My car developed a new problem on thursday. on my way home from work, I was going about 35 in 3rd gear. The car in front of me slowed down so I took my foot off the gas, and as it was winding down, it backfired (loud). Is this a timing issue or a carb issue? It is a 78 2.3 4 speed, Holley 5200. 85,300 miles (original) I rebuilt the carb 4 years ago (about 9000 miles ago) and it has been fairly problem free except for choke issues (that I have fixed). Occasionally when shifting from second to third it 'pops' from somewhere in the engine compartment on the passenger side. it has all of its smog equipment including air pump. It also has new plugs, wires, cap and rotor. I looked at the exhaust manifold and I can't see any cracks (I had another pinto with a cracked manifold). I don't have a timing light, so I don't know where the timing is set, but I haven't messed with it in the 5 years I've had the car. The exhaust is original except for a new catalytic converter 4 years ago (Must be a cheap one, the heat shield rattles). The car idles fine and accelerates smoothly.
Where do I start?
The backfire is probably from unburnt fuel in the exhaust system igniting.
I would suggest it is your ignition system.
Before you blame the electronic ignition, try changing everything in the ignition system...
Cap, rotor, spark plugs, & spark plug wires.
Change the air filter while you are at it. It can cause a rich mixture if plugged.
When changing the rotor, remove the felt pad under the rotor.
Add a drop of oil and replace the felt pad. Now add a drop of oil to the felt pad.
If you still have a problem...Next look if the timing belt is in good condition.
Check your plugs/Wires cap and rotor, IF there is mosture in the cap it might cause it to backfire or if its worn out. Could also just be a leak in the Exaust that caused it. (you stated its popped before) Check everything before you start replacing. if it looks worn out replace it.
Quote from: discolives78 on December 13, 2008, 02:24:29 PM
My car developed a new problem on thursday. on my way home from work, I was going about 35 in 3rd gear. The car in front of me slowed down so I took my foot off the gas, and as it was winding down, it backfired (loud). Is this a timing issue or a carb issue? It is a 78 2.3 4 speed, Holley 5200. 85,300 miles (original) I rebuilt the carb 4 years ago (about 9000 miles ago) and it has been fairly problem free except for choke issues (that I have fixed). Occasionally when shifting from second to third it 'pops' from somewhere in the engine compartment on the passenger side. it has all of its smog equipment including air pump. It also has new plugs, wires, cap and rotor. I looked at the exhaust manifold and I can't see any cracks (I had another pinto with a cracked manifold). I don't have a timing light, so I don't know where the timing is set, but I haven't messed with it in the 5 years I've had the car. The exhaust is original except for a new catalytic converter 4 years ago (Must be a cheap one, the heat shield rattles). The car idles fine and accelerates smoothly.
Where do I start?
I already replaced the plugs, wires, cap and rotor. I think I'm going to get a new exhaust gasket (manifold to pipe) I need to disconnect the exhaust anyway to get the battery tray out, and then check the timing belt and timing. I doubt moisture under the cap as our humidity usually doesn't exceed 45% and we havent had precipitaion in a while, but I'll check while I'm oiling the felt washer under the cap. Thanks for the advice.
What is the purpose of this felt pad? Also, I don't think I have mine anymore, I don't recall ever seeing it when I replaced my cap, rotor and plugs yesterday. What type of oil should be used on this and why is it important?
MY guess deceleration valve mine does the same thing slowing down especial if i let off and slow down fast with an automatic transmission
phil
Felt pad...
The felt pads purpose is to hold some oil and to prevent it from being thrown around.
The purpose of putting a drop of oil under the felt pad and one on the felt pad is to lubricate the centrifugal advance.
If you grab your rotor and rotate it, it should easily spring back.
Forgot to say...
The felt pad is under the rotor in the distributor shaft.
Take it out with a small screwdriver or small needle nose pliers.
If you have never lubed the distributor...
Add a couple drops of engine oil and re-install the felt pad.
Then add a drop or two of oil to the felt pad.
later, just use one drop of oil at each spark plug change.
The odd thing you mention about checking the dissy is the statement about it springing back when rotating...If I try to turn my distributor rotor, it doesn't move at all.