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Low RPM Misfire
This is driving me insane. My 3400 in my Grand am GT with 64,900 miles on it seems to have a misfire at lower RPMS that clear out without any hesitations or "hiccups" when the throttle is pressed. Note, however, that the car has 124,900 on it, but my engine and transmission have 60k less.
My power seems alright and I do not get any hesitation or anything at any RPMs. The car feels pretty much normal when it is above 1500 or so. Under that, it drives well, but when I press the throttle with my hand, it still misses at that RPM.
At idle, my RPMs do not surge at all; they are rock steady where they belong - at about 650. I have sprayed starter fluid on all vacuum lines to no avail. I listened around the engine for a hiss with a rubber hose in my ear (lol) and found nothing. My coils have all been checked and two were swapped out. My plugs and wires have been changed, I have checked spark only to find that all six wires produce a nice blue arc.
I also unbolted the down-pipe to see if the catalytic converter was clogged up, but the engine ran exactly the same with the pipe disconnected. I put a vacuum gauge on the upper intake manifold and the vacuum read between 18.5 and 19 in-hg; the needle swayed very very little. I have changed every fuel injector, the fuel filter, and air filter (as maintenance). My head gasket blew a couple of months ago, but this problem started about a month before it blew. I know exactly when the head gasket went because the car overheated on the highway when an idler pulley broke off causing the belt to fly off. I have performed a compression test and all of my cylinders held at least 175-180 for 5 minutes without losing any compression. My head gaskets and everything above has been replaced as required/recommended.
I disconnected my pcv hose from the valve and plugged up the end of the hose where the valve should be and started the car. It ran exactly the same so no valve cover/pcv valve problems there. Also, My O2 sensors are both brand new. I saw that my harmonic balancer wobbled a bit so I swapped it off for the other one that was on my 1999 engine. The balancer is nice and steady but the problem is the same.
This is definitely a misfire rhythm. There are no codes stored in the computer, so obviously there is no Service Engine Soon light.
Thank you to anyone who responds!!!!!
My power seems alright and I do not get any hesitation or anything at any RPMs. The car feels pretty much normal when it is above 1500 or so. Under that, it drives well, but when I press the throttle with my hand, it still misses at that RPM.
At idle, my RPMs do not surge at all; they are rock steady where they belong - at about 650. I have sprayed starter fluid on all vacuum lines to no avail. I listened around the engine for a hiss with a rubber hose in my ear (lol) and found nothing. My coils have all been checked and two were swapped out. My plugs and wires have been changed, I have checked spark only to find that all six wires produce a nice blue arc.
I also unbolted the down-pipe to see if the catalytic converter was clogged up, but the engine ran exactly the same with the pipe disconnected. I put a vacuum gauge on the upper intake manifold and the vacuum read between 18.5 and 19 in-hg; the needle swayed very very little. I have changed every fuel injector, the fuel filter, and air filter (as maintenance). My head gasket blew a couple of months ago, but this problem started about a month before it blew. I know exactly when the head gasket went because the car overheated on the highway when an idler pulley broke off causing the belt to fly off. I have performed a compression test and all of my cylinders held at least 175-180 for 5 minutes without losing any compression. My head gaskets and everything above has been replaced as required/recommended.
I disconnected my pcv hose from the valve and plugged up the end of the hose where the valve should be and started the car. It ran exactly the same so no valve cover/pcv valve problems there. Also, My O2 sensors are both brand new. I saw that my harmonic balancer wobbled a bit so I swapped it off for the other one that was on my 1999 engine. The balancer is nice and steady but the problem is the same.
This is definitely a misfire rhythm. There are no codes stored in the computer, so obviously there is no Service Engine Soon light.
Thank you to anyone who responds!!!!!