Engine Compression Testing

[retepsnikrep]

I tested the compression on by 250,000 mile engine today as part of a major service.

All cylinders came out around 235psi which seems quite high. Anyone else done the test? Results?

Couple of tappets a bit loose so sorted them.

One thing i did find was that spark plugs were the wrong ones, it had A plugs in a B head!!
Luckily I had a set of secondhand B plugs so have fitted those. I really should have checked them before now since i bought the car, so my own fault.

Yellow 120,000 mile car is having clutch changed next week and whilst gearbox is out i'm changing the IS bearing as well. I'll also add a couple of heat sensors to the IMA motor/rotor so I can monitor IMA temp in future.

[joecvt]

Peter, for compression testing, are you using the IMA motor or the 12v starter?....IIRC, you should be using the 12v starter or else the numbers will be higher.

JoeCVT = Just your average CVT owner

[retepsnikrep]

I don't understand why using the IMA makes much difference?

Yes it will reach peak pressure sooner, but it is still the same volume being compressed so the ultimate pressure should be the same. Ok i accept it might be slightly raised as it has less time to leak past the pistons/valves due to the faster cranking.

If the cranking speed makes a really significant difference it must makes testing on engines with 12v starters very inaccurate, as depending on cranking battery, starter wear, temp etc speed of engine will differ making any sort of comparisons between veihicles difficult.

The main purpose of todays exercise was to detect any wild imbalance which there doesn't appear to be so I'm happy.

[joecvt]

According to the service manual (Standards and Service Limits - Engine Assembly) Page 2-2 in my 2000 - 2003 manual, it says:

Compression: Pressure check at 250 rpm with wide open throttle. Turn off battery module switch to use starter motor. Minimum 128 psi, maximum variation 28 psi.....

Your numbers using the IMA are nearly double the minimum standard (according to the manual - 128 psi)

I know others have down this test recently....Perhaps they can post their compression test results here and note if this test was performed using the IMA motor or with the 12v starter (IMA disabled).

JoeCVT = Just your average CVT owner

[Willie Williford]

You also have to realize that starting with the IMA spins the engine at 1K rpm.
I checked mine a long time ago, I'll have to check the "thread" and see if I posted the results. Can't remember which page it was on.
Another INSIGHTER posted his number recently, but he was useing the IMA for starting and showed 200+ numbers also. I don't think he has retested with the 12V starter or posted as of yet.

HTH

Willie

[02insight]

I checked mine some time ago, and it was around 200psi, this was with the 12v starter, throttle wide open, and I let it crank about 7-8 times where the needle isnt increasing anymore.

I am guessing your fuel injectors are also already disconnected, because fuel in the cylinders may affect it as well.

also I think there might be a slight difference in psi between doing the test when engine is cold vs running temperature. I did mine when engine was hot.

[N2oExpresS2k]

I did it with the engine cold and fuel injectors unplugged last week and got 190 on all cylinders using IMA @ WOT. I really don't think it makes a difference whether you use the IMA or the 12 volt. The engine won't produce more pressure from the higher RPM, it will just get there faster IMO. BTW, I posted some info on the spark plug indexing thread you might find interesting. Just because you had the wrong letter spark plugs in your car doesn't mean they shouldn't be there. All OEM plugs have a little mark on them to show you the position of the ground electrode. This mark should be facing the injector side of the engine, i.e. open side of the plug should be facing the firewall. I spent 45 dollars at Honda when I bought the car to put OEM plugs in it and now i'm kicking myself when I checked their orientation.... All wrong, i'm getting much better MPG performance with 1.99 denso plugs from the auto parts store since they're indexed properly with indexing washers.

[eq1]

Adding my figures for posterity...

Compression test, 12 volt starter, fuel injectors disconnected, wide open throttle, about 5-10 revs, give or take, engine at operating temp:

dry:
1) 225 2) 225 3) 185
wet (with about 1 teaspoon motor oil poured down each hole):
1) 270 1st spin, 260 2nd 2) 260 1st spin, 240 2nd 3) 270 1st, 250 2nd.

I think the FSM specs are wrong; it's not 128 psi.

[Willie Williford]

They indicate............."minimum" compression........Not Maximum.
eq1.........Edit for miles on engine.
HTH
Willie

[Eli]

Yeah, the FSM specs are minimum allowable compression.

And yes, please post details about your engine.. model year and miles.