I'd say until you know it's blowing past the rings, don't prepare to point fingers. Ensure there are 19 teeth between cam marks and all the other physical timing shenanigans are sorted and confirmed. You already checked base timing several times so unless you index anything, roll with it.

For leakdown, listen for hissing at the dip stick or oil cap (rings). Listen to manifolds/runners and plenums (valves).

It seemed like your regiment for break in should have been fine if doing a bunch of vacuum pulls, you said you where up on a hill. But if it is rings, just re-hone, re-ring, try again.


But don't get too far ahead of yourself. Pressure test your charge piping, listen for leaks. Check timing, and check leakdown. Then develop a contingency knowing those results.
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timing off, as in the timing belt was off a tooth? otherwise the spark timing doesn't matter in a scenario where the spark plug is removed.

compression numbers are almost always worthless, you need to at least do dry/wet to see if adding oil raises the compression significantly in one cylinder vs the rest. That's a big indication the rings are tired.

I wanted to do a wet compression as well with a teaspoon of oil but friend didn't think it was necessary...

I'm just going to rent shit from autozone and deal with it myself. If the tools aren't the best is it's fine as long as results are consistent.

Re: timing being off, I meant if things are off a tooth on the belt, not the base timing on tuner studio.

timing belt teeth will fuck up a compression/leakdown check.

They'll fuck up a compression test, but in theory you can still do a leakdown test as long as they aren't off by a huge amount.

--Ian

That makes sense.

Devil's advocate.... It wouldnt localize to one cylinder with the rest within the expected spec if this was solely due to the timing right? Obviously it could be the timing AND something else correct?

Thanks for the help. I'm just trying to learn what the thought process is for diagnosing this kind of issue.

So I'll plan to do the leakdown (and dry/wet compression) and then the timing. If the timing is off, I'll plan to redo the compression and leakdown.

i would have expected all healthy cylinders to behave similarly regardless of timing mistakes

depending on the teeth positions, a valve could be open when you expect it to be closed... telling about a friend.

If you're going to check timing anyway why do leakdown/compression first? If you check timing first you won't have to redo anything if it's off.

it takes like 25 seconds to check the timing.

But that would mean all valves would be open when you'd expect it to be closed. A compression test would be similar between all cylinders still, right?

Did you do the compression test with the throttle open or closed?

I thought it was supposed to be done with the throttle open?

Check your valve lash. It's easy. And then triple check you mechanical timing. I know you checked before, but do it again anyway.

it is

Yup, pretty sure that's how I did it. Had things in flood clear mode even though I had the injector fuse and fuel pump relay pulled.

Is this a good way to do it? (From the FSM)

https://forum.miata.net/vb/attachmen...1&d=1422766539

Just do that and slip the feeler gauge under to see what the clearance is?

If I do end up having to measure the shims, I have micrometers.

Retard the valve lash?
​​​​​​Retard the leakdown?

I think we're still in retard the compression territory.

Just ordered a leakdown and compression tester so I can do ish at home. Going to borrow a friends compressor. Just as an aside, is a pancake compressor from harbor freight enough to do a leakdown? I think they're supposed to be good for 125 ish psi and you only need 100 to do a leakdown.

Is 125>100?

Just make sure that the tank/reservoir is a decent size. Since it'll be flowing a bit, you might run into the compressor kicking on all the time.