rare back fire out of intake
 

Ok it wont do it all the time but once in a while. I did anouther tune up do it bothered me because it did it all the time i drove. But i replaced the wires and pluges and now it will do it once in two to three days. I had the coil pack replaced again when the bcm was replaced last year. It threw a cel when they replaced the bcm and they replaced it at the same time. I took it in to a shop and there is no codes or any thing they could get off of it. I am just frustrated because i am thinking on just junking it do to it being in the shop more times than i am on a date. The monte is just becoming a expencive date than whats it is worth love the ride but not whats going on. The plugs are ac delco platinums called for the car and the wires are ac delcos as well. the trans is been flushed as well as a oil change as well as a radiator flush. I dont know if it is a low pressure from fuel pump. I am going to get the fuel system checked but i am hating it do to the back fire out of the intake.

Try cleaning the MAF?

Here is a copy and paste from another site 2CarPro's. Seems like there are limited areas that will cause you to backfire. Anywhere from a vacuum leak to a clogged fuel filter. Scope it out you might have a light bulb moment.
I have had a few highly explosive backfires in my upper intake manifold when I suddenly slow down and then get back into it. Alot of unburnt fuel just sitting there for a second and then POW!! No cracks yet, I have the newer upgraded UIM.

There are two kinds of backfires, one is produced from the engine air intake and the other is produced from the tail pipe of the exhaust system. The cause for a backfire condition can vary depending on the malfunction of a particular system. Some backfires can be extreme enough to cause damage to related components. Anytime a backfire is observed immediately diagnose and repair as needed. If the engine is running rough it can produce a backfire. A backfire occurs when there is an imbalance in the air to fuel ratio required for your vehicle to operate properly.

If the fuel mixture is too lean (not enough fuel) you may have a backfire in the intake manifold gasket, or too rich (too much fuel) you may get a backfire out of the exhaust system. It is important to observe the location of the backfire. The information below is separated into two sections; the first section contains possible causes for backfires in the engine intake. The second section contains possible causes for backfires in the exhaust system. (Note: if the engine is misfiring and the engine backfires while the engine is under load please visit, engine misfires.

Car Repair Information Guide - Backfire In The Engine Intake System

Step 1 - The ignition system in your car is designed to operate at a specific voltage and amperage output. If this voltage/amperage is forced to "spike" due to faulty or inferior tune up parts it could cause the system to "crossfire". A crossfire condition can allow the electrical discharge for a particular spark plug circuit to transfer to a alternative cylinder. Depending on were the cylinder is in the combustion process it can produce a backfire in either the intake or exhaust systems. Always replace ignition components on a regular mileage schedule and use high quality replacement parts.

Step 2 - Your engine's fuel system is designed to run on a constant fuel pressure. If this fuel pressure drops it can cause a lean mixture which in turn causes the engine to backfire. There are several reasons this can take place such as a faulty fuel pump, clogged fuel filter or a malfunctioning pump or a fuel pressure regulator. The best way to check for this condition is to perform a fuel pressure test. This is done by locating the fuel pressure test port and attaching a fuel pressure gauge and reading the fuel pressure while the engine is running.

Step 3 - Engine ignition timing is to be set at a specific degree in relation to the crankshaft of the engine. If this timing becomes mis-aligned it can cause low power, poor gas mileage, engine detonation (pinging) and backfiring. To check the engine timing locate the number one cylinder of the engine. This number one cylinder will be the forward most cylinder of the engine. On straight 4 and 6 cylinders engines it is pretty obvious, but on "V" style of engines like the V8 it is a little more tricky. The cylinders heads on every "V" style of engine are offset from one to the other. One cylinder head is more forward than the other.

The most forward cylinder head is the side of the engine where the number one cylinder is located. The forward most cylinder is the number one cylinder. Next, locate the crankshaft timing marks, most engines timing marks are at the front of the engine on the harmonic balancer. Near the balancer there is a small pointer or scale to align the balancer mark to. When the engine is running this gauge or pointer should align with the mark on the balancer. When the engine is running the timing light will strobe and illuminate the balancer mark as it spins.

To adjust the timing loosen the distributor and turn slightly one way or the other to achieve the desired setting. Once an adjustment has been made re-tighten the distributor hold down bolt or bolts. Some engine's timing marks are located at the rear of the engine on the flywheel. Before you begin start and run the engine until warmed to operating temperature. Connect the positive and negative leads of a timing light to the battery. Observe the timing tag either on the engine or engine compartment for the timing specification and procedure. If the specification and instruction cannot be found consult a car repair manual.

Step 4 - Distributor style ignition systems are designed to operate at high voltage. If moisture is present inside of components like the distributor cap it can cause internal ignition crossfire. This crossfire condition can allow the electrical discharge for a particular spark plug circuit to transfer to a alternative cylinder. Depending on were the cylinder is in the combustion process it can produce a backfire in either the intake or exhaust systems. To check for this condition remove the distributor cap and inspect for moisture. If moisture is present dry components thoroughly and reassemble. (some cars are not equipped with a distributor)

Step 5 - The engine in your car is designed to run on a specific ratio of air to fuel (14 to 1). If this ratio increases by withholding fuel it can cause the engine to back fire through the intake system. The number one reason for this condition is a plugged fuel filter. If your fuel filter has not been changed for over 30,000 miles it probably needs to be changed. Remove the fuel filter and inspect if dirt is observed replace the filter. (note: some cars fuel filter is located in the gas tank and is not serviceable, these cars are quipped with a lifetime filter). Next the ratio can be incorrect because of an air intake boot that has failed or other vacuum leak. If a failure is detected replace part with new and recheck.

it is a 07 i dont think there is a fuel filter to replace to be honest i have asked about that when i first did a tune up on the monte. but thank you for the input about it. it gave me some thing to do over my two days off to clean and look more.

Please read this forum thread. Apparently the 06 and above Monte's do not have fuel filters to replace.

https://montecarloforum.com/forum/ge...-urgent-13242/

what i meant is clean tha maf and check the fuel pressure. if the fuel pressuer is low cause one of two things relay or fuel pump going bad. the other thing zippy remember the post that is on this thread. when i read it it meantioned fuel filter i mentioned 7th gen didnt have them do to looking in on them. the pump just relies on a sock. i already replaced the fuel pressure regs for it when i first noticed the intake back fire the first time it did it. thinking it was the first cause. now i am nerrowing it down when i asked

Excellent work there Sherlock!! LOL, thats what this takes is some sleuthing and such! Hope this works out pretty darn soon for you. :) :)

its getting air and fuel but it still intake back fires. fuel pressure is there maf is clean i guess time for a really bfh of a sledge hammer. did i ever say i now notice why gm stoped making the 3.5 v6. i understand why they came out with the new 3.6 v6. just wish the monteys came with them instead of the 3.5. thanks for the heads up nighthawkjcp. also no thanks on the help zipp the superior complex wasent really what i needed to hear. but thanks any way with the sherlock coments as well love the books as will as the movies but keep it civil. sledg hammer will always help to deside on a new route. on a engine for a example or a quick sale what ever comes first i hope on a engine.

It's all one can do is try to offer up suggestions. Not even trying to be superior. Sorry if you took it that way. I know how things get when one is frustrated. Don't even be around me when I'm ticked without a hard hat, tools are usually flying.... Sometimes the BFH does one good...... :(

How did your plugs look when you replaced them ?
Could be a vacum leak , a fuel injector failing / wires to injector ?