic/2/3094.html

Sounds like the adaptation run is what brought the car to life - or was it intermitently lively before that?
Phil

[Martin Cockett]

Phil,
No I think the adaptation run helped but the 'on-song' periods are so dramatically better than what it is usually like, and have occured before and after adaptation that I don't believe that is the answer. I did the adaptation a few weeks back and it is only in the past few days that the car has been transformed again. This morning I sensed it slipping back to business as usual although difficult to tell on a slow commuter run through York.
Cheers
Martin

[Martin Cockett]

Well, I have checked the resistance across the three pins on the APC solenoid and found the following:

Assuming pin 1 to be closer to the drivers side (the left most when viewed from above), the resistance across 1 and 2 settled at about 3 ohm (falling from about 6 or 7 ohm) whilst no reading at all was obtained across pins 2 and 3 or across 1 and 3.

Any idea what this means?

Thanks
Martin

[cdcarlsson]

I would suggest that one of your APC's coils has gone open circuit (in other words it's broke).
The voltage from the battery enters through the centre pin (unless they changed the APC solenoid again after '93 and I don't think they did) and from there the ECU grounds either the left or right hand pin one at a time at a frequency of 90Hz. This causes the disc within the APC solenoid to vibrate first one way then the other 90 times per second, alternating the pressure coming in the 'C' port from the turbo compressor first to the Wastgate ('W' Port) then the Intake ('R' Port). The amount of pressure 'shown' to the wastgate is varied by the pulse width to the W port varying.

If one of your coils is broken (open circuit) then your APC solenoid cannot function properly. It could be that this is an intermittent fault with the coil making up every now and again allowing full power to be gained.

Nick.

[Martin Cockett]

Nick,
Thanks - I had come to the same conclusion last night. Before driving home, I disconnected the solenoid and was till getting loads of boost. It appears that the wastegate port is stuck closed rather than open and so with the solenoid disconnected the car has not reverted to base boost. My experience over the past 18 months must then be associated with the wastegate port intermittantly sticking closed which would seem to imply that the better performance I experienced during those periods was abnormal. In a way this is disappointing as I had assumed all along that friskier mode of the car was as it should be rather than the lack lustre mode. I suppose it may be that with the solenoid clearly on its way out the trionic system had misadapted and was limiting the amount of boost to compensate for the fault. Anyway, I will try to source a replacement and will report back.

Many thanks for the help
Martin