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Discussion Starter · #1 ·
Okay I know what to do but I am not sure which fuse or relay to pull. Also what are the average compression numbers that a high mileage 900 Turbo should be able to do? Thanks in advance.
 

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Discussion Starter · #3 ·
Disconnect all the wires from your spark plugs, take out all your plugs and make sure you know which order they went in, pull fuse or relay (not sure which one yet), screw in tester into spark plug hole crank it over for a few sec. or whenever the meter stops going up, and then do it again for the rest of the cylinders. I just need to know which fuse or relays I need to disconnect.
 

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You probably already know to warm up the car or drive it for a little first.
But I would pull the fuel pump fuze 32 (that what it is for my NG900); depressurize the fuel system; and pull the DI cassette cable or (coil cable if older car). shouldn't be no more than 2 bars between cylinders...
and 10 bars or more are good readings...generally

rcmdesign,
basically like QC was saying...
warm up the car;
disable the fuel and coil system;
pull the plugs(wires if applicable), making sure of where they go;
plug in a compression tester/guage into a spark plug hole;
turn over the car about 5 times or so;
take your readings;
repeat for the next cylinder until done (sounds like a recipe or something).

if you see unusual low readings or differences, drop a little oil in a cylinder, retake your test to see if it changes or not... and that's another story.

a good idea on hi mileage cars, and helps determine whether you need to rebuild, replace a blown head gasket, determine if bad rings, valve problems, carbon problems.......and so on.

hope it helps...


regards...
 

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That sounds pretty easy to do.

Although it seems pretty simple, would someone mind doing a tutorial on it w/ some pics because I've personally never used a compression tester. I think that it would be pretty useful information for our tutorial section.

Ced
 

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Discussion Starter · #7 ·
I will take pictures and write a tutorial if you want me to. I am just about to go out and do it now. I am not sure at the range I should be in but I know for my DSM it should be from 170-210 PSI but whatever I get I will post up here and maybe some of you guys will know if thats about average or not.
 

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sorry about the bar specs... got use to talking bar as opposed to psi since my research on higher spec gauges "across the pond".

look for differences of not more than about 30 psi between cylinders..and anything above 145psi is supposed to be good.

About 2 years ago, had to have my engine replaced because I blew my head gasket, but also shorted my oil supply to the bottom end at the crank. SAABs don't work to well with spun crank shaft bearings... :lol:

Turns out the oil strainer inside the NG's are closely netted, and anything you put in to shake off caked oil in some passages ends up clogging the strainer. Regular oil changes strongly recommended..but I'm not a proponent of oil cleaning additive stuff anymore, especially if you don't want the headache I had.

I didn't believe anything the SAAB guys wanted to tell me....had to check for myself...and no amount of oil was helping the readings come up...., but didn't help my pocket....after about $4500 spent. :shock: the horror

Let's see if I can remember....the dominoe theory...blown gasket, water mix into oil, spun crank bearing.., piston rings problems... I can laugh a little about it now like a bad dream, as it was my only car at the time, and the first time I heard that horrible knocking sound. :shock: but learned a lot about the motor after that day....and still cheaper than a new car with unknowns..

regards
 

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Discussion Starter · #9 ·
Well here are my results. I pulled everything I could find that would supply power to the fuel pump or anything like that so I pulled the #30 fuel pump fuse, (G) fuel pump relay and (F) fuel closing. Did the compression test and this is what I got. Cylinder #1 = 160PSI, #2 = 160, #3 = 150, #4 = 140. Keep in mind this is a very high mileage 900. Anyway during the test I never smelled fuel and when I pluged everything back in the car started up just fine so the relays and fuse I pulled must have done the trick to stop the fuel. If you guys want me to make a write up on it just tell me who to talk to and I will try to get one here soon.
 

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Discussion Starter · #11 ·
saabkid37 said:
where did you get a compression tester?
You can buy them at just about any auto parts store. I got mine at Auto Zone. You might be able to find them at some hardward stores too. They are only like $20.
 

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based on your readings....I'd say #4 is suspect, and you should add oil to all four and retake the test... to see if it changes. Good if it increases, but bad if it doesn't. The low readings indicate something more to look at.

If this was a V8 I'd start thinking about replacing the head gasket considering how close those readings are in the adjacent cylinders. Replacing head gasket on a high mileage car is a whole lot cheaper than replacing a warped head.

I blew a gasket internally as opposed to externally, so was hard to detect...other than the red idiot light came on (hmm no wonder..lol) ...so was hard to see. Supposedly most SAABs blow head-gaskets by design internally, but there are exceptions to the rule.

Have you noted anything leading you to suspect something might be wrong to do this type of test? i.e..., loosing coolant, milkey brown oil...(definately time to investigate the problem then), or something like that indicating it might be time to consider, or just saw the high mileage and thought it was time?

regards
 

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#4 might be a little suspect. Generally you want them to be about the same. I think when I did my car (month ago) I got like 150, 145, 155, 140.

I did not bother to disconnect the fuel pump. Also you will want to do a Wet test. where you squirt about a teaspoon to a tablespoon worth of oil in the the cyc. then run the test. Not sure what this proves, but my dad had me do it. Car will smoke Just a little (read alot) when you goto start it again.

my car is a stock C900T with 220K on it.

ian
 

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Discussion Starter · #14 ·
DC_SAAB said:
based on your readings....I'd say #4 is suspect, and you should add oil to all four and retake the test... to see if it changes. Good if it increases, but bad if it doesn't. The low readings indicate something more to look at.

If this was a V8 I'd start thinking about replacing the head gasket considering how close those readings are in the adjacent cylinders. Replacing head gasket on a high mileage car is a whole lot cheaper than replacing a warped head.

I blew a gasket internally as opposed to externally, so was hard to detect...other than the red idiot light came on (hmm no wonder..lol) ...so was hard to see. Supposedly most SAABs blow head-gaskets by design internally, but there are exceptions to the rule.

Have you noted anything leading you to suspect something might be wrong to do this type of test? i.e..., loosing coolant, milkey brown oil...(definately time to investigate the problem then), or something like that indicating it might be time to consider, or just saw the high mileage and thought it was time?

regards
Nothing led to me doing this test. I just wanted to see what it was considering it had pretty high mileage. I might do the oil test but I don't really want to have to replace the rings or even the headgasket to fix anything. I just wanted to make sure the car was running okay on all 4 cylinders and to make sure I didn't have like a burnt valve or anything. They all seem to be close enough to eachother where I'm not to worried about it. Besides I only paid $500 for the car to begin with. I just lucky it's in this good of shape.
 

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I would check and retorque your heads too...

Depending on the age of the car some say carbon deposits cause the unusual high readings relative to your car's specs; mine would suggest your hi is normal for my ng900, but the 145, and 150 are generally pointing to a blown gasket between the cylinders.

however if you get excessively high readings try heating up the engine..or running it hard before the test, it helps to burn off carbon deposits..

good luck...

regards
 

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another important reason to put a little oil in and rerun the test...will help determine whether the problem is in the head..or in the block...typically readings that don't change point to your piston rings

hope this helps

regards
 
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