Loud backfire after changing spark plugs

[flani33]

I recently changed spark plugs put in new collector gaskets and manifold gaskets to fix some leaks. The engine backfired very loudly during the first test drive. Drove it the next day 50 miles and it was fine. It happened again the day after and since my right ear was ringing I think it was the passenger side out of true duals with stock manifolds.

Pulled the plugs, checked the gaps at .40, checked firing order and that was all fine. Drove the next 2 days with no problem. It seems to backfire if i'm dogging it around town because it happened again today. It idles well as far as I'm concerned and has never backfired like this before.

I assume a cylinder isn't firing and I plan to check the points. It seems easy to say that I caused this problem or the changes have shown an underlying problem. I put in same plugs that i took out. Any advice would be helpful. Thanks

351w, holley 600

 

[Rustytruck]

Plug gaps for points are usually .032. Shouldn't be an issue. but you never know. I would check the points gap and make sure their on the wide side of tolerance. I would check your timing and also check and see that the vacuum diaphram in the distributer still holds vacuum. If your backfiring make sure any vacuum plugs you use are still intact. Make sure there is no carbon tracking inside the distributer cap and the top of the coil are clean dirt build-up adn a little moisture on top of the coil can wreak havoc.

 

[flani33]

I was checking cylinders and removing wires individually. The rpm drops on all cylinders except when I remove #3. I took out the plug and it was dry black carbon. I brought the gap down to .32 but it didn't help. The wire was firing on the exhaust manifold when i tried. I could try a different plug but it's new.

 

[flani33]

Ok, did some more research, I have an electronic magnetic trigger dizzy. Sorry, I'm not familiar with them. All the times I've heard this loud "backfire" the engine died briefly or I had to pull to a stop and restart it with no problems.

 

[flani33]

New update, engine dies and then w/ my foot still slightly on the gas it backfires which makes sense. The engine definitely died before it backfired though. I have had brief interruptions in power for the last 6 months but never figured it out. Kind of like the engine dies for a split second and then comes back on. I'd say now that the problem has gotten worse and the engine dies for seconds that a time while driving.
This bronco's my DD, trying to get it right before winter comes. Thanks again.

Chris

 

[Rustytruck]

So with electronic ignition open up the plug gap to .045
clean and tighten your battery cables at both ends especially the ground on the engine block. clean under the starter solonoid and the voltage regulator and make sure the bolts are tight. Make sure the wire connections are tight. Make sure you have a ground wire from the battery to the body in addition to the one going to the block. Make sure your coil wires are making good contact and the center wire is making good contact at both ends. Swap the dirty plug to a new location and see if it cleans up and the one swapped gets dirty. you can also remove N03 wire and swap with another one and see if the problem goes with the wire. all this costs nothing but time.
take off all the keys off your keyring and just use the ignition key and see if things get better a worn ignition switch and a heavy key ring are not a good match.
Start up the Bronco and while its running start wiggling some wires around the ignition and the starter solonid and see if the engine starts skipping. Stay away from the plug wires or you may get a good zap but if you have been pulling plug wires you already know this.

 

[Dan74Bronc]

Mine did the exact same thing. Would momentarily die then sometimes would backfire when it started back up. Spent a lot of time ohming stuff out but couldn't find the problem until one day it quit for good. Turns out the magnetic pick up in the dist was going bad then completely went bad. I replaced the dist with parts store reman and haven't had a problem since then.

 

[flani33]

Thanks for the info. I don't know how old the pick-up and distributor are. Probobly worth a shot.

I cleaned up behing the starter solenoid and the body/block grounds but the voltage regulator looks bad and is stuck to the fenderwell somehow. I drove aroudn for about 200miles and the truck died once while driving. I had taken all the keys off my keychain. I'm back at work and won't be able to work on the truck for sometime. Could a faulty voltage regulator cause the engine to die?

 

[Justafordguy]

I wouldn't think so but if there is a short in the wires running to it that could cause the problem. You need to check the wiring from the ignition switch to the coil very close and make sure it's good.