Ran a relative compression test

[Strikeking10]

My Cobra has been burning a little oil on first start up in mornings and at WOT, from the research I did and the techs I talked to it looked like it would be my Valve guide seals, so ordered those and dropped it off at my local Ford dealership to do them, they pulled it in to start them and did a Relative Compression test and they called me to tell me the results, ive never seen it with %'s so idk how bad it really is but they are thinking something more serious inside the engine like rings or something and are recommending a rebuild. #5 is down 5%, #6 is down 3%, #2 and #7 are down only 1%

Anyone know how bad it really is? and sorry for the large picture I tried to flip it also but it didnt work.

 

[Crimson2v]

No way I would say that engine needs a rebuild just from a relative compression test. If you are concerned about the base engine, have a manual compression test done and a leak down test. These two tests will tell you the condition of the engine.

 

[Russo]

You need to do a manual compression test. Techs love to use IDS to do a compression test cause its the lazy way out.

 

[Crimson2v]

You need to do a manual compression test. Techs love to use IDS to do a compression test cause its the lazy way out.

I would say lazy or hacks run that test and when it shows a cylinder that is only 5% down says it needs a motor. Good mechanics do what I mentioned in my post.

 

[DSG2003Mach1]

we did a relative compression test on my motor while checking out some other things and one cylinder was down something similar to your #5, my tuner said it was no cause for alarm, obviously something was a little off but nothing to worry about at that point. It pounded out over 700hp that night

later on I suffered an oiling failure and had to tear down the motor, there was nothing obviously wrong or damaged in that cylinder

 

[Strikeking10]

From what ive been reading 5% in a car this old isnt anything to worry about, i can ask them to do a leak down test and see how it is, but should I just have them go ahead and do the valve guide seals and get those done so I can stop burning some oil?

 

[Crimson2v]

How much oil do you burn over an oil change interval? If it was mine I would not want to have to go into the motor for a slight oil consumption issue.

 

[Blueline]

Have you had the blower off lately? Our cars are notorious for smoke on start up and wot when the pcv system dumps oil over time and fills the lower intake, just a thought

 

[Strikeking10]

I haven't changed the oil yet but it is due for one so I'll check how much is in there, and I swapped out the blower for a Tvs 2 months ago

 

[Strikeking10]

Got a manual compression and leak down test done today. Any one have some recommendations as what to do?

Dry ..........with Oil squirted in
#1 190....... 215
#2 170....... 215
#3 180....... 215
#4 185....... 210
#5 135....... 185
#6 145....... 195
#7 185....... 220
#8 180....... 220

 

[brian97cobra]

your a little more than 12-15% difference in cylinders 5 and 6. could be a small leak in the headgasket under boost.

but your numbers are not terrible... but it shows the beginning signs of an issue.

id drive it til I was prepared to repair it. just don't beat on it.

 

[gmtech]

What were the results of the leakdown test? Did cylinders # 5 & #6 show excessive leakage? Compression results show an issue with 5 and 6 so the next thing would be to find out where its going?

 

[Strikeking10]

ill get all the details today when I pick it up later, it runs and drives great and has never had a issue, the TVS made 568/535 at 19.5 psi and 15 degrees of timing on 92 pump with the way it is now, ill most likely hold off till winter time to pull the engine, that way I can save up and do it right and upgrade everything also while im in there.

 

[Strikeking10]

Will be picking my car up tonight after work, they didnt do the leak down test just a wet and dry compression, they didnt see a need to do the leak down cause the engine would have to come apart anyways and we'd see the problem once its open, Ill probably just drive it a few more times to work then park it for the winter and then order everything I need.

I was thinking of getting a MMR rotating assembly either the 900 or 1000 and just use my block, cause i would like to run e85 and maybe nitrous eventually