Leak Down Test Results

[TheUser]

I'm new to the 4.6L side; I used to post in the 5.0 forums a lot, but have been out of it for a couple years now.

2000 GT 4.6L.

Will not start. I did a leak down test with a harbor freight leak-down tester, and got varied results. I did all cylinders twice.

The throttle body was propped open, air filter/pipe off, dipstick out, and radiator cap off.

I found the compression stroke by installing the spark plug fitting w/ hose from the leak-down tester into cylinder #1 and cranked it over by hand until it blew air out. Then, I removed that, put a screwdriver in the spark plug hole and waited until it got as high as it would go.

Did the test, and just went around in firing order doing the same thing for each cylinder. Once I got the first round done, I was reminded that if the previous cylinder was on the compression stroke then the next cylinder in the firing order would be, so I went straight to the screwdriver to find TDC.

ANYWAY, lol, on to the horrible results:

**This test was done on a cold engine as the engine will not start. I suspected a blown head gasket before the test. No coolant in the oil, and I haven't seen any oil in the coolant, either.

#1 - Test 1: 35; Test 2: 50; Average: 43
#2 - Test 1: 53; Test 2: 55; Average: 54
#3 - Test 1: 43; Test 2: 50; Test 3: 70; Average: 54
#4 - Test 1: 55; Test 2: 73; Average: 64
#5 - Test 1: 55; Test 2: 75; Average: 65
#6 - Test 1: 52; Test 2: 60; Average: 56
#7 - Test 1: 53; Test 2: 54; Average: 54
#8 - Test 1: 68; Test 2: 70; Average: 69

During the first test, #3 caused air bubbles in the coolant, but didn't repeat in test 2 or 3 (that's why I tested the 3rd time).

The only other places I could hear leaking air was a little out of the intake on my cylinders, but nothing major. Also, each time there was air leaking from the spark plug hole of the cylinder I was testing.

I've read that about 10% leakdown is bad...why in the world would my numbers be so high?

This engine has a factory 38,000 miles.

 

[TheUser]

wow...this forum is dead compared to what the 5.0 forum was when I was last here...

 

[wmburns]

I wish more ppl would put as much effort into their posts as this. Very good.

Sorry for the delay. I wanted to make sure that I had time to respond in a way that did justice to your work.

My experience with the Harborfreight leak down tester is that the results depend greatly on how the initial calibration is done. As such, the results from test round to round can vary greatly.

However, if the calibration is not altered during the test, the results should still be useful to compare cylinder to cylinder. But it not obvious to me there's a cylinder to cylinder head gasket break.

The bubbles in the coolant is an important symptom IMO. As for why later tests did not give any bubbles, is it possible that all of the coolant had been pushed from the motor thus giving the air a direct path out the de-gas bottle? Thus the bubbles would not be seen.

What I'm having a hard time understanding is how this could be so bad as to keep the motor from starting. You would think it would start but run like crap.

What has been done to confirm the usual no start causes such as no CKP signal, no FRP signal, stuck closed IAC, bad MAF? Has spark and fuel injector pulse been confirmed?

 

[Maxpowers]

If there is no major oil in coolant or coolant in oil, one would think it would still start on a bad HG. Only other reason would be if too much coolant got in and hydro locked the motor.

Please give the whole story about what happend to get you to this point.

 

[TheUser]

I didn't include some of the info because I tried to just include the pertinent info and "cut to the chase" so to speak, but I do not have a problem elaborating:

Bought the car on craigslist (120 miles from my house). Test drove it down the street and back, but it didn't have the electric fan installed (radiator had been replaced), so the guy said not to go far so it didn't overheat.

Bought the car and went back to get it. I figured driving the highway w/o the fan would be fine since the fan should only be needed when you're not going fast enough to pull enough air across the radiator. Not in this case...the car got hot about 2 miles down the road, so I pulled over. Had my friend take me to the auto parts store and bought some wire and clips and bungied the fan to the radiator and wired it straight to the battery (just to get it home obviously).

No go. Got about another mile or so and it was smoking really bad, so bad that I couldn't see. Oil was leaking from somewhere on to the exhaust and burning off so bad that it filled the car and rolled from behind. The car was hot and just shut off. It would not restart.

I got it home on a trailer a few weeks later and it's sat since then. Cranks, but no start. I managed to catch the engine bay on fire while trying to do a compression test (coil packs still attached & gasoline from moving the fuel rail up a bit), but luckily it was just the gasoline that burned and I got it out before it did any real damage.

Really, I don't know that it's a blown head gasket causing the no start, but it started before all this happened, and I have no reason to believe the IAC or MAF are bad. I'll have to figure out what the other acronyms mean and make sure they're good.

My 91 did the same exact thing when I first got it...blown head gasket and ring, but it was supercharged at the time.

Thanks for the help guys.

As far as the harbor freight leak-down tester. I guess the recalibrating you're talking about is dialing it in to the "set" part on the the right gauge. I did that each time, so maybe I wasn't using the same calibration. Hmm. Something I'd use more often I would have bought a better one, but I'll use this a couple times and it will sit.

 

[TheUser]

Seems like if there were coolant in the cylinders, it would push out the spark plug hole when I rotate the crank.

 

[wmburns]

Did you save the results of the compression test?

It seems like to me with a fire on the top end, this opens up the possibilitiy of virturally anything going wrong. Have you checked the fuses? Have you confirmed spark? Have you confirmed injector pulse? Have you confirmed fuel pressure?

What happens if the throttle is held half way open during cranking?

What happens if the MAF is disconnected before cranking?

 

[Lugnuts]

Where exactly was the fire and was it just a flash or did it burn for a few seconds before you got it out? What did you use to put it out? Simple questions but can become relevant.
I would back up. Check same stuff you were used to with the 5.0 - fuel, air and spark. If you got all three then something should be happening. Even if cylinders are leaking down it should fire (pardon the expression). I would guess one is missing and step one will be to fine out which, then find out why the one is missing.