How far off do you think a leakdown test is with a cold engine? Also how important is it to have the pistons all the way up the bore?

To get to all my plugs I have to pull the headers and I didn't want to mess around with pulling the headers on a hot engine, so I decided to do the leakdown test cold. This is what I got on the four I did last night... #1) 20% #3)65% #5)40% #2)70%.... #1 was done at TDC and the others were all done with me being able to spin the pushrods, so the valves shouldn't be cracked open at all. It's a snapon leakdown tester, a nice peice that I borrowed from a local shop owner/racer. The sound on the air leak all seemed like it was going through the cylinders, not the valves.

I've been having some REAL bad runinng problems. I guess it could be possible that it washed down the cylinder walls with this running problem, but I still think that maybe the horrid leakdown was the cause of the running problem in the first place. Whats odd, is with leakdown's this high, it seems like the engine would show some obvious signs like a bad miss, uneven sounding cranking, excess oil consumption, blowing smoke out of the breathers/dipstick, even with the PCV connected... but I'm not getting any of this stuff. Uses a little oil, but nothing much. If on the highway only, (2500 rpm for hours and hours on end) it'll suck about half a quart every thousand miles, but still not enough to worry me too much. The running problem I've been fighting involved me making a PROM for a 26lb injector constant when I have 30lb SVO injecters so the engine is getting roughly 20% more fuel and its still running slightly lean according to the o2's. Also the MAF is only reading around 190gr/s at WOT so the engine is obviously not running well.

I've talked to some local guys and they claim with a cold engine the reading isn't as accurate but it should be CLOSE and fairly CONSISTENT. But I'm not so sure who to believe.

I'm thinking the next course or action is a compression test then maybe tear down time. Who thinks the engines trash?

 

just because the push rods can be turned by hand doesnt mean that the valves are sealing ... where the air is going will tell you where the problem most likely is ... is the air escaping from the carb. , the dip stick tube or the exaust pipe ... i almost always have to do leak down test on a cold eng. since they dont run by the time i see them ... the piston really should be at tdc (or slightly after) on its power stroke ... hope this helps ...let us know what you find ... tao

 

I like to see 5 being very good, 35 getting a little low. Cold test are ok but not a good as hot. The main thing is to do the test correct. The cylinder you are testing MUST be at top dead center, both valves closed and the connecting rod straight up and down.
Mark the flywheel 0 and 180 to know. then inject 100 psi into cylinder and how much are you loosing, they should be within 10 to 15 % of each other. On a wrecking yard motor, you may have to remove the valve covers and tap on the valves stem rocker to seat the valves better (knock off the crap from setting). Listen to the exhaust, cooling system, intake ==No noise! Slight noise from PCV or oil breather. All's ok or a problem with valves intake exhaust, head gasket if cooling system. Must be major to be piston rings etc.
Next, compression test. wet and dry
1. Throttle all the way open.
2. battery charger on
3. all cylinders dry
4. 3 to 4 squirts of oil 1 cyl at a time
5. turn off fuel or spark or both
6. crank 4 to 5 revelutions and watch the first puff, it should be half the total like 65 to 130 ok much less and you may have cam or breathing problems.
all should be within 10 %
also, the wet should not be more than 20 % of dry or ring wear excessive.
Ignore wet tests on low compression cylinders.
Ok, compression rule of thumb 125psi to 165psi OK
70psi just helping the engine
lower bad
Get the map right soon. the comupter can control or take a lot of fuel away.
If you do not have a scanner to see the data, get a heated O2 sensor, a bung ( to weld it the exhaust ), and an analog air/Fuel ratio meter from summit and you can see the mixture right now!

Then make some maps!
Having fun!!

 

Marked the balancer and did it according to the firing order.

New results:
1:22%
2:18%
3:16%
4:33%
5:28%
6:12%
7:18%
8:xxx

#4 was doing all sorts of weird stuff, 33% was the highest I got, but just a few degrees difference and it would show 50% even with the rockers removed. cylinder #8 just wasn't going to happen with AC being in the way so I couldn't get the fitting to start for the leakdown tester.

I know their a little high because of it being cold, but I still think I've got at least 2 cylinders that are screwed.

Oh well time for the 407! Anybody seen any good deals on retrofit hydrualic roller lifters anywhere? I'm really hating myself for not jumping on the 2 sets I saw for sale in the last year. I don't really want to run a flat tappet but that may be the only way I can afford to build it right now.

 

My father seems to disagree(something about tuition next year??), he thinks my engine is just fine despite the leakdown results.

Just a simple matter of opinion, with this amount of leakdown would it be possible to run some mid 12 second ET's? How much HP is this really making me lose? Mod's in sig...