new developments on my 87 spg and questions included [Archive] - SaabCentral Forums

: new developments on my 87 spg and questions included

21-08-02, 11:14 AM
Ok i have done rings and pistons the piston in the 2nd cyl was melted on the side :cry: timing i believe cause to putting a new distributor in w/o alligning it correctly. Anyway problem solved and the car runs beautifully new rings do wonders :D . Before i took it apart i was getting high yellow to a bit in the red boost out of it now i only get a little in the yellow though don't notice a power decrease the new rings more than make up for the loss in boost though i have tinkered with the pots F and P only per kevin's apc thoery and website and have noticed no change in boost levels i have put the 500ohm resistor in R42 and have put the 30,9K ohm resistor in r138 and the pots F is at full and p is at 6:30 or so just a tweak from 6 o clock still no change i am frustrated it even has a new knock sensor (dealer $80 ouch) but the boost levels do not change spool up is great though the amount of boost isn't there. I have noticed that the actuator valve above the radiator fan right next to the ignition coil is clicking an awful lot that I take it is letting all my boost out? pls adivise on this one

Johann F
21-08-02, 02:30 PM
If the solenoids clicking a lot - could be a faulty APC - or it's picking up some noise it thinks is knock. Try removing the sensor still wired up and driving (carefuly) with it hanging free. If it's picking up noise actual noise it will now go like a rocket - stop in that case as you have no knock protection. Also make sure your brake pedal is not bouncing around ( weak return spring or misaligned sensor) as this will cut back boost.Check your timming - over advanced and or no retard on boost and you are likely to knock at low boost if you are on poor fuel. Also check all your APC system connections and power/ground wires - the multi connector under the APC box can work loose if not properly secured. Check your base boost also - pull the APC fuse and see how much boost you get in 3rd on a hill - should be between 1/3 and 1/2 in the yellow - a basic check but it wont deal with the solenoid clicking. BTW - how did you knw the nock sensor was bad ? - they are usualy very reliable.

21-08-02, 04:53 PM
thanks for the reply i replaced the knock sensor for reasons of the old one the case was cracked and i felt a new one might give a more accurate reading on the engine. I will try all of these tests the timing i believe to be right on i timed everthing to tdc when i put it back together only thing i could not find was where to line the flywheel up to the 0 degree mark came to the left part of the starter cover i coulnd't find the stock mark it was not very well explained in the book so i put a bolt in the 1st cyl combustion chamer and watched very carefully as the bolt rose and fell as i turned it over and the engine started on the first kick i was very pleased although it had started well in the past and when it started the lifters were very noisy but that soon went away and no longer exists the knock sensor definitely picked that up i heard it until i drove the car around the block keeping it under 3K rpm to break the bearings in and seat the rings though now it doesn't give boost but pulls like none other cause to the new rings all u boost heads new rings do wonders in my opinion.
the brake pedal is not loose it is pretty tight and i am running amoco 93 octane the best they offer with out putting racing gas in it. and the knock sensor how tight should it be put to the block hand tight or more?

21-08-02, 06:05 PM
ok i have done these tests the brake pedal is fine nice and tight.The knock sensor when taken off block but still plugged in provided me with mid yellow boost thats it i got more taking the waste gate hose off before the ring job. I took the apc fuse out and got exactly same amount of boost as before with the apc fuse connected the max boost for both conditions were the same. With the fuse out i got a it into a hint of yellow hill or no hill and no matter the gear same amount of boost it was oddly the same as when i had every working part connected i only got a hint of yellow out of it although there is one thing the dashpot right by the throttle plate is broken don't know why or how,didn't hit it durring reassembly who knows would that cause problems? i dunno still confused about the boost

21-08-02, 07:27 PM
Have you checked what base boost is set at? There's a proceedure at the townsend site! You really need to hook up a seperate boost gauge, which will give you an accurate reading, as the saab gauge dosen't really tell you what psi you are achieving!! Set base boost @6-6.5 psi for maximun performance :! :!

Janne Selinummi
21-08-02, 07:57 PM
Yeah, and you really should invest in an air/fuel mixture meter as well... I would have been able to save one T16 engine if I had had such a meter in that car. It's really useful for engine safety, and a great help for power tuning as well.

21-08-02, 11:23 PM
is the boost gauge working???
you say the car runs great but with no boost it would be a pig

just a thought

Johann F
22-08-02, 07:13 AM
Right - as you have no change in boost with the APC disconnected some component in the whole APC setup is faulty and the system is 'failing safe' and only giving you base boost. Mid yellow is an adequate indication that the base boost is set about right - an accurate guage would give you a more precise reading but I don't think this is the problem at the moment. If there is still only base boost with the knock sensor removed ( but connected) then it's unlikely the engine is knocking as a result of fuel mixture or timming faults as the unit can not detect knock. If you unhook the solenoid line to the actuator and take a drive - again with care - and you get hard fast high boost ( please only do this with care) then it's pretty certain you have a fault in the APC system. Er then it's trial and error by checking all the connections, replacing parts with known god ( borrowed !) ones etc. My fist action would be to get hold of anothet APC box and try that - I've had them fail before. You said you did some mods to it - try reversing these and setting it back to originalk spec?. AF meters are very useful - but only the professional wide band variety. The typical meters that hook up to the stock 02 sensor will only realy tell you if you running at the 14.7:1 ratio they are highly inaccurate at lean or rich mixtures as their reading varies with temperature.

22-08-02, 08:55 AM
sorry forgot to tell u i am one step ahead i grabbed one out of the yard out of an 87 turbo and it didn't change my boost i installed it right at the yard to tell how it was working on the way home no change in boost level i also did mods to the box here and there no change either so i am a little worried it is almost like the apc is being bypassed or like u said playing it safe with my base boost level so i will set base boost from the townsend site and we'll see what we come up with in the mean time i will be looking out for a old box to install.

Johann F
22-08-02, 10:48 AM
Like I said - if you are getting 1/2 yellow with the APC disconnected the base boost is about right - I wouldn't waste time trying to reset it now.You have eliminated 3 things now; APC box, base boost and knock sensor. This leaves wiring contuinuity and power feed, solenoid, brake cut out switch and pressure sender.

22-08-02, 12:18 PM
I bought a gauge to test boost levels i will need it in the future anyways no biggie so i told u about the box and the line was disconnected before the rings i can guarantee the high fast boost though the flapper (wastegate arm) was free and flapped i as i got boost? but so i will try it again and it will determine that i have apc problems? Ok so then why if i put a diff box in from the yard does it still give base boost where is the ground located for the apc even though that may not be it and these "This leaves wiring contuinuity and power feed, solenoid, brake cut out switch and pressure sender" what are they are where are they located and are there tests for them as well?The gauge gave me a max reading of 3.5 psi boost with everything connected the vaccuum was reading 25.5 thats alot or is it normal?

23-08-02, 12:51 AM
Boost is everything you get ABOVE normal atmospheric pressure, which is about 1,0bar (Don't know about psi for sure, but I think atmospheric pressure is about 14psi?). So anything ABOVE 1,0bar (14psi)is boost when measured against vacuum. So your reading of 25,5psi against vacuum is actually 11,5psi turbo boost pressure. One funny thing about turbos in general...In engineering turbo is something that operates normally at range of zero to one bar overpressure (and is driven by exhaust gases). Anything clearly above 1 bar is concidered as a compressor, so you guys with 1.2-1.4bar of max boost pressure are technically speaking driving with a compressor Saab (and we all now what car maker is using "kompressor" labels on there highly overprized vehicles) :D


23-08-02, 09:57 AM
yah i am not familiar with atmospheric pressure vs. psi the vaccuum was actaully guaged in Hg(?) I only can go by what is on the guage unless someone has a conversion factor for the psi vs atm press. My guage has vaccuum on one side measured in Hg and the boost on the other side meas in psi and it read 16psi when i had a problem feel free to read this forum:

23-08-02, 05:40 PM
I had a bad earth fault in my n/s/r tail light once which stopped the boost from working. (apparently the US spec 900's had a common earth fault in the tail lights???) If the APC sees the brake light going on it dumps all the boost via your clicking solenoid. A second hand lamp holder/cluster cured it on mine.
On my newest car I cut the wire on the brake light switch which feeds the APC. I think it's the yellow one, a quick check in the wiring diagram will tell you for sure.

24-08-02, 01:12 AM
yeah one would think he is putting on the brakes and doesn't need the gas at the same time or well boost as the case may be oh well there are many faults in the fail-safe apc system for example overboost fuel switch hmmmmm yeah well thnks for ur post it will be useful.