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In my #4 and #5 cylinders my compression is ~ 130 psi the rest are ~150. Why are these cylinders so low? Is motor f*cked?

Chris
 
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possibly the cylinder walls are screwed up because the car was running overly rich or detinating. You might need new rings? You might need new pistons, there could be a hairline crack in the ringland of the piston, who knows. How was the compression test ran?

i dont think that you would be able to tell what was wrong with your car just by a compressin test, you would need a mechanic to check things out.

But im no expert, so I might be wrong.
 
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no matter what condition your compression was tested under, the difference between each cylinder compression should be less than 15psi I think..check the manual again.
once you find out you have a low compression, it could be alot of things, but unless you have money and ready to do repair, dont even bother trying to guess what could be wrong IMO.
these compression #s are not the worst I've seen, you probably dont have a 430wrhp+ strong BPU, but the car should still pull pretty good into 360-380WRHP depending on the overall condition of your car.

I know its hard to get that # out of your head, but try not to freak out...you still OWN a supra, repair can be made anytime.

good luck

Jonas
 
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Zerosoul said:
no matter what condition your compression was tested under, the difference between each cylinder compression should be less than 15psi I think..check the manual again.
once you find out you have a low compression, it could be alot of things, but unless you have money and ready to do repair, dont even bother trying to guess what could be wrong IMO.
these compression #s are not the worst I've seen, you probably dont have a 430wrhp+ strong BPU, but the car should still pull pretty good into 360-380WRHP depending on the overall condition of your car.

I know its hard to get that # out of your head, but try not to freak out...you still OWN a supra, repair can be made anytime.

good luck

Jonas
Thanks for the support Jonas. I laid down 390 rwhp a few days ago with a boost leak. Is a mechanic the only way to determine what is wrong?

Chris
 

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DANKAHOLIK said:


Thanks for the support Jonas. I laid down 390 rwhp a few days ago with a boost leak. Is a mechanic the only way to determine what is wrong?

Chris
You can easily check if it a ring vs. valve issue by putting about a tablespoon of oil into the low cylinders(s) and repeating the test. If the numbers increase chances are the ring seal is poor, if they remain the same then either the intake or exhaust valves are not seating properly.

If you really want to know have a competent mechanic do a leak down check, this will pinpoint the problem and let you know just how bad it is.

Also, did you do the test warm or cold, and did you disable the fuel injectors (pull EFI fuse 1&2)?

I would not panic over those numbers. In fact I might do the test over just to make sure the gauge was well seated, you might want to try another gauge if there are any doubts about the one you used.
 

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Chris,


I'd recommend that you combine all recent posts (Not holding boost, vac @ idle, etc.) into one and repost. That may add some clues to what the actual problem may be.

Also, I know a good mechanic in my area (Hwd) and if he's in town, I'll ask him tomorrow about the low compression #s and see if he has any ideas?
I'll let you know.


Jay :cool:
 

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i didn't want to start a new thread for this... i have a 95 5-speed and will be doing the compression test for my car tomorrow... what numbers should i be looking for? thanks
 
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Discussion Starter #8 (Edited)
Lagtime,

Lagtime said:


You can easily check if it a ring vs. valve issue by putting about a tablespoon of oil into the low cylinders(s) and repeating the test. If the numbers increase chances are the ring seal is poor, if they remain the same then either the intake or exhaust valves are not seating properly.

If you really want to know have a competent mechanic do a leak down check, this will pinpoint the problem and let you know just how bad it is.

Also, did you do the test warm or cold, and did you disable the fuel injectors (pull EFI fuse 1&2)?

I would not panic over those numbers. In fact I might do the test over just to make sure the gauge was well seated, you might want to try another gauge if there are any doubts about the one you used.
Damn, I forgot to warm up the car. What will the difference be if you do it on a cold motor? How about w/o the EFI fuses pulled?

Chris
 
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Discussion Starter #9
supra_10 said:
Chris,


I'd recommend that you combine all recent posts (Not holding boost, vac @ idle, etc.) into one and repost. That may add some clues to what the actual problem may be.

Also, I know a good mechanic in my area (Hwd) and if he's in town, I'll ask him tomorrow about the low compression #s and see if he has any ideas?
I'll let you know.


Jay :cool:
I posted all these problems separately because they came up one after another. First was the vaccum problem, then I not holding boost on the dyno, then doing a compression check when i got home. Sorry for inconvinience.

Chris
 
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Discussion Starter #10
*wishlist*supraTT said:
i didn't want to start a new thread for this... i have a 95 5-speed and will be doing the compression test for my car tomorrow... what numbers should i be looking for? thanks
N/A -
Max: 185 psi or more ; Min: 156 psi

Turbo
Max: 156 psi or more ; Min: 128 psi

Difference between cylinders: 14 psi or less

Chris
 

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Re: Lagtime,

DANKAHOLIK said:


Damn, I forgot to warm up the car. What will the difference be if you do it on a cold motor? How about w/o the EFI fuses pulled?

Chris
A cold motor can make the difference between cylinders larger, and compression may be lower than with the motor warm, especially for an older, higher mileage motor. The manual says to test it warm, BTW.

Pulling the EFI fuses is the easiest way to prevent the injectors form spraying fuel while you are cranking the motor during the test. You don't want the injectors firing because it washes the oil off the cylinder walls and contaminates the oil.

Really, do the test over with a warm motor, EFI fuses pulled and your throttle plate blocked open.
 
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Discussion Starter #12
Lagtime

One more question before I redo the test. How many times do you crank the motor for the final #'s? Or do you just crank it until you get highest # possible?

Thanks,
Chris
 

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Re: Lagtime

DANKAHOLIK said:
One more question before I redo the test. How many times do you crank the motor for the final #'s? Or do you just crank it until you get highest # possible?

Thanks,
Chris
Best way is to have someone watching the gauge, and crank for the highest number. It may take 4~6 compression strokes to get there.

Make sure your battery is fully charged, or your numbers will drop as you get to the last cylinder since the motor will be spinning more slowly.

Good Luck!
 
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Discussion Starter #14
it doesnt really matter if the car is warm or cold. or course the # will be different when the car is warm, ut the main thing is to get all cynlinder # to be no more than 15PSI difference. as long as they are in that range, you're fine. in your case, the # between cylinders are a biyt more than 15PSI which means there is a compression problem, but its not that bad. different gauge reads differently, just like different boost gauge reads differently. some are more accuate than others.
if you got 390RWHP with boost leak, you're still doing good. that means you have around 430hp at crank, not strong BPU, but you still have a very fast car at hand. I got similiar # as you boosting 16PSI, havnt had any problem with any car:D
 
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