98cobra+75280z Posted June 5, 2012 Share Posted June 5, 2012 (edited) Hey guys I need some help. Like the title says I am having a weird noise coming from the front of the motor. I am embeding a video of it but just in case it doesn't embed properly I will try and explain. First off the motor is an '82 l28et with around 125k on it. I am running 440cc injectors and 15psi with MS1 controlling it. IMG_00381.mov The sound to me sounded like a blown header gasket, my brother replaced the gasket and the sound still persists. Its very loud like a bunch of air is escaping the motor. If you put your hand right behind the dizzy you can feel a rush of air (possibly exhaust given the warmness of the air). My second thought was that the head gasket popped. I'm still thinking this is the reason for the sound, however there is no coolant coming from the spark plug when I pulled them and there is no bubbles in the coolant system as well as no smoke coming from the tailpipe. Im stumped and not wanting to tear into the motor just to find the head gasket is fine and then be back at square one. Any ideas on what it could be? Thanks for your help. Edited June 5, 2012 by 98cobra+75280z Quote Link to comment Share on other sites More sharing options...
Zmanco Posted June 5, 2012 Share Posted June 5, 2012 Sounds like an exhaust leak and from your description, probably between the exhaust manifold and the head. Look for carbon deposits to indicate where the exhaust is escaping, but in any event, you'll need to pull the exhaust manifold and the offending cylinder should become obvious when you look at the gasket. Quote Link to comment Share on other sites More sharing options...
98cobra+75280z Posted June 5, 2012 Author Share Posted June 5, 2012 Sounds like an exhaust leak and from your description, probably between the exhaust manifold and the head. Look for carbon deposits to indicate where the exhaust is escaping, but in any event, you'll need to pull the exhaust manifold and the offending cylinder should become obvious when you look at the gasket. That was my first thought as well, My brother took the exhaust manifold off yesterday and replaced the gasket and that video was shot after the new gasket was installed. I know the manifold is cast iron how brittle are they. Is is possible the manifold is cracked. Once again I havent had a chance to personally look at the car being in Michigan for the summer. Quote Link to comment Share on other sites More sharing options...
98cobra+75280z Posted June 5, 2012 Author Share Posted June 5, 2012 Here is a picture of the gasket that came off the car. This had me pretty confident that the problem would be solved by the new gasket but it wasn't. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted June 5, 2012 Share Posted June 5, 2012 Exhaust manifolds can crack. Since you've already changed the gasket, take a hose and put one end in your ear, and move the other end around the manifold with the engine idling. You'll know when you've found the leak Quote Link to comment Share on other sites More sharing options...
ctc Posted June 5, 2012 Share Posted June 5, 2012 L28ET exhaust manifolds are know to warp. Make sure it is perfectly flat or you will have exhaust leaks. Quote Link to comment Share on other sites More sharing options...
98cobra+75280z Posted June 5, 2012 Author Share Posted June 5, 2012 L28ET exhaust manifolds are know to warp. Make sure it is perfectly flat or you will have exhaust leaks. Can the manifold warp quickly and unexpected. What I mean is the car was being driven and my brother got into some boost and all the sudden the sound appeared. Could the manifold have warped that quickly. I will check on it though. thanks for the suggestion Quote Link to comment Share on other sites More sharing options...
ctc Posted June 5, 2012 Share Posted June 5, 2012 (edited) It might have warpped when you released the torque on the bolts and two end studs. If the gasket blew, you need to make sure the manifold is flat before you reinstall it. It's just good practice. Edited June 5, 2012 by ctc Quote Link to comment Share on other sites More sharing options...
98cobra+75280z Posted June 5, 2012 Author Share Posted June 5, 2012 It might have warpped when you released the torque on the bolts and two end studs. If the gasket blew, you need to make sure the manifold is flat before you reinstall it. It's just good practice. Ok, thanks for the tip. I will check on it Quote Link to comment Share on other sites More sharing options...
rags Posted June 5, 2012 Share Posted June 5, 2012 Actually, the picture of the ext/int gasket doesn't look like it was leaking at all. I can't play the vid here at work but can tell you that a blown head gasket does NOT have to leak coolant or oil and can only let combustion escape externally to the engine. From your description it sure sounds like the head gasket is the culprit. Do a compression check to make sure. Joe Quote Link to comment Share on other sites More sharing options...
98cobra+75280z Posted June 7, 2012 Author Share Posted June 7, 2012 Actually, the picture of the ext/int gasket doesn't look like it was leaking at all. I can't play the vid here at work but can tell you that a blown head gasket does NOT have to leak coolant or oil and can only let combustion escape externally to the engine. From your description it sure sounds like the head gasket is the culprit. Do a compression check to make sure. Joe well guys it looks like its my turn for some bad luck. I cant do a compression test yet since the car will not start now. Seems like either some fuses are blown or the starter is done. Won't be able to check on it until this weekend but hopefully I will make some progress. Thanks for the suggestions. Quote Link to comment Share on other sites More sharing options...
rayaapp2 Posted June 7, 2012 Share Posted June 7, 2012 Idle the engine. Pull one spark plug wire off at a time until you find one that doesnt drop the rpms as much. The fire ring(part of the head gasket) can blow out the side of the block and sound just like a bad exhaust manifold gasket. This has happened several times on different L series blocks I have run. There was just a post about this as well. If you do not have an obvious partially dead cylinder then go back to looking for an exhaust leak. This is just an easy way to determine if you have lost integrity of a cylinder that should be fast enough to eliminate your question. Ray Quote Link to comment Share on other sites More sharing options...
98cobra+75280z Posted June 11, 2012 Author Share Posted June 11, 2012 (edited) Made the trip home over the weekend and was able to get the car to start and run. So I warmed it up and then performed a compression test, with the following results. Cyl # ; Compression 1 : 40 2 : 98 3 : 104 4 : 107 5 : 103 6 : 101 So i went ahead and ordered a head gasket but I won't be able to work on the car until July. Thanks for your guys help and suggestions Edited June 11, 2012 by 98cobra+75280z Quote Link to comment Share on other sites More sharing options...
rayaapp2 Posted June 12, 2012 Share Posted June 12, 2012 Made the trip home over the weekend and was able to get the car to start and run. So I warmed it up and then performed a compression test, with the following results. Cyl # ; Compression 1 : 40 2 : 98 3 : 104 4 : 107 5 : 103 6 : 101 So i went ahead and ordered a head gasket but I won't be able to work on the car until July. Thanks for your guys help and suggestions Unless you were using a cheapo gauge all those numbers are low. Id guess you have lost the gasket at #1, but the other 5 cylinders are low as well. A leak down test is in order on the remaining 5 if you have a good compression tester to determine where the failures are at with the others. It may be time for more than just a gasket and surface job. You will need to have the cylinder head check and surfaced to make the repair complete, possibly the block decked as well so you have a good surface to work with. No sense in going through all that if you need more work done to the motor as well. food for thought Quote Link to comment Share on other sites More sharing options...
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