I have a 2003 Saturn Vue AWD V6 with 108,000 miles that has had an annoying problem with backfiring. The issue mainly occurs in the winter after I come to a stop at the end of a highway exit ramp. The noise isn’t very loud, but noticeable as it “pops” about 5 or 6 times before going silent. Over the past year or so, I have replaced the spark plugs and both ignition coils (both of which had small cracks in the housings) and the noise remains.
I don’t know if this is another hint or a red herring, but my car has had some issues with rough shifting and hesitation as I let off the throttle on the highway. Any help would be appreciated. I love this car but these lingering problems are really getting to me.
You should definitely have stored fault codes, and looking for those is where you should start.
The Techron is a good suggestion. If the pintles (the little needle valves in the injectors) aren’t all closing properly, you’ll be getting these symptoms.
A simple vacuum leak could be causing the problem too. Depending on its location it can cause improper fuel metering or lean operation (lean can make the cylinder too hot and can cause self-ignition).
I wouldn’t be surprised if the problem were in the throttle position sensor and/or a gummed up throttle plate and idle air control valve. A check for codes would improve the odds of getting good start at correcting the problem. Drop by a McParts store and post your results.
Good comments above. During deceleration like that, the engine has to make some adjustments to compensate, often modifying the ignition timing, completely shutting off the fuel flow to prevent unburned gasoline getting to the exhaust, etc. If the sensors it uses are not working correctly, like the throttle position sensor, airflow, vacuum sensors, throttle sticking, for example, it can’t determine when to make the necessary adjustment.
If all the sensors are working then the next on the list would be leaking fuel injectors, or valve problems.
So, I looked into it and my car isn’t giving any error codes. A few months ago I also thought it was a leaky injector and used fuel additives like Techron and Sea Foam with no success, so I just assumed it wasn’t the injectors. I’m not sure what else it could be and what tests I can perform to try to narrow things down.
Also, the backfire isn’t very intense, so that might be why I’m not seeing an error code. It is a string of light pops, sort of similar to a muffled party popper.
If you want to get to the bottom of it, a fuel pressure test is probably in order. They can check for leaking injectors as part of that.
You mention “hesitation” when decelerating. If you mean by that when you are slowing down you have a hard time adjusting the throttle so it slows down smoothly, or say when you are driving in a neighborhood and trying to slowly round corners the car tends to jerk forward, then jerk backward, rather than smoothly modulating the speed as you press or remove pressure on the accelerator, that can be a sign of dirty fuel injectors. It shows up more at low speed/rpms b/c that is when the injector has to put out a small amount of fuel. It is like when you have a water faucet on the fritz, sometimes is will work fine at full force, but you can’t get it to reliable put out a trickle of water when you like.
The hesitation actually happens in two separate scenarios.
When I am driving on city streets and I am barely touching the throttle (maintaining the same speed), the car occasionally feels like I am tapping the brakes. Then, when I press the throttle to accelerate, the car pulses like it is struggling in a low gear.
When I am driving on the highway and I let off the throttle, it occasionally feels like I am lightly holding onto the brakes.
I sounds like it’s being starved.
I liked George’s suggestion to test the fuel pressure as well as his analogy of the eater faucet.
Let me ask, is this going to be repaired by a shop? If it is, let me suggest that you simply describe the symptoms clearly and let the shop do the diagnosis. Certainly you can and perhaps should tell them of suggestions you’ve received, but don’t make the mistake of not allowing them the freedom to go down their own path as they make discoveries.
I have a friend with a 1995 Dodge RAM with the 3.9L v6. It is a 5 speed manual and it sometimes does little pops out the tailpipe when you have it in gear going down a big hill or other engine braking siuations. I know the timing chain has some slack in it as this engine was known for that problem. I wonder if this is contributing to this issue but I think the main issue is probably that the truck is driven rarely and that the injectors are gummed up and not closing properly. The ignition system has been tuned up recently.
There are no codes present in this vehicle either. It is also a 1995 so just pre-OBD2.