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Discussion Starter · #1 ·
I have posted a few times about this, but still haven't fixed my problems. Basically, the car drives fine normally, but if ever I decide to drive it a bit harder, I notice it doesn't have the performance it once did. I am running a swedish dynamics red series apc, which used to allow boost to get a bit into the red zone, but now my boost climbs no further than a little bit below the red zone.

I took the car to a saab/volvo specialist the other day and got them to have a quick look at it. They confirmed that the car felt like it was under-boosting, and checked the air mass meter and apc solenoid, both of which worked fine. They said they suspected either an exhaust blockage somewhere that was preventing adequate gas flow through the exhaust, or a bypass/dump valve that was stuck open, causing recirculation of air through the turbo instead of going into the engine. They didn't do any more work on the car because they said it was likely to get expensive, and I didn't have a whole lot of money to throw at the issue (in fact they tested the apc solenoid and air mass meter free of charge).

I am running the 2.1 head, with 3 bar FPR and have recently set the correct ignition timing and ensured I have a working vacuum advance/retard for the dizzy. Spark plugs, dizzy cap and rotor are all new.

I am thinking that an exhaust blockage is unlikely because if I replace the APC solenoid with a manual boost controller the car seems to have a lot more power, although this obviously leaves it much more vulnerable to damage through knocking etc.

I recently replaced the small diameter vac line from the intake manifold to the dump/bypass valve, and today I disconnected the large diameter tube going to it from the throttle body and tried to blow air through there. The mechanic said that this should not allow air flow through it with the car off, and as I was unable to blow any air through there I assume it is functioning properly.

I also tried swapping APC box back to the original, in case the swedish dynamics one had any issues. This didn't seem to have much of an effect, with boost still sitting just below the red zone. I did however notice that at this maximum boost, the swedish dynamics box used to give the exhaust a sort of "fluttering" sound at high boost, whereas the original does not. With either box the car does not have the power it should.

I am lost for what to check next given that my apc solenoid, apc computer, dump/bypass valve all seem to be working? I would have thought I would have far lower boost with a dysfunctional knock detector. As always any help would be great
 

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This is only a suggestion, but you say you have reset the timing. The cause of these problems can be highly elusive, but you say the car has less power. Can you feel this through the seat of your pants or are you judging it by the boost gauge? Very small variations of ignition timing can have a significant effect on the maximum boost readings. If your timing was very slightly retarded before and you have now advanced it, it will have the exact effect on your boost gauge you describe, all other things being equal.
 

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Discussion Starter · #3 ·
I can definitely feel that the acceleration isn't what it used to be, and the lower reading on the boost gauge is what alerted me to the fact that it is probably boost related. Although it was quite a while ago when I set the ignition timing, I think I remember having to change it a non negligable seeming amount to get it to what is specified on the sticker in the engine bay.
Although I set it as best as I could, as you know the plastic sight that you are meant to look through has hoses etc. above it, making it hard to look properly perpendicular to the sight, so maybe there is a small degree of error there?
I could perhaps try retarding it slightly to see what happens? Although I am unsure about the dangers of doing so, or how many degrees of retard would be reasonable to try
 

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I tried to explain last time Julian that the reason the exhaust makes a fluttering sound is due to the APC system telling the solenoid to open/close which subsequently open and closes the waste gate on the turbo to maintain that boost value ( for you this is just below the red zone) The result is hot exhaust gases travelling at different speeds into the exhaust - they are also different temperatures, causing a change in exhaust sound. It is not diagnostic of anything, just a normal observation. It may be LOUDER in a blocked exhaust, sometimes you can hear this whooshing sound as the air is forced through a restriction in the pipe (often the cat)

The difference between the two boxes could simply be the different settings affecting the rate that the box tells the APC solenoid to open the wastegate, one may just be slower than the other. This is entirely possible as grey box APC's as the one I have pulse the solenoid slowly (I can hear it in my 2.5" exhaust as a slow almost once per second quiet/loud) but in other T16's I've been in (where I can also hear it) it's much faster. In cars with big exhausts and custom elbows they probably don't hear this sound as readily.

Have you considered maybe your 'red series' APC isn't actually turned up to go past 12psi - maybe it's failing/faulty, maybe it was a fake. I mean it's something to consider if it gives same values as your other box.

If you're saying you aren't noticing the boost gauge needle dropping back at higher RPM the car probably isn't knocking - meaning you should have the 14psi (into the red) boost the red series apc is SUPPOSED to deliver.

You can figure out if this is indeed the case IF you install a knock light. You can determine in an instant if the boost is limited by the APC system due to knock or if it is just the fact the boxes aren't tuned to go above 12psi. If you installed a knock light you could also check to see if you were getting knock with your MBC, best of both worlds. You need a couple of meters of thin gauge wire, a large 6000 candle or so LED I think a resister and some crimping/soldering time - it would probably take an hour or two. Much quicker an cheaper than continuing to hunt aimlessly.

What have you got to lose, perhaps buy another APC box and modify it following a guide, then test it out if you don't want to install a knock light.
 

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I can definitely feel that the acceleration isn't what it used to be, and the lower reading on the boost gauge is what alerted me to the fact that it is probably boost related. Although it was quite a while ago when I set the ignition timing, I think I remember having to change it a non negligable seeming amount to get it to what is specified on the sticker in the engine bay.
Although I set it as best as I could, as you know the plastic sight that you are meant to look through has hoses etc. above it, making it hard to look properly perpendicular to the sight, so maybe there is a small degree of error there?
I could perhaps try retarding it slightly to see what happens? Although I am unsure about the dangers of doing so, or how many degrees of retard would be reasonable to try
I would just retard it slightly to assess the difference. There are no dangers in doing so. I would suggest you put a mark from the dizzy collar to the cam cover to register exactly where it is now. Then retard it by about 0.5-1mm between the mark on the collar and the cover. Retard as you will know is anti-clockwise from the front of the car. I can virtually guarantee this will give you more boost. See what you get on driving? If you can be bothered check what the timing is on the flywheel just for reference in the future if it gives what you want.

I know it can be difficult sometimes to see the timing marks, but where are you looking? I've known guys using the wrong hole. It's not the round hole on top. You have to look slightly from the front, then you can line up with the mark on the plastic cover.
 

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Wait a minute.....

In this picture, I have been using the line in the round hole that I have circled in red. Is this right, or should I be using the line circled in green?

If I have been doing it wrong all this time, it will be a serious hand on face moment. I don't know where I got the idea it was the circular one
No it is not the circular one. It is the thin line in the plastic to the right of the circle that you use to line up your timing marks.
 

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Discussion Starter · #7 ·
fuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu

haha, I will re-do the timing tomorrow...

Thanks
 

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:roll: DIYers eh :lol:

:D good luck!
 

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BINGO BANGO ... :) we have a winner ....

IF ... you can beg steal or borrow .. get a hold of a timing light where you can *dial* in the required setting .. and get the guy who loans it to you to demo :)
 

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So you were using the wrong hole eh. You wouldn't be the first. It's the big aperture in front of the round hole. No wonder it was out. It helps if you can put a white line in the timing reference groove in the plastic cover and if you can turn the engine over do the same to the degree mark at 16° or 18°, whichever you use. This helps a lot when you strobe it. As other guys have said, beg, borrow, or steal a strobe timing light. It's virtually impossible to get correct without it. This error will have significant effect on your boost level.
 

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I use my wife's or daughters fluorescent nail polish. I also mark the block mark when I have the cover off. Colored chalk can also work better than white, since you are now looking for a color not just a white mark.
 

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Discussion Starter · #12 ·
Yeah I have a strobe timing light. Just set the timing correctly then by putting a bit of nail polish on the correct mark, and took it for a drive. Similar at low revs, but WOW, it revs up way more freely now, and the acceleration is heaps better. THANKYOU!!
 

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Discussion Starter · #13 ·
Out of interest, what is the circular hole I was looking through intended for? Just to throw off the home mechanic? :cheesy:
 

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Think Jim Mesthene said it was for a Saab service tool. Can't remember what exactly it was for but I'm going to assume something to do with timing lol, can't remember.
 

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Yep, Jim said there was a special Saab plug that went in there and dowloaded alll the info about the driver and the driver's family to the 15 Cray computers in Troll-land. That or he said there was a plug that went in there for reading the time on a machine.
 
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