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Old 06-17-2010, 10:49 PM   #1
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Default My 99 10th Anniversary engine runs as aweful as my spelling..

So a little bit of an introductary to my problem. My 10th Anniversary has 56,000 miles. Decided to do a little 60,000 mile maintainence, timing belt, bearings, seals, high-performance clutch, new head gasket, freshened head. Got my motor reassembled and damn it runs aweful... Now I don't have the oxygen sensors installed yet, but what I know is that it you run the car in short ten and ground then it doesn't rely on o2 signal anyways.

I did a compression check this afternoon with the warmed up motor, here is what I got.

no.1=200 psi.
no.2=190 psi.
no.3=200 psi.
no.4=200 psi.

What the hell is causing such a horrible idle and a miss, if I can't get this thing working, looks like i'll be buying a new motor. All I know is the engine was pretty much fine before I disassembled it and the ironic thing is the compression is much better than before.., in which a single cylinder never acheived over 190 psi.
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Old 06-17-2010, 11:01 PM   #2
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First thing that comes to my mind is that the cams aren't aligned properly with the timing belt.
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Old 06-17-2010, 11:17 PM   #3
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A new engine wont solve the problem, and be a pointless waste of your cash.

I agree, probably a bit off on the timing belt.

However, I would also check some other stuff. One of my first swaps, I did new TB gaskets. Put one on backwards, which basically created a massive vac leak. Car ran like absolute crap. So that item number one to check. Any time I have bad idle issues or weird boosting and AFR issues I ensure no vac leaks.

Next is plugs wires and coils. Then injector wiring. Then connections to things like cam/crank sensors.

Check the oil, any shavings in it?
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Old 06-17-2010, 11:55 PM   #4
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if I were off on timing then surely my compression readings would be poor. I am looking to ignition as the culprit to this bitch, that or the mass air flow meter...

Also, i've done several timing belt jobs and thats a mistake I just don't make all the time... We will see... And does anybody not agree that those compression readings are outstanding... 200 psi with only 5 percent difference between cylinders...
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Old 06-18-2010, 12:39 AM   #5
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Its ******* awesome, which is why you should keep the engine and all this work you have done
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Old 06-18-2010, 03:45 AM   #6
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What kind of vacuum is it pulling down at idle? is the needle fluttering or fluctuating much?
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Old 06-18-2010, 08:59 AM   #7
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if your intake cam is set to open too early, it may have a 'positive effect' on your compression numbers, making them higher than average (200 is higher than average) because the valves will be closing closer to BDC instead of after BDC. When the engine is spinning at a decent speed, (in the powerband) you want the intake valves to be open until slightly after BDC.

your exhaust valves open at the bottom of the stroke and close at the top. a misaligned exhaust cam will not affect compression numbers.

Bottom line: Your timing is off.
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Old 06-18-2010, 05:27 PM   #8
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Timing is off.
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Old 06-19-2010, 04:41 AM   #9
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Ah, who has been dicking around with my thread subject? I know I didn't do that, lol.

Well good news! Problem has been resolved, I double checked my intake manifold and found that I forgot to re-install two vacuum tubes, one that has something to do with the visc, as well as the 3/16 line that leads to the cruise control. This obviously improved my idle considerably, but the engine still had a slight and random miss. So, I purchased new BKR-5E11 spark plugs and a new set of wires. Problem solved. Idle is perfect...

So I took it for a test drive in open loop, as I have yet to weld the primary
O2 bung into my MSM exhaust, but I was very impressed and the car feels noticably stronger than it did when I first bought it, best of all , that by replacing the head gasket, I was able to eliminate the coolant boiling over. (Cylinder pressure?)

All this and a shame that I have a fellow paying 9000 dollars for the car, but he will be getting one unique little 10th Anniversary. 56,000 miles. 200 psi compression with less than 5% tolerance between cylinders.

Interesting fact is that the 04-05 Mazdaspeed Miata exhaust system (downpipe, midpipe, and muffler) is a complete bolt-on to the 99-2000 cast iron manifold and possibly 2001-2005 tubular style as well. It's not a real free flowing exhaust on the turbocharged miata, but the 2.25 diameter tubing of the msm exhaust works great on a naturally aspirated Miata and it has a very nice sound to it as well! True the baffling is different in the MSM mufflers, but I didn't hear any raspy or droining noises.
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