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Discussion Starter #1
hey guys,

my parents own a 1992 mazda 929 3.0L with exactly 200, 000 miles on it. just today the car started having some trouble with very rough idling and burning of oil. i pulled the plugs and the passenger plug closest to the firewall was covered with oil (the piston was also fairly wet from what i could see through the plug hole). my dad bought a set of new wires for the car about 3 weeks ago so i got some plugs from the stock pile we have for the car and replaced them along with the wires. there's still a rough idle and burning of oil (i really wasn't expecting it to fix the burning of oil, but the rough idle). do you guys have any ideas as to what the problem could be?

thanks,


stan
 

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Discussion Starter #3
that's what i was afraid of, but is there a possiblity of something else causing the problem? i was also thinking that it could be the valve seals (any input on that).

thanks for you input glowing escape.
 

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A Leakdown test on that cyl will tell you if its a ring or valve seal problem. If the test is good for leakdown, probably a valve seal, bad probably the rings
 

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Discussion Starter #5
should i use a 100 psi source? what is an acceptable leakdown (2%-5%)?

what exactly does tdc mean when you set the crank/piston?

thanks for the info.
 

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tdc means when the piston is at top dead center you have to do a leak down with the piston at tdc on the compresion stroke , under well in the 10-15% is good but if its over 40% thats when you need to really worry but the closer to that 40% it is you know it .


Jurgen
 

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believe it or not, i worked on a car that 100% leakage in 2 cylinders out of 4 and still ran like a champ....just had to add coolant all the time. this was in a early dodge daytona (the fwd ones from the 80s and 90s). our teacher in college was like....this isn't supposed to work like that.

Wiz
 

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jarends00 said:
believe it or not, i worked on a car that 100% leakage in 2 cylinders out of 4 and still ran like a champ....just had to add coolant all the time. this was in a early dodge daytona (the fwd ones from the 80s and 90s). our teacher in college was like....this isn't supposed to work like that.

Wiz
you sure you guys couldt get thouse pistons on bdc maybe or the pressure was driveing the cylinder down caz at 100% whatever the air was going you didt say where it was going i dont see how it can run perfect with 100% on 2 cylinders
i had to do this on a contour today and number one was giveing me a little hard time to get it on tdc but i got it i got 13-15 psi on 3 cylinders and 35 psi on number one and it ran fine .


Jurgen
 

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Not sure about the pressure, or leakdown rate. To be honest, I usually let a shop do the leakdown test for me (one of the few tests I'm still not quite sure how to run).

TDC Refers to when the piston is at the top of it's travel (no more possible upward movement). There is a mark for the number 1 Cyl TDC on the crank usually, but the others, I'm not sure. On my bird I usually put a long WOODEN dowel in the spark plug hole and rotate the engine (by hand). The dowel will show you the travel of the piston. This works on the 4.6L because the spark plug holes are on the top of the engine. May be different on the Mazda.

Start with a compression test before you go to a leakdown test. This can tell you the same things, but in a different way. The procedure for this is in ANY Haynes manual under general engine overhaul procedures. If you don't have one, I'd be happy to type it out for you, its just kind of long.. let me know.
 

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Discussion Starter #10
thanks for all your help guyz.

Thumper91, thanks for the offer but i don't want to inconvience you so i'll find it on the net.

once again thanks
 
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