Low Compression in cylinder # 2.

sailaholic · Postby **sailaholic** » Mon Jan 20, 2014 2:12 pm

Ahh rogger. Hadn't thought about the bond failing between the inner and outer.

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hks_kansei · Postby **hks_kansei** » Mon Jan 20, 2014 2:27 pm

Probably something to keep an eye out on your other car too.
Common thing for a red motor to do, and I think it applies to the 253 as well (yours is a 253 isn't it?)

Postby **NitroDann** » Mon Jan 20, 2014 2:36 pm

IF you put something long thin and stiff like a long screwdriver or wire down the number 1 spark plug hole, vertically, you then turn the engine over and carefully find TDC. Its easier if you draw a few horizontal lines on the screwdriver so you can easier see it go up and down, because TDC to the degree is a VERY fine movement vertically.

So you find that and then check is the pulley timing marks line up with the timing belt cover timing marks and show top dead centre.

If the keyway is damaged (SUPER common on early 1600's) or if the rubber damper bond has started to fail (SUPER common on anything 20 years old) then the marks on the pulley will not be in the correct spot.

Because timing is done from the camshaft not the marks on the crank pulley timing is not affected UNLESS somebody has set the timing manually with a timing light. If they have changed it from factory based on incorrect timing marks due to a damaged or worn pulley they have just set the timing totally wrong.

However I think you have a valve issue or something not timing. But this test is free and you may get a surprise.

Dann

hks_kansei · Postby **hks_kansei** » Mon Jan 20, 2014 2:42 pm

NitroDann wrote:IF you put something long thin and stiff like a long screwdriver or wire down the number 1 spark plug hole, vertically, you then turn the engine over and carefully find TDC.

I'll just jump in and add, in case it's not clear to people who haven't done this before.

turn the engine over BY HAND

I just had mental pictures of somebody launching a screwdriver into orbit because they cranked it on the starter.

Postby **NitroDann** » Mon Jan 20, 2014 2:58 pm

Yes, and you HAVE TO turn it clockwise.

Anticlockwise will put the slack on the wrong side of the belt and give you a false reading by a few degrees.

Dann

speed · Postby **speed** » Mon Jan 20, 2014 6:46 pm

hks_kansei wrote:
NitroDann wrote:IF you put something long thin and stiff like a long screwdriver or wire down the number 1 spark plug hole, vertically, you then turn the engine over and carefully find TDC.

I'll just jump in and add, in case it's not clear to people who haven't done this before.

turn the engine over BY HAND

I just had mental pictures of somebody launching a screwdriver into orbit because they cranked it on the starter.

Ok, that part I knew but I understand the need to state it on a forum.
Thanks Dann

speed · Postby **speed** » Mon Jan 20, 2014 6:51 pm

manga_blue wrote:In closed loop (low-mid throttle and less than 4000rpm) the ECU uses just the O2 and ECT sensors to set mixture. In open loop (mid-full throttle or greater than 4000rpm) the ECU uses its inbuilt fuel map and AFM, IAT ad ECT sensors to set mixture.

What is the ECT sensor and where is it located?
Also is the IAT the idle control/stepper motor?

Thanks again.

manga_blue · Postby **manga_blue** » Mon Jan 20, 2014 7:21 pm

ECT = Engine Coolant Temp, Green connector at the back of the head on an NA6. Common fail point and when it fails it usually reads too cold so that the ECU maintains a rich (cold start) mixture.

IAT = Intake Air Temp. Built into the AFM in an NA6? Not really a common fail point.

speed · Postby **speed** » Tue Jan 21, 2014 7:07 pm

manga_blue wrote:ECT = Engine Coolant Temp, Green connector at the back of the head on an NA6. Common fail point and when it fails it usually reads too cold so that the ECU maintains a rich (cold start) mixture.
IAT = Intake Air Temp. Built into the AFM in an NA6? Not really a common fail point.

Thank you very much.

manga_blue · Postby **manga_blue** » Tue Jan 21, 2014 8:42 pm

It's easily tested.

speed · Postby **speed** » Wed Jan 22, 2014 3:32 pm

manga_blue wrote:It's easily tested.

You are a wealth of knowledge!
Part of me wishes that the car wasn't booked in tomorrow, so I can run more tests...

Once the problem is isolated, I'll let everyone know what it was.

Thanks for everyone's assistance

speed · Postby **speed** » Tue Jan 28, 2014 11:55 pm

manga_blue wrote:After that then:
Lean: Check entire intake system for air leaks, fuel pressure regulator weak, fuel pump pressure/delivery, injector blockages and spray patterns. Replace fuel filter and PCV valve.
Rich on closed loop: replace O2 sensor (single wire ones are only good for 60,000kms anyway), replace ECT sensor.
Rich on open loop: replace ECT, check AFM and IAT operation/voltages, fuel pressure regulator stuck

Mechanic has confirmed that my timing is actually correct.

Today I replaced the ECT sensor which seems to have improved performance.
Will change out the plugs (again) tomorrow and see where I'm at after a decent drive.

I've already replaced the O2 sensor and fuel filter, so I'm all good there.

Can anyone direct me to where I can find the specs for my AFM???

Figure I've come this far so may as well check the AFM, replace PCV valve, check the fuel pressure regulator, then injectors as was suggested to me by manga_blue.

Thanks again!

manga_blue · Postby **manga_blue** » Wed Jan 29, 2014 5:37 am

speed wrote:Can anyone direct me to where I can find the specs for my AFM???

Figure I've come this far so may as well check the AFM, replace PCV valve, check the fuel pressure regulator, then injectors

http://www.mediafire.com/?7ab5bsnenws155k
Full NA6 Mazda Factory manual. Password is bcotton. Check out Control System from page 270.