Leak Down Test

[03 Cobra]

This is word for word that is on my recipe from ford. No techs were there for me to ask any questions.

Compression in Cylinders. Check and advise leak down check and found

(leak down test)
Cylinder %
1 = 5%
2 = 18%
3 = 5%
4 = 5%
5 = 5%
6 = 20%
7 = 24%
8 = 5%

Cylinders 2,6 & 7 leaking Passed the exhaust valves Did not hear any leakage in the block or intake, Recommend installing new Head

(RECAP This is the compression NOT DONE BY FORD nor is it on the recipe)

Cylinder PSI

1 = 148
2 = 148
3 = 148
4 = 138
5 = 148
6 = 115
7 = 125
8 = 125

 

[RD SNAKE]

might as well put some new pistons in there too!

 

[Steeda30]

Damn.

I have horrendous leakdown #'s on this engine (rebuilt) with 30k miles on it. It seems to run decent but the leakdown #'s indicate it's trashed. All are 30%-40% with one being 12%. Couldn't tell where it was leaking from. :shrug: Not sure why it'd be leaking down like this, nothing has happened to it.

 

[mike302]

I have bad valve seals too, im just going to go with the revised heads

(Don't know why they went out out of no where it just started to smoke up on start up went to get it checked and I was told my valve seals/Guides are out!)

 

[spincobra03]

can someone tell me what the numbers should be and what the percentage indicates. My guess is they are all supposed to be consistant with one another. Is 5 percent good??

 

[Steeda30]

5 to 10% of leakdown is considered good - they should all be somewhere around that. Compression #'s should be around 150-160 from what I've seen, some guys have 165-170. But as long as they're fairly consistent you're ok, I believe it's that the lowest cylinder be within 10% of the highest.

 

[03cobramanIII]

This is word for word that is on my recipe from ford. No techs were there for me to ask any questions.

Compression in Cylinders. Check and advise leak down check and found

(leak down test)
Cylinder %
1 = 5%
2 = 18%
3 = 5%
4 = 5%
5 = 5%
6 = 20%
7 = 24%
8 = 5%

Cylinders 2,6 & 7 leaking Passed the exhaust valves Did not hear any leakage in the block or intake, Recommend installing new Head

(RECAP This is the compression NOT DONE BY FORD nor is it on the recipe)

Cylinder PSI

1 = 148
2 = 148
3 = 148
4 = 138
5 = 148
6 = 115
7 = 125
8 = 125

you did have the piston on TDC right ? if its not dead on the motor will turn one way or the other .
not right.

i would drive it awhile and check 1 more time. jmo

 

[mike302]

I believe your engine should be warmed up(operating temps) and also take off the relay(fuse) for the fuel or press that fuel cut button in your trunk then do it again if it wasnt done when you did your compression check

 

[Steeda30]

you did have the piston on TDC right ? if its not dead on the motor will turn one way or the other .
not right.

i would drive it awhile and check 1 more time. jmo

I'm wondering if that's the cause of my terrible leakdown #'s. It was not in gear either.

 

[03cobramanIII]

I'm wondering if that's the cause of my terrible leakdown #'s. It was not in gear either.

if its not on tdc ,when you plug the air connector on , if its not right on tdc the motor will turn which ever way either backward to soon , or clockwise if to late its got to be just right so the motor dont turn
sometimes you can bump it get it on the 1 st 4th time , and sometimes it takes 20 times, a cylinder, to get it so it wont turn get a bump switch hook it to starter, thats the way i do it. and yes dont let the car cool down to much. good luck!

 

[Steeda30]

Well we used a socket on the crank pulley and stuck a long thin rod down into the cylinder and turned the crank until the rod stopped moving up and figured that was TDC? I may have them do it again, it was the shop that built the engine that did the test.

 

[03cobramanIII]

if the crank moves, it pushing the piston down to the bottom depending on what stroke its on one vavles close the other a valve is open.? i use the hose on the leak down when it blows my finger off i stop . like a said it takes awhile on some cylinders and some you can get and just a few bumps. ill do mine soon.

 

[03 Cobra]

you did have the piston on TDC right ? if its not dead on the motor will turn one way or the other .
not right.

i would drive it awhile and check 1 more time. jmo

I did not do the Leak Down Test my self. I had Ford do it and there for i am not sure if the piston was on TDC ( also I don't know what TDC is so I would not know any how LOL)

 

[Dana]

There are some inconsistancies between the two tests. This may indicate that the results are not as accurate as they could be. There does seem to be similarites between cyls # 7 & 6 though, so there is probably something going on inside.
New heads may not necessarily fix the problem. Pulling the heads will probably be the only way to determine just what the problem is though.

 

[mike302]

Sorry for changing the subject around a lil, but do bad valve seals/guides go out cause our cars to lose power(if yes about how much, a lot?) and does it cause us to lose Boost???

 

[Dana]

Sorry for changing the subject around a lil, but do bad valve seals/guides go out cause our cars to lose power(if yes about how much, a lot?) and does it cause us to lose Boost???

They would have to be really bad to cause any significant loss of power. The guides try to keep the valves straight and thus force the valves to seat correctly in the head when they close. If they are worn slightly, it probably doesn't have much impact on the closing position, but if worn an extreme amount, there could at least be alignment problems and thus leakage of the compressed mixture. The guides also force the valves to align properly with the rest of the valve train. Misalignment here can also cause loss of performance if extreme.
The second function of the guides and the seals is to prevent excessive amounts of oil from entering the combustion chamber. Oil doesn't produce the same HP as gasoline. As the seals (and guides) wear, more oil seeps past them and into the cylinder.
Worn seals are most obvious on startup, after the motor has been shut down for some time. When worn, they will produce a brief cloud of blueish smoke when the motor is restarted.
Extreme cases of worn seals/guides can foul spark plugs.

These are just the basics and I'm sure others can provide more technical descriptions.

Dana

 

[mike302]

They would have to be really bad to cause any significant loss of power. The guides try to keep the valves straight and thus force the valves to seat correctly in the head when they close. If they are worn slightly, it probably doesn't have much impact on the closing position, but if worn an extreme amount, there could at least be alignment problems and thus leakage of the compressed mixture. The guides also force the valves to align properly with the rest of the valve train. Misalignment here can also cause loss of performance if extreme.
The second function of the guides and the seals is to prevent excessive amounts of oil from entering the combustion chamber. Oil doesn't produce the same HP as gasoline. As the seals (and guides) wear, more oil seeps past them and into the cylinder.
Worn seals are most obvious on startup, after the motor has been shut down for some time. When worn, they will produce a brief cloud of blueish smoke when the motor is restarted.
Extreme cases of worn seals/guides can foul spark plugs.

These are just the basics and I'm sure others can provide more technical descriptions.

Dana

Thank You!:thumbsup: