I have a 2009 1500 with the flex fuel 5.3l that has a rough idle and a strange intermittent knock of a sort. The ‘knocking’ seems to coincide with the RPM and it’s generally rough idle. The knocking goes away under load and has no issues running, in fact, it runs great other than idle. So far, I’ve replaced plugs, wires, changed oil, cleaned MAF. It has the occasional P0172,P0175 code combo and hard cold start but I’m pretty sure that’s just linked to the bad alcohol reading. I don’t have an advanced scanner to reset the alcohol content so I’m just driving it in the hopes it’ll clear itself after enough fill ups. I just need help in getting steered in the right direction for this knock though. It’s fairly concerning. Here is a link to a YouTube video of the noise
SOLVED! Intermittent knock/tick with erratic idle
- Thread starter myork831
- Start date
Mooseman
Moderator
For those error codes, you have to get the alcohol sensor reset. Maybe disconnecting the battery for more than 30 minutes might do it. If not you will need to locate someone with a scanner.
This worked. I watched for ignition leakage while it was running in the dark and found the one causing the miss. Just a bad wire in my case. The lack of codes and normal power under load definitely made me lean towards something different but this was it.
Very glad to see that the problem was something Simple to Fix at a Cost of Just a Few Dollars. :>)
Also.... There may be a fairly inexpensive way to get out of the GM Flex-Fuel Re-Set Purgatory as well:
The Foxwell NT510 Elite Scan Tool can perform a Fuel-Alcohol Reset in GM Vehicles in the 07-13 GM Trucks Running RICH and Setting the P0172 and P0175 Codes:
Foxwell NT510 Elite available on Amazon for $189.00
https://www.amazon.com/dp/B019QCG5RE/?tag=gmtnation-20
And the more exotic Xtools Model D8BT Professional Level Scan Tool can also perform the Fuel-Alcohol Reset in GM Vehicles in the 07-13 GM Trucks Running RICH and Setting the P0172 and P0175 Codes:
Xtools Model D8BT available on Amazon for $649.00
https://www.amazon.com/dp/B09N8VTBVH/?tag=gmtnation-20
And from Eric "O" at SMA (South Main Auto) following up on what others Fired Dual Parts Cannons at on another Earlier Model GMT800 throwing the P0172 and P0175 "RUNNING RICH" Codes... BUT... Solving The Problems by doing some Deeper Diagnostics:
Also.... There may be a fairly inexpensive way to get out of the GM Flex-Fuel Re-Set Purgatory as well:
The Foxwell NT510 Elite Scan Tool can perform a Fuel-Alcohol Reset in GM Vehicles in the 07-13 GM Trucks Running RICH and Setting the P0172 and P0175 Codes:
Foxwell NT510 Elite available on Amazon for $189.00
https://www.amazon.com/dp/B019QCG5RE/?tag=gmtnation-20
And the more exotic Xtools Model D8BT Professional Level Scan Tool can also perform the Fuel-Alcohol Reset in GM Vehicles in the 07-13 GM Trucks Running RICH and Setting the P0172 and P0175 Codes:
Xtools Model D8BT available on Amazon for $649.00
https://www.amazon.com/dp/B09N8VTBVH/?tag=gmtnation-20
And from Eric "O" at SMA (South Main Auto) following up on what others Fired Dual Parts Cannons at on another Earlier Model GMT800 throwing the P0172 and P0175 "RUNNING RICH" Codes... BUT... Solving The Problems by doing some Deeper Diagnostics:
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So the saga continues for me… After about a week the ticking came back. I pulled #1 sparkplug and found oil and have attributed this to an AFM issue. I’ll be gathering the parts to do an AFM delete and hopefully it fixes the issue.
You've probably already sussed this issue out... But while things from the Motor are all torn down.. consider having the Heads gone through by a Machine Shop, if possible ... or at the very least, replace the "Viton" Valve Stem Seals yourself to eliminate Valve Train Cast-Off Oil from draining down the Valve Stems and entering the Combustion Chambers.
With the Heads removed... De-carbonizing the Valves & Valve Seats and Combustion Chambers "On The Bench" with a soak in Berryman's Chem-Dip won't hurt one bit, either. NOTHING Beats using THIS Technique as a Passive, Low VOC, Non-Destructive Carbon Busting Method:
This Video is worth the viewing by others also curious about everything involved with an LS Engine AFM Delete:
Don't Forget... While the Engine Heads and the Intake Manifold are OFF the Block... Take the Time to Replace the Oil Pressure Sensor with an OEM Version AND Replace that Internal S/S Screen & Black Plastic Oil Filter tucked way down inside that OP Sensor cavity back there!
Use the Proper Harmonic Balancer Removal Tool AND the Proper H-B Installation Hardened Extra-Long Threaded Rod, Nuts and Washers Tool Kit as well. Don't be Tempted to use that Old TTY Crankshaft Bolt to "Draw in the H - B..." Toss that Damned, Useless Thing into your Metal Trash Drawer.
With the Heads removed... De-carbonizing the Valves & Valve Seats and Combustion Chambers "On The Bench" with a soak in Berryman's Chem-Dip won't hurt one bit, either. NOTHING Beats using THIS Technique as a Passive, Low VOC, Non-Destructive Carbon Busting Method:
This Video is worth the viewing by others also curious about everything involved with an LS Engine AFM Delete:
Don't Forget... While the Engine Heads and the Intake Manifold are OFF the Block... Take the Time to Replace the Oil Pressure Sensor with an OEM Version AND Replace that Internal S/S Screen & Black Plastic Oil Filter tucked way down inside that OP Sensor cavity back there!
Use the Proper Harmonic Balancer Removal Tool AND the Proper H-B Installation Hardened Extra-Long Threaded Rod, Nuts and Washers Tool Kit as well. Don't be Tempted to use that Old TTY Crankshaft Bolt to "Draw in the H - B..." Toss that Damned, Useless Thing into your Metal Trash Drawer.
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