what the hell is wrong with my car?

[wytbishop]

Come to think of it...throwing a BP in there would fix the problem...if it was less worn out than the engine you have in there now. Probably couldn't be any worse than what you have.

Funny story...one of the guys at the parts store I used to use long ago would always say "throw a new cam in it!" no matter what the issue was. More often than not, throwing a new cam in would have actually led to the solution...though it rarely needed a new cam.

True story. I was there.

[SuperK]

That was back in 1965, right, senor member?

[myfirstmazda]

well, I did a compression test. it was informative, but I don't quite know what to make of it. I tested cold, then warmed up the engine till the fan kicked on and tested again. Readings were as follows:

cold:
1: 120
2: 120
3: 130
4: 140

now the weird part:

hot:
1: 120
2: 120
3: 120
4: 120

the plugs in 3 & 4 were darker than the others, but why would their pressure drop when warm? (& yes, I know they're reading a little low)

[Ryan]

Those are terrible numbers.

anything under 140 is rebuild. Standard is 186.

Cold compression is meaningless, as the motor spends very little time running cold. You could stretch it to help support a diagnosis, but thats all.

The fact that they're all close together is comforting.

Have you done a leakdown test? Pour a table spoon of oil down the cyl and do the test again. The oil helps the rings seal. If the compression goes up, rings. If it doesn't change, your valves aren't sealing properly.

Those numbers alone are enough to point at rings... usually valves cause more random compression issues. A seriously bad lone cylinder.

[myfirstmazda]

I thought 135 was acceptable. I haven't put oil in the cylinders, mostly cause I didn't have a bottle handy. Other people I have asked about my problem suggested it may be related to the fuel pressure regulator. opinion? I don't have a tester, but I can get one.

[Ryan]

SOHC http://www.mx-3.com/manuals/showimg.php ... B1-010.gif" onclick="window.open(this.href);return false;
DOHC http://www.mx-3.com/manuals/showimg.php ... B1-010.gif" onclick="window.open(this.href);return false;

Either way, 120 isn't 135, and its even less 140.

A fuel pressure regulator does not affect compression.

Plus, it would probably fail-open, resulting in less fuel...

If you were burning fuel enough to cause it to smoke, you'd get like 150 km's on a tank...

Regardless, here is the procedure for testing the regulator: http://www.mx-3.com/manuals/showimg.php ... F1-120.gif" onclick="window.open(this.href);return false;

knock yourself out

[wytbishop]

Qu'elle suprise.

[myfirstmazda]

please explain to me how a set of worn-out rings can cause extra fuel to be pumped through the engine when cold. my understanding of rings is that when they are worn out, they will allow oil to go past them into the cylinders, but this gets worse as the engine gets hotter beacuse the oil gets thinner. there is an old forklift at work that does exactly this. it probably burns as much oil as it does gas by now. I'd bet it has compression in the 60's. I'm not trying to get an attitude again, but automotive engine control systems are a little confusing to me. see, when I said I was a mechanic, I should have specified. I am a tractor-trailer mechanic, mostly trailers. I have worked on cars, but I started getting confused when they started putting computers in them. anyway, I don't get how my low compression would cause the extra fuel. also, it's not like it's doing this all day long, just for about a minute. but yes, my mileage has dropped since this started. I've lost about 50 miles out of a tank.

[Savin]

My guess would be: Low compression > incomplete combustion > lack of power> car tries to make up for it by dumping more fuel. Any way you put it, it is almost definitely your rings. You compression rings are toast and your oil rings are probably not far behind.

[Ryan]

50 miles a tank can be accounted for by many many things. I guarantee you that 50 miles/tank are not accounting for visible incomplete combustion.

I can also guarantee you that you are burning oil at 120 psi. My black GS is at 150, and it burns it visibly. Much easier to see and smell it without a cat though...

How much are you getting per tank?

Any why are you so dead set on this over-fueling thing anyway?

[SuperK]

your loss of milage might be attributed to loss of compression. However it could be also the amount of ethanol they're dumping in the fuel. Call it conspiracy theory, in the winter my milage ALWAYS goes down. They say cold air gives you more power but less milage. The amount of ethanol they dump in fuel also seems to increase in the winter. Some people complain they can't find a darned gas station in the winter that doesn't put ethanol in the fuel... and ethanol does burn more inefficiently than dinoline. less compression, less power, more strain on the engine. It all interconnects, however your smoking is still attributed to burning substance other than fuel.

[myfirstmazda]

I really wish you guys could smell this stuff- it's definitely not oil. I have been around lots of engines that burn oil, and this ain't it. the only thing being consumed at an abnormal rate is the fuel. we already know it's not coolant. I mean, what else could it be?

[Ryan]

well, I still say oil, because no matter what you think, s--- has to make sense, and fuel doesn't make sense.

Unless you're getting ~200 km's to a tank, I would never say fuel.

If you're just waiting for us to agree with you, you'll be waiting a long time. So if you're dead set on fuel, go pick up a new set of injectors, an FPR, a coolant sensor, and O2's. If that doesn't fix it... well, I guess you're wrong.

[SuperK]

I wanna cry

[myfirstmazda]

if this was oil, it'd be knocking after a week at the rate it's burning. I'll keep ya posted.