302 won't stop pinging
Junior User
Joined: Jun 2015
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From: Sebring OHIO
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Senior User
Joined: Sep 2016
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Will do. My regular yard has around 3 of these trucks with 302s. Seems like most stuff still works but everything is all rusted out from all the salt on the roads.
Fleet Owner
Joined: Oct 2005
Posts: 20,786
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From: Kentucky
No feedback signal from the MAF causes the computer to run in open loop/default mode. This usually pulls timing and enriches the fuel/air mixture. Both will significantly lessen the chance of pinging.
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Senior User
Joined: Sep 2016
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Do you have a wiring diagram so I can ohm check the wiring between the sensor and the computer?
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Senior User
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I was wondering about that and if it doing that might be covering up another issue that I have somewhere else.
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Cargo Master
Joined: Mar 2010
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From: Laramie, WY
Unplugging the MAF sensor should put the PCM in open loop. Sounds to me like something related to closed loop operation/feedback. It would be interesting to know what the oxygen sensors are reading when the truck goes so lean. Does this truck have 1 or 2 oxygen sensors?
Edit: RLA2005 already said this.
If possible, monitoring ignition advance, oxygen sensor readings, throttle position, coolant temp, and intake air temp under various conditions (i.e. engine load) would be helpful. I'm not too familiar with OBD-I scanner capabilities but its a simple thing to graph with OBD-II scanners.
Edit: RLA2005 already said this.
If possible, monitoring ignition advance, oxygen sensor readings, throttle position, coolant temp, and intake air temp under various conditions (i.e. engine load) would be helpful. I'm not too familiar with OBD-I scanner capabilities but its a simple thing to graph with OBD-II scanners.
Thread Starter
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Senior User
Joined: Sep 2016
Posts: 219
Likes: 1
Unplugging the MAF sensor should put the PCM in open loop. Sounds to me like something related to closed loop operation/feedback. It would be interesting to know what the oxygen sensors are reading when the truck goes so lean. Does this truck have 1 or 2 oxygen sensors?
Edit: RLA2005 already said this.
If possible, monitoring ignition advance, oxygen sensor readings, throttle position, coolant temp, and intake air temp under various conditions (i.e. engine load) would be helpful. I'm not too familiar with OBD-I scanner capabilities but its a simple thing to graph with OBD-II scanners.
Edit: RLA2005 already said this.
If possible, monitoring ignition advance, oxygen sensor readings, throttle position, coolant temp, and intake air temp under various conditions (i.e. engine load) would be helpful. I'm not too familiar with OBD-I scanner capabilities but its a simple thing to graph with OBD-II scanners.
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Senior User
Joined: Sep 2016
Posts: 219
Likes: 1
Due to me not having the knowledge/time to be diagnosing this issue, I brought the truck to a local shop. Apparently there is a tsb for the spark plug wire routing that they will be trying. They said that if this doesn't fix the issue they think its a cylinder running too hot due to a plugged water jacket(coolant was brown sludge when I bought the truck 2 years ago). They also said the passenger side manifold is cracked right by the exhaust port that has the cylinder that has the pinging. The exhaust temperature in this spot is about 100 degrees hotter than the rest of the manifolds. Is it possible that the exhaust leak or a plugged water jacket be causing my problem?
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Senior User
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They also flow checked the fuel injectors(they were good). Compression was around 140 psi in all cylinders and they used a camera to look in the cylinders and the pistons(did have a small ring of carbon on the edge of the piston) and cylinder walls were clean and still had factory machining marks and cross hatches were still visible on the cylinder walls.
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Senior User
Joined: Sep 2016
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I got a call back from the shop and they said the pinging is gone. They flushed the cooling system with CLR and got a bunch of rusty sludge coming out of the engine. This was causing the combustion chamber to run too hot and ping. 
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Senior User
Joined: Sep 2016
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I got my truck back from the shop and got to drive it myself. The pinging is completely gone. 
Thanks everyone for all your help. It was good to be able to knock some stuff off the list of possibilities before I brought it to the shop.
Thanks everyone for all your help. It was good to be able to knock some stuff off the list of possibilities before I brought it to the shop.
