Ignition timing retarding under load/ hesitation
Thread Starter
TECH Resident
Joined: Mar 2012
Posts: 859
Likes: 402
From: Texas
Ignition timing retarding under load/ hesitation I'm dealing with a 2011 Silverado with an LMG 5.3, 207K miles.
It was brought to me for a bad hesitation under load. Truck came in with NO DTCs.
When driving the truck and giving it more than about 1/4 throttle, it feels almost like clogged catalytic converters; like the engine wants to rev up, but can't. (They aren't clogged, by the way; I checked.)
It is NOT misfiring at this time.
While viewing live data on the scanner, I saw that at those times, ignition timing will retard to anywhere from 0 degrees ATDC to -10 degrees.
If you ease off the gas pedal, it goes back to BTDC numbers.
Truck is stock from what I can tell. All sensors seem to be reading normally, fuel pressure is good. Has new AC Delco plugs gapped to specification.
Has anyone ever seen this before, and if so, what was the cause?
If not, does anyone have any suggestions on what to check next?
It was brought to me for a bad hesitation under load. Truck came in with NO DTCs.
When driving the truck and giving it more than about 1/4 throttle, it feels almost like clogged catalytic converters; like the engine wants to rev up, but can't. (They aren't clogged, by the way; I checked.)
It is NOT misfiring at this time.
While viewing live data on the scanner, I saw that at those times, ignition timing will retard to anywhere from 0 degrees ATDC to -10 degrees.
If you ease off the gas pedal, it goes back to BTDC numbers.
Truck is stock from what I can tell. All sensors seem to be reading normally, fuel pressure is good. Has new AC Delco plugs gapped to specification.
Has anyone ever seen this before, and if so, what was the cause?
If not, does anyone have any suggestions on what to check next?
TECH Resident
Joined: Oct 2006
Posts: 993
Likes: 173
From: Euless, TX
Teching In
Joined: Aug 2023
Posts: 3
Likes: 1
Extreme heat soak can cause the issue. My Express van with the stock air box hits nearly 200°F IATs around town this time of year. The timing pull causes the engine to lose a ton of power. The timing has to be pulled to prevent detonation though. Elevated coolant temps also pull timing. Combine the Coolant and IAT timing adders or in this case subtractors and it is very easy to get negative timing values.
Log torque mgt advance and the other various torque management type PIDs and you will have your answer. Negative timing being commanded is almost always a torque management event and logging it should show you where.
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Joined: Aug 2023
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Finally found the problem, sadly it was after a catastrophic failure. The timing chain broke (at idle thankfully). 2 intake valves kissed a piston but luckily didn’t bend any valves. The cam gear and crank gear had significant signs of wear. Wound up doing a DOD delete with a new timing set and oil pump and the issue is no longer present….looked like the engine had not had the oil changed at regular intervals at some point in it’s life. Problem solved, customer is happy, glad to have this issue behind me.