Random Misfire/back fire
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Freshman User
Joined: Apr 2014
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Random Misfire/back fire
I have a 1978 ford f150 with 302 v8 in it. It was having a hard time starting in the morning so i decided to do an oil change....ran fine then i wanted to change the ignition system (spark plugs, wires, distributor cap and rotor, and ignition coil) i changed one wire at a time then one spark plug at a time. Now when it starts up every few seconds it back fires at idle then when i put it in gear it gets really bad it misses back fires jumps and stalls out if i give it any gas.
Parts i used
-motorcraft platinum spark plugs
-accel super stock 8mm high temp wires (i have headers)
-bwd cap and rotor
-bwd ignition coil
Parts i used
-motorcraft platinum spark plugs
-accel super stock 8mm high temp wires (i have headers)
-bwd cap and rotor
-bwd ignition coil
Cargo Master
Joined: Jun 2014
Posts: 2,212
Likes: 322
From: Central Florida
It might be best to start from square one as they say.
The firing order on your truck should be:
1 - 5 - 4 - 2 - 6 - 3 - 7 - 8
The distributor rotor turns COUNTERCLOCKWISE
The # 1 position on the distributor cap faces to the REAR
The engine cylinder / spark plug locations are numbered :
firewall
4 - 8
3 - 7
2 - 6
1 - 5
front
source: 1978 ford 302 firing order
NOTE: The 302 HO engine has a different firing order (1-3-7-2-6-5-4-8) but this probably doesn't apply to your situation.
So, remove the distributor cap and turn the engine until the rotor points to the rear. Find the terminal on the cap closest to the rotor when installed. That's where your #1 wire should be. Correct if not. With that as a start point, make sure all wires are in the proper firing order. Also make sure that the connection on both ends is solid. With the rubber boots on some ignition wires, it is possible to look like its connected when, in fact, it is not.
This process will at least assure you that your firing order is correct. Then, if you're still seeing the symptoms you can move to other possible causes.
The firing order on your truck should be:
1 - 5 - 4 - 2 - 6 - 3 - 7 - 8
The distributor rotor turns COUNTERCLOCKWISE
The # 1 position on the distributor cap faces to the REAR
The engine cylinder / spark plug locations are numbered :
firewall
4 - 8
3 - 7
2 - 6
1 - 5
front
source: 1978 ford 302 firing order
NOTE: The 302 HO engine has a different firing order (1-3-7-2-6-5-4-8) but this probably doesn't apply to your situation.
So, remove the distributor cap and turn the engine until the rotor points to the rear. Find the terminal on the cap closest to the rotor when installed. That's where your #1 wire should be. Correct if not. With that as a start point, make sure all wires are in the proper firing order. Also make sure that the connection on both ends is solid. With the rubber boots on some ignition wires, it is possible to look like its connected when, in fact, it is not.
This process will at least assure you that your firing order is correct. Then, if you're still seeing the symptoms you can move to other possible causes.
Thread Starter
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Freshman User
Joined: Apr 2014
Posts: 27
Likes: 0
i have true duel exhaust and it back fires on the driver side cylinder number 5 when i pull that spark plug the back fire stops and truck runs normal so i tried pulling other spark plug wires but the engine would barely run so that one cylinder is the only one giving me problems....could i have a burnt valve?
Freshman User
Joined: Dec 2011
Posts: 48
Likes: 0
I am with Flowney, if it didnt do it before it has to be something you did. Making sure your rotar is lined back up is crucial. Definately sounds like timing is way off and order might be changed around.
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Laughing Gas
Joined: Sep 2003
Posts: 968
Likes: 5
From: Corbett, Oregon
Assuming that all is correct and where it should be I would be suspect of the new components.
Check and see if the plug in #5 is cracked or otherwise damaged. If all looks OK swap the #5 plug with another plug and see if the problem moves with the plug.
If the problem moves with the plug, you have found the culprit. If the problem stays with #5 check the plug wire and it's connections, then do the "swap it out" routine like you did with the plug.
If the original problem persists I would do a compression check as a starting point.
Remember, when trouble shooting, don't assume anything. Check and double check everything, even if you just did.
Be systematic and prove out one item at a time. Never make more than one change without confirming the change.
Good luck.
Check and see if the plug in #5 is cracked or otherwise damaged. If all looks OK swap the #5 plug with another plug and see if the problem moves with the plug.
If the problem moves with the plug, you have found the culprit. If the problem stays with #5 check the plug wire and it's connections, then do the "swap it out" routine like you did with the plug.
If the original problem persists I would do a compression check as a starting point.
Remember, when trouble shooting, don't assume anything. Check and double check everything, even if you just did.
Be systematic and prove out one item at a time. Never make more than one change without confirming the change.
Good luck.
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