Compression test values too high - 1991 Toyota Tercel

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).

These values are absolutely OK for motor in good condition. It is caused by
velocity of air which is a little compressed even in bottom dead center.
My english is a little poor so somebody may explain it better.

J. Lejsek

"Daniel Beardsley" <dbeardsl@gmail.com> píse v diskusním príspevku
news:1114880981.664294.119120@o13g2000cwo.googlegroups.com...[color=blue]
> 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).
>[/color]

"Daniel Beardsley" <dbeardsl@gmail.com> wrote in message
news:1114880981.664294.119120@o13g2000cwo.googlegroups.com...[color=blue]
> 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).
>[/color]
Pressures sound about right - correct range is probably around 80 to 215
PSI. More important is the difference between cylinders, which should not
exceed 15 PSI.
--
Ray O
correct the return address punctuation to reply

"Ray O" <rokigawa@tristarassociatesDOT.com> wrote in message
news:1bfcf$4273fa8a$180fead6$23206@msgid.meganewsservers.com...[color=blue]
>
> "Daniel Beardsley" <dbeardsl@gmail.com> wrote in message
> news:1114880981.664294.119120@o13g2000cwo.googlegroups.com...[color=green]
> > 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).
> >[/color]
> Pressures sound about right - correct range is probably around 80 to 215
> PSI. More important is the difference between cylinders, which should not
> exceed 15 PSI.[/color]

You mean 180? I think also the difference is not so much PSI, but more like
10% between the highest and lowest rating?

I'm not sure what this engine specs are, it does have a specific compression
rating, you will have to look this up. If it is high than you most likely
have some carbon build up. You can remove carbon with water injection or a
product called Seafoam which works really well. Being that the car is 15
years old that's probably the cause.

If you use the Seafoam just feed it into the throttle body with a spray
bottle, or let it suck it out of the bottom half of a styrofoam cup using a
vacuum line to the TB. This will produce a LOT of white smoke, so beware.
Some people also feed the Seafoam into the cylinder, install the plugs and
crank the engine a few times, let it sit for 30 minutes and start the car.

I just rebuilt the engine and removed the carbon buildup in the
process. The compression ratio is supposed to be 9:1 and the Chiltons
manual says a brand new engine should get about 140 -150psi.. so yeah,
it's too high.

Interesting theory, that hadn't occrured to me. Though I don't think
that the air could be compressed that much in bottom dead center, but
your theory sounds the best so far... Except that I've done
compression tests on other cars and they always come out normal (100 -
130 psi), i.e. close to their designed compression ratios.

"Danny Beardsley" <dbeardsl@gmail.com> wrote in message
news:1114905585.608374.27320@f14g2000cwb.googlegroups.com...[color=blue]
> I just rebuilt the engine and removed the carbon buildup in the
> process. The compression ratio is supposed to be 9:1 and the Chiltons
> manual says a brand new engine should get about 140 -150psi.. so yeah,
> it's too high.[/color]

What exactly did you 'rebuild'? As far as somebody suggesting velocity of
the air, I highly doubt that has anything to do with it.

Danny Beardsley wrote:[color=blue]
> Interesting theory, that hadn't occrured to me. Though I don't think
> that the air could be compressed that much in bottom dead center, but
> your theory sounds the best so far... Except that I've done
> compression tests on other cars and they always come out normal (100 -
> 130 psi), i.e. close to their designed compression ratios.[/color]

Air in the cylinder is NOT pressurized at BDC. In fact, at cranking speeds,
you have no compression until the piston moves up the cylinder sufficient to
close the intake valve. Now ... if you have your valve timing off a tooth
where the intake is closing very shortly aft BDC, then cranking compression
will be higher than normal. Normal cranking compression with the throttle
OPEN is often in the 140 to 180 psi range. Closed throttle perhaps 30 psi
less.

I didn't rebuild the whole engine, but I did completely tear apart the
head and replaced all gaskets and seals (head gasket, valve stem oil
seals, intake gasket, exhaust gasket, ...) While I had the head off I
removed the carbon on the head and on top of each piston.

On 30 Apr 2005 10:09:41 -0700, "Daniel Beardsley"
<dbeardsl@gmail.com> wrote:
[color=blue]
>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).[/color]


Are you sure your calculations for the ratio are correct?
Does it seem to have a lot more power than before the rebuild? <g>
What octane gas are you running?
If you use the lowest available does it ping a lot?

....

I don't see why they wouldn't be correct, unless "compression ratio"
doesn't really mean what I think it means.
It runs a tad better, but not enough to justify the compression I'm
seeing, 13:1 is akin to putting a turbo on.
I'm using 87 regular. No, it sounds/runs beautifully.

"Josh" <nobody@noplacenowhere.never> wrote in message
news:NIGcnfIXUejPn-nfUSdV9g@ptd.net...[color=blue]
>
> "Ray O" <rokigawa@tristarassociatesDOT.com> wrote in message
> news:1bfcf$4273fa8a$180fead6$23206@msgid.meganewsservers.com...[color=green]
>>
>> "Daniel Beardsley" <dbeardsl@gmail.com> wrote in message
>> news:1114880981.664294.119120@o13g2000cwo.googlegroups.com...[color=darkred]
>> > 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).
>> >[/color]
>> Pressures sound about right - correct range is probably around 80 to 215
>> PSI. More important is the difference between cylinders, which should
>> not
>> exceed 15 PSI.[/color]
>
> You mean 180? I think also the difference is not so much PSI, but more
> like
> 10% between the highest and lowest rating?[/color]

Oops, typo - I meant to say 180. The problem with using a percentage
difference between the highest and lowest rating is that the allowable
difference varies with compression. 10% is a fair rule of thumb, 5 to 10
PSI difference is acceptable, 15 PSI difference is at the high end of
aceptable, whether it is a high compresison engine or not.
[color=blue]
>
> I'm not sure what this engine specs are, it does have a specific
> compression
> rating, you will have to look this up. If it is high than you most likely
> have some carbon build up. You can remove carbon with water injection or a
> product called Seafoam which works really well. Being that the car is 15
> years old that's probably the cause.[/color]

Since the OP replaced the head gasket, I would hope that whoever did the
work would not put it back together with a heavy crbon buildup on the
pistons or valves.[color=blue]
>[/color]

--
Ray O
correct the return address punctuation to reply

"Philip" <1chip-state1@earthlink.n0t> wrote in message
news:VGYce.2383$7F4.66@newsread2.news.atl.earthlink.net...[color=blue]
> Danny Beardsley wrote:[color=green]
>> Interesting theory, that hadn't occrured to me. Though I don't think
>> that the air could be compressed that much in bottom dead center, but
>> your theory sounds the best so far... Except that I've done
>> compression tests on other cars and they always come out normal (100 -
>> 130 psi), i.e. close to their designed compression ratios.[/color]
>
> Air in the cylinder is NOT pressurized at BDC. In fact, at cranking
> speeds, you have no compression until the piston moves up the cylinder
> sufficient to close the intake valve. Now ... if you have your valve
> timing off a tooth where the intake is closing very shortly aft BDC, then
> cranking compression will be higher than normal. Normal cranking
> compression with the throttle OPEN is often in the 140 to 180 psi range.
> Closed throttle perhaps 30 psi less.
>[/color]
Did someone machine the heads or did you use a non-OEM head gasket? Either
could account for higher compression.

If the engine runs properly without pinging, performance is good, and you do
not have excessive difference in compression between cylinders, I'd say
drive it.
--
Ray O
correct the return address punctuation to reply

On 1 May 2005 16:08:04 -0700, "Danny Beardsley" <dbeardsl@gmail.com>
wrote:
[color=blue]
>I don't see why they wouldn't be correct, unless "compression ratio"
>doesn't really mean what I think it means.[/color]

I only asked because I am ignorant of how to get the compression ratio
from the PSI produced in a cylinder.
[color=blue]
>It runs a tad better, but not enough to justify the compression I'm
>seeing, 13:1 is akin to putting a turbo on.[/color]

Or using the wrong gasket <g>
(Can you actually get a change of 4 or 5 to 1 from a gasket??!)
[color=blue]
>I'm using 87 regular. No, it sounds/runs beautifully.[/color]

Then as someone else suggested: Just drive it!

Seriously, if you had 13:1 ratio it should ping like hell on 87 octane
(Does a 91 Tercel have a knock sensor?).

In any event, good luck with the rebuilt engine.

....

You are doing something wrong, but the good news is you are doing the same
thing worng repeatedly and the test results are that all cylinders are
within as narrow range, and this is good.



"Daniel Beardsley" <dbeardsl@gmail.com> wrote in message
news:1114880981.664294.119120@o13g2000cwo.googlegroups.com...[color=blue]
> 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).
>[/color]