cylinder psi test

texmirage · Jul 24, 2011

Went to Autozone and rented a compression test tool pulled all the plugs out and tested each cylinder. turned the car over a few seconds then went ot the next cylinder. They all came out to be 75.
Can a car run well with numbers that low?
The car is all stock with x pipe and flows welded in. 94 gt convertable it runs 9.5 in the 1/8th consistently(I don't know if thats good or not)

I do have a issue with the car running hotter that usual. it never over heats but gets to halfway point often. ive changed ever having to do with water except the radiator.

Sorry for the long story but just trying to give as much detail as I could. Oh! and the car has about 270k.

HISSIN50 · Jul 24, 2011

Was the car up to temperature?
Did you let the reading max out before shutting the key off?
Was the throttle propped wide open?
Was there a charger on the battery between each test?
Was the test done dry and then wet?

texmirage · Jul 24, 2011

DANG IT!!!!!!!! THROTTLE WAS NOT OPEN. you my friend are a life saver

HISSIN50 · Jul 24, 2011

It's not that big of a deal but little things add up. The biggest variables are obviously being sure the gauge is allowed to max-out its reading and that the motor is hot (though hyper pistons don't see as much thermal delta as forged pistons do).

texmirage · Jul 25, 2011

Wel they all went up to 90. lol

Zero Signal · Jul 25, 2011

They should still be over 100. My motor is in bad shape and will pull 105-130. I healthy stock motor at 100k miles may be in the 150 range.

revhead347 · Jul 25, 2011

That's still real low. I think the engine is a little to worn. Certainly not worth modifying if it's just going to lose that much energy.

Kurt

texmirage · Jul 25, 2011

Yeah.... I'm not too worried about it. It still gets me from point a-b(work) very reliably. I have an explorer v8 motor I was thinking about having rebuilt then just putting that in the car. then i'd have a fresh motor. This way I can do it a little at a time. All I want to do the car is gt 40 heads, intake, and cam. I wont do much to it other than that.

HISSIN50 · Jul 25, 2011

You might want to test the gauge on another car to be sure that it sees a normal reading (to rule out an issue with the gauge or some other issue that's affecting the results).

VibrantRedGT · Jul 25, 2011

Well if the numbers are consistent in all cylinders it's much better then one or two be extremely low. In other words if you pulled 90psi in all the cylinders then one cylinder was like 25psi it probably wouldn't be your daily driver for much longer.

texmirage · Jul 25, 2011

VibrantRedGT said:
Well if the numbers are consistent in all cylinders it's much better then one or two be extremely low.

Thats why i'm not really worried about too worried about it. But i'll be looking to freshin it up at the end of the year, my son will be driving it to school in a year or so.

texmirage · Aug 3, 2011

ok.... the 90psi was annoying me because I know the motor is healthier than that, so I checked my timing. WAAAAAAY off! this is how bad it is...
you know where the timing check point is(left ofthe Harm. bal). Well it turns out I couldnt read ity well because when the timing light hit the TDC mark is hitting on the RIGHT side of the Harm. bal. I think what MIGHT have happened is I didn't take out the spout when I replaced the chain and set the timing. at least I potential issue to cure my 90 psi. lol better than a rebuild

HISSIN50 · Aug 3, 2011

I'm not sure I follow your logic here.

Chythar · Aug 3, 2011

texmirage said:
ok.... the 90psi was annoying me because I know the motor is healthier than that, so I checked my timing. WAAAAAAY off! this is how bad it is...
you know where the timing check point is(left ofthe Harm. bal). Well it turns out I couldnt read ity well because when the timing light hit the TDC mark is hitting on the RIGHT side of the Harm. bal. I think what MIGHT have happened is I didn't take out the spout when I replaced the chain and set the timing. at least I potential issue to cure my 90 psi. lol better than a rebuild

I did that once, basically set my timing to be 10* ATDC rather then 10* BTDC. Car ran like poop at 10* ATDC, obviously. And as you know (now), always take out the SPOUT plug so the computer doesn't try to advance the timing when you're trying to set it.

texmirage · Aug 3, 2011

How did you fix it? pull the spout out then set the timing?

toyman · Aug 3, 2011

It's not clear to me where you are reading on the timing mark. From the attached image the timing is read from the straight edge on the far right of the pointer.

texmirage · Aug 3, 2011

That is where I TRY to read it.
Picture the top of the HB as 12 O'clock. The Correct place to read it (your picture) would be close to the 11 O'clock position. When I put my timing light on mine there is nothing there. My degree marks read about the 1 O'clock position. Sorry if im confusing you guys.

toyman · Aug 3, 2011

Is your pointer missing? You just read the timing at the straight edge which would be close "just before 12 o'clock" ie. 10* BTDC.

texmirage · Aug 4, 2011

I'll take a picture today that'll make it easier.

Zero Signal · Aug 5, 2011

I think he's saying that when the timing light flashes, the degree marks aren't even visible under the pointer, but can only be seen way over to the right at 1 o-clock which would make the timing off like 30°.

If your spout is out and your timing was off by that much, I don't see how it would run at all. Is your balancer the original? If so, the counterweight may have spun to make it that far off. Still, ignition timing won't change the compression reading. Cam timing might.

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