4 replies to this topic

[engr_dave]

Got my car back from the dealer after water pump and timing belt replacement. It looks like there was indeed some valve-piston contact --it idles, but very roughly.

So, I decide to test compression before dismantling the top of the B5234T motor. The manual says,

"Remove:
- timing pick up connector
- HT lead cover

Lock Throttle Open
Remove spark plugs and connect ignition switch 115 8263. Connect connector between alternator (+) and service output on control module"

By "timing pick up connector", I assume they mean the camshaft position sensor? Why is this step necessary?

Since I don't have "switch 115-8253" can I just crank the engine over using the ignition key? I suppose this will dump fuel into the cylinders as I am cranking... but since I'm going to pull the head... does it matter? Or is there a way to wire a simple push-button switch to "dry crank" the engine?

P.S. I took some of the turbo plumbing off the top of the engine in preparation for head removal and it was quite oily inside. Is this normal?

Thanks,
Dave

[Chopper]

What kind of car are you doing this to?
If it's an 850, all you need to do is (with a full battery charge) as follows:

1.) bring the engine up to temp, shut it off.
2.) Remove ECU/EFI fuse
3.) Remove Spark Plugs
4.) Plug test tool into a spark plug hole
5.) Press down on the throttle 100%, then crank the car 4-7 times, until the needle on the compression gauge stops rising

Record your number, and move on to the next cylinder. Depending on model and engine type (turbo or not) compression numbers change. They should all be relatively the same and not have more difference than like 20psi across cylinders. I believe the minimum for an 850 turbo is 156psi.

[Rule 308]

There is a remote starter connection on the car, depending upon year model it will either be on the front of the the DLC (data link connector or the "blink box")connector over by the washer reservoir (early model) or on the later ones it will be in the fuse/relay box by the left strut tower. It is a single spade connector, hook a jumper wire to one end and your remote starter to the other, hit the button and it cranks. So long as the key is off you will not have to worry about the ignition or injection running. Like Chopper said you will want to have the throttle locked open so the engine can breathe and is not sucking against a closed throttle plate. When you crank it around make sure you are consistent, if you look up the specifics on compression testing you will find that often times it is recommended that you crank each piston 4 revs and note your number. I have seen plenty of people who crank them until the guage stops as well. Remember, when that engine is running it does not get 4-7 attempts to bring that compression all the way up before it fires it off, so take a look at those numbers as you are cranking and don't be afraid to do it a couple of ways while you are in there. Often times I will do just that, crank it 4 revs, note the number, realease the pressure, and then crank it 6-7 times or until the guage quits rising and note that number as well. If your numbers come out OK or maybe a little inconclusive I would consider doing a cylinder leak down test on it. I don't know if you are familiar with it or not but it is a tool similar to the compression tester. You screw a hose into the spark plug port when the piston is at TDC compression and then you pressurize the cylinder. The tool has two guages on it, one to show inlet pressure and one to show what the actaul pressure in the chamber is. So if you have 100 PSI going in and the actual pressure in the chamber is 75PSI then you are loosing 25% of what you are putting in there, not good. I forget that exact specs off the top of my head but anything under a 10% loss should be OK. Now if you are leaking a bunch you have to figure out where it is going, passed the rings and into the crankcase, passed an open valve and into the intake manifold? This where it gets a little gray as you are listening for the sound of escaping air and typically it will sound like there is a little coming from everywhere i.e. dipstick tube, oil fill cap, throttle body etc. Oh yeah, the easiest way to find TDC COMPRESSION stroke is with a whistle screwed into the spark plug hole (yeah, they make such a tool). It will whistle when you are coming up onto compression and not when you are coming up onto exhaust.

Edited by Rule 308, 27 April 2004 - 09:05 AM.

[tenn850]

I disconnected the fuel before doing compression test. Remove the fuel pump relay while the engine is running and wait for it to die. Like this you do not have fuel pressure and won't flood or damage the CAT.

For 850 NA engine it should be arround 170-190 psi max. For Turbo it is lower since it is 2.3 litter engines.

Read the first reading (stop) on the gauge since that is your first stroke compression. Then read the max, after 2-3 strokes. Then if a cylinder shows low values, put a table spoon of oil (engine oil Daa!! ) from the plug whole and do the test again. If this improves the compression then you have piston ring leaks.

The engine needs to be warm when you do this, so the metal expands as it should during normal operation. Remove the plug only on the cylinder you test, some mechanics suggest.

Edited by tenn850, 28 April 2004 - 03:26 PM.

[Chopper]

I disconnected the fuel before doing compression test. Remove the fuel pump relay while the engine is running and wait for it to die. Like this you do not have fuel pressure and won't flood or damage the CAT.

For 850 NA engine it should be arround 170-190 psi max. For Turbo it is lower since it is 2.3 litter engines.

Read the first reading (stop) on the gauge since that is your first stroke compression. Then read the max, after 2-3 strokes.

ECU fuse will do same thing as fuel relay, but with much less hassle. You don't have to run it until the car dies.

2-3 strokes may not be enough...sometimes that works for me, sometimes it takes as many as 6.