CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

My Olds Aurora is misfiring and backfiring

Hey Guys
Quick history,
My car was backfiring last month, my shadetree mechanic changed out the plugs, plug wires, tranny filter oil and filter and the backfires stopped, they are back. My 96 Olds is backfiring when I jump on the gas and it’s “bouncing” or idling with “skips” at a stoplight (rough idle). Add to this, I didn’t drive it for 3-4 days and the battery was dead when I came to start it (possible vampire drain). I’m thinking fuel filter on the misfires since we put new plugs in already (these issues always mean fuel or fire). I need your input please, I’ve spent so much already trying to fix this. Thanks

Will a scan tool help if this is fuel related? I mean a handheld, not the $5,000 dealer scan machines.

Check your fuel pressure. The regulators were a problem back then. I don’t know how a scan tool would check fuel pressure, even OBD II. Other than that check ignition again.

Backfires are often caused by ignition timing problems, valve problems, or mixture problems. Is the check engine light on? Have the diagnostic codes been checked yet? If not, that’s the place to start. Get all the diagnostic codes, active and pending and post them here. Backfiring unlikely to be caused by the fuel filter imo. But if you need a new fuel filter anyway, good time to replace that in any event.

Hi George, and thanks for helping again…the last time we ran an OBDII scan, the result was multiple random misfires, then we changed the plugs and wires, cleared it up, but they’ve returned. You can feel the “hiccup” when sitting at a stoplight, it’s missing, and it backfires if I step on the accelerator too quickly.
I should say, I noticed my serpentine belt seems too loose and one other clue…when I start my car the last few days, I have to turn the key 2-3 times before it responds? I don;t believe it’s the starter as I know what grinding teeth sound like/or failing bearings, it’s literally just not responding to the key-turn unless I turn it quite deliberately. I was afraid to shut my car off when I picked my boy up at school today. Any clues on the poor reaction to the ignition key turn? Solenoid? Timing? (my shadetree got his timing gun stolen)

Thanks again Bing,. you actually helped me figure out the initial problem (I changed the plugs but not the wires)
As soon as we changed the wires it ran great for 2 weeks, but the rough idle is back, you can feel it “hiccup” when idling. Also, if this helps, when I turn my ignition, the key won’t start the car the first time, I have to turn it quite deliberately 2-3 times before it starts…

If I had to guess if you pull your plugs they will be fouled, let us know if all or some or none are fouled

I forgot to tell you, when I didn’t drive my car for like 4 days, I came out and it was dead as a doornail, and I mean so dead my charger wouldn’t start it, I had to use another car…can this be related or do you believe this is a separate issue. I know what a bad starter sounds like, and this isn’t that…solenoid maybe? Ignition switch, timing? My serpentine belt doesn’t seem tight enough, I can easily flip it over with one hand (this is an old-school test, it should be too tight to easily roll the belt over with your fingers of one hand) Thank you so much

If you mean you turn the key to “start” but you don’t hear that normal rrr rrr rrr sound indicating the starter is cranking the engine, first thing to do is make sure the battery is good, and the connections at the battery posts are clean and tight. This is a very common complaint we get here this time of the year, as the colder temperatures affect the entire starting circuit, including the battery and the starter motor. Note: the symptoms of a failing starter motor are not usually grinding noises. The most common symptom is a single click sound when turning the key to “start”.

I

Missing can cause backfires. The gas and air come into the engine, but don’t get burned, so the gas/air just goes into the exhaust system, where it heats up and explodes, causing a “pop”, a backfire sound. Once you get the misfire problems corrected the backfires should go away. suggest to re-check the OBD II diagnostic codes before making any further guesses about what’s causing the missing.

Plugs and wires were changed 2 weeks ago, once we changed the wires this problem disappeared, it reappeared a few days ago

How do you plugs look now is what I am asking.

Just changed them 2 weeks ago so I can’t imagine they look too bad

OK George, I think it’s time I bought a scan tool, I can’t just keep paying for scans at $90-$110 a pop

This may explain quite a bit, I have so many random electrical failures, my drivers seat won’t move, my trunk will only release using my remote (not the dash switch), my cruise control quit working…one window labors badly going down, my rear view mirrors won’t move…

I must admit I’ve left my window open several times when it rained and water could have easily gotten into the door jam where the mirror and car seat buttons are

I don’t know how to check ignition, and did you see the photo of the broken wire I found on my block? George thinks it’s a ground wire for my battery, (even though the battery is under the back seat, there is an “annex” under the hood where you can jump your car without accessing the actual battery