1991 Toyota Tercel - Compression test too high

1991 Toyota Tercel

Ok, I've done a compression test several times on this car in the last
week or two and I'm getting numbers that are way too high. I'm doing
it properly from what I can tell, but I must be missing something. I'm
getting between 190 and 200 PSI, which means a compression ratio of
about 13-13.5:1 which is obviously wrong.

I just replaced the head gasket and the car runs absolutely fine. I
get the car warmed up, I remove all the spark plugs, unplug the fuel
injectors, screw in the tester and crank it over for 10 seconds or so.
The compression tester lurches a bunch and the gauge goes up every
compression stroke, it slows down around 190-200 and doesn't go up much
higher. The only thing I can imagine is that fuel is getting into the
cylinder and dieseling. I don't know what to think really. I've
tested the compression tester with my air compressor and it reads
correctly (+/- 3 PSI).

I assume you are only going 3 engine revolutions doing this, that is how a
compression test is done?
"Daniel Beardsley" > wrote in message
ups.com...
> 1991 Toyota Tercel
>
> Ok, I've done a compression test several times on this car in the last
> week or two and I'm getting numbers that are way too high. I'm doing
> it properly from what I can tell, but I must be missing something. I'm
> getting between 190 and 200 PSI, which means a compression ratio of
> about 13-13.5:1 which is obviously wrong.
>
> I just replaced the head gasket and the car runs absolutely fine. I
> get the car warmed up, I remove all the spark plugs, unplug the fuel
> injectors, screw in the tester and crank it over for 10 seconds or so.
> The compression tester lurches a bunch and the gauge goes up every
> compression stroke, it slows down around 190-200 and doesn't go up much
> higher. The only thing I can imagine is that fuel is getting into the
> cylinder and dieseling. I don't know what to think really. I've
> tested the compression tester with my air compressor and it reads
> correctly (+/- 3 PSI).
>
>



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Really? I was unaware... but why would the pressure continue to get
higher if the pressure in the tester = the cylinder pressure. In
fact, I would think that you'd want to make sure to go at least more
than 3 rotations (more than 1 compression stroke) cause on the first
stroke, a bit of the high pressure air flows into the tester reducing
the total pressure by a smidge.

By continually cranking the engine you can mask poorly seating valves or
rings as the additional pressure help to seal these areas, the standard has
always been three revs and about 60% of the final reading on the first
revolution is acceptable. Also make sure you hold the throttle open somehow.
"Danny Beardsley" > wrote in message
oups.com...
> Really? I was unaware... but why would the pressure continue to get
> higher if the pressure in the tester = the cylinder pressure. In
> fact, I would think that you'd want to make sure to go at least more
> than 3 rotations (more than 1 compression stroke) cause on the first
> stroke, a bit of the high pressure air flows into the tester reducing
> the total pressure by a smidge.
>




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What kind of compression guage are you using?
I've misread the dial on my analogue compression guage.
Once I figure out what was wrong it came out okay.

I also turn the engine over until the pressure stops rising - about 6 times.
It comes out fine, down 5% from new due to it's age.


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A decent screw in one with psi and Kilo Pascals (kpa). I've tested it
on an air compressor and it measures correctly. It's a simple dial
gauge wi increments from 30psi up to 300psi

Do you have a manual which tells you what it should be? I have a 4
cylinder GEO Tracker 1.6l and the service manual say standard 1400 kPa
(199 psi) Minimum 1200 kPa (170 psi). This engine runs on 87 octane.
Also remember the read will change based on cam timing.
Stan

Daniel Beardsley wrote:
>
> 1991 Toyota Tercel
>
> Ok, I've done a compression test several times on this car in the last
> week or two and I'm getting numbers that are way too high. I'm doing
> it properly from what I can tell, but I must be missing something. I'm
> getting between 190 and 200 PSI, which means a compression ratio of
> about 13-13.5:1 which is obviously wrong.
>
> I just replaced the head gasket and the car runs absolutely fine. I
> get the car warmed up, I remove all the spark plugs, unplug the fuel
> injectors, screw in the tester and crank it over for 10 seconds or so.
> The compression tester lurches a bunch and the gauge goes up every
> compression stroke, it slows down around 190-200 and doesn't go up much
> higher. The only thing I can imagine is that fuel is getting into the
> cylinder and dieseling. I don't know what to think really. I've
> tested the compression tester with my air compressor and it reads
> correctly (+/- 3 PSI).

I do have a manual, It's a Chiltons and it covers 1984 - 1995 I think,
so it's a quite a range, though they say it should 140-150 when brand
new. Note, this isn't the original engine, it was replaced by the
previous owner with a "30,000 mile" engine from japan. Maybe I should
just forget about it and just look at the numbers even if they seem too
high.

"Danny Beardsley" ) writes:
> I do have a manual, It's a Chiltons and it covers 1984 - 1995 I think,
> so it's a quite a range, though they say it should 140-150 when brand
> new. Note, this isn't the original engine, it was replaced by the
> previous owner with a "30,000 mile" engine from japan. Maybe I should
> just forget about it and just look at the numbers even if they seem too
> high.
>

I have Chilton's Import Car Manual for 1983-1990. For the '89 Tercel with
1456 cc engine it says compression of 184 psi but for all 1990 Toyotas it
says look at the sticker under the hood. It says the sticker numbers might
be changed during production so they trump any numbers in Chliton's
manuals.

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Solved.

Hum, I don't know why I didn't think of this before... I guess it's
been a while since I took a thermodynamics or physics class. The
gas-compression in a cylinder causes the gas to heat up and thus
increases it's pressure beyond the 8.9:1 volume ratio. infact, if the
process is totally adiabatic (no heat in the air is lost to the
cylinder walls), the pressure ratio should be about 8.9 ^ 1.4 = 21.3
times atmospheric pressure which gives about 313 psi. Under cranking
speeds, the process is pretty far from adiabatic, which is why the
pressure is lower...

I guess that solves the compression problem 200psi is fine, just me
over simplifying things.

Thanks everybody!