Tech / General EngineWhy is my car making that sound? My car won't start! Combination questions? Don't see a board for your problem or have other technical or engine specific questions? Post them here!
Welcome to ThirdGen.org!
Welcome to ThirdGen.org.
You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, at no cost, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, join the ThirdGen.org community today!
I did a dry compression test and got 100-125 psi on 1,3,5,7
and 195-200 psi on 2,4,6,8
Which side is the problem? I know 100 is low, but isn't 200 really high?
And I have a post in the tbi section I started (spark knock), but when I posted this question no one's answering it so I thought it might be better here.
This ad is not displayed to registered members. Register your free account today and become a member on ThirdGen!
__________________ It's not the Ride, it's the rider.
Sponsored Links
Registered users do not see this ad. Click here to register for free!
Mismatched heads maybe - has your engine ever been rebuilt? 200 Does seem a little high, but it depends on the compression ratio. If you happen to have the valve covers off, you could check the casting numbers on both heads.
__________________ North Texas Third Gen Association 1988 GTA 5.0/M5/3.45 LSD, T-Tops, Digital Dash, Leather - Current Ride 1983 Firebird S/E - Stripped 1995 Chevy 1500 5.7 Ext. Cab - Daily Driver
Even mismatched heads shouldnt make a difference that big. Something went wrong during the test. Did you hold the throttle all the way open? Was the battery still good by the last cylinder? Were all the plugs out of the other 7 cylinders? I'd say redo the test.
Even mismatched heads shouldnt make a difference that big. Something went wrong during the test. Did you hold the throttle all the way open? Was the battery still good by the last cylinder? Were all the plugs out of the other 7 cylinders? I'd say redo the test.
Yeah I'm gonna redo the test. I didn't have the throttle open, or all the plugs out. But it sure is a pain with those air tubes in the way. I'm doing it underneth but still. I've only had the car a month, and I'm pretty sure the engine has never been opened.
Yeah I'm gonna redo the test. I didn't have the throttle open, or all the plugs out. But it sure is a pain with those air tubes in the way. I'm doing it underneth but still. I've only had the car a month, and I'm pretty sure the engine has never been opened.
Ok - when you do the test, you have to have the throttle all the way open, and you have to have all the spark plugs out, to do it correctly.
Would be wise to have a battery charger (preferably with 'engine start') hooked up as well if its possible, just to keep from running the battery down.
I just redone the test with plugs out, throttle open, and engine hot. I only did cylinder 1 and 3 because of the results. Cylinder 1 had 100 psi, with 3 squirts of oil it had 120 psi. Cylinder 2 had 80 psi this time (lower), and 90 psi with oil. So it seems like bad rings but how come it doesn't smoke and how could only one bank (the drivers side head) be low and the other so high?
Could it still be a head gasket? I'm pretty sure someone got it hot because the connector on the temp sensor for the fan was broke off when I got it. But there is no sign on coolant leaking in the engine or oil in the water.
And just a reminder it runs really good other than a rough idle. That's what has me so puzzled.
How many times are you spinning the engine over? Should let it spin over at least 3-4 times for each cylinder you test. Have you adjusted the rockers recently? If they are a bit too tight, the valves won't completely seal and the readings will be low.
Have you adjusted the rockers recently? If they are a bit too tight, the valves won't completely seal and the readings will be low.
That sounds like the most plausible explanation for the R-L split on the readings. Maybe the driver side was misadjusted at some point and the passenger side was not touched. Just a WAG. Cant hurt and not all that hard to check.
Shoulda checked just one on the other side to make sure your reading was still a lot higher... but I'm thinking your original results were probably fine.
A leak down can give you a better idea where it is, valves or rings.
They just showed how to build one the other day for cheap on the HP block with a hollowed out used spark plug n a air hose fitting.
__________________ 86 Pontiac Firebird
[68 Firebird hoodscoops, custom notchback,
custom rear mounted tach, inverted wing.] http://www.thirdgen.org/techboard/v6...-all-over.html
I love my new notch-back. See link for newer pics and above mods.
I thought about the valves being tight too right after the first test and checked them. They where actually loose. I put them at zero lash and half a turn, even though alldata says 1 1/4 turn. That just seems too tight. As for the leak down test, I don't have a tester but I was thinking about putting some compressed air in the cylinders and listening around for it. I really want to go ahead and pull the head off and look at the gasket. Probably going to be a dead end though. I have a neibor with a lot of engine assembly experience, and he told me if I get the machining done he would assemble it for $200.00. I'm seriously thinking about just jerking it out and getting it over with.
How many times are you spinning the engine over? Should let it spin over at least 3-4 times for each cylinder you test. Have you adjusted the rockers recently? If they are a bit too tight, the valves won't completely seal and the readings will be low.
I thought about the valves being tight too right after the first test and checked them. They where actually loose. I put them at zero lash and half a turn, even though alldata says 1 1/4 turn. That just seems too tight. As for the leak down test, I don't have a tester but I was thinking about putting some compressed air in the cylinders and listening around for it. I really want to go ahead and pull the head off and look at the gasket. Probably going to be a dead end though. I have a neibor with a lot of engine assembly experience, and he told me if I get the machining done he would assemble it for $200.00. I'm seriously thinking about just jerking it out and getting it over with.
Thats what a leak down test is, blowing compressed air into it to see where it leaks. If ya search [im not doing it for ya] the HP TV website you should find the vid on how to build it.
__________________ 86 Pontiac Firebird
[68 Firebird hoodscoops, custom notchback,
custom rear mounted tach, inverted wing.] http://www.thirdgen.org/techboard/v6...-all-over.html
I love my new notch-back. See link for newer pics and above mods.
