compression test result


New Member
Jan 19, 2007
My GN has 157,000 miles on it and I don't know the history of it. It has a miss at idle and stutters at wot. It runs fine in between idle and wot. If I mash the pedal it stutters, if I slowly push the pedal to the floor it accelerates fine.I have checked and changed the basic stuff.(other than a ajustable fuel pressure reg/fuel filter I have not done anything with the fuel system)I was going look at injectors,fuel pump/hot wire kit but I am concerned about compression test reults. #1-135/ #3-135/ #5-100*/#2-145/#4-145/#6-145. Should I be concerned about cylinder #5 and if so what steps do I take to find out what is going on with cylinder #5.

any help would be appreciated.
thanks, mike
Sounds like you have an ignition problem to me. I would thouroghly check your ground wire connections behind your cyl heads prior to buying a new coil. I recommend Casper's ground kit. If you buy a new coil make sure to get a GM coil from a GM dealer. Do NOT BUY AUTOZONE or Wells brand coils- waste of money. If the coil doesn't do it and your wires are not producing lightning in the dark then you might want to look at testing/replacing the ignition module. I went through a few coils before I realized some joker didn't hook up one of the ground wires in back of the head. Then, no more coil problems. GM warranties them for 90days. I have had mine on for 2.5yrs & 5K miles, no problem.

As far as the #5 cyl all I know is that they are supposed to be within 10% of each other. My car is way off too but it runs smooth. All mine are around 120 and then #6 is 160!
that #5 cylinder is low on compression. Try putting alittle oil in that cylinder and see how much the compression comes up. also if you can take a pin light and take a look at the piston and see what it looks like.
Something is not right with your number #5. Anytime a cylinder is that far off (assuming the test was done right) it means there is a problem. Period. I would try the oil check. Also, was this done warm or cold? If the oil check doesn't change anything it very well could be a valve.

Edit: I wouldn't go spending a bunch of money on coils and ignition modules until you get your engine problem figured out.
+1 you need to find out what is wrong with that cylinder before throwing more money at it.