Backfires High Rpms

[Kev1990]

Hello I have a 1993 HONDA ACCORD EX F22A6 when revving the rpms high the car backfires real loud like BOOM! Not all the time when it's in high rpms it does it. I'm going to be checking for engine codes later today.

[GhostAccord]

When was the last time you checked the valve clearances?

You could try a compression test / leak down test to see if it is the valves.

Also could be some sort of ignition or fuel issue, weak coil, bad spark plugs, timing is off..etc..etc....

[Restless]

I'd check your spark plug wires first and make sure they are all in the right order first. Then either look at your spark plug gap or try replacing your spark plugs with some new ones and see if that helps or stops the problem. But like GhostAccord mentioned it can be any of the following things he mentioned.

[Kev1990]

I believe I have symptoms of a vacuum leak. Can a vacuum leak cause the car to run lean and backfire?

[GhostAccord]

Are you having these backfire issues while driving the car or while in park and revving the engine?

Vacuum leak symptoms usually show up as an erratic or sustained high idle. Not so much an issue of exhaust backfiring. Vacuum is more of an issue on the intake side of the engine. unless you have a leak in the EGR vacuum system... but even then, that is more of an engine miss or bogging issue than it is backfire.

A true backfire is caused by unburnt hydrocarbons (fuel) igniting outside the combustion chamber, or while the exhaust valve is still open.

[H311RA151N]

While on the throttle or after you let off?

If I take mine up to 5,000rpms or so in the lower three gears and let off for few seconds I get an explosion out of the muffler that lights up the night. It's due to a leaky exhaust gasket somewhere (or that's what I read anyways) and the fact that my engine burns so much oil.

Just figured I'd ask.

[Kev1990]

Hmm it seems to happen when I max the car out lol. Once again I was trying to set the base timing like I did on my F22A1 yesterday but this F22A6 stalls when I go to unplug iacv so I heard that's a vacuum leak the engine itself has a bit of power and seems pretty healthy but it has a couple of exhaust leaks also this is not my car it's my family members car. When I was checking it out in general it's a quart low on oil and the cooling system is almost completely empty if not empty and I see no leaking. The idle air control valve along with fast idle control valve I'm sure needs to be cleaned but the hoses to them are swollen where they connect but not leaking yet plus recently two of the valves started tapping a bit louder then usual but yet the other two are quiet. It feels like it has some hesitation but has some great power when maxing it out when I hold it at a rpm level it jumps/varies 50-200 rpms and at idle will go around 750-900 maybe even 950. I believe I hear minor backfires too just at idle even lower rpms maybe a misfires?

[GhostAccord]

If you unplug the IAC and the engine stalls that is usually do to a lack of air in the air fuel mixture entering the combustion chamber. A vacuum leak usually means more air entering as apposed to less. This could be due to the internal throttle body ports could be clogged or the set screws could be out of adjustment.

Have the throttle body idle set screw or throttle plate stop screw ever been adjusted?



Fixing any exhaust leak(s) that might be found between the cylinder head and the O2 sensor is a must. This will cause the ECU to think the engine is running lean, therefore it will add more fuel.

Once you fix the exhaust leaks and clean out the IACV you should reset the ECU.

Have you tried resetting the ECU/PCM?

if your are unsure how to do this it is simple.
• Disconnect the (-) battery terminal for 60 seconds.
• Start the car with no electrical load. No A/C, No lights, No radio etc etc.
• Let it idle for 5 - 10 minutes before you touch anything, including the gas or brake pedal.
• After the 10 minute warm up take the car for a quick stop and go drive
• Then a quick rip out on the highway.

This will reset your long term and short term fuel trims to reflect the current state of the engine.

[802cb7]

If you unplug the IAC and the engine stalls that is usually do to a lack of air in the air fuel mixture entering the combustion chamber. A vacuum leak usually means more air entering as apposed to less. This could be due to the internal throttle body ports could be clogged or the set screws could be out of adjustment.

Have the throttle body idle set screw or throttle plate stop screw ever been adjusted?



Fixing any exhaust leak(s) that might be found between the cylinder head and the O2 sensor is a must. This will cause the ECU to think the engine is running lean, therefore it will add more fuel.

Once you fix the exhaust leaks and clean out the IACV you should reset the ECU.

Have you tried resetting the ECU/PCM?

if your are unsure how to do this it is simple.
• Disconnect the (-) battery terminal for 60 seconds.
• Start the car with no electrical load. No A/C, No lights, No radio etc etc.
• Let it idle for 5 - 10 minutes before you touch anything, including the gas or brake pedal.
• After the 10 minute warm up take the car for a quick stop and go drive
• Then a quick rip out on the highway.

This will reset your long term and short term fuel trims to reflect the current state of the engine.

Is that true on obd1?