mike rousseau Posted April 19, 2011 Report Share Posted April 19, 2011 (edited) My buddy changed the head gasket on his 2004 grand prix and it running rough at idle... Compression is all over the place... He's thinkin leaking/ dirty exaust valve\valves... Wondering if anybody knows a good additive or cleaner or something so he doesn't have to Tare apart the whole motor again... Or If anybody thinks it's something else... Let me know plz Thnx guys Edited April 19, 2011 by Musky Mike Link to comment Share on other sites More sharing options...
morieris Posted April 19, 2011 Report Share Posted April 19, 2011 If he is checking compression he has a gauge, so bar the engine over until the valves are supposed to be closed and pressurize, find out if/where the air is coming out and you will find the problem. Link to comment Share on other sites More sharing options...
mike rousseau Posted April 19, 2011 Author Report Share Posted April 19, 2011 We put air to the cylinder and could here it hissing at the exaust... That's why he figures it's his exaust valves leaking and giving bad compression... Link to comment Share on other sites More sharing options...
cuzza Posted April 19, 2011 Report Share Posted April 19, 2011 Seeing as he didn't touch the valves and assuming it was OK before the gasket failed, it may be that the new gasket isn't sealing properly or the head has warped. Is the compression off on just one cylinder? Link to comment Share on other sites More sharing options...
bigbuck Posted April 19, 2011 Report Share Posted April 19, 2011 Have him try Seafoam, maybe there is some carbon buildup that might be causing it to not shut completely. But, it is probably a broken valve spring, bent pushrod, bent valve, warped head........ Good luck. Link to comment Share on other sites More sharing options...
mike rousseau Posted April 19, 2011 Author Report Share Posted April 19, 2011 Two cylinders that aren't together are low compression... 80 & 90... It seems to have full power when he's driving... Just idles terrible and obd code for random misfire keeps coming up Link to comment Share on other sites More sharing options...
mrpike Posted April 20, 2011 Report Share Posted April 20, 2011 Two cylinders that aren't together are low compression... 80 & 90... It seems to have full power when he's driving... Just idles terrible and obd code for random misfire keeps coming up May have a bad wire I just had the samething on my yukon. put on new wires and we are good to go. I had one bad wire number 8 CHECK IT OUT. Link to comment Share on other sites More sharing options...
Dara Posted April 20, 2011 Report Share Posted April 20, 2011 My exhaust valve leaks once in a while too....the wife slaps me every time she hears it Link to comment Share on other sites More sharing options...
cuzza Posted April 20, 2011 Report Share Posted April 20, 2011 My exhaust valve leaks once in a while too....the wife slaps me every time she hears it LMAO - get some carb cleaner in there Dara, Creemore make a good one O/P - if it overheated when the gasket failed, it probably the head, it needs to go to a machine shop to be skimmed. If the head bolts weren't tightened correctly and in the right order that could cause the gasket to leak as it won't seat it properly. Link to comment Share on other sites More sharing options...
DanD Posted April 20, 2011 Report Share Posted April 20, 2011 Did he have the heads pressure/vacuum tested when they were off? Depending on how hot the cylinder head(s) got when the gaskets failed; there’s a good chance that a couple of the valves have became warped. The valve head will actually become out of round and the exhaust valves are more prone to it. The exhaust valves on a properly running engine, run very close to red hot; when a head gasket blows, the coolant entering the combustion chamber will quench the valves causing them to warp. Why it seems to run ok off idle is because inertia is helping things to smooth out; but at idle all 6 slugs have to be contributing for the engine to run smooth. I’d say that he’ll be busy this long weekend pulling the heads and then sending them in for a valve grind. If he does pull the heads again; tell him not to even think of reusing any of the new gaskets he’s just installed. Especially the head gaskets they use a crush method in the composition of the gasket that only works once to seal the combustion chamber. Dan. Link to comment Share on other sites More sharing options...
Roe Bag Posted April 20, 2011 Report Share Posted April 20, 2011 (edited) Squirt some oil into the two bad cylinders. Crank the engine over a couple of times. (all plug wires removed or coil wirE) Do another compression test. If the compression comes up then it's losing compression past the rings. If it's stays the same then it's a valve, warped head, or head gasket. If he didn't tourque the head bolts accurately and in the proper sequence, he may have warped the head. Check out this link: http://olybrake.com/pdf/fel_pro_torque_specs_guide.pdf Edited April 20, 2011 by Roe Bag Link to comment Share on other sites More sharing options...
DanD Posted April 20, 2011 Report Share Posted April 20, 2011 Squirt some oil into the two bad cylinders. Crank the engine over a couple of times. (all plug wires removed or coil wirE) Do another compression test. If the compression comes up then it's losing compression past the rings. If it's stays the same then it's a valve, warped head, or head gasket. If he didn't tourque the head bolts accurately and in the proper sequence, he may have warped the head. Check out this link: http://olybrake.com/pdf/fel_pro_torque_specs_guide.pdf We put air to the cylinder and could here it hissing at the exaust... That's why he figures it's his exaust valves leaking and giving bad compression... By this they have already confirmed where the compression leakage is. That is if they did the leakage test with the suspect cylinders at TDC of their compression stroke? Dan. Link to comment Share on other sites More sharing options...
Roe Bag Posted April 20, 2011 Report Share Posted April 20, 2011 By this they have already confirmed where the compression leakage is. That is if they did the leakage test with the suspect cylinders at TDC of their compression stroke? Dan. Agreed DanD. Could be the piston was somewhere in the exhaust stroke. The exhaust valve will be open and air will be heard at the exhaust. Tough to determine the actual position and stroke without removing the valve cover again and noting the position of the valves. The addition of oil has always worked for me. Provides a temporary improved seal at the rings causing an increase in compression. If the leak is at the top end there will be no change. Link to comment Share on other sites More sharing options...
ecmilley Posted April 20, 2011 Report Share Posted April 20, 2011 can i guess that it's a 3.8 l engine? Why were the head gaskets replaced to begin with? my expierence with this engine is that the upper intake fails and leaks coolant into the engine when this happens it is entirely possible to hydrolock the engine and bent a connecting rod everso slightly when this happens the bad cylinder(s) will have a lower compression and a misfire at idle. do you have access to a scan tool? if so moniter the misfire data if it starts to smooth out at higher rpm and return to high misfire numbers at idle this can be caused by a bent rod (or sticking egr, vacuum leak ect but sounds like you ruled them out) Link to comment Share on other sites More sharing options...
SBCregal Posted April 20, 2011 Report Share Posted April 20, 2011 what engine is in it? the 3.1 and 3.4 v6 have different length pushrods for the intake and exhaust valves, maybe one got switched around? Link to comment Share on other sites More sharing options...
ecmilley Posted April 20, 2011 Report Share Posted April 20, 2011 what engine is in it? the 3.1 and 3.4 v6 have different length pushrods for the intake and exhaust valves, maybe one got switched around? seen that a few times as well on the 3.1 3.4 engines Link to comment Share on other sites More sharing options...
DanD Posted April 21, 2011 Report Share Posted April 21, 2011 what engine is in it? the 3.1 and 3.4 v6 have different length pushrods for the intake and exhaust valves, maybe one got switched around? In 2004 they (GM) only offered the 3.8Lt in the Grand Prix; either a VIN code 2 or 4; the 4 code being the supercharged engine. Yea asked my youngest tech here about the different length pushrods in the 3.1. He has a bent valve sitting on the shelf at the computer station here in the shop; as a reminder. LOL Both of the 3.8Lt engines use the same length pushrods for intake & exhaust. Dan. Link to comment Share on other sites More sharing options...
Bernie Posted April 21, 2011 Report Share Posted April 21, 2011 Did he have the heads pressure/vacuum tested when they were off? Depending on how hot the cylinder head(s) got when the gaskets failed; there’s a good chance that a couple of the valves have became warped. The valve head will actually become out of round and the exhaust valves are more prone to it. The exhaust valves on a properly running engine, run very close to red hot; when a head gasket blows, the coolant entering the combustion chamber will quench the valves causing them to warp. Why it seems to run ok off idle is because inertia is helping things to smooth out; but at idle all 6 slugs have to be contributing for the engine to run smooth. I’d say that he’ll be busy this long weekend pulling the heads and then sending them in for a valve grind. If he does pull the heads again; tell him not to even think of reusing any of the new gaskets he’s just installed. Especially the head gaskets they use a crush method in the composition of the gasket that only works once to seal the combustion chamber. Dan. This is very good advise as well as from some others. Make sure you check the heads for cracks and warps, especially because it was overheated. Link to comment Share on other sites More sharing options...
mike rousseau Posted April 21, 2011 Author Report Share Posted April 21, 2011 (edited) He bought the car with a blown head gasket... He usually gets a really good deal cause it's a pricy job... But he can do it himself... So that's why there is some missing info here... He wants to avoid replacing another head gasket due to the cost and possible negative outcome... He would rather buy a engine from the wrecker... 600-800 bucks What we are trying to find out is if there in a way to try cleaning the valves with a cleaner without taking the engine apart? Like a 10 dollar can of some magic cleaner...lol Cause if he has to rip that engine apart again he'll probably just swap it for another one that has a 3 month garaunty for 700$ Edited April 21, 2011 by Musky Mike Link to comment Share on other sites More sharing options...
DanD Posted April 21, 2011 Report Share Posted April 21, 2011 I’d say put the $10 towards a case of beer; because he’s likely going to get thirsty pulling that engine down or out. Confirm that the issue is a leaking valve and then have the heads redone; these 3.8lts didn’t get the nickname of “iron horse” for nothing, the bottom ends are all but bullet proof. Dan. Link to comment Share on other sites More sharing options...
POLLIWOGG Posted April 22, 2011 Report Share Posted April 22, 2011 If its a 3.8 I Think I know what the problem is, I watched a guy fix one 2 weeks ago after 2 shops told the owner to replace the motor after billing her$700 trying to fix it. In the plastic intake where the EGR valve goes through beside a water passage it melts a hole through the plastic leaking coolant into the intake making the motor miss like a blown head gasket and eventually can fill the cylinders if it gets bad enough. Check for loss of coolant and or pressurize the rad if you can get the tool for it or just pull the EGR out of the manifold and look for a hole. If its real bad you will see all kinds of antifreeze in the intake. If its the same motor I'd almost bet $ this is the problem. Link to comment Share on other sites More sharing options...
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