Boost Odyssey (long post...)

[hsolakidis]

Ok, here is the problem: I'm only getting half boost. The car is a 1991 CS Carlsson auto with APC/DI.

Here's what I've already done:

1. Checked all the vacuum hoses. Look good.

2. Took the W vacuum line off the APC solenoid. I was getting plenty of boost that way, so turbo is ok.

3. Reconnected the W hose and unplugged the APC solenoid. Again plenty of boost. However, I read in several posts and websites that disconnecting the APC solenoid should give me only base boost, I was getting full boost as in (2).

4. Checked wastegate rod. I took the rod off, unbolted the exhaust so that I could see the wastegate. Looked ok, but had quite a bit of free play. I haven't seen another one so I can't comment any further.

5. Checked bypass valve by blowing/sucking in the small vacuum pipe coming out the rear of the valve. No leaks there.

6. Checked spark plugs. Regapped them. No effect.

7. Checked APC voltage, resistance and air flow while on and off. It is definately working, it is buzzing hapilly. Everything is normal.

8. Sprayed APC solenoid with suitable lubricant/cleaner. No effect.

What I haven't checked yet:

1. Knock sensor. Couldn't find the bloody thing! Found two connectors behind the engine, under the manifold and behind the starter motor as someno suggested. One had a single wire, the other more than 2. Is it one of those?

2. Brake pedal switch. But since the cruise control is working, I don't think it's that.

Can't think of any thing else to check. I suppose I could try another DI casette and see if it does the trick. However, I doubt this is it...
I'll try to find another APC solenoid to check with. However, mine has passed all the tests. Could it still be bad?

Observations:

1. While on axle stands, I had someone rev the engine while I was looking at the wastegate actuator. Boost went up to atmospheric pressure, and I could see the rod moving to the end of its travel. Is that normal, or should the wastegate remain closed for longer?

2. I cannot understand why disconnecting the APC solenoid should give you base boost. How would the wastegate open in order to reduce the boost without the APC solenoid? It looks to me that the wild boost I'm getting without the solenoid connected is correct.

Is there anything I've missed? I could use a few good ideas....

I'm sorry for the long post, but I really want to get my Carly sorted!

Thanks in advance

Harry

[hsolakidis]

Update: It seems like I am now getting base boost with the solenoid unplugged. Yesterday I was getting boost off the red line. Strange....

My mechanic is convinced it is the balance shaft chain which is fitted incorrectly and/or the sprockets are worn, and as a result the knock sensor is limiting boost. I will be taking the timing cover off this weekend.

[hsolakidis]

Another updte: Today the car is boosting even less, and I also get less negative pressure (at the boost gauge) at idle. Is that a hint for something?

[hsolakidis]

BTW, what would Saab charge to diagnose such a problem? Anyone knows?

[Damo9K]

Harry

Have you taken it to south west saab in hanham 0117 940 6151

A good friend of mine is a partner there (Ian) he's an ex saab master machanic and knows his S**T.

Im sure he would be your best port of call - he has all the saab diag tools and cheaper that Williams saab.

Cheers

Damo

[hsolakidis]

Ironic.....That's the mechanic I'm referring to!

[adrian]

Sorry to bang on about the same thing but given huge boost and base boost with solenoid disconnected I'd try another solenoid. Other thought is the pressure transducer - easy to check. Sounds like your mechanic should know his stuff so maybe he is right, but swapping that solenoid valve is very easy. On the older APCs pin19 could be grounded through a LED to tell you if the APC was seeing knock - is there a similar pin output on the DI/APC?

[hsolakidis]

I have tried a different solenoid today. Same results. The solenoid is now consistently giving base boost, powered or not. I have not checked the pressure sensor. Can you tell me where it is and how to check it?

Thanks

Harry

[adrian]

Above the brake pedal - remove trim and its a flat black thing with a pipe into the centre and electrical connection (3pin) off the side. I used Townsend site for details when I last checked mine (18months ago). Basically it was to measure resistance across specific terminals when pressure applied to it (I use a Halfords foot pump for this - but dont use your foot!). Not really sure if a disconnected (knackered one) would give you base boost, guess if it was telling the DI/APC that you have 20psi all the time them DI/APC would keep wastegate open all the time?
Sounding like your man is right.
Please let us know the cause when you find it

[quarryeff]

I'm mystified about your comment that wastegate actuator was fully open 'at atmosheric pressure'. Do you mean that? I understood that the wastegate should remain shut until peak (or near to peak) boost is reached.

[hsolakidis]

What I observed was that when revving the engine in neutral, with the boost going from whine (negative prressure) to white/yellow border (atmospheric pressure,no?), the wastegate opened as the revs went up. I now understand this is normal, as the solenoid is not like a switch that opens when max boost is reached (as I originally thought), but rather that it opens/closes many times a second and the frequency of these changes, plus the amount of time spent in each state, adjusts boost pressure.

Am I right or completely wrong?

Harry

[cdcarlsson]

As I understand it Harry, you're correct on all counts.
I believe you can only get the boost pressure up to 'atmospheric' in neutral and not actually get positive boost, why I'm not sure. Whether it's to preserve the engine I don't know.
Nick.

[adrian]

In neutral not enough airflow to spin the turbine fast enough to spin the compressor fast enough to raise much pressure. Without a load on the engine, the engine revs limit is hit before you can have the throttle opened enough to get the airflow up (for long enough).

[adrian]

Harry,

Just remembered that on my 90 9000Carlsson (which I'm breaking) I had a similar problem to you with boost being limited to base. But it only ever happend when the engine was cold and cleared itself after 10 miles or so. Now this engine has no balance shafts. I tried everything on Townsends web site, check all voltages at the DI/APC connector, changed solenoid valve, pressure transducer and still the problem persisted. In the end I admitted defeat and fitted a Dawes device manual boost controller, basically a pressure relief valve (with a small down stream bleed to release the pressure). Set this to 12psi (for insurance purposes - i.e. no modification!) and everything worked fine (no APC of course).

[hsolakidis]

Adrian,

I must admit I am giving thought to this approach. My other option would be to take the car into the dealer and let him find out what's wrong. I know which one is cheaper, but I also know that the dealer option is probably best for the engine (not bypassing APC). There may be a very good reason behind the lower boost, and fitting a boost controller may cure the symptom but not the cause.

On the other hand.... Bypassing the APC is cheap, relatively safe (many people have done it), and quick....

What do the rest of you think?

What is the dealer likely to charge for finding the cause? Anyone who had previous experience?

Where can I find a boost controller in the UK? How much?

Thanks
Harry