Cylinder Compression

[dope96clipse]

i kno the specs but just need opinion. my brothers car which i want to purchase has about 130k on it .. its a 91 gst. he did a compression test 2 days ago an it read 120's across the board an with oil added to it up to 200. not even 15k ago he tested it and it was in the 150's was wondering if neone else thinks its just a little odd that it dropped that much that fast, 15k = maybe 4 months. i told him to borrow a good reliable comp tester since his is a 20dollar autozone special .. any input is much appreciated.. vehicle back ground, upper end is maybe 20k old max, uicp an intake pipes upgraded, 15psi boost stock turbo an exhaust, 660cc inj wit afc2. runnin mobil 1 10x30 oil, changed every 2500-3500 miles if not more.

 

[project94tsi]

wow 15,000 miles in 4 months, alot can happen during 15,000 miles. Get a good compression tester and test it again, make sure the car is warmed up and you have the throttle plate in the fully open position when you test it again.

 

[dope96clipse]

why would u do it at WOT??

 

[oldman]

why would u do it at WOT??

To allow the cylinders to breath freely, check your other procedures against this article.

 

[dope96clipse]

thanks, ill talk to my bro an have him test it that way, hes 90 miles away from me. and i never heard of having the car at WOT my school never said anything about it in any classes an im almost done..ill have to ask my teahers thanks

 

[oldman]

thanks, ill talk to my bro an have him test it that way, hes 90 miles away from me. and i never heard of having the car at WOT my school never said anything about it in any classes an im almost done..ill have to ask my teahers thanks

It's really not that big of a deal, couple of psi the most. Focus on the other parameters prescribed in the article. Is the car smoking? Have him pull the dipstick and smell for gas.

 

[dope96clipse]

i was home last weekend an i checked his oil, smells fine, an no smoke outta the exhaust, dipstick or oil fill cap.. he checked the compression the next day after i left home for work, he said his car burns about 1/2 qrt every few weeks but i think his turbos screwed, had a wee bit of shaft play a year ago an has been beat to hell since..

 

[oldman]

Then verify the compression test results with a known good gauge, make sure the car is fully warmed up and apply only a cap full of oil.

 

[dope96clipse]

ok thanks, i will get back to this post tom. afternoon, please check back someitme tom. late afternoon an i will have some results you have been a help

 

[dope96clipse]

talked with my brother, he retested the car after verifying his gauge worked on another car. the readings through all 4 cyl were between 120-130 never varying over the 14 limit. he said that when he WOT during driving he sees small amounts of white smoke but only at wot and that started around 6 or so months ago but hasnt gotten any worse. As far as his oil smelling like gas it doesnt anymore, but a few months ago it did, but that was also when he got his 660cc injectors and was extremely poorly tuned an rich as all hell so i beleive that was the cause of the gas in oil cuz it hasnt done it lately. if anyone else has an idea please let me know, im going to make a few calls up where my bro lives to see if i can get him to a shop to get a leakdown done.

 

[oldman]

What about the wet test? 120-130 isn't good at all considering the service limit for 1g is 121, leak down would be my next step as well. Good luck.

 

[dope96clipse]

with the wet test it would jump to 200

 

[dope96clipse]

i was talking to some teachers at my school and one of them mentioned carbon build up which i never thought about, he said it would actually raise the C/R and in turn would have cause alot of blow by possibly damaging the rings but the damage aside he also said that it would cause the spike to 200+psi with the wet test. now if my brother was to do a foam cleaning a few times since im damn sure there is alot of carbon due to untuned 660cc inj with out a larger turbo, would cleaning the carbon possibly help the compression test results?

 

[oldman]

i was talking to some teachers at my school and one of them mentioned carbon build up which i never thought about, he said it would actually raise the C/R and in turn would have cause alot of blow by possibly damaging the rings but the damage aside he also said that it would cause the spike to 200+psi with the wet test. now if my brother was to do a foam cleaning a few times since im damn sure there is alot of carbon due to untuned 660cc inj with out a larger turbo, would cleaning the carbon possibly help the compression test results?

Your teacher is right about carbon build up but it will not make a 80+psi difference. How much oil did he put in for the wet test? A little cap full will be enough, too much oil will also create a big jump in a wet test. In any case, if you're 100% sure the tester is good and all proper procedures have been followed (including amount of oil during a wet test). Only a leakdown test will tell you for sure what's going on.