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Discussion Starter · #1 ·
120-105-115
125-115-115

Background: My fathers Car 94 PGT 190k miles. cared for, never beat. About 10k miles, took the car to a car repair shop, they were supposed to replace the timing belt tensioner etc... He paid for it, it was fine for about a week. Then car quit. I came to look at the car, the timing belt jumped off of the cam gears. I took the covers off, they only replaced the belt. Long story short, got the money back from the repair shop, then I put in all new pullies etc... whatever comes in the kit. No problems car ran great.

Recently, car was shut off, parked over night, then it wouldnt start the next day. Fuel Cutoff light is on. Checked compression, it was low, so i took the covers and all that off and the timing is dead on. Two marks on back cam lined up one on front is lined up and the crank is pointed right at the notch.

I guess I dont know where else to go to check where the compression could be going. Its low on the front and rear banks, so I guessed it wouldnt be the head gaskets, I will be checking oil shortly, but I would be amased.

Any ideas let me know. Thanks
 

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Any pics of the marks lined up ? I assume you took all the plugs out and tested each cyl with the throttle wide open and at least 8 compressions for the readings ?

Mazda's stated lowest compression figure is 140 for the v6, with a max difference between cyls of 20.
 

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Could just be the way you checked the compression. It is my understanding that engines just dont randomly lose all compression and fail to run one day out of the blue. (normally its on one cyl, maybe 2 if they are leaking together)
Also your timeing wont affect your compression test.

If the motor was running previously, check everything that could prevent it from running now.

Start with checking for spark.
Then check for fuel (take a off the hose thats bent in a U on the fuel rail, place a waterbottle on the line and crank the motor over a few sec.) Make sure fuel is pumping.
Next check timeing, you got it dead on it seems
If its an ATX, check the neutral safety switch, that thing has gave me a mess of problems on my car.
It could be somthing simple as a loose sensor.
 

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Also your timeing wont affect your compression test.
yes it will, if its pretty far off.

if the valves arent open/closed at the exact time they should be you wont get the full amount of air in or you will be letting some air out when its compressing.


from my experience it takes about 100 psi for motors to run. i was told buy my teacher at school that 60 is all a motor needs (cause thats where fuel atomizes), but i think hes full of shit.

x2 on making sure your reading the right numbers. those sounnd like 1 or 2'nd crank numbers.
 

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Discussion Starter · #6 ·
I dont have pics, but i have timed a few of these with no problems.

I did take out all of the plugs and turned the car over at least 8 times, with throttle open. THe compression would jump tp ~90 after the first crank but little after that maybe 10-20psi.

This car always had a problem with jumping time, so i figured that is what it was but it wasnt. Otherwise everything else is good. Any ideas to check, dcould it be head gaskets, that would be weird because both banks are doing it, i cant figure out what would affect both banks besides the belt.
 

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if it were a head gasket, i would not suspect that every cylinder would read that low.

have you tried putting a little motor oil in it and seeing what it bumps up to?

if it bumps up to like 140 or 150, try to start it.
Ive seen quite a few cars that the rings just lose their tension on and once started will work just fine.

but thats generally on cars that have sat for a long time, and older cars at that. Just sitting overnight should never cause what you said.
 
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