So the wife’s 19 Tahoe (5.3l) went over 100k and having had it since under 50k, I knew it was time for spark plugs. I picked up AcDelco spark plugs and wires from Rock Auto. Replaced the plugs and wires Saturday, inspected everything, they came gapped at .040, wires all looked good and came with dielectric grease on the connectors. I just put a bit of antisieze on the plug threads, started by hand, and tightened slightly passed hand tight.
Started fine, but had the check engine light and it had a rough idle. My neighbor used to be a shop mechanic for a local power company, he now runs the shop, but still has all his stuff. We hooked it up to his Apollo-Dg scan tool and it showed a P0300 error, but now specific cylinder. He suggested rechecking the plugs and wires and if all was good there, new coils. Checked the plugs and wires, thought maybe I over tightened, but they were fine. Wires seated firmly.
Picked up new coils Sunday and installed them. Rough idle was immediately gone. No shuttering when accelerating, everything ran smoothly. Wife drove it on a 4 hour round trip Sunday afternoon with no issues other than what she described as a rough shift when slowing from freeway speed.
She came home, we hooked the scan tool up again (it didn’t clear the check engine light the last time) and got that cleared. Still ran fine. Took it for another test drive and the check engine light came back. Today after work, we hooked it up again,cleared the code, and monitored. All cylinders were working fine. No detected misfires. No sensor issues. Air mixture was fine. We checked each coil and they are working fine. I took it around the neighborhood again, no issues. Took it up to the corner to put gas in it and got it up to 70…no issues. Cruise at 55, fine. Accelerated out of cruise to 65…check engine light. Cruise and front collision systems deactivated (everything is connected to the computer so it wasn’t a surprise, they started working soon after). Came back, neighbor suggested disconnecting the battery for 15 minutes and driving it again. Did so, check engine light was gone, driving in the neighborhood was fine, got out on the main road and hit 60+….check engine light back on. Just to reiterate, there’s no actual rough idle or issues with acceleration now. If anything the RPM needle might move the slightest amount at idle, but it’s barely a blip. The only now is the check engine light and this weird hard downshift. Now other engine codes than the P0300.
I’ve read up on the P0300 error and there seem to be quite a few things that can cause it. My assumption (possibly wrong) is that it has to be related to the plugs/wires since that was when the issue first appeared. Neighbor is going to call his friend who is the lead tech at the local Chevy dealer to see what he says. He’s thinking a bad wire, but I just keep going back to it being the generic P0300 error which indicated random misfire. That said, none of the cylinder showed misfire at idle or even under load in the driveway. Anyone have any other ideas?
Started fine, but had the check engine light and it had a rough idle. My neighbor used to be a shop mechanic for a local power company, he now runs the shop, but still has all his stuff. We hooked it up to his Apollo-Dg scan tool and it showed a P0300 error, but now specific cylinder. He suggested rechecking the plugs and wires and if all was good there, new coils. Checked the plugs and wires, thought maybe I over tightened, but they were fine. Wires seated firmly.
Picked up new coils Sunday and installed them. Rough idle was immediately gone. No shuttering when accelerating, everything ran smoothly. Wife drove it on a 4 hour round trip Sunday afternoon with no issues other than what she described as a rough shift when slowing from freeway speed.
She came home, we hooked the scan tool up again (it didn’t clear the check engine light the last time) and got that cleared. Still ran fine. Took it for another test drive and the check engine light came back. Today after work, we hooked it up again,cleared the code, and monitored. All cylinders were working fine. No detected misfires. No sensor issues. Air mixture was fine. We checked each coil and they are working fine. I took it around the neighborhood again, no issues. Took it up to the corner to put gas in it and got it up to 70…no issues. Cruise at 55, fine. Accelerated out of cruise to 65…check engine light. Cruise and front collision systems deactivated (everything is connected to the computer so it wasn’t a surprise, they started working soon after). Came back, neighbor suggested disconnecting the battery for 15 minutes and driving it again. Did so, check engine light was gone, driving in the neighborhood was fine, got out on the main road and hit 60+….check engine light back on. Just to reiterate, there’s no actual rough idle or issues with acceleration now. If anything the RPM needle might move the slightest amount at idle, but it’s barely a blip. The only now is the check engine light and this weird hard downshift. Now other engine codes than the P0300.
I’ve read up on the P0300 error and there seem to be quite a few things that can cause it. My assumption (possibly wrong) is that it has to be related to the plugs/wires since that was when the issue first appeared. Neighbor is going to call his friend who is the lead tech at the local Chevy dealer to see what he says. He’s thinking a bad wire, but I just keep going back to it being the generic P0300 error which indicated random misfire. That said, none of the cylinder showed misfire at idle or even under load in the driveway. Anyone have any other ideas?
. All I know is I installed them all the same way, tightened the same amount. I took all the driver's side plugs out just to make sure and they were all fine (didn't feel like tearing into the passenger side).
