22R
For the 22R there are several common backfiring issues, and I will explain them and their causes individually.
- Leaking exhaust.
Ideally an exhaust system creates a low-pressure "void" around the exhaust ports of the head, where the hot gases are drawn into the lower-pressure length of the exhaust system. If there were a hole in your exhaust, this void would not exist, causing rich exhaust to build up, and eventually detonate inside the exhaust manifold, creating a series of "pops" when you shift, or throttle down.
Sounds like: That annoying rice burning tuner down the lane. You know the one.
Causes: damaged, rotted-out, or missing exhaust system.
Fixes: replace the damaged parts of the system, repair or replace the muffler.
Worst-case scenario: you'll eventually lose your manifold gaskets.
- Tight Exhaust Tappets.
This happens to everybody, as their truck sees more use, the exhaust tappets tighten to the point where they are unable to close all the way. You will have a loud "gunshot" bang out the tailpipe while decelerating if your engine is cold. If the engine's hot, you will hear a "chugging" sound, as the exhaust valves float a bit.
Sounds like: BANG! as soon as you let off the throttle, or a deep budda-budda-budda-budda out the pipe, especially out the downhill.
Causes: Tight Exhaust Tappets
Fixes: a tune-up. Get those valves adjusted.
Worst-case scenario: You can eventually burn out your valves. Backfiring can cost you mufflers, cats, or manifold gaskets. I had my exhaust downpipe get blown off the manifold.
- Leaking Diaphragm on Auxiliary Acceleration Pump.
This is unique to the carbureted motor. The AAP squirts a little extra fuel into the mix when the engine's cold. When the diaphragm is failing, it allows fuel to leak from the carb into the intakes, which can ignite, causing the backfire. It's a very loud detonation, comparable to the exhaust tappets bang, but it happens when you apply throttle, release it, and apply again. It occurs while the engine is cold.
Sounds like: BANG! the kind you want to happen in the face of the casual tailgating idiot, but the kind of BANG! you never ever want to hear.
Causes: Failing AAP diaphragm.
Fixes: a carb rebuild kit. The AAP is located outside the main body of the carb, on the driver's side (USA) facing the valve cover. Accessing it does not require a full carb rebuild, and the swap can be done on a manageably cool engine in an hour or two.
Worst-case scenario: Various damage across the exhaust system is fully possible. Burned valves or rings are likely with time.
- Detonation (aka "knocking")
I will refer to this as detonation as opposed to a knock, because there are other engine knocks, too. detonation occurs if the fuel mixture is either:
a: Too rich, and excess fuel is left in the open cylinder, and ignites with residual heat.
b: To lean, your engine is therefore running hot, and fuel is partially igniting as it enters the cylinder.
c: Out of time. The dizzy or coilpack could be sparking the plug just a little too late, and the borderline ignition between a tight or an open chamber is causing problems.
Sounds like: Popcorn popping in a can. If you've ever been in the pits of your local racetrack before the big event, you've heard it.
Fixes: Consult your temp gauge, and adjust your fuel mixture on your carb. If it's too hot, add more fuel, the opposite if it's at the right temp, but smells like partially-combusted fuel. Check your smog pump to make sure it's not throwing a false rich smell you way first.
Adjust timing at the dizzy/coilpack, check your plug wires for wear or shorts.
Worst-case scenario: A lean is always a bad thing, and can really harm your engine over time. Running rich means you'll never pass smog, and detonation, or any kind, can cause some nasty sooting and burning damage.
