[Bartek]

I know it was rolled over and over in the past but I haven't found description of situation like mine. When engine's cold everything's allright. Chattering starts when engine is warm. It works like this - when I push the brakes it stops chattering, but when I take the foot out of brake pedal it starts to ta-ta-ta-ta-ta-ta-ta almost continously. Usually at idling, at the street lights, but as you know it's hard to hear if it's clicking while driving. I checked and cleaned solenoid, checked for proper blow/suck - everything looks allright. I replaced even rotor arm for a new one. No change. Once again - it starts chattering only when engine's warm.

Could it be connected with my problem of losing power? (apc gauge goes almost to yellow/red zone but it needs few milimeters more to reach the border and those few milimeters are critical for boost :evil: ). I lose boost a little ONLY when the engine gets warm. When it's cold (not stone cold ) it goes a lot faster and better.

I checked 900aero.com but I didn't find the answer. I know general rules of solenoid's work but can't imagine what makes it to chatter and let the boost out to the air. Please help what to check, what to replace.

 

[trackside]

Had this happen and it was a faulty APC box - changed it and it was fine.

 

[Bartek]

I've got red one ((((
Is there a way to check it? Is there a way to fix it?

 

[Raub]

Had this happen on my old 900. The APC harness plug wasn't fully seated into the box.

 

[Bartek]

You mean it was loose? Wasn't plugged correctly in the box?
You also have chattering solenoid of this cause?

 

[trackside]

"Is there a way to check it" - change it for a known good one - if the problem goes away you have found your problem. No idea how to diagnose or fix a faulty APC - cheaper to buy a used one. Buy a standard box and mod it to Red box spec for the price of a couple of resistors and a bit of solder.

 

[Bartek]

What about cruise control? Has it something to do with solenoid? Could it have something to do? Mine CC doesn't work. Never did.

 

[Raub]

You mean it was loose? Wasn't plugged correctly in the box?
You also have chattering solenoid of this cause?

Yes, it was loose.

 

[Basre]

I've run into this problem Twice.
Problem is there are Several causes for the Damned 'Clacking' . BUT after examining and calibrating every single piece of the APC system..took weeks.
I discovered that the APC box connector was not seating properly.. and in the other instance it was the ECU connector that had a almost invisible amount of corrosion on it's tangs.. Contact spray 'fixed' it .. instantly.
Gotta Love those poor quality Bosch components.

 

[trackside]

"What about cruise control? Has it something to do with solenoid? Could it have something to do?" - no. If the solenoid is chattering at idle the APC unit is faulty/it's malfunctioning - if any other system fails the APC just fails safe i.e it doesn't work.

 

[Basre]

Nonsense.. If you have spent time and effort onna Saab boost control system that statement would'nt be there
CLacking can come from a faulty Pressure Transducer.. but it can be pressure tested and recalibrated if one is serious about it.. and doesn't want to spend the $200 for a fresh one.. on the chance it might be deceased.
Clacking can also be due to a Vacuum leak.. anywhere.. even from the Brake Booster... More reasons than some might think possible.
Suggest reading the Bentley Manual on Diagnosing 'Base Boost'.. it's long and involved.. but there is no other more reliable method.. to sleuth out boost issues
(lack of it, usually
In long discussions with genuinely experienced Saab Mechs: APC unit failures are theoritically possible.. but both these guys have..never.. experienced/seen a genuine electronic failure.
The connectors however are a known trouble spot. Often substituting a replacement unit 'works' Cuz the connection has been reestablished.
Getting it right can be an arduous adventure..

 

[Bartek]

Basre, seems like know what you're talking about . I've got Bentley. After unplugging solenoid I've got quite stable base boost to the half of yellow zone. What now? APC is solidly plugged. I cleaned the connectors. I cleaned solenoid - from outside 'cause I couldn't open it. You said - ECU connectors. You meant main ECU at the right side, passenger knee holster? I think I'm gonna remove lower dash to check eveything inside - I mean pressure transducer. I think Bentley has the solution for this. Any more hints, please?

 

[trackside]

"If you have spent time and effort onna Saab boost control system that statement would'nt be there" - well I have and I also know of several instances of APC unit faliure as well as my own. It's old electronics and they do go wrong. Granted the pressure transducer may be a cause of solenoid activity at idle as the APC may think there is boost. Single clicks are not uncomon if you hit the brakes or some other system linked to the APC but if it is chattering it is a different story. The only way to solve this is to test and if possible substitute every APC component with a known good one - my money is on the APC unit if there is constant chatter at idle - if it's just a case of it not working then it could be anything.

 

[Bartek]

Hey guys. What about leaky/stucking EGR? Could it be the reason of chattering solenoid?

 

[trackside]

Bartek - nobody is going to diagnose this problem for you - we have given you some advice but you have to at some stage get stuck in and start swopping out components. The EGR valve has nothing to do with the APC.

 

[Bartek]

Sorry, I didn't mean to . Problem is I've got some irritating mechanic here, no spare parts and no one else to help me. Car behaves weird and I'm checking all the possibilities by myself. The mechanic told me the reason of poor boost is stucked EGR valve. After thorough reading of Bentley troubleshooting section I didn't see any hint leading me to EGR but I wanted to be sure. It's also some kind of vacuum. And believe me - not true I am not getting my hands into it. Honestly I still can't clean them properly since Tuesday . Once again sorry.

 

[Jezzadee]

Don't worry about it - the whole point of the forum is to ask questions. Unfortunately I don't have any answers - I don't know anything about APC cars anyway. If you suspect the EGR system is at fault try doing a search on "EGR system" for some details on it. Put it in quotation marks because if you don't it doesn't search EGR as the word is too short. I know from having just read a couple of threads while doing a search that they do get blocked up and that many people remove them and say the car goes better as a result. If you remove it that is one more thing to rule out.

 

[Bartek]

The EGR valve has nothing to do with the APC.

Just to make things clear and if somebody will ever look for the answers. In fact EGR has nothing to do with APC but it CAN affect the boost. EGR sends a little amount of exhaust gases back to inlet manifold. If EGR is stuck it continously pushes hot burnt mixture back to cylinders, so there's no way for engine to work in proper way. Thx to one of previous DeLorean's post for this info. Bentley must have missed something :cheesy:

 

[CoastCard]

Just got first MOT on 'my little project' today. Flew through - Yipee!! Being the first time I have driven it, I noticed these exact symptoms:
1) v. low boost reading which drops off (like a cutout).
2) Chattering that disappears when the brake is applied.
3) Jerky acceleration.
Just sat at my desk to check out the posts (and notice I missed a Bentley manual on e-bay while sitting in the sun ) and look what was in front of my eyes. I look forward to progress reports and doing some Bentley diagnostics together .

 

[GlenM]

Bartek,

Did you manage to cure your clicking APC solenoid, and if so how? I have exactly the same problem and I am currently trying to get hold of a second-hand pressure transducer to try.