Engine back fires

[Rainer S.]

Just started my 63 SWC Fuelie after a long winter. When I ran the motor last year, I adjusted timing etc and it ran OK with the occational "miss", which I was planning to investigate after storage. ( the car has been under a 5 year restoration).
I installed the spark plug shielding last winter, except the cover over the distributor.
When I started the car up, it backfired, on what apears both banks. The backfiring did not go away as the motor warmed up (didn't want to cont running it).
What is the likely cause of the back-firing, or "missing" ? There is a popping sound coming from the exhaust...
Is there a way to narrow down the root cause ? Can someone stear me in the right direction ?


Rainer

[David D.]

Re: Engine back fires

Just started my 63 SWC Fuelie after a long winter. When I ran the motor last year, I adjusted timing etc and it ran OK with the occational "miss", which I was planning to investigate after storage. ( the car has been under a 5 year restoration).
I installed the spark plug shielding last winter, except the cover over the distributor.
When I started the car up, it backfired, on what apears both banks. The backfiring did not go away as the motor warmed up (didn't want to cont running it).
What is the likely cause of the back-firing, or "missing" ? There is a popping sound coming from the exhaust...
Is there a way to narrow down the root cause ? Can someone stear me in the right direction ?

Rainer

Hard to say for sure with little provided, but.....
Sounds like it could be timing to me....did you remove and re-install dizzy, or loosen since start of storage? I would check.

I would then check plugs, wires, coil and points to make sure your spark is strong enough to burn all gas supplied to cylinder(s).

Just my opinion...
David

[Harmon C.]

Re: Engine back fires

Poping in exhaust is sometimes valve adjustment.

[Timothy B.]

Re: Engine back fires

Rainer,
I don't know much about F/I but after checking the usual things, points wires etc it sure sounds like a lean miss to me. That can make it backfire and pop out the exhaust because lean is slow to burn so something in the FI may be out of adjustment.
I would start with the simple things first, if the wires are reproduction try to start the car at night to see if they are leaking and go from there.

[Rick A.]

Re: Engine back fires

assuming you had the distributor out during restoration, agree with David - start with the distributor and work from there

[Duke W.]

Re: Engine back fires

What you are describing is afterfiring. "Backfiring" is when the engine spits back through the carb/air meter.

Afterfiring is caused by lack of ignition of the fuel/air mixture in the cylinder. Then, when the combustible mixture is ejected through the exhaust port, hot exhaust from other cylinders causes it to ignite, and you hear a "pop" in the exhaust.

A burned valve can cause this so a compression/leakdown test may be in order.

"Leakage" or a short in either the primary or secondary ignition circuit is also a possible cause. Leaking or shorted plug wires can often be seen if you can close the garage and eliminate all light. Look for blue flashes.

Other than a steady reading on a dwell meter can indicate a primary circuit problem. If you don't have a dwell meter you can just use a voltmeter.

Points? Ballast open? Condenser shorted to ground? Coil shorted to ground? Cracked dist. cap or rotor? All are suspects.

Duke

[Robert D.]

Re: Engine back fires

after checking timing i would do as duke said and check for arcing against the ignition shielding especially if you just put it on and it started the problem.

if all these things dont solve your problem pull the valve covers and make sure nothong under them is broken.

[Rainer S.]

Re: Engine back fires

Thank you, all, for such good advise.
I double checked that the ign wires are seated on the spark plugs and at the distributor-OK. Did not check for arcing with the lights off yet- will have to wait till the W/E.
The wires are new, The distributor was not rebuild, just checked and set-up for point gap.
Will have to look further. Ran it again this morning and the popping almost stopped after a while, after it warmed-up.
Will do a leak-down first and check for correctness under the valve covers, hope it's not due to a burned valve..

Rainer

[Michael H.]

Re: Engine back fires

Just started my 63 SWC Fuelie after a long winter. When I ran the motor last year, I adjusted timing etc and it ran OK with the occational "miss", which I was planning to investigate after storage. ( the car has been under a 5 year restoration).
I installed the spark plug shielding last winter, except the cover over the distributor.
When I started the car up, it backfired, on what apears both banks. The backfiring did not go away as the motor warmed up (didn't want to cont running it).
What is the likely cause of the back-firing, or "missing" ? There is a popping sound coming from the exhaust...
Is there a way to narrow down the root cause ? Can someone stear me in the right direction ?


Rainer

Rainer,

If the car was running somewhat decent last time you shut it down, it's highly unlikely any new major internal engine problems mysteriously appeared over the winter. If it has a burned valve today, it had a burned valve last year too.
Are you very sure that you didn't disturbe the firing order when you were working on the shielding and other misc? An incorrect order will cause the exact problem that you describe.
Another possibility is a partially or nearly completely plugged fuel injection nozzle. This is somewhat common after the car has been in storage for a long time. Bits of dried fuel can collect at the nozzle and plug the screen.

Next time you fire up the engine, only run it for about 30 seconds and shut it down. If you then feel the exhaust manifolds near each runner, you may find that one is cold while the rest are warm. That would at least narrow it down to a cylinder without requiring a lot of fancy equipment.
I would inspect the spark plug that you remove from the cylinder that is not firing. If it's dry, that would point to a plugged FI nozzle. If it's wet, that would probably indicate an ignition problem. (bad wire...firing order etc)

[Rainer S.]

Re: Engine back fires

Rainer,

If the car was running somewhat decent last time you shut it down, it's highly unlikely any new major internal engine problems mysteriously appeared over the winter. If it has a burned valve today, it had a burned valve last year too.
Are you very sure that you didn't disturbe the firing order when you were working on the shielding and other misc? An incorrect order will cause the exact problem that you describe.
Another possibility is a partially or nearly completely plugged fuel injection nozzle. This is somewhat common after the car has been in storage for a long time. Bits of dried fuel can collect at the nozzle and plug the screen.

Next time you fire up the engine, only run it for about 30 seconds and shut it down. If you then feel the exhaust manifolds near each runner, you may find that one is cold while the rest are warm. That would at least narrow it down to a cylinder without requiring a lot of fancy equipment.
I would inspect the spark plug that you remove from the cylinder that is not firing. If it's dry, that would point to a plugged FI nozzle. If it's wet, that would probably indicate an ignition problem. (bad wire...firing order etc)

Mike, that's a good way to narrow it down. I will try that tomorrow...

Rainer