Backfired After Not Starting Up For 3 1/2 Months

[kings1527]

Is this normal?

I've spent the last 3 1/2 months redoing everything from the water pump, alternator, changed the fuel lines, oil sending unit, plugs, wires, cap, rotor, belts, and painting/detailing all of the engine parts. A complete engine compartment overhaul, but didn't do anything with the timing or anything like that. The most I did was pull the valve covers and timing chain cover off to paint them.

I cranked the car for several cranks but decided the battery needed to be charged so I charged it overnight. Then I re-installed the battery and cranked it for about 5 seconds and a loud bang with smoke came mainly from the driver's side exhaust. I didn't do anything else until I got some advice as to what the problem could be.

Have others experienced this and is "normal' after having the car sit for that long? What should I check? Thanks!

Alex
6575

[dmc6960]

Did you remove the ignition distributor at all?

Is the cap seated square? Plug wires all in the proper order?

Ignition is the most likely cause of this.

[kings1527]

Did you remove the ignition distributor at all?

Is the cap seated square? Plug wires all in the proper order?

Ignition is the most likely cause of this.

Thanks. I checked the wires about three times when I connected them. I'm 99.9% sure I did the wires right. I'm confident about the cap, too. I never removed the ignition distributor; just the cap and rotor. All that said, I'll go back to check as much as I can with the manifold back on and tear it down again if need be.

Could it be that a good amount of fuel sat for a couple days in the exhaust after my failed attempts to start it with a battery that was really low? Then when I started it a couple days later with a full battery, it ignited the unburned fuel from a couple days ago?

Thanks for all advice anyone has.

Alex
6575

[WelmoedJ]

This happens every now and then.

I had an alike situation where I could crank, but a weak battery prevented starting.
After a recharge and some hours later, I also had the "bang"!
Waited a moment then started again and the engine ran without any sign of problems.

There has been info on this issue in other threads on this forum.

[Ron]

Could it be that a good amount of fuel sat for a couple days in the exhaust after my failed attempts to start it with a battery that was really low? Then when I started it a couple days later with a full battery, it ignited the unburned fuel from a couple days ago? Makes good sense...fuel can sit in the cylinder(s) waiting a fairly long time as well.

[kings1527]

Thanks guys. I figured this might be "normal" but I'll still go back and double check the ignition components.

Thanks Welmoed. I took a good look on a search for "backfire" but nothing came up along the lines of my problem. Do you have a link for the other thread? I'd like to hear about the experiences that others had with this.

Thanks again for all the help. I appreciate it.

Alex
6575

[WelmoedJ]

Thanks Welmoed. I took a good look on a search for "backfire" but nothing came up along the lines of my problem. Do you have a link for the other thread? I'd like to hear about the experiences that others had with this.

Alex
6575

I did notice this kind of discussion some time in the past, perhaps this year.
However it could have been part of another thread.
Did you also do a search in the text or only the subject line?
Anyway I seem not able to recall where or in which thread I read alike info.

[kings1527]

I did notice this kind of discussion some time in the past, perhaps this year.
However it could have been part of another thread.
Did you also do a search in the text or only the subject line?
Anyway I seem not able to recall where or in which thread I read alike info.


Ok, thanks for the help. I might've found a couple threads where the topic might be hidden in. Thanks again.

Alex
6575

[WelmoedJ]

I cranked the car for several cranks but decided the battery needed to be charged so I charged it overnight.
Then I re-installed the battery and cranked it for about 5 seconds and a loud bang with smoke came mainly from the driver's side exhaust.

I have taken your above tekst out of the first message.
Recalling my "load bang", I think it was more a kind of loud, short and sharp bang.
Especially the sharpness of the sound is what I remember.
More like firing a gun or so.
It was not what I have experienced with backfires from other cars in the far past.
Is that also what you experienced?

[kings1527]

I have taken your above tekst out of the first message.
Recalling my "load bang", I think it was more a kind of loud, short and sharp bang.
Especially the sharpness of the sound is what I remember.
More like firing a gun or so.
It was not what I have experienced with backfires from other cars in the far past.
Is that also what you experienced?

I think we're talking about the same thing. That's exactly what mine sounded like....like a gun that fired. And you're right...not like a typical car backfiring as it drives down the road; but a very loud, short, sharp bang...just like you described. And I remember white smoke that came out. Very white.

Alex
6575

[DMCMW Dave]

And I remember white smoke that came out. Very white.

Alex
6575

White smoke like that is gasoline. OR coolant, but that doesn't explode.

[cdrusn]

I think we're talking about the same thing. That's exactly what mine sounded like....like a gun that fired. And you're right...not like a typical car backfiring as it drives down the road; but a very loud, short, sharp bang...just like you described. And I remember white smoke that came out. Very white.

Alex
6575

With regards to your question concerning whether it could have been unburned fuel from a few days before. Take a tablespoon of gas and put in on a pie plate and let it sit over night. Anything left? More than likely in my experience it's a vacuum leak that is allowing more air than fuel to enter the mixture control unit and making a too lean mixture that back fires. Look for vacuum leak at the cold start valve going into the fuel regulator. Make sure all you vacuum connections are tight, use the vacuum hose diagram to make sure your vacuum connections are correct.

[kings1527]

With regards to your question concerning whether it could have been unburned fuel from a few days before. Take a tablespoon of gas and put in on a pie plate and let it sit over night. Anything left?

I thought about that but I also considered the following:

1) I tried cranking the car about a good 5-6 times on a bad battery, so the amount of fuel that was introduced was pretty significant,
2) The engine itself is contained and not exposed to air,
3) My car is garaged and out of the elements

After considering all that, I thought most likely the leftover fuel was the problem. But you bring up good points. I picked up Hervey's silicone vacuum set (very nice, by the way) and installed that. All of the connections fit on very snug but I'll double check everything. I'm 99.9% sure about those, too. I double, triple, quadruple-checked the plug wires, vacuum lines, and grounds during installation.

As long as I'm not going to hurt anything (other than my ears), I'll give it a shot again on Monday since I won't be home until then.

Thanks for the help, everyone. And if anyone else has any ideas, please keep them coming.

Alex
6575

[kings1527]

Did you remove the ignition distributor at all?

Is the cap seated square? Plug wires all in the proper order?

Ignition is the most likely cause of this.

Jim...you are the winner. As embarrassed as I am to say, I put the distributor cap on upside down. :banghead:

What can I say? Amateur at work...

As soon as I swapped everything around and put it back together, it fired right up. The only problem is I now have a high idle at around 2k when it gets warmed up. Hmmm..


Alex
6575

[kings1527]

It was the lower adjustment screw; below the screw that hits the microswitch. It fell out of adjustment during the rebuild and I had to back it out. Now I'm at an idle around 1k, which is where I was before I tore everything down for a valley rebuild.

I swapped out all my vacuum lines with Hervey's silicone lines so I may have inadvertently fixed a minor vacuum leak which could've caused my high idle before. Now, maybe hooking a dwell meter up and adjusting the CO might fix the idle problem. It's running rich after the mixture unit was torn apart.

Alex
6575