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Lower Boost then normal under WOT

2K views 22 replies 7 participants last post by  -Saab_Story- 
#1 ·
Hello.
I know that it looks like this subject had been discussed to death, however I didn' find the problem with the exact symptoms of mine...so, here is the story.

I changed oil yesterday, then around 4 hours later, i notice that it looks like the car had lost some of its power. Then I notice that the boost needle only goes about 2/3 into the orange, instead of going to the edge between orange and red. So, I stopped, opened the hood and visually checked the hoses. Everything looked allright. However, there is a valve on the driver's side of the radiator(APC?) and before, I remember giving small blips of throttle i could hear some action from the valve. Yesterday there was no sound coming from it whatsoever, no matter how hard the blips were. So, here is my plan of action:

1)Regap the plugs to .9mm
2)If above doesn't cure it, the is there a way to check if the APC valve is working?
3)If both of the above don't help, then Ill try a DI cassete.

Does that look like the most probably places to check?

Thanks a lot,

Klim
 
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#2 ·
Try this!

Well, I'm no expert, but I'd suggest pulling the APC fuse to see if you get the same boost (to see if you're stuck at base boost).


If you get the same 2/3 orange with the fuse out, then I'd label, then disconnect the hoses to the BPC, then give it some WD-40 and compressed air.

If you get a lower boost reading, or if the above doesn't fix it, then it could be something else, but I'd still clean the BPC.

Good luck!
--Reuben
 
#3 ·
Thanks fot the answer! I didn't know there was a fuse for APC valve...do you mean a fuse for the APC valve or for the APC system? I see you got one of the earlier models, and as far as i know, the ECU and APC systems are different systems on you car, however, on later cars, APC system is integrated in the overal trionic ecu...Ill check though.

Just an update, today(12F, no garage:() i regapped the plugs. They were 1.3-1.4 mm. I regapped them to 1.1(haynes manual), put some dielectric grease on it. The first couple of drives the boost went FAR into the red area, the car drove awesome:D. However, on like 5th drive boost came down to 2/3 orange again:(

Actually, I noticed a pattern, I remove the DI cassete, and for 3-4 drives, boost is good. Then it goes to 2/3 of orange zone. Did anyone have the same pattern? Does it mean that the DI cassete is bad? Maybe plugs?

Oh saabmasters, I need help, saab-boost=no fun:(

Thanks,

Klim
 
#5 ·
First the APC valve two simple checks
1) resistance across pin 1-2 & 2-3 look for 2.5 to3ohms = coils good
2) blow in any port air should only come out one other port, if air leaks out the third port then the shuttle valve is leaking / stuck clean with WD 40 but if can not get it to seal then its time for a new valve, even a small leak to the third port will upset your boost ranging from not getting enough to getting to much
also note leaking hoses from the APC has the same effect especially the middle one

Second ECU adaption
It takes time / miles to adapt to any engine changes, your plugs were over gaped then you reduced the gap, this will effect the ECU & if it negatively adapts (to protect the car) it takes longer to recover. force of habit I always disconnect the battery when i,m changing anything, this resets the ECU - then do adaption runs to get a good base setting. you generally do get a more aggressive boost initially which can tail off a bit as the ECU sort's itself out.

Boost tail off
you should get a bit of boost tail off, above 2nd gear its RPM related not gear. The ECU will indeed push this if its gets any bad vibes from the sensors etc.. (negative adaption) You may well have a DI on its way out after running with the plugs over gaped but go the APC checks / hose leaks / adaption etc first before you spend loads of $$

Oil change?
No idea why changing the oil should have instigated this, possible red herring but maybe you've inadvertantly upset wiring from a sensor that was a bit dodgy - crank position sensor / water / inlet temp sensor etc.. maybe worth checking there is no cracks in the wiring etc / also you may have upset one of the small vacuum hoses which are prone to become brittle over time, an intermitant leak in one of them could be your problem

ECU output to the APC - you,ll need an electronics response to this, but if you find the APC coils have failed then you can also get failure of output circuit from the ECU to the APC solenoid - not a common thing
Please do respond back with the solution, often the question is asked but the final answer not submited
have fun
 
#6 ·
Thanks for all the answers!
Allright, the thing is teasing me. Today, i took her for a drive. Didn't touch anything from the last post I did(where i was saying that it looks like when every time i disconnect the DI cassete, the boost becomes normal). Well, the point is that the boost today was great, as that time when I first drove the car after regapping:D So, maybe the ECU adjusted itself finally. I think we will have to just wait and see if t goes back to 2/3 of orange zone, becouse right now, the boost without any tweaking on my part is aggressive...the car just stayed overnight...

Thanks,

Klim
 
#8 ·
mulik51 said:
Thanks for all the answers!
Allright, the thing is teasing me. Today, i took her for a drive. Didn't touch anything from the last post I did(where i was saying that it looks like when every time i disconnect the DI cassete, the boost becomes normal). Well, the point is that the boost today was great, as that time when I first drove the car after regapping:D So, maybe the ECU adjusted itself finally. I think we will have to just wait and see if t goes back to 2/3 of orange zone, becouse right now, the boost without any tweaking on my part is aggressive...the car just stayed overnight...

Thanks,

Klim
This is a common problem with the apc valve sticking... I have had good luck cleaning them out with wd-40 and then blowing out good with compressed air. If you do not have an air compressor, take it to a tire shop or auto shop and borrow their air nozzle and blow out the valve and try again. If it works great for a few days and then starts to act up again, it may be time for a new valve. If it works great and continues to work great, you just had a little dirt or trash in the valve and it was sticking. Its a common problem and I have blown mine out more than 10 times in 2 years with my two saabs, I also had to buy 2 new apc valves though. Good Luck, John
 
#9 ·
This car is getting more bizzare with every day.
Here is what I found. For two days i was very puzzled by he fact that in the morning car has nice boost, goes to the middle of the red zone. However in the evenings the boost wouldn't go farther then 2/3 orange zone. I allready started thinking that moon had some kind of depressing affect on the beast, when I got the idea that in the evenings it is dark and in the days it is light. So, maybe the headlights have some affect on it...so I did an experiment, In a morning, warmup the car, drive-nice boost. Turn the lights on-bad boost. First thought-bad alternator. However, i get bad boost with just the parking lights on, and i get good boost with no lights but with heater, fan, radio on. Therefore, not lack of power...

Did anyone have something like this?? This is just weird for me...

Thanks,

Klim
P.S. I don't know if it is normal or if it is relevant, but my car turns on its low beam lights with all the inside ligting and everything every time i press brake pedal. Release the pedal, and the lights turn off...
 
#10 ·
You have some kind of electrical short or faulty ground somewhere it sounds like. I was going to say its colder in the morning and you usually get better boost than in the heat of the day, but it now sounds like you have discovered a direct link between your headlights and parking lights being on and low boost. It may rob enough power to start killing the ignition system?

I guess it is possible your batter is going dead, have the battery and alternator checked at checker for free. The lights do pull a lot of amps. If all is ok then you have to start tracing out your wires and grounds:cry:
Start tracing out your headlight wiring system and look for bad grounds, spliced wires and corrosion. I hate electrical problems, good luck, John
 
#11 ·
This one is interesting, your boost is designed to tail off to Base boost when you trigger the brake light switch, now if you,ve got a power link between the lights & the brakes then when you put the lights on it maybe thinking the brakes are on??

sounds like there is a diode in the circuit somewhere which has failed
 
#12 ·
Hmm, so if it a diode, how do I check for it?
Yesterday I remembered that there is a voltmeter in the car. So, the things is that with no lights and good boost, I get 14.3-14.5V. Lights on and I get 13.7-13.9V. Is that a low voltage or it is allright?


Thanks,

klim
 
#13 ·
I checked the wiring diagrams today. I saw that there's is a wire going from brake switch to the ECU. I am thinking, if I disconnect it, then ECU won't see the break at all, and then even if the lights and the break are connected, it shouldn't affect the boost, right? This wasy I will be able to check if it is indeed not enough amps or something wrong with the wiring. I think the latter is true because today I drove the car with the lights on and it showed 14.2V(when the car is cold it gives higher voltage apparently). The boost stayed at 2/3 yellow. Som the break/lights connection seems to be more probable...

What do you think?

Thanks,

Klim
 
#14 ·
Remove the brake light only for a test to confirm, the obvious reason for having this set up is safety. You could sort of test it by doing a base boost run using the brake light switch method
Do it with out the lights on, watch the boost drop when you tap the brakes whilst giving it WOT
Do it again but just switch the lights on when you give it WOT, do you get same boost drop?
When I mentioned a diode its only a guess based on another experience. I would get all my wiper & washer pump circuits coming on when I switched on my ignition, it was funny but not practical. Turned out to be a diode inside one of the front headlight wiper motors. When it failed it allowed the main power feed to back flow through the common live in that circuit ( diodes are like electrical one way valves) - sounds like you could have a similar problem & it will be on the common power feed in the lighting circuit
cheers
 
#15 ·
Thanks.
Ill try this test, because collected all the data in one piece, it definitly looks like there is a connection between two circuits. First, I noticed that when the lights are on, then the stop light is on(as far as i know it shouldn't be). Second, when i press the brake the lights come one even when the car is off, meaning that lights are able to pull electricity from the battery through the brake circuit(BTW, lights light up very dim). Interesting thing though is that when i turn on the parking lights, pressing the brake pedal doesn't cause low beams to come on, however, the boost is at 2/3 and the third stop light is on. Does it tell anything to anyone, or is this insignificant piece of evidence?
Probably ill have to get my voltmeter out and start tracking the short down:(

Thanks a lot,
Klim
 
#16 ·
One more thing which i didn't say becouse i didn't think it was relevant at all, but with the kind of bizzare problem encountered it looks like everything might be...my stop light on the passenger side birned, so, i changed the light bulb...i did the same time i changed oil, so, after this i started getting this problems with boost. I think the lightblulb i used is almost identical to the original one(I think pepeboys said that it was 9003B or something and i just bought 9003, so, almost the same thing). Could it have any effect on it?

Thanks,

klim
 
#17 ·
Ok, here is an update.

Yesterday I performed the test of pressing the brake a bit under WOT. It reduced the boost to exactly the same level as when the lights are on. So, point proven.

I went and took out the light bulb i replace. Didn't fix anything. Then I took out stop light bulb in the same light. Also didn't fix anything. However, when I took out both of these bulbs, I dind't get the short, and I get good boost even when the lights are on. So, correct me if I am wrong, but this means that the wire which goes TO the stop light bulb shorted to the wire which goes TO the rear tail lamp. Any famous places where this short could happen in these cars? Maybe the indicator of broken bulbs on the dashboard? I think Ill have to take my volmeter out:(, however, at least I can drive normally at night:D

Thanks,

Klim
 
#18 ·
There,s a couple of area,s worth investigating
1) the rear light cluster has a printed circuit board, give this a clean, you can get cross connections due to corrosion
2) your "pictogram" box of tricks ( the one that tells you if the doors are open etc..) its got a bag full of diodes inside it which are driven from a common feed. If a diode has gone inside this box of tricks then maybe its feeding a common signal back
3) you,ve got the filiment monitor which signals the pictogram, it also appears to have a common feed to the pictogram. Its full of relay switches maybe the brake light relay is stuck closed & when you put a new bulb in you closed an open circuit
I,d go to a freindly breakers & try the good old plug n play routine to sort this one
Summary = recon more likely to be one of the units as described rather than a wire issue
Thanks for reporting back your findings
 
#19 ·
mulik my 88 9000 turbo is having the same problem as your car. I cant even give my car WOT otherwise it will backfire and and cut out and start bucking really bad. I have to ease it into boost and I'm also having the smae problems with the tail lights backing off the boost. I also have another wiring problem. whe my ingition is off and the headlight switch is on the headlights will tur on when I press on the brake peddle.
 
#20 ·
I don't know about backfiring, but headlights on with ignition on and break pedal depressed is what I had. Try taking out first, stop and tail light bulbs out of the passenger side, and then out of the drivers side(one bulb didn't fix for me, I had to take out the tail light bulb and stop light bulb from the passenger side, that's how i drive now:D). Basically you will disconnect the circuits and even though there is a short, you will be able to get some boost:D
Try that.
However, your car is way earlier then mine, so, you have different boost control(APC, ignition and ECU) and etc, but probably the theory(trailing of the boost when break is depressed) is the same.

Good luck,

Klim
 
#22 ·
-Saab_Story- said:
for some reason though my brake lights and my tail lights turn on when I turn on the headlights.
Right, there is a short somewhere...try getting the bulbs out as I posted earlier and see if you still get the same behavior...

klim
 
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