po300 - Maintenance and Repair Forum

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po300
Tuesday, November 20, 2007 3:41 PM
Does low compression cause cylinder misfire? If so how do i fix??


owner of 2002 ls sport cavalier and 2007 cobalt ss

Re: po300
Tuesday, November 20, 2007 4:19 PM
Yes. A low compression cylinder can cause misfire or at least a misfire code since the low compression cylinder is not contributing much. It is fixed by rebuilding the engine or repairing/replacing the cylinder head or replacing the head gasket depending on what causes the low compression
Re: po300
Tuesday, November 20, 2007 4:22 PM
its a brand new rebuilt engine. compression is 8-5.1. compression test is 130-150-160-150.. Throwing po300. Changed ingniton coil pack. The one from chevy. Still misfires?. Could this be a sensor i forgot to hook up? ground? What about this little rubber coil. 2002. ecotec


owner of 2002 ls sport cavalier and 2007 cobalt ss
Re: po300
Tuesday, November 20, 2007 9:21 PM
make sure you have all your injectors plugged in ?



Re: po300
Wednesday, November 21, 2007 4:17 AM
I don't think your compression readings are low enough to cause a missfire.

Could it be anything like these:-

http://www.j-body.org/forums/read.php?f=11&i=129800&t=129800


http://www.j-body.org/forums/read.php?f=11&i=128425&t=128425


Alont
Re: po300
Wednesday, November 21, 2007 6:58 AM
I read both of those already. No. I checked my injectors while i was turning my car over all seems to be working ok. The middle ones 2,3 both shoot at same time then 1 and 4 at same time. I unhooked all the vacc lines and it runs really good on 3 cyclinders then. But still not 4. What about the Air intake control. Could it be stuck closed and no air getting in it. Also a valve stuck? so whats the intake valves and make sure they are going up and down right?


owner of 2002 ls sport cavalier and 2007 cobalt ss
Re: po300
Wednesday, November 21, 2007 8:30 AM
just noticed my fan cuts on right away to.


owner of 2002 ls sport cavalier and 2007 cobalt ss
Re: po300
Wednesday, November 21, 2007 10:18 AM
Wait a minut.... you injectors should be firing sequentially... not like you describing...

It sounds exactly like you car is in limp mode for some reason... the non sequential firing of the injectors combined with the fact your rad fan is on all the time is a dead give away for that.

Is your CEL on?... If I where you.. I would have a good scan tool hooked up to it and see if you can find any codes that may point to whats causing the problem.





Re: po300
Wednesday, November 21, 2007 1:35 PM
yes po300 cel is on. my car is in a diff shop. supposed to be the best guy around here. im sick of the sh*t. Hopefully i'll never had to put another motor in and this will be the last one. Soon as its fixed i'll state what the cure was. And post pics and videos car some cool @!#$.


owner of 2002 ls sport cavalier and 2007 cobalt ss
Re: po300
Thursday, November 22, 2007 4:20 PM
when my other engine blew up could the computer keep starting my new engine in limp mode??? maybe that what it is.. a shop has my car but how do i reset it if its in limp mode? reflash?


owner of 2002 ls sport cavalier and 2007 cobalt ss
Re: po300
Tuesday, December 04, 2007 3:51 PM
the mechanic (s) at this place cant' figure out the problem. I need some more help from any one that has an idea. Like i said its throwing the po300 code. Cylinder misfires. I've changed igintion moduale and that wasn't it. THe coil pack houseing i've heard people talk about. Are they refering to the igintion moduale pack or the actual piece it bolts on to. ( 2002 ecotec ) I have not changed the coil pack houseing because i do not no if they go bad. What sensors c0uld maybe be not connected/broke/ to make this happen. could this be engine timing ? i had a machine shop build engine. please ask me any questions you need to know thanks


owner of 2002 ls sport cavalier and 2007 cobalt ss

Re: po300
Tuesday, December 04, 2007 7:35 PM
Quote:

compression test is 130-150-160-150.


I would think the 130 is just a tad bit low compared to the others. What did they check? There are a number of ways to lose compression. Bad rings, head gasket, cracked head, warped head, warped block, improperly adjusted valves, cracked piston, cracked cylinder, and loose spark plugs. If its a head gasket, cracked cylinder or head, and warped head or block you would most likely be pushing coolant out your overflow. Bad rings and cracked pistion would most likey be pushing oil out the dipstick or causeing the dipstick to pop out of the tube.



Re: po300
Saturday, December 08, 2007 10:07 AM
well i have some more information on my car. the shop told me that they think my head is cracked. there is steam coming from the number 1 cyclinder and antifreeze all over the plug. They are pulling the head of monday. Now my question is i called they machine shop and told him this and he said he tested it. Should he be lieable for this? This is my first performance engine so i dont know much about warrenties. So i say something to him?


owner of 2002 ls sport cavalier and 2007 cobalt ss
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