Constant "pinging"
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Junior Member
Joined: Nov 2003
Posts: 2
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From: East Coast, USA
Constant "pinging"
I'm new here guys and I need some help. I have a 1986 F150, 4.9 six with a one barrel carb. The truck has 108,000 miles and is good shape with one glaring problem....it pings under partial throttle all the time. It's driving me nuts. I've tried higher octane, but the pinging doesn't stop. It has been doing this awhile....maybe moreso after I overheated it last winter when it was frozen and I drove it a few miles before I noticed (not enough anti-freeze and no dash lights.....what can I say ?) My mechanic replaced the water pump and it has been fine, but the pinging is making me batty . The truck does ok under a load, but at partial throttle....PING, give it gas, no ping, let off the gas, no ping.....partial throttle, almost any gear P I N G ! My mechanic says smog stuff may be the problem (I'm not buying that) and says my timing is alright. Help me out....PLEASE!
Technical Article Contributor
Joined: Nov 2002
Posts: 2,804
Likes: 9
From: Wisconsin
Sounds to me like you have a lot of carbon built up in the cyls. Some Lube Control in the oil and Fuel Power in the gas will soften the carbon and clean it out.
Here is a link where some test were done.
LC FP report
I'm just guessing , but you may have excessive blow-by when the engine works harder that is preventing pinging. Blow-by can go down one cyl on the power stroke, and up another that is on the intake stroke.
Where to get LC and FP
Or just www.lubecontrol.com
Lube Control
Here is a link where some test were done.
LC FP report
I'm just guessing , but you may have excessive blow-by when the engine works harder that is preventing pinging. Blow-by can go down one cyl on the power stroke, and up another that is on the intake stroke.
Where to get LC and FP
Or just www.lubecontrol.com
Lube Control
Member
Joined: Nov 2003
Posts: 12
Likes: 0
Senior Member
Joined: Mar 2001
Posts: 4,506
Likes: 6
From: Puyallup, WA
When was the last time the timing was set/tuneup? I'm not sure if it'll have a vacuum advance on the dist or not, but maybe something with that too?
I had a '86 5.0 GT with electronic ignition, but you still had to set the timing. It had an electronic advance, so it either worked or it didn't........
On the GT, I had to disconnect a wire harness to the dist to set the timing correctly. I think it was 12* ATDC.......
Good luck!
I had a '86 5.0 GT with electronic ignition, but you still had to set the timing. It had an electronic advance, so it either worked or it didn't........
On the GT, I had to disconnect a wire harness to the dist to set the timing correctly. I think it was 12* ATDC.......
Good luck!
Senior Member
Joined: Feb 2002
Posts: 152
Likes: 0
I had an 83 with the same carb with no computer feedback. A few things I would check.
Use a plastic straw (like the one from a can of carb cleaner) and place it under the egr valve through the holes in the underside. Rev engine to 2200 RPM while holding straw and feel if the valve moves. It should move and stay open at a constant speed engine speed. If it doesn't open it WILL ping.
Next use a vacuum source and hook it to the EGR valve while the truck is idleing. The truck should stumble and run rough when vacuum is applied if the passages are open.
There is typically a EGR vac line "dump valve" that releases the vacuum to the EGR valve at WOT. Make sure it is adjusted properly so it only activates at real WOT.
The I6 is known for carbon build up. Others mentioned cleanup methods.
Look at the advance weights in the distributor. The springs get streched and give too much advance too soon. This will cause pinging even if the timing is right on.
That carb is lean to begin with, so if the jets are varnished or dirty the fuel delivery will only get worse. This will also cause lean ping at cruise. A loose throttle shaft is another possible problem. The carbs are easy to rebuild if the throttle shaft is tight.
The carb comes loose from the intake, the base gasket gets smashed, and the screws coming up from the bottom of the carb some loose. This is all caused by the air cleaner hold down bolts that are almost always missing. The big housing puts alot of force on the carb and its mountings. The wing nut bolt thing is not enough, replace the gaskets and tighten things as needed. Then use all the hardware to bolt the air cleaner housing down.
There is a bridge that the air cleaner wing/bolt thing attaches to on top of the carb. The screws that hold the bridge have big heads so they don't fit through the carb. If one has fallen into the carb it will cause fuel delivery issues. Look down the bore of the carb (engine off) for the screws if they are missing or have been replaced. There is only one place for them to go. Also don't use replacements with small heads, they will fit through the carb and create a whole new kind of "pinging".
Lastly, the intake gaskets are prone to leakage. They will typically cause a miss, but many leaks will cause an overall lean condition. I use carb spray to find the leaks.
The brake boosters fail and create vacuum leaks. A hard pedal or hissing noise at idle with your foot on the brakes will tell you there is an issue here.
Use a plastic straw (like the one from a can of carb cleaner) and place it under the egr valve through the holes in the underside. Rev engine to 2200 RPM while holding straw and feel if the valve moves. It should move and stay open at a constant speed engine speed. If it doesn't open it WILL ping.
Next use a vacuum source and hook it to the EGR valve while the truck is idleing. The truck should stumble and run rough when vacuum is applied if the passages are open.
There is typically a EGR vac line "dump valve" that releases the vacuum to the EGR valve at WOT. Make sure it is adjusted properly so it only activates at real WOT.
The I6 is known for carbon build up. Others mentioned cleanup methods.
Look at the advance weights in the distributor. The springs get streched and give too much advance too soon. This will cause pinging even if the timing is right on.
That carb is lean to begin with, so if the jets are varnished or dirty the fuel delivery will only get worse. This will also cause lean ping at cruise. A loose throttle shaft is another possible problem. The carbs are easy to rebuild if the throttle shaft is tight.
The carb comes loose from the intake, the base gasket gets smashed, and the screws coming up from the bottom of the carb some loose. This is all caused by the air cleaner hold down bolts that are almost always missing. The big housing puts alot of force on the carb and its mountings. The wing nut bolt thing is not enough, replace the gaskets and tighten things as needed. Then use all the hardware to bolt the air cleaner housing down.
There is a bridge that the air cleaner wing/bolt thing attaches to on top of the carb. The screws that hold the bridge have big heads so they don't fit through the carb. If one has fallen into the carb it will cause fuel delivery issues. Look down the bore of the carb (engine off) for the screws if they are missing or have been replaced. There is only one place for them to go. Also don't use replacements with small heads, they will fit through the carb and create a whole new kind of "pinging".
Lastly, the intake gaskets are prone to leakage. They will typically cause a miss, but many leaks will cause an overall lean condition. I use carb spray to find the leaks.
The brake boosters fail and create vacuum leaks. A hard pedal or hissing noise at idle with your foot on the brakes will tell you there is an issue here.