Curious, how many times did you crank the motor over? Was the reading still climbing when you stopped? Where'd you get the tool from?



My dip stick was leaking and it was annoying as heck. Replaced it with a new one because the seal at the very top was shot. Do your valve covers have decent baffling? What kind of breather cap?

 

You are right about the atmospheric pressure having an effect. I'm in Denver at 5280 and my results would be 115-125 on an engine where most people got 140-150 at sea level. 8400ft is pretty high so the effect would be even more.

Also it could just be the gauge not being super accurate.

I think you're fine.

 

A larger overlap cam and or cam timing will lower cranking compression, also the tthrottle needs to be wide open during the test.

 

• 1000' = .9711
• 2000' = .9428
• 3000' = .9151
• 4000' = .8881
• 5000' = .8617
• 6000' = .8359
• 7000' = .8106
• 8000' = .7860
  multiply your readings by 1.214

Blowing out places like the oil dipstick or valve cover gaskets indicates that you don't have a correctly flowing PCV set up for whatever reason.

 

Where here does your pcv line run to perhaps?

 

Ignition timing will have no effect on a compression test.

Compression test should be done with all 8 plugs removed, the throttle plates blocked wide open, the engine warm, and the battery fully charged. Crank the engine until the needle stops rising. Most of the time that is around 12 revolutions (6 compression "strokes"). You can hear them as they occur.

You're readings are GREAT as far as cylinder variation goes, and if all the cylinders only increase 5psi with oil added that's an indication that ring sealing is fine too. Yes, the altitude will affect the overall reading and if the motor runs well, doesn't smoke or foul plugs, etc., I wouldn't worry.

Just FYI - the '85 5.0HO in my '66 is a reman that now has about 10k on it. If I go out thrashing on it my driver's side valve cover will be wet with oil mist from my open breather cap/oil filler, my dipstick will be pushed up out of the tube by a couple inches, and my PCV grommet will be "leaky". This isn't really out of the ordinary. The PCV system operates at it's best when decelerating or at idle and it's WORST at WOT, since the vacuum is low. Sure, it's wide open, but there ain't a lot of "suck" there so some extra blow-by finds other places to go.

I wouldn't worry too much and just keep a nice, absorbent towel in the trunk.

 

Have you tried measuring vacuum at your PCV hookup?

 

Sears sells a nice Craftman brand compression gauge kit at a resemble price. Buy it and I'm willing to lay my money down that you will gain 25 to 30 psi across the board.

Z

 

Motor cranked over 8 times - gauge stopped climbing at 6 but I ran it to 8 every time just to be sure.

One tool was from O'Reillys, the other was from Harbor Freight. The O'Reillys tool is the one that only read 60psi, the Harbor Freight one is the one that read 100.

Didn't know there was a seal on the dipstick tube! Interesting, and something I'll have to check. The valve covers have never been an issue in the past and I believe that they have good baffling in them. They're older Cobra valve cover repros from sometime in the 80s or 90s, I believe. Breather cap is the standard chrome push-in type and it is brand new as of last week.

Atmospheric pressure factors in with your compression ratio to give you your pressure results from a test, correct? I recall reading somewhere that atmospheric pressure * compression ratio = cylinder psi in pressure test. So assuming I have a compression ratio of 9-10:1, and atmospheric pressure here is ~10.9, then 100 is right in the ballpark for the correct cylinder pressure. At sea level with atmospheric pressure of 14.7, the same engine would have a cylinder pressure of 130-150 or so.

 

PCV runs to the specified port on my throttle body EFI - there's only one that it could fit on. I read somewhere just now that some people are having to use a baby zip tie to hold the PCV out of the valve cover just a bit so it gets proper clearance with the baffles on some valve covers. So possibly my PCV valve is working, but getting blocked so it's not as effective as it should be? I'll try the zip tie trick to see if that helps at all.

Glad that my cylinder pressure readings were normal though... was fearing burned valves from all the ethanol I had to run through on my trip! I have no idea if this engine was built with hardened valve seats.

 

What's your vacuum reading at the hookup?

 

Kelly, it is not uncommon for people to remove the baffles in the cobra valve covers as they will interfere with some aftermarket roller rockers. Additionally the lower atmospheric pressure will make it easier for the system to blow oil out at WOT when there is insufficient vacuum through the PCV.

 

Kelly, it is not uncommon for people to remove the baffles in the cobra valve covers as they will interfere with some aftermarket roller rockers. Additionally the lower atmospheric pressure will make suck it easier for the system to blow oil out at WOT when there is insufficient vacuum through the PCV.

If you are using the older Scott Drake Cobra-Powered-By-Ford valve covers be advised that they have the worst oil baffle arrangement that I have ever come across. It is nothing like the original Cobra valve covers, or the stock Ford valve cover baffles.

I fought excessive oil consumption with those Scott Drake valve covers for years, spaced up the PCV valve, used an oil catch can , etc. But they suck oil like no other valve cover I've ever run across. I don't know if the newer Scott Drake valve covers are the same.


Z.

 

Agreed, for your altitude those compressions are fine.
If the engine were worn there would also be larger variations between cylinders since they don't wear evenly.

On the breather, might be worth checking the pipes are nice and clear. Sometimes stuff collects in them causing reduced efficiency at wider throttle openings whilst behaving fine at idle.

 

You may want to try a grommet that goes in the hole in your valve cover then your pcv goes into that, that has a slit in it that keeps from pulling oil and only pulls gases. Keeps the pcv clean. My Cleveland at idle would pull oil into the intake from the vlve cover till I used that grommet. Some, which I will set up this winter use a baffled oil catch can in between the PCV and intake and may need drained occasionally. I use an oil catch can on the front of my engine with a filter on top to pull fresh clean air through the system then out the pass side valve cover to the intake. There are no breathers just bungs for oil fill which are blocked off. no oil residue anywhere and no worries of blockage.

 

Here's an off the wall thought. As noted above, the compression seems good, but, IIRC, you've noted in various places that you feel like the car has incorrect mixture (despite EFI), poor brake booster performance, and oil seeping out as though the PCV isn't working. That all could be explained by a vacuum leak, possibly in the brake booster. It could also just be old car at 8400 feet...

 

Does the elevation affect vacuum? I bet the elevation is the root of the issues. You efi is probably going to be off for a while, because all your learning logs got populated at a much lower elevation. This is probably causing all your other problems. Vacuum could be low, causing the pcv and booster issue. Have you talked to the efi guys and see if they recommend anything? Maybe throw it back into a learning cycle?

 

I would think that your engine will still make enough vacuum for your pcv valve to work even up in the clouds up there where you are.

You may just need new valve cover gaskets for that problem. I have had problems with them leaking due to periodic valve lash checks until I got the new fangled Felpro's that have the steel core inside and metal inserts at the bolt holes. They are wonderful. No more valve cover leaks. I have had the valve covers off 3 times since I got these and they are still leak proof. I think the Felpro number is 1684.

I don't know if the stock 289 has the rubber dipstick seal or not. I have a chrome aftermarket one like below which has a cup on the dip stick and the rubber seal on the tube to help it seal better;

 

Working on getting my vacuum gauge - it's in the mail but mail takes a long time out in the sticks, apparently. Should've been here today but maybe tomorrow!

 

Its all been stated by other folks posting. Nothing new here:
Blow-by is usually created when piston rings become so worn they allow pressure from the combustion process to pressurize the internal engine. Some of your symptoms are textbook symptoms. Checking cylinder integrity with your compression check, or better yet, a leak down test is the key. The chart from macstang confirms what I googled as a reasonable ratio of variance at your altitude. Unsure what your compression should be, but with your minimal variance, I would lean towards PCV. the crankcase ventilating system must relieve internal pressures.On my drag boat, I have venturi tubes on my headers that dynamically lower the internal engine pressure instead of PCV, increasing ring seal.No doubt in my mind of its ability to increase power.At the most basic level, it makes a real difference in ring seal.When I test my PCV system, the engine's idle speed will drop 100 rpm..