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Discussion Starter · #1 ·
What I have:

1985 EFI, 2.25" from the cat back with a 3 chamber flow master. The throttle body has been bored out. I recently put that on. The engine was rebuilt and balenced about 35k miles ago. There is a drop in K&N air filter installed.

What I've done recently:

Full tune up- new plugs, wires, cap, rotor, fuel filter (what a b***h), belts, timing adjusted, valves adjusted.

The problem / question: <IMG SRC="smilies/confused.gif" border="0">

Recently, the engine started pinging pretty bad when I was running regular gas. It had been fine for the year the engine had been in it. So I ran some engine deposit cleaner through it with no real affect (it was slightly better). I moved up to 89 octane gas and now it runs much better. It feels like it has much more power and the pinging isn't there. To me that means that the knock sensor was most likely really retarding the timing when running 87 octane.

I am wondering that if with the new throttle body, should I make some adjustment to the AFM?

Also, when I let off the gas under load (like letting the engine slow me down), it often sounds like the engine is almost backfiring. Any idea what this means?
 

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check your timing. it sounds like it is advanced too far. the knock sensor retards the timing when it detects a "KNOCK" or "PING" retarding the timing should reduce the enging "KNOCK". check for an exhaust leak. sometimes when you back off the throttle the exhuast can suck air in through a leak. this will create a POP sound.
 

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You might also try pulling the EFI fuse for 15-20 minutes so the ECU will reset. It could help.
 

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odds are you will need to adjust the AFM due to the throttle body and exhaust, i would also recommend stepping up and running super, that is all i run in mine and have no pings, also check for exhaust leaks as far as the backfire thing.
 

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This is taken from the service manual
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PROBLEM: Pinging or knocking engine sounds when engine is under load

1. Incorrect grade fuel

2. Ignition timing incorrect

3. Carbon build-up in combustion chamber. Remove cylinder head and clear cumbustion chambers

4. Incorrect spark plugs
 
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