FLYNAVY53
06-15-2021, 03:47 AM
The motor in my C20 Suburban was built by Thompson Motorsports back in 2014. Its a basic LQ4, stock crank and rods, Mahle forged pistons, small cam, 317 heads milled to 67cc chambers....nothing exotic.
I'm running the Holley Terminator TBI set up and finally got a proper tune from Andrew a couple months ago. The truck has never run better. Within the past few weeks, I've been getting intermittent back fires and the truck has really started to run poorly at light/part throttle. Everything with regard to the tune still looks correct....temps, AFR, sensor readings, etc. I've also noticed its developed a slight tick at idle. Its more than what you would associate with an exhaust leak (which I checked for with soapy water on the headers and did not find) but not as pronounced as what you would associate with rod knock. As you increase the RPM, the tick/knock goes away.
I've got a new set of coils, plugs, wires, and coil harness arriving today. All of that currently on the motor was pulled from the junk yard, so this will at least eliminate the possibility of an ignition issue.
My other thought was a bad/spongy lifter? As best I can tell, the noise is coming from the driver side bank. From what I've read, with a bad lifter, the sound you hear is the valve slamming closed, missing the ramp on the cam and smacking the seat.....does that sound accurate? If that was the case, would that valve being out of timing result in the periodic backfire I'm experiencing?
To make matters more interesting, I have movers arriving tomorrow to pack up the entire house as we move from Norfolk to Austin. This truck is my only mode of transportation for the next two weeks, before I have to drive it cross country to Texas. So I need to get this sorted....even if that involves pulling some cylinder heads in the parking lot of my buddy's condo over the next two weeks.
Thanks for the help guys!
I'm running the Holley Terminator TBI set up and finally got a proper tune from Andrew a couple months ago. The truck has never run better. Within the past few weeks, I've been getting intermittent back fires and the truck has really started to run poorly at light/part throttle. Everything with regard to the tune still looks correct....temps, AFR, sensor readings, etc. I've also noticed its developed a slight tick at idle. Its more than what you would associate with an exhaust leak (which I checked for with soapy water on the headers and did not find) but not as pronounced as what you would associate with rod knock. As you increase the RPM, the tick/knock goes away.
I've got a new set of coils, plugs, wires, and coil harness arriving today. All of that currently on the motor was pulled from the junk yard, so this will at least eliminate the possibility of an ignition issue.
My other thought was a bad/spongy lifter? As best I can tell, the noise is coming from the driver side bank. From what I've read, with a bad lifter, the sound you hear is the valve slamming closed, missing the ramp on the cam and smacking the seat.....does that sound accurate? If that was the case, would that valve being out of timing result in the periodic backfire I'm experiencing?
To make matters more interesting, I have movers arriving tomorrow to pack up the entire house as we move from Norfolk to Austin. This truck is my only mode of transportation for the next two weeks, before I have to drive it cross country to Texas. So I need to get this sorted....even if that involves pulling some cylinder heads in the parking lot of my buddy's condo over the next two weeks.
Thanks for the help guys!