Lead down test, could use some help interpreting results

[jpcobe]

I did my first "leak" down test today (misspelling on the title, and I can't figure out how to change it). I used the 'stick something in the spark plug hole' method to find TDC. I think twice I missed it, but I repeated those cylinders. Based on my results, I think I've got problems. But I wanted to see if anyone could find a flaw in my process.

Equipment, OTC leak down tester that has two gauges, both in PSI. Pancake air compressor. I started at cylinder 1. That one I didn't follow instructions on (instructions on tester said to equalize left hand gauge at 90, I did 100 based on a YouTube video). I did that for cylinder 2 as well, I think. I followed the firing order listed on my intake manifold (1843572). After round 1, I started the motor to make sure I didn't screw anything up. then I did two more cylinders (3 and 2) once more. And as I sit and write this down, I see I missed cylinder 6. Damnit. Either way, here are my results for each:

Cylinder 1: Left gauge (LG) 100 (no notes after equalized), Right gauge (RG) 19
Cylinder 8: LG 100, RG 16
Cyl 4: LG 90 -->81 (after equalized), RG 14
Cyl 3: LG 90-->84, RG 15 (initial test tail pipe hiss, but I think I missed TDC)
Cyl 3, round 2: LG 90-->80, RG 43 (oil filler cap was blowing some smoke)
Cyl 5: LG 90-->85, RG 14 (a little hiss from carb, but again, might have missed TDC).
Cyl 7: LG 90-->80, RG 14 (tail pipe)
Cyl 2: LG 90-->72, RG 12 (carb hissed, I rotated motor until it stopped hissing, thinking I missed TDC again).
Cyl 2, round 2: LG 90-->78, RG 62, (oil filler cap hissing).

So, if my understanding is correct, if I missed TDC, I might hear hissing from carb or exhaust. But I shouldn't hear anything from the oil filler cap, even if I missed TDC, right? No bubbles in radiator.

I think I've got bad rings in cylinders 2 and 3. Maybe some valve problems in 5 and 7. But, I suspect those issues are more attributed to my noob status than engine problems.

Thoughts? I also took photos of my spark plugs for each cylinder, but can't figure out how to download them just right now. I saw a lot of carbon deposits on 3, and 2 looked light brown on the ceramic part.

Sorry for this mess of data. It's in a spreadsheet on my computer, but I don't know how to paste it. Anyway, am I looking at a rebuild? Or did jack my methods up so bad that I need to do it again? Thanks.

Jeff

jpcobe is online now Report Post

 

[hagar]

Your figures are really too hit and miss to be conclusive.
How many miles are on the AMC 304 , 5,000 0r AMC 150 ,000 ?
Did you do a compression test wet and dry and record those figures ?
Based on compression readings, the leakage test is them performed.
You are always going to have some leakage, even when at correct TDC.
A new or low mile engine could have acceptable limits of 8% to 10% per cylinder.
You really don't want to have readings above 10%, but wear and tear on your AMC 304 will dictate that.
The leakage test confirms valves or rings. The compression wet test will verify that as well.
If the air leakage is higher than normal, yes you can hear it blowing out intake or exhaust (valves) or back thru the crankcase (rings).
Maybe redo the leakage test and report back here.
Sometimes, as soon as you introduce air into the cylinder, the air will push the piston down and rotate the engine slightly. So it's really important to have each individual cylinder at TDC exactly.

 

[Posi]

The engine should be warm when doing a leak down or compression test, you didn't mention the engine was warm.

 

[jpcobe]

Odometer shows 85k. Engine was cold. I read multiple sites that said it's better to do warm, but cold will work--the readings will just be lower. I just got a compression tester as well, and will work on that next weekend. I expected some evidence from oil filler cap, but not as much as I got in cylinders 2 and 3. TDC shouldn't have made that much difference on those figures would it? The rings would still be expected to seal the cylinder up to the same degree. And twice I did notice the cylinder move when the air was introduced. I reset the cylinder and redid those.

Having said that, I appreciate the answers. I'll re-do the test warm and see what shows up. It was my first time doing it, so I wanted to get some feedback on my results/methods to see if I was missing a key step, or to find out if there was a big error.

Bottom line is I don't want to put a lot of money into a foundationally unsound engine. Things like carb work and new exhaust aren't too expensive really, but I don't want to do it on an engine that's about to go and have to do it again on a new one. I'm considering a 360 swap which could mitigate some of that. But, for now, I'm just trying to get to the bottom of my engine concerns before I make too many expensive choices.

Thanks again.

 

[Peanut Butter]

If I missed something along the way, I'm sorry, but what exactly are your engine trouble symptoms?

 

[Lumpy Grits]

Also-When crank'n the engine. Engine must be fully warmed up and have the throttle 100% open to draw the max amount of air/fuel it can.
Why are you do'n this test with only 85K on the engine?
LG

 

[jpcobe]

So, here's the background, which I didn't really cover. Bought Jeep with around 82k miles on the odometer. Had a number of leaks. I had all the gaskets replaced, still leaks. Motor had a lot of caked on oil, so hard to tell where its coming from. I had some vacuum leaks, had the carb rebuilt, worked for a while, then they came back. I haven't had trouble with that lately. Next, when driving with jeep at constant RPM, it seems to surge or miss, but I [don't] recall it backfiring. Gas odor pretty strong when starting, and fuel mileage is not great. However, lately I've been going about two miles one way, so it doesn't get fully warmed up. Plus, it's burning oil. It's noticeable out of the tail pipes. A few months ago, I replaced my oil filler cap, it was an aftermarket style without the rubber line connection. After a few drives, I would open the hood, and find it lying on the intake manifold. I haven't done any off-road driving, only street driving, so the only thing I can think of is maybe pressure-even though that doesn't make much sense to me. I know I'm not jarring it loose. I'm not a mechanic, but did some reading and understand a 'leak down' test is one way to judge engine health. I just got a compression tester as well, and will be working that, hopefully, next weekend. Past issues with the motor also included fuel boiling off the carb and out of the fuel line through the engine. I never had that problem with my old Camaro in high school, but this Jeep left me sitting at gas stations a couple of times. I relocated some fuel lines and that seemed to help. These new issues have me wondering if its worth chasing on this motor, or if it was perhaps just abused in its past, and needs a rebuild--that's the reason for the test. Plus, I enjoy learning DIY style, so this was an opportunity to get into things.

Since it is no longer my daily driver, I'm doing this work myself, but my learning curve is steep. Thanks again for the questions and the help.

 

[Torxhead]

A issue with surging or ignition missing could be a bad ignition control module. It is located just behind the coolant recovery bottle on the left fender well. One way to test its condition is to put your hand on it after a drive, it should not be hot to the touch. Sometimes a bad one will have some melted plastic seeping out of it.

 

[Turbogus]

Wow, and I though 'Black Betty' had issues. In my case it was only the carburator, thank Heavens.

 

[jpcobe]

LG--that would be for a compression test, correct? So far, I've only done the leak down test. Engine isn't running for that. I'll account for the throttle as noted when I do that. Thanks.

 

[Turbogus]

Had a number of leaks. I had all the gaskets replaced, still leaks. <~ Can you narrow down what is leaking; fuel, coolant, oil or fuel? I'm assuming oil.

Had the carb rebuilt, worked for a while, then they came back. <~ Was it a professional shop, a friend or gargage that did the rebuild? How thorough did they rebuild it? Did they just change the gaskets? Did they adjust the float and float drop? Verify needle and seat for correct stoppage and flow?
Next, when driving with jeep at constant RPM, it seems to surge or miss, but I recall it backfiring. <~If it was backfiring out of the carburator it may be a symptom of running too lean, while out of the tailpipe backfire can mean too rich of a mixture.

Gas odor pretty strong when starting, and fuel mileage is not great. <~ This may be an indication of running too rich.
Plus, it's burning oil. It's noticeable out of the tail pipes. <~ Is the color blue, or black? Again, if it's a rich condition the exhast fumes would be blackish in color, while blueish would normally be oil burning.

A few months ago, I replaced my oil filler cap, it was an aftermarket style without the rubber line connection. After a few drives, I would open the hood, and find it lying on the intake manifold. <~ This normally means that pressue is building up in the crankcase and the factory oil/breather cap makes for PCV, or Positive Crankcase Ventlilation. Lack of having this can leak to additional oil leakage so this would be one thing I'd address right away.

I've never accomplished a leak down test before and there's folks on this forum and elsewhere that'll certainly have detailed information about procedures.

Plus, I enjoy learning DIY style, so this was an opportunity to get into things. ~ Way to go, early on back in the 80's I had a mentor that was a mechanic on a dirt track oval team in the '60's that was invaluable tome back then.

When you can, please post photos of what is going on an it'll help others discern more easily whats going on.

 

[Lumpy Grits]

LG--that would be for a compression test, correct? So far, I've only done the leak down test. Engine isn't running for that. I'll account for the throttle as noted when I do that. Thanks.

You should do a comp test then a leak-down.
You don't run an engine for a comp-test-EVER. Just 'crank' it.
You need to 'fill' the cylinder to measure the time it takes to 'drop' psi.
Have you look'd for vacuum leaks? As that's what it sounds like you have IMHO.
LG

 

[mtnwhlr]

Sounds like you have carb problems and it needs a rebuild and it blowing the oil cap off sounds like pressure building up do you have a PCV valve and a vent

 

[jpcobe]

Thanks all. Correction: I'm tracking engine isn't running for compression test-I miss rwrote that...meant turning over. Thanks for clarifying though.

Carb. A shop in town rebuilt. I don't know to what level they did it. That was in KS, I've since moved to KY, but it was last spring.

PVC. Best I can tell the stuff is there, but at least one hose is plugged coming out of the intake manifold. I don't know what it is-might be that? It's behind the carb.

Leaks: oil. I've not seen coolant. I've not seen fuel. Rear main was a big culprit before, along with valve covers. Replaced, valve covers a little damp on one side (can't remember which). Still dripping from rear, but can't be sure if it's old or new. I think one may take some elbow grease, and degreaser to clean it up so I can tell.

Tailpiece smoke is blue or white- I never could distinguish. I'm thinking more blue. But with colder temps and condensation I can't really tell. That said, my coolant is never low.

Filler cap is same as it had when purchased. Not factory. I don't have factory air cleaner either. This one has felt and holes in the bottom lip that I think is supposed to allow it to vent...but probably not emissions friendly. Is that where the line I have plugged goes?

I appreciate the help. I'll get pics with my iPhone tomorrow and try and post of my intake and let you have a look.

Cylinder #3...looks bad to me, but don't know how to read it.

 

[Turbogus]

'Black Betty' came with a large K&N housing and filter that I still use (recharged periodically) and with some plumbing bits from NAPA including hose nipples I was able to make a solid connection to the bottom of the air cleaner using scissor cut gaskets and it's worked well. This was one of my first mods, I can take pictures if you need a reference.

In your attached photo the insolator of the plug looks to have good color, but I do see traces of oil (or fuel?) around the rim.

 

[Torxhead]

Jpcobe, you might just want look look up on how to read spark plug deposits on the www. Along with how to use a vacuum gauge for further engine analysis.

 

[Lumpy Grits]

What is the plug make and the number on the side?
I have run Autolite 985 in mine for decades.
X2 on learning to use/read a vacuum gauge.
LG

 

[jpcobe]

I tried checking out spark plug pics on a few sites. Mine weren't represented well enough for me to tell. But, now worries, I'll keep after it. When I was flying, we always had a vacuum gauge in the cockpit, and I'm wondering why we haven't done this in cars. I may mount one in the Jeep. First, I'll take the advise and do a test.

As for the spark plugs, these are all Champions, I'll have to check the numbers next time I pull them.

Work is crazy this week, and will be for a few more, and I haven't been getting home before dark, so I'll get after some of this on Saturday/Sunday to see where I'm at. Hopefully I can do a compression test and post a pic of my intake at a minimum.

I appreciate the suggestions.

 

[Turbogus]

Perhaps I've just had bad luck over the years but Champion plugs haven't seem to work well on my Ford, Jeep and certainly my bike. On the Ford and Jeep I stick with Autolites and they seem to burn very well.

 

[Hedgehog]

Some of the very best plugs 've ever used were Champions. That's what is in my CJ right now. They were great in my Harley, lawn mowers, snow mobiles and chainsaws. The Ford Bronco got the best mileage with champion spark plugs.