Backfire from auto lite 4100 / power loss
03-25-2019, 10:28 AM
#1
Thread Starter
Join Date: Dec 2018
Location: Nevada
Posts: 4
Backfire from auto lite 4100 / power loss
Driving my 66 mustang the other day, running good all of sudden hell broke loose. Very bad backfiring and also loss of power,manage to back home. When checking it out at home I did a compression test, that seemed fine but what I noticed it seemed popping/ backfiring noise coming the carb! Any suggestion's????? I do ave the original 289 in it.
03-25-2019, 01:44 PM
#2
Gentleman's Relish
Join Date: Feb 2005
Location: AZ
Posts: 13,090
Timing or running really rich. Smell any gas?
While off, check TDC of pistion 1 with the direction your distributor rotor is pointing.While your in there. Check the cap for cracks or signs of arcing.
Is it just at idle or under power that you get the backfire? Are you vacuum or mechanical advance, points/condensor or electronic upgrade?
If mechanical check your springs aren't broken, damaged, or stretched. If vacuum, check for a vacuum leak.
If that is sorted, check the timing at idle and at 2000 rpm. Should be within specs (don't know what that is off the top of my head).
While off, check TDC of pistion 1 with the direction your distributor rotor is pointing.While your in there. Check the cap for cracks or signs of arcing.
Is it just at idle or under power that you get the backfire? Are you vacuum or mechanical advance, points/condensor or electronic upgrade?
If mechanical check your springs aren't broken, damaged, or stretched. If vacuum, check for a vacuum leak.
If that is sorted, check the timing at idle and at 2000 rpm. Should be within specs (don't know what that is off the top of my head).
03-25-2019, 02:39 PM
#3
Banned
Join Date: Jan 2018
Location: Pennsylvania
Posts: 2,327
Your title suggests you put those spark plugs in, and that's when it started.
Backfiring out the intake is either a valve stuck open, lean mixture or spark plug
wire(s) connected to the wrong cylinder(s).
Lean fuel mixture breaks out into several sub categories:
A.). Vacuum leaks
B.) Air entering the intake without passing through the MAF on Mass Air cars (89-95 models).
C.) Failure of the MAF, BAP/MAP (Baro or Manifold Air Pressure, same sensor, different name), ACT (air charge temp), or ECT (engine coolant temp). These should set a code in the computer.
D.) Leaking exhaust gases from EGR valve at WOT or EGR opening when it should not be open.
E.) Poor fuel delivery due to bad fuel pump, clogged filter or bad fuel pump wiring. Look for low pressure or fluctuating pressure. Standard injector pressure is 39 PSI at idle, with the vacuum line disconnected from the regulator and capped.
F.) Clogged fuel injectors.- see the cylinder balance test below
H.) Fuel injector wiring problems causing injector not to deliver rated flow.
I.) Computer problems: (computer problems are not common like sensor problems)
J.). ROM has bad data in fuel or timing table. This should also set a code in the computer.
K.) Failure of one or more of the computer's driver transistors for the fuel injectors. No code set on this one. Use a noid test light to test the injector wiring & injector drivers,
L.) MAF calibration off or mismatched to injectors.
M.) ACT or ECT bad. Sometimes the sensors will be off calibration, but not bad enough to set a code. If they falsely read too high a temp, the engine will back off fuel delivery.
N.) Firing order off or spark plug wires out of sequence.
An exhaust push through the intake is not a backfire, but you can get a "Pshhhhh" though
the intake and out the carb. That would be a timing issue, if the timing chain slipped and
the intake valves open early on the exhaust stroke.
Any time I have seen the explosion type backfire through the intake was valve related.
Backfiring out the intake is either a valve stuck open, lean mixture or spark plug
wire(s) connected to the wrong cylinder(s).
Lean fuel mixture breaks out into several sub categories:
A.). Vacuum leaks
B.) Air entering the intake without passing through the MAF on Mass Air cars (89-95 models).
C.) Failure of the MAF, BAP/MAP (Baro or Manifold Air Pressure, same sensor, different name), ACT (air charge temp), or ECT (engine coolant temp). These should set a code in the computer.
D.) Leaking exhaust gases from EGR valve at WOT or EGR opening when it should not be open.
E.) Poor fuel delivery due to bad fuel pump, clogged filter or bad fuel pump wiring. Look for low pressure or fluctuating pressure. Standard injector pressure is 39 PSI at idle, with the vacuum line disconnected from the regulator and capped.
F.) Clogged fuel injectors.- see the cylinder balance test below
H.) Fuel injector wiring problems causing injector not to deliver rated flow.
I.) Computer problems: (computer problems are not common like sensor problems)
J.). ROM has bad data in fuel or timing table. This should also set a code in the computer.
K.) Failure of one or more of the computer's driver transistors for the fuel injectors. No code set on this one. Use a noid test light to test the injector wiring & injector drivers,
L.) MAF calibration off or mismatched to injectors.
M.) ACT or ECT bad. Sometimes the sensors will be off calibration, but not bad enough to set a code. If they falsely read too high a temp, the engine will back off fuel delivery.
N.) Firing order off or spark plug wires out of sequence.
An exhaust push through the intake is not a backfire, but you can get a "Pshhhhh" though
the intake and out the carb. That would be a timing issue, if the timing chain slipped and
the intake valves open early on the exhaust stroke.
Any time I have seen the explosion type backfire through the intake was valve related.
03-25-2019, 06:50 PM
#5
Banned
Join Date: Jan 2018
Location: Pennsylvania
Posts: 2,327
If the cam had a flat spot, that would effect the open height or duration of the effected
valve; but yes, the popping usually starts out at high rpm, and gradually work down to
lower rpm as the lobe completely flattens out. Rather than a complete and very violent
backfire, it will typically manifest itself as a popping sound through either the intake or
exhaust. Of course, through the intake or exhaust depends entirely on which lobe is dead,
so a flat exhaust lobe causes popping back through the intake. The flat intake load would
cause a miss.
Lifter tap is a very common symptom of flattened cam lobes, and is often the very first and
most noticeable one. However, it's possible for an engine to have one or more completely
wiped lobes with no lifter tap at all; that depends on the design. Again, the tapping may be
worse at idle and low rpm, and quiet down when hydraulic lifters pump up with oil.
I also find it hard to believe that it all of the sudden wiped a lobe, if you did not get the
beginning signs as explained.
valve; but yes, the popping usually starts out at high rpm, and gradually work down to
lower rpm as the lobe completely flattens out. Rather than a complete and very violent
backfire, it will typically manifest itself as a popping sound through either the intake or
exhaust. Of course, through the intake or exhaust depends entirely on which lobe is dead,
so a flat exhaust lobe causes popping back through the intake. The flat intake load would
cause a miss.
Lifter tap is a very common symptom of flattened cam lobes, and is often the very first and
most noticeable one. However, it's possible for an engine to have one or more completely
wiped lobes with no lifter tap at all; that depends on the design. Again, the tapping may be
worse at idle and low rpm, and quiet down when hydraulic lifters pump up with oil.
I also find it hard to believe that it all of the sudden wiped a lobe, if you did not get the
beginning signs as explained.
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