Did a leak down test on my motor, was having problems with a misfire, poor fuel mileage and smoking all the time. (blue smoke). Truck is a 85 f150 with a 89 engine which i made carbed. have a holley 4brl with clifford intake. Did the leakdown on cyl 1 and at tdc on the compression stroke. Applied about 65 70 psi down into the cyl. and immediately air came rushing out the oil cap. I also cked for air coming out the carb and tailpipe. none present just the oil cap and breathers. it was alot of air too, if i would put my hand over it and plug the hole air would try to push my hand off and would eventually come up outta the carb?? dont know why. same results on 3 other cyls. all at tdc on compression stroke. Compression test results are 90psi on cyl 1 with the choke plate open on the carb. 115 with it closed, once again dont know why. I dont suspect a burnt valve or anything, head is reman and has about 250 miles on it. what do you guys think. obviously something with the rings, broken, cracked piston?? let me know, time for a rebuild

 

sorry forgot. engine is a 4.9 liter

 

If the air is coming out the the oil filler it means the air is flowing past the compression rings.
In the world of aircraft engines, 80 psi input, with 75% loss max = 80 over 60 on the gauges.
Is this a home made tester or an aircraft leak down tester.

I did a leak down check on my 4.9, it was hard to find TDC as there are no marks for 120 deg and 240 deg on the fly wheel.

Jim, the aircraft mech

 

Hopefuly you only have stuck rings, that are stuck with carbon, here is something that may help, Take 50% ATF and 50% water and shake it together untill it looks like Pepto Bismul remove all the spark plugs, squirt about 5 oz into each CYL. rotate the crank by hand, let sit for about 5 min and rotate again, keep rotating the crank every few min for about 1 to 2 hrs, then get a old blanket and cover the top of the eng and heads, crank the starter for about 10 seconds to blow out the ATF water Mix, do a comp. check, if good, replace the spark plugs and start the eng, it will smoke like hell for a few mins, untill the atf burns out, add 1 quart of ATF to your eng oil, drain the eng oil after 500 miles, the aft is high detergent and will clean the inside of your engine. Water softens the carbon and the AFT cleans and lubs the rings, I have used this to unstick rings for over 35 years, it works great, if the problem is only the rings that are stuck/frozen with carbon. hope that helps, Chellie

 

all good info thanks will give it a try. also have a knockin/ clacking noise at 2600 rpm on up. that kinda concerns me though

 

That could be your timing chain, slapping the sides of the cover, normally an engines reciprocating parts will knock at any rpm. change the timing chain for sure

 

these motors have no chain, or belt, the crank gear and cam gear mesh together

 

Your right, I got it confused with the 4.6 the holley 4bl threw me off

 

That noise is very likely PISTON SLAP

WikiAnswers - How would you know if its piston slap

here is some info i found on the web to Diag the knock,


PKRWUD
Senior Member Join Date: Sep 1999
Location: Ventura, California
Vehicle: 1995 Ford F150
Posts: 3,078

A little info on bottom end engine noises:


Main Bearing Knock:
Main bearing knock is usually apparent when the engine is pulling hard, when an engine is started, during acceleration, or at speeds above 35 mph.

Loose Flywheel or Broken Flexplate:
A loose flywheel or broken flexplate can usually be detected by this procedure:
1) Advance engine idle to 2000 rpm.
2) Turn off the ignition switch.
3) When the engine has almost stopped, turn the switch on again.
4) Repeat this procedure several times.
5) If the flywheel is loose or the flexplate is broken, a distinct knock will be heard every time the ignition switch is turned back on.

Harmonic Balancer:
A separated harmonic balancer will generally produce a heavy rattling noise that can be heard at low speed.

Rod Knock:
Excessive connecting rod bearing clearance noises are usually a light rap or clatter much less in intensity than main bearing knocks and the loudest when the engine is "floating" or running with a light load at from 25 to 35 mph. The noise will become louder as engine speed is increased. By grounding out each of the spark plugs, one at a time, you can determine from which cylinder the noise is coming. The noise may not be eliminated entirely by grounding, but it will be reduced considerably in intensity. The easiest way to ground out the cylinders is by inserting a 1.5" piece of 5/32" vacuum hose on each terminal on the distributor cap, and then placing the spark plug wires over the vacuum hose. With the alligator clip end of a non-powered 12 volt test lamp attached to ground, touch the test light tip to the vacuum hose to ground out that cylinder.

Piston Slap:
Piston slap is loudest when the engine is cold, and lessens or disappears after the engine is warm. When driving the vehicle (at from 25 to 30 mph) the noise will increase in intensity as the throttle is opened and additional load is applied. To detect piston slap, try the following procedure:
1) Pour several ounces of 40 weight engine oil into the suspected cylinder(s).
2) Crank the engine for several revolutions with the ignition turned off. This will allow for the oil to work itself down past the rings and act as a cushion.
3) Install the spark plug(s).
4) Start the engine.
5) If the noise is eliminated, the engine has a piston slap condition.

Piston Pin Noises:
Piston pin noise is usually the result of excessive piston pin clearance. This will cause a sharp, metallic, double-knock sound most noticable when the engine is idling. Sometimes the noise is more audible at car speeds of from 25 to 35 mph. To test for excessive piston pin clearance noise, use this procedure:
1) Run the engine at idle speed.
2) Retard the spark to reduce the intensity of the knock.
3) Return the spark timing to the normal setting.
4) Short out each spark plug, one at a time. The double-knock sound will become more audible at the cylinder with the loose pin.

 

how many miles does the eng have ?

 

the guy i bought it from said it had 89k on it. i really have no way for sure of knowing so thats the best i can tell you

 

If you have high mileage, and i think you do, use Valvoline 20w60 raceing motor oil, it will help to cushion piston slap if thats what you have, i would use it any way, since your using a 4 bl carb, looks like you want to do some raceing

Valvoline XLD HI-VIS

Valvoline XLD Hi Vis is a 20w/60 high viscosity enhanced mineral oil . It is a shear stable lubricant designed for engines requiring a viscous lubricant . XLD Hi Vis is especially suited where oil consumption may be an issue .

XLD Hi Vis reduces oil consumption & maintains oil pressure in high mileage engines .

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just yesterday i put 20w 50 in it. didnt really do anything at all. sometimes oil psi drops to 18 psi when hot running it all day even with 20w50

 

Wow, its time for a overhaul you have lots of bearing clearance if 20w50 did not help to bring up the oil press up. Take care, Chellie