Backfire!

[16valex]

Why does my car backfire? It is a 97 528I BMW. I think I get a better answer here then at a BMW forum and I'm not crazy :=)

 

[DieselPower]

Improper timing, ignition problems, fuel problems, heavy carbon deposits in the cylinder's and the list goes on. There are numerous thing's that can make a engine backfire but in short it is due to fuel ignition in the cylinder when it shouldn't.

 

[MOPAULY]

As mentioned, it is firing off a spark with fuel in the cylinder when it shouldn't be. Does it backfire through the exhaust or through the intake? Is there anything else the engine has been doing that seems different?

 

[16valex]

Backfires at the exhaust not intake thanks goodness. by the way thank you for the responses, but I will take this thread out of here, I feel a bit silly, after all this is about KUBOTA, sorry folks I'm out of here.

 

[JIMTORL]

My BMW 528 does the same thing.
I have spent a lot of $$$$ over the 6 years of ownership and nothing ever worked (BMW dealers & local Mechanics). It only does it within the first 5 min. of operation.
I guess it's just the nature of the beast.
But my new B3030 runs great
Jim

 

[N80]

My old '75 Jeep Cherokee would backfire repeatedly if you ran through deep water and gave the engine a good splash. Water would get in the distributor cap. Pull it off, wipe it clean and give it a few shots of WD40 and it went away. Finally ended up putting some grease or something around the cap to seal it. That thing was the biggest peice of junk I've ever driven.

 

[16valex]

You see, I don't have any problem if it just backfires once in a while then it would be fun, but this thing is throwing codes, and the code is "catalyst efficiency below threshold my CEL engine light is ON.

I have spent quite a bit of money into it, so far new cat converter, new O2s, new secondary pump and valve..It has gotten to be a money pit lately. I'm waiting for some coil packs to show up and see if it gets better. Thank you all.

 

[BrianW]

When I was a young auto mechanic it used to drive me nuts when people would say they had a backfire problem when they really have an afterfire problem. Backfire means the path is backwards to the normal path, in other words, a fire through the intake. An afterfire is through the exhaust. In a afterfire situation raw fuel is building up in the exhaust and then being ignited. Many things can cause this, but when you bring it to someone to fix make sure you tell them you are having an after fire through the exhaust. Many mechanics use the terms incorrectly also. Sometimes it is hard to fix a problem as a mechanic because you don't know what the real complaint is due to communication errors. This is especially true when you drop of a car and relate the problem to the service manager, who then relates it to the mechanic. Kinda like the old telephone game you played in grade school.

 

[DieselPower]

Actually the definition of a backfire is:

Websters
Main Entry: 1back·fire
Pronunciation: -"fI(-&)r
Function: noun
1 : a fire started to check an advancing fire by clearing an area
2 : a loud noise caused by the improperly timed explosion of fuel mixture in the cylinder of an internal combustion engine

Dictionary of Automotive Terms Abbreviations

backfire:
[1] Passage of unburned fuel mixture into the exhaust system where it is ignited and causes an explosion (backfire) prematurely.
[2] Sometimes ignition takes place in the intake manifold by a flame from a cylinder because the intake valve leaks. Burning of the fuel mixture in the intake manifold may be caused by faulty timing, crossed plug wires, leaky intake valve, etc.
[3] A welding term referring to a short "pop" of the torch flame followed by extinguishing of the flame or continued burning of the gasses.


Don't see anywhere where it sais it has to be through the intake. I am a mechanic and know dozens of others and we all call a out of sequence ignition a backfire, dosen't matter if it's out the front or back. Might be the reason mechanics alway's ask is it backfiring through the intake or exhaust.

 

[MOPAULY]

You see, I don't have any problem if it just backfires once in a while then it would be fun, but this thing is throwing codes, and the code is "catalyst efficiency below threshold my CEL engine light is ON.

I have spent quite a bit of money into it, so far new cat converter, new O2s, new secondary pump and valve..It has gotten to be a money pit lately. I'm waiting for some coil packs to show up and see if it gets better. Thank you all.

I think your car would be OBDII...have you had it scanned for the exact codes from an auto parts store such as Autozone? I assume the parts replaced thusfar have been on your own accord and not the advice of a dealership or repair facility?

I don't know what your mileage is but it may be covered under the emissions warranty for the vehicle if it is an emissions component at fault. My wife's Honda had an issue recently and when I diagnosed the code it turned out to be a faulty vent valve for the charcoal canister. I took it to Honda with the code and description, they verified the problem and it was replaced under warranty.

Keep in mind the federal government extends emissions warranties well beyond factory warranty, somewhere in the range of 80 or 85,000 miles.

Anyway, I would first start with the exact codes from the ECU. You may also want to invest in a set of factory service manuals for the car if not a basic Haynes manual.

 

[16valex]

Hi Mopauly,

The car has over 142K miles so emission law is no longer effect. I have a peake OBDII scan reset tool, but it is limited to details it just usually very general and the code is " catalyst efficiency below threshold" like every one has said it could be a number of things, any lean or rich in the mixture ratio can throw this code, but I think my car's timing is off during cold engine unburnt gas enter the exhaust and causing backfire, I believe if I can stop the backfire then the code will go away, maybe my coil packs are getting a bit weak.

Though the car has quite high miles but performance still very flawless so I plan to keep it and therefore I don't mind spending the money fixing it, beside the cat and O2s are original that's also why I replaced them, usually the cat and O2 should fix this problem but not this time for me.

I believe my problem is ignition, timing and maybe fuel but likely not. I welcome any advice out ther while you're idle with your tractor.

 

[dfkrug]

16valex:

I, too, have a B-M (98 M3), and though I like the car, I would not
buy another. Many failures I never see with my Japanese iron, and
I have owned and worked on many scores of cars.

I do all my own work and I use the Auto Xray 4000 for OBD2 analysis.
I have had codes come up that are BMW-specific and more detailed
than the basic OBD2 codes. Unfortunately, the codes are not
published and BMW does not sell a service manual. The Bentley
aftermkt manual does not cover them. If it were not for BMW enthusiast
websites, I would not have been able to find the code descriptions
without going to a dealer.

On your problem, you have replaced a lot of stuff, incl the most likely
culprits. I like your idea of looking for an intermittant coilover next.

 

[16valex]

Hi there DFKrug,

Wow, a real Bimmer enthusiast with the M3 to show too. You are not kidding about BMW it stands for Breaks My Wallet lol. I too, try to do every thing myself. It has been three years now without ever bring it to the dealer, I better knock on wood when saying this.

The problem that I have with jap's cars like Lexus and Acura they don't come with rear wheel drive and number two is no manual shift available, I don't like auto slushbox.

I have to agree with you that Bimmers are more troulblesome, its weakest point is the cooling system. However, it is addictive for some reasons.......

 

[cp1969]

Did you mention a secondary air pump, as in air being injected into the exhaust? Look close at that circuit; excess air getting into the exhaust can make it backfire.

 

[dfkrug]

Hi there DFKrug,

Wow, a real Bimmer enthusiast with the M3 to show too. You are not kidding about BMW it stands for Breaks My Wallet lol. I too, try to do every thing myself. It has been three years now without ever bring it to the dealer, I better knock on wood when saying this.

The problem that I have with jap's cars like Lexus and Acura they don't come with rear wheel drive and number two is no manual shift available, I don't like auto slushbox.

I have to agree with you that Bimmers are more troulblesome, its weakest point is the cooling system. However, it is addictive for some reasons.......

What!? If I get rid of the M3, I will replace it with a new Infiniti G35
coupe w/ 6 sp MANUAL. It is available as RWD or AWD. Most Japanese
performance cars are RWD. Even Acura's NSX is RWD. I have only
owned one auto tranny car, and it was just for 6 mo while my wife
recovered from a broken leg and could not shift a clutch (that was a
280Z). I DO like hydrostatic ATs in my tractors.

My M3 is a 98 and I just hit 80K miles. The wife drives it mostly. It
has had a failed thermostat, failed air injector valve (which killed the
aux electric air pump), bad brake light switch, failed rear shock mounts,
failed remote locking, and a poorly shifting 1st gear. All are fixed, but
I have not found the cause of the failed remote locking yet. I have to
live with the 1st gear issue.

 

[MOPAULY]

I'm guessing that you replaced any sensors after the cat when it was replaced to? "catalyst efficiency below threshold" definitely would make me think a sensor past the cat is picking up bad readings or has gone bad. I'm a third that likes to work on everything them selves when possilble

I'm surprised BMW does not sell a factory service manual.

 

[16valex]

It has been four days and about 200 miles now without the code after I reset it. The last thing I did to the car was changed the oil to a thicker and back to conventional from synthetic type. Wish me luck folks, I think I'm on to something here. I will report back in a few days...........

And Mopauly, I did replaced all four O2 sensors. The coil packs just came but I will holding them out for now.

DFkrug, I was not to clear when I complained about the lack of manual and rear wheel drive. What I want is a decent size four door sport sedan with manual gear box, plus all the toys and technologies and must be able to accomodate 5 people ( I have three kids :=) ), and lastly must be fun to drive that is why I picked the 5'er. I also have a 330xi, but I'm going to sell this one soon, and will get another E39 maybe 530 or 540. If I go with Japanese ToyotaLexus is the only one I touch but their lines of cars are so dame boring. enough said.