extremely low compression new to dsm's

[baggedmazda]

i picked up a 91 gsx it was not running it spins freely they just could never get it running. i checked out the ecu changed the coolant temp sensor and checked the mpi fuse. i have spark and fuel to at least the rail.

i went out yesterday armed with my compression tester and the results where bad 50 psi across the board when the last people had the car they said they redid the timing it looks ok on the cams i haven't pulled the covers down low to check the bottom 2 not alot of time for me to work on it.

could timing cause that low of compression without messing the valves up could it be a headgasket? any thing else i could be missing

i got this car for a good enough deal that i could learn about dsm's and have a decent daily out of it and arm myself with some knowledge of them i plan on swapping a 4g63 in to my next mini truck down the road a bit

 

[MichaelSuch]

Its doubtful it's the headgasket if its 50 across all 4. If they say the redid the timing it most likely jumped time due to a bad hydraulic tensioner and you probably bent valves. But when you did the compression test, did you have the throttle wide open? If you had it closed it will yield low results. Compression tests should be performed on a warm engine.

Did the ECU have any leaky capacitors? When you turn the key to the "on" position, does the CEL go off after 5 seconds and does the factory boost gauge go to the center of the gauge? What exactly happens when you try to start the car?

 

[baggedmazda]

Its doubtful it's the headgasket if its 50 across all 4. If they say the redid the timing it most likely jumped time due to a bad hydraulic tensioner and you probably bent valves. But when you did the compression test, did you have the throttle wide open? If you had it closed it will yield low results. Compression tests should be performed on a warm engine.

Did the ECU have any leaky capacitors? When you turn the key to the "on" position, does the CEL go off after 5 seconds and does the factory boost gauge go to the center of the gauge? What exactly happens when you try to start the car?

test was done at wot cant test on a warm engine as it dont start.

ecu looked brand new no swollen or leaky caps. i dont get a cel light on when turning key boost goes to center and rpms jump when turning over.

when starting its truns over slow could be to a under charged battery but it was reading 14 volts. it stumbles for a second every once in a while i tryed spraying starting fluid in there it didnt change anything when cranking maybe i am not getting injectors firing either buddy looked at the cas placement and said it was fine just dont have a test noid to see if its firing

 

[AlaskanDsm]

50psi across all 4 cylinders makes me wonder if timing is correct as fore-mentioned. Check the timing marks and verify it didn't jump timing.

 

[RogueTalonTSI]

If a motor sits for a significant amount of time I like to pour a cap of fresh oil into the sparkplug holes, after all oil is partly responsible for the rings sealing.

 

[baggedmazda]

I did pour a cap full of 50w into cylinder 3 and it raised it to 70 psi. I have no clue how long the thing has sat

 

[2GbTalonGuy]

I would do a leak down test next.

 

[LiquidX]

First check the timing to ensure all timing marks line up. It can take up to 6 full rotations for them to line up. Pull out the plugs to make it easier to turn.

If the marks are lined up, then proceed to do a leak down test. If it's not lined up, get a full timing kit and hope that the valves are not bent.

 

[baggedmazda]

I am going to be building a leak tester before sat to test a buddy 2g and will do mine sat also

 

[LiquidX]

I would highly suggest not trying to drive it until it's fixed.

 

[baggedmazda]

the closest I have come to driving it is steering it off my goose neck trailer it hasn't ran in who knows how long

 

[Absit]

I am going to be building a leak tester before sat to test a buddy 2g and will do mine sat also

I hope you understand the difference between a "boost/vacuum leak test" and a "leak down test", they're very different tests with very different equipment and purposes.

 

[baggedmazda]

ah maybe I read it wrong I guess I will be looking into this

 

[ssicb]

here buddy:

leak down
http://www.dsmtuners.com/forums/articles-engine-fuel/338152-compression-leak-down-testing.html