Backfiring
Thread Starter
Racer
Joined: Dec 2007
Posts: 262
Likes: 12
From: Montgomery Alabama
Backfiring
A genius, I am not. Went to my mechanic on Thursday, flushed the radiator, replaced thermostat, bought new radiator cap and recharged the air conditioner (Alabama Heat). By the time I got home no air conditioning. Must be leak. Bought sealer. Now, here is the question: she now idles fine but backfires when accelerating, Why? I would ap preciate your sage advice
Marines
Marines
Safety Car
Joined: Aug 2002
Posts: 3,842
Likes: 230
From: SANTA CRUZ CA
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
If the engine coughs out the intake, there is a intake valve hanging up.
If out the exhaust, it is an exhaust valve.
Also, since these cars have smog pump gulp valves, if one goes bad, it can cause the engine to "pop" as the valve is just open.
Because there is only one catalytic converter, it is hard to determine the side that is popping.
If it were me, I would adjust the valves, and determine that the cam is still good.
With today's oil, If you are not running synthetic oil, deisel oil, or adding a cam preservative, you are looking at a flat cam in the future.
SOOOOOO
take a compression check after adjusting the valves, and you might be farther ahead.
All cylinders should be within 5 Lbs onn a new engine.
a 25 year old engine with 75,000 miles should be within 25 lbs of each other.
any low cylinders, take out the plug for that cylinder, give that cylinder a couple squirts of engine oil through the plug hole.
If the compression comes up, it is rings.
If the pressure stays at the same level, it is a valve.
If out the exhaust, it is an exhaust valve.
Also, since these cars have smog pump gulp valves, if one goes bad, it can cause the engine to "pop" as the valve is just open.
Because there is only one catalytic converter, it is hard to determine the side that is popping.
If it were me, I would adjust the valves, and determine that the cam is still good.
With today's oil, If you are not running synthetic oil, deisel oil, or adding a cam preservative, you are looking at a flat cam in the future.
SOOOOOO
take a compression check after adjusting the valves, and you might be farther ahead.
All cylinders should be within 5 Lbs onn a new engine.
a 25 year old engine with 75,000 miles should be within 25 lbs of each other.
any low cylinders, take out the plug for that cylinder, give that cylinder a couple squirts of engine oil through the plug hole.
If the compression comes up, it is rings.
If the pressure stays at the same level, it is a valve.
