yes, ANOTHER "are these compression numbers ok"

redcoupe86 · 01-11-2006, 07:05 PM

I have an '86 carerra with 117,000 miles here are my numbers.
This was done with a engine that had been shut down 4-5 hours:

#3 = 160 #6 = 167
#2 = 152 #5 = 150
#1 = 160 #4 = 160

my only really concern is #6 - its 11% out.

I did the compression to #1 with the engine off for about and hour and the it read 175.

What do the lords of Porsche knowledge have for coment. Am I in any trouble here?

Joe Bob · Joe Bob's Garage

2 and 5 aren't that good either.....

I do it with ALL the plugs out with a HOT engine....

Did you consider tossing in a teaspoon on 30-40 weight oil and redo the low holes?

Do you have the equipment for a leak down?

aigel · aigel's Garage

Those numbers look just fine. If you calculate from the highest number 167, 150 is barely more than 10% away. I wouldnt' worry. If things go bad, you would have severe differences. Also consider uncertainty in the measurement.

George

aigel · aigel's Garage

Another rule says that you want all clinders within 20 PSI. You also make that rule.

George

redcoupe86 · 04:47 AM

Quote:

Originally posted by mikez
2 and 5 aren't that good either.....

I do it with ALL the plugs out with a HOT engine....

Did you consider tossing in a teaspoon on 30-40 weight oil and redo the low holes?

Do you have the equipment for a leak down?

What would be the best way to get oil in - I don't just want to put oil in at the top of the valve cover, there's alot of dust and stuff that would get pulled into the cylinder.

Any suggestions. Oh, all my plugs were out. As for the leakdown, what tools are necessary and how much do they cost?

Rot 911 · 01-12-2006, 05:05 AM

I don't see any concern with those numbers. But like Mike says, a warm engine will give you more accurate numbers than a cold engine. I would redo the test with the engine warm, but don't put oil in the cylinders. Oh and the throttle should be wide open.

redcoupe86 · 01-12-2006, 05:18 AM

Quote:

Originally posted by Kurt V
I don't see any concern with those numbers. But like Mike says, a warm engine will give you more accurate numbers than a cold engine. I would redo the test with the engine warm, but don't put oil in the cylinders. Oh and the throttle should be wide open.

Why would you not put oil in the cylinders? Do you mean not to do it by pouring down at the valve cover or just not at all?

Joe Bob · Joe Bob's Garage

Oil squirted in a low hole and a recheck showing a higher number tells you that the rings are the reason for the lower compression....and yes, WOT while testing.

Rot 911 · 01-12-2006, 05:34 AM

Quote:

Originally posted by redcoupe86
Why would you not put oil in the cylinders? Do you mean not to do it by pouring down at the valve cover or just not at all?

Because you want accurate compression numbers before you recheck with oil in the cylinders. And testing warm may give you higher numbers than what you are presently showing.

aigel · aigel's Garage

Is there any problems or syptoms with your engine? If not, I would not worry.

George

redcoupe86 · 08:35 AM

Well, interesting you ask. . .

When I had the car PPI'd it was in Houston. Not knowing who to have the owner take it to (I live in Louisiana) I looked on this site, found a name and I also asked the owner. The owner mentioned a name that was mentioned on this site so I sent it to that place (Kobe motors).

Well I drove down on the day of the PPI, if it was good I was going to purchase the car. When I got there the mechanic said he had already done the compression test (I did not get a leak down - I know I should have) and had the numbers all written down on a piece of paper. They read 150 across, no deviations and the paper had know greasy prints on it. If you've ever done a compression test yourself you know you dont do all 6 cylinders then right down the numbers, you do one, then right down the result then then next and so on. So the piece of paper should have had some grime on it. But it was spotless. In the excitement of the moment I didn't quite think of that on until later. However, I saw the compression tester on his work car so didn't think nothing of it. I figured he'd done the work.

So this fact has been nagging at me for a while. Plus the fact that in the lobby of the shop there was a picture of the car for sale - same car I was buying. Apparently they had worked on the car and knew the PO well.

Being new to Porsches and not know what one is suppose to sound and feel like (my location doesn't afford me the opportunity) I did a lot of reading and reasearch and looked the car over good. Understand that I drove to Houston two times to look and test drive the car.

Well since I've bought the car I've only put 450 miles on it. The last few times I drove it, with the excitement of the buy has worn off, I've begun to notice that the start up and idle before it warms up it rough and that when i blip the throttle the engine has this vibration I cant place. I've met two Pelicans here since I've bought the car and using their cars for reference and asking them quesions has made me wonder if I had dropped a cylinder due to this vibration I didn't see in their cars. Furthermore, I've notice this popping sound when I give it gas. Not when I acclerate mind you, just when I blip the throttle or at the end of acceleration. If I just sit there and blip the throttle it will pop a few times but once it gets that out of its system if I keep blipping it it wont pop. It will however pop on downshifts and sometimes on upshifts, but not as loud there. Yesterday I drove it alot and got it full warmed up and I noticed that the while it still popped on downshift sometimes it would not pop on blipping the throttle in neutral. So now my mind has startted to wonder if its a brocken head stud. So removing the valve covers and checking the studs is my next deal. BTW, what is the proper way to "check" head studs?

The two Pelican buddies came over earlier this week and looked over the hoses for vacuum leaks and check for exhaust leaks and didn't find anything of significanc.

Understand I have a Steve Wong chip and a Fabspeed exhaust with Cat bypass.

So all of my testing was to find out about the popping and the vibration I get when I goose it. The may or may not be related.

Wheeeeew, that was a lot of typeing

DW SD · 01-12-2006, 08:34 AM

Maybe you just need a tune up? An electrical miss will cause popping (unburned fuel in the exhaust causes popping, usually). Could be plugs, wires, distributor cap, rotor, etc. Your compression #s aren't perfect, but they are not bad, either. The engine should run smoothly with those numbers. If one was down at 130 or less, I'd be more concerned. Usually a bad cylinder is less than 1/2 of the others. Perfect is within a few percentage points of one another, but this is far from something to lose sleep over. Check it hot, do a tune up and drive it (while resting easy).

Doug

redcoupe86 · 08:50 AM

Quote:

Originally posted by DW SD
Maybe you just need a tune up? An electrical miss will cause popping (unburned fuel in the exhaust causes popping, usually). Could be plugs, wires, distributor cap, rotor, etc. Your compression #s aren't perfect, but they are not bad, either. The engine should run smoothly with those numbers. If one was down at 130 or less, I'd be more concerned. Usually a bad cylinder is less than 1/2 of the others. Perfect is within a few percentage points of one another, but this is far from something to lose sleep over. Check it hot, do a tune up and drive it (while resting easy).

Doug

"resting easy" - somthing hard to do when you think something is wrong!

I've had a few restless nights if you know what I mean.

I have put in new plugs and ignition wire, but not rotor or cap. What else is envolved on a "tune up". BTW, there are no Porsche shops around, my friends told me a one fella in town who works on peoples Porsches. I may need to get in contact with him.