what would cause a instant compression loss?

[marsh63]

well i just did a cylinder head replacement last night. its a 1990 n/t eclipse 4g63 and i had the car running with about 180 lbs of compression across all the cylinders

now today i have 120 across 2 of them and 150 in the other 2 and it wont start. the timing is dead on and the valves are all seating fine. also when i added oil it went up to about 220 in each cylinder

so what is wrong with my car? could this be a headgasket? help me!!!!!!

i only ran it for like 20 minutes after i put the new head on it. im using a 3 layer cometic headgasket.

i have oil pressure so i dont think it killed my cylinder walls.

 

[92 GSR-4]

. Yeah I've built ONE engine. The one in my GSX that has lasted 5 years now, eaten 3 clutches, and shattered a transmission, now in the 11's on PUMP. Oh wait...the 7 other engines I've built for myself, my father, and my friends also have held together. Maybe I know a thing or two.

And while I may not have FP2X cams (FP1's), my compression did not change when I swapped. Maybe your profile is radical, but for an engine to make only 120PSI sounds shaky to me. Sounds like an overall powerloss too.

 

[dsm-onster]

Wow. That advice sounds familiar? Oh yeah, look at my very first post in this thread. That was my first piece of advice. So does curbing misinformation on this board mean copying exactly what I have already suggested? Or maybe somehow I was wrong by suggesting that and now your right? I'm confused..

I know you're confused. You did good. Here's a pat on your back. You provded some good info. And you provided some bad info. Accept it. And stop cluttering the thread. You already mentioned this. You're wasting at least the OP's time.

 

[92 GSR-4]

Awww thanks! You warm my heart. Honestly this is cluttering the thread. I would like to see the solution to his problem.

 

[hpexperts]

wow!

 

[DSM1G90]

A wet test will ALWAYS INCREASE COMPRESSION in a DSM because the oil that is sitting in the dish is now displacing the air in the cylinder. It increases the overall volume of the piston, and you will get a higher pressure reading.
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Now, ignorance is gonna kick in here since I suddenly graduated from a 4G37 to a 4G63T, bypassing the NT version of this motor. Thus, being a NT motor, do they contain the same dished pistons, or are they flattop since the NT runs a higher compression - 9.2/1 than what we turbo folks play around with?

Thus, would doing the wet test be valid for a NT motor?

i learned at work was to take off all the spark plugs and attach them to the wires and lay them over the plug tubes, make sure the thread or body of the plug is touching the motor for ground and crank the motor. If you see big flames comming out of each cylinder you have a descent spark/fuel combo. BUT if the spark is not strong enough it would work with the plugs and no compression but with compression the spark sometimes

.. DANG! saw something like this on YouTube - I was hoping that the kid doing this wuld blow his face off!! Most retarded and to include DANGEROUS thing I ever heard and saw...! One can easily do the spark test (blue for hot, yellow for cold) to see if the spark is hot enough - or look at the plug itself: If it's black, you KNOW you got a cold firing plug (or bad ignition pak), or if it's clean and white, then you go nutting to worry about on the ignition side of the equasion.

-DSM

 

[marsh63]

You're getting irritated because you and others said the wrong things and get called on the carpet for it. The informtion does NOT indicate a mis-torqued head. It's my job to curb misinformation no matter how well meant.

Like now! YES!!!! A mirror finish IS required for a MLS headgasket to seal properly. The Copper Coat isn't strong enough to seal out the imperfections. It will fail before a stock composite will fail in the same conditions. No reason to install a +$100 headgasket if it isn't better than a $16 special from Partsdinosaur.com. Too many have done this and failed for it to be an acceptable route with a metal headgasket.

But, I do agree that an engine can run with 120psi compression. One of mine runs high 11s as a FWD with 125-135 across the board on a fresh rebuild. I have FP2Xs. So the cylinder filling at 250 (starting) rpms is much lower than stock cams. So, retorquing the headbolts won't help it start again. No matter how high the compression numbers may yield.

Marsh63, why not double check your timing marks? . . . That would rid you of one possibility.

timing is still dead on. also the fuel is about 3 months old so its not all that great. i added 5 more gallons to the fuel tank of primium and it fires alot better but wont stay running its a fuel issue on why its not running right.

i also have to get another ecu for it. i am using the ecu out of my other n/t dsm to start this one.

i am just going to replace the headgasket with a composite one. if that dosnt work for my compression then ill rebuild the motor. but as far as the leakdown test went the car didnt leak out the bottom end so the rings are fine.

thank you for all the help so far.

 

[dsm-onster]

If you put some good gas in it and it fired. Perhaps draining all the fuel and starting fresh is in order?

Have you unplugged the MAF and tried to start it again? If it runs or runs better, this would indicate a bad MAF. Now that it will start but not run, have you checked the plugs? Do they smell like gas? Are they black?

Also, if it's been a while since you've started it, there's a possibility that several or all of the injectors are "sticky". I've had this happen to me. You'll have to pull them and press on the pintle while blowing through the other end. If you hear your breath when you press in the pintle then the solenoid is not stuck. If not, then you'll have to push on the pintle *cautiously* until it frees up. It should move about 1-2 mm.

MAF, airleaks after MAF, injectors, fuel, fuel pump, fuel filter, fuel line. These are few of the possibilities .

Thus, being a NT motor, do they contain the same dished pistons, or are they flattop since the NT runs a higher compression - 9.2/1 than what we turbo folks play around with?

The N/T piston is dished. But less dished.

 

[92 GSR-4]

Your fuel is fine. I wonder...have you checked your ignition to see if it is actually firing?? are you sure you have spark? What about air signal? A logger would be great.

 

[marsh63]

i have spark but the previous owner put a aftermarket coil park on it so i bet thats the problem. but also the plugs are coming out black. the spark is a blue spark and the cas is set correct. im thinking the injectors are dirty and or bad.

 

[JeffGST]

Now, ignorance is gonna kick in here since I suddenly graduated from a 4G37 to a 4G63T, bypassing the NT version of this motor. Thus, being a NT motor, do they contain the same dished pistons, or are they flattop since the NT runs a higher compression - 9.2/1 than what we turbo folks play around with?

Thus, would doing the wet test be valid for a NT motor?

Yes, the NA pistons are also dished pistons. Have you ever seen 9.0 to 1 DSM pistons like off the shelf JE pistons? They are definitely a dish design.

All you are doing when you pour oil through the spark plug hole is filling the dish with oil. This will displace the air during the compression test, which will artificially inflate the compression numbers. This will give you a false pressure reading.

 

[ontario AWD]

Why did you pull the head in the first place?I had a similiar experience a while back,thought i blown my head gasket because of low compression in two cylinders.Turned out all the ring lands had broken off the pistons but they looked fine from the top.

 

[marsh63]

Why did you pull the head in the first place?I had a similiar experience a while back,thought i blown my head gasket because of low compression in two cylinders.Turned out all the ring lands had broken off the pistons but they looked fine from the top.

2 bent valves from the previous owner thinking he knew how to do a timing belt replacement.

 

[dsm-onster]

Have you run a straight edge through the center of your cam gear bolts to see if all the timing marks are in line?

 

[marsh63]

Have you run a straight edge through the center of your cam gear bolts to see if all the timing marks are in line?

after i rebuilt the head i did the timing and its dead on now. the previous person screwed up and thats why i pulled the head.

 

[marsh63]

well the car runs great now so yeah im happy.