My car has been eating ignition modules lately. (2 GM modules in the last 3K miles)
I have some friends who are helping me isolate and fix the problem so I'm not posting for help on that. My concern is in regard to what has been happening the instant they fail. In both instances I was on the freeway cruising steadily around 65 mph. The scenario is the same.......sudden loss of power followed by 1 or 2 "shotgun-like" backfires that would make a Green Beret duck and cover. Oh, and then the "Service Engine Soon" light would come on. After coasting to a stop and replacing them on the side of the freeway (I always carry a spare module) the car would start right up, idle fine and drive home with no problems.

Anyways, I was wondering about whether these TREMENDOUS backfires are causing any damage to my engine.
Oops, almost forgot to mention that I have an 86 GT Auto.

Thanks, Kit

If it's backfiring through the intake, you won't have any problems. If it's backfiring through the exhaust, you might blow out your muffer or cat.

quote Originally posted by ryan.hess: If it's backfiring through the intake, you won't have any problems. If it's backfiring through the exhaust, you might blow out your muffer or cat.

Huh?
If it's backfiring at all it's bad. As for damage, It all depends on how badly it backfires.
Thru the intake it can damage injectors, vacuum ports, throttle bodies, etc.
Thru the exhaust it can damage O2 sensor, Catalytic converters, mufflers, exhaust gaskets, It could even crack an exhaust manifold if it is strong enough.

I am not saying that these items have been damaged, But they are things you should check just to make sure they did not get damaged.

If you have been eating modules, I would look at a few things.
How is the pick-up coil?
How is the ignition coil?
Are the screen vents in the bottom of the distributor clean?
The grease should be a thin even coat, Too much (too thick) and it could have a reverse thermal effect.
Are there any exhaust leaks near the distributor/coil area that could cause a more heat?
Is the blower motor on the right side of the trunk working?

Hi, you may want to try the heat srink compound on the modual===radio shack

On a bit of a side note to this to help you understand what backfiring is all about I have a funny story.

Quite some time ago I worked for a cable company and we had an old ford pickup truck that had some backfiring problems. Anyways, we had to drive from the shop to the site everyday and to get there we had to go through a tunnel.

You can see where this is going I think..

So, everytime we went through the tunnel we'd try to make it backfire because it echoed in there and sounded kinda cool (at the time..)

We also had another smaller truck that one other guy would drive with us and most always followed because the reliablity of the older truck was a bit iffy.

Anyways, so one day we're going through this tunnel and we had discovered in a past trip that if you turn off the engine for a second and press the gas and then start 'er back up, you could get some good bang out of it.

Well this time we left it off for a good 5 seconds or so after flooring it to get a bit of momentum and when we started it up again the HUGEST bang went off in the tunnel and according to our buddy behind us, flames came out the back.

It was funny, we all had a good laugh and went back to the shop.

We go back, looked at the muffler and it had a hole in it... Needless to say, it needed replacing.

In conclusion, backfiring is funny to some, but in all cases is bad for the vehicle.

------------------
88 Fastback GT
My blog: www.sti-media.com/blog/

Backfires are sometimes fun, until it happens through the carburator on a carburated car and burns the whole car down.... err (my mom's stupid ford did it when she was driving it.)

------------------
'87 Fiero GT - 60k, Dark Cherry Metallic
I'm in the "Oh God" stage of working on my Fiero.

Ultimate, LOl... We used to do it with company trucks also--we would get going down a real steep hill & right in front of this old guys house (that used to chase us as kids) we would let her rip, one day we let it go and left 1/2 of the exhaust all over the road --other cars hit it--got the company # off the truck , we ended up paying for a few odds-n-ends out of our own pocket--but well worth every penny...

Thanks for all the replies...I will check all the things you guys mentioned. My suspicion is that I might have produced a small hole in the muffler, if anything.

Anyways, I am replacing a whole bunch of things just because the motor has 105K+ on it and I want to eliminate this problem completely once and for all. I just ordered a Ocelot (Fierostore) distributor, GM coil, GM module, coil to distributor wiring harness, module hold-down screws and the grey wire harness that goes to the other half of the coil. Whuffo will be helping me put it all in when he has time.

As for the blower in the back, Whuffo said I have the option of making it run all the time if I want. I might just do that if problems persist when were done. By the way, I do use the Radio Shack paste!
Thanks again, Kit

I had an ignition module problem too, and the backfiring burst my muffler.

quote Originally posted by Oreif: If it's backfiring at all it's bad. As for damage, It all depends on how badly it backfires. Thru the intake it can damage injectors, vacuum ports, throttle bodies, etc.

Okay, I agree with you on the exhaust parts, but none of the above ^^ is true.

At best you'll see about 50psi in an intake manifold when a backfire occurs. The injectors see that every time the engine is running. Vacuum ports? Throttle bodies? Give me an example where a backfire destroyed a throttle body. Doesn't have to be on this board with 10,000 members... just any example from the web.

quote Originally posted by ryan.hess: Okay, I agree with you on the exhaust parts, but none of the above ^^ is true. At best you'll see about 50psi in an intake manifold when a backfire occurs. The injectors see that every time the engine is running. Vacuum ports? Throttle bodies? Give me an example where a backfire destroyed a throttle body. Doesn't have to be on this board with 10,000 members... just any example from the web.

So what you are saying is a backfire powerful enough to blow a hole in the side of a muffler won't do anything to the intake side?

How does the port injectors on a Fiero see 50 psi???? It's PORT injection NOT DIRECT injection. When the air/fuel is ignited the intake valve is closed. If you are referring to a forced induction set-up, When is the last time you saw a Fiero 2.8L running at 50 psi on the street?? Most street engines barely see anything over 28 psi at the most. Also the pressure from a turbo or a supercharger is not a shock wave. The shock wave of a backfire is way more violent.

It's not just pressure, It is also the heat that a backfire produces as well.
An intake backfire is the air/fuel being ignited and traveling back up the intake.
I never said "destroy" I said damage. It can blow out gaskets and injectors at 50 psi, (actually even as low as 35 psi can blow out gaskets) damage vacuum switches like the EGR and MAP sensor use, Bend/warp throttle plates in the TB (and carbs as well). I have even seen where a backfire has bent/damaged the shroud on the tip if the fuel injector causing a bad spray pattern. Not to mention the carbon residue that everything gets coated with. It all depends on how violent the backfire is. On high performance race engines that are normally aspirated and using racing fuel, a violent backfire at high RPM can blow an intake manifold to pieces.

What exactly do you want for "proof" pictures?

[This message has been edited by Oreif (edited 04-04-2006).]

yes, intake backfires can be nasty too. thats why dragster top ends are STRAPPED to the motor, along with the usuall bolting. many spectators have been hit with flying intake junk. yes, thats a bit extreme, and doesnt really apply here. backfires are 1 or more cyl charges of fuel air mix going BOOM outside of the usual nice safe enclosure of engine block. my muffler burst at a seam, and it was from many backfires, not just one. but, boy did I hear that one that actually popped it

the pressure in the exhaust could supposedly, if the backfire was close to the valve, pop the valve open slightly, put slack in the pushrod/lifter, and then it'll slam itself back shut, slamming on the cam. yes, its a stretch.

quote Originally posted by Oreif: So what you are saying is a backfire powerful enough to blow a hole in the side of a muffler won't do anything to the intake side? How does the port injectors on a Fiero see 50 psi???? It's PORT injection NOT DIRECT injection. When the air/fuel is ignited the intake valve is closed. If you are referring to a forced induction set-up, When is the last time you saw a Fiero 2.8L running at 50 psi on the street?? Most street engines barely see anything over 28 psi at the most. Also the pressure from a turbo or a supercharger is not a shock wave. The shock wave of a backfire is way more violent. It's not just pressure, It is also the heat that a backfire produces as well. An intake backfire is the air/fuel being ignited and traveling back up the intake. I never said "destroy" I said damage. It can blow out gaskets and injectors at 50 psi, (actually even as low as 35 psi can blow out gaskets) damage vacuum switches like the EGR and MAP sensor use, Bend/warp throttle plates in the TB (and carbs as well). I have even seen where a backfire has bent/damaged the shroud on the tip if the fuel injector causing a bad spray pattern. Not to mention the carbon residue that everything gets coated with. It all depends on how violent the backfire is. On high performance race engines that are normally aspirated and using racing fuel, a violent backfire at high RPM can blow an intake manifold to pieces. What exactly do you want for "proof" pictures?

A muffler is commonly made of crimped sheet metal. It is weak compared to an intake. The 50 psi I was referring to was the fuel rail pressure. 50 psi on either end of an injector will not harm it. The time that the intake is actually pressurized is so short that it wouldn't have time to bend the throttle blade. The intake is like swiss cheese. Most all vacuum sensors/accessories are run by lengths of vacuum line. That works to dampen any pressure spikes.

With the millions of people posting their stories on the internet, I'd imagine there are quite a few stories about backfires destroying throttle bodies. I just searched and couldn't find one. Note that I'm not talking about forced induction backfires, which would have a higher peak intake pressure. Yes, I've seen nitrous backfires blow apart 1/4" thick aluminum manifolds. For NA that's not an issue.

quote Originally posted by ryan.hess: A muffler is commonly made of crimped sheet metal. It is weak compared to an intake. The 50 psi I was referring to was the fuel rail pressure. 50 psi on either end of an injector will not harm it. The time that the intake is actually pressurized is so short that it wouldn't have time to bend the throttle blade. The intake is like swiss cheese. Most all vacuum sensors/accessories are run by lengths of vacuum line. That works to dampen any pressure spikes. With the millions of people posting their stories on the internet, I'd imagine there are quite a few stories about backfires destroying throttle bodies. I just searched and couldn't find one. Note that I'm not talking about forced induction backfires, which would have a higher peak intake pressure. Yes, I've seen nitrous backfires blow apart 1/4" thick aluminum manifolds. For NA that's not an issue.

I NEVER said destroy a throttle body. I said damaged.

Funny I typed in:
"engine backfire intake damage" under Yahoo and got this as the 6th result:
http://www.cartrackers.com/Forums/live/YourLemon/395.html

I hope someone out there can help me out. Last Jan. my '97 Bonneville SE (3800 V-6, ~68k) literaly exploded with fire during start-up. The intake shattered and fire engulfed the engine compartment.
I have done extensive research on the net and have discovered that this is a real problem and that GM has been under investigation by NHTSA for nearly 600 similar cases since at least Oct '02. It is suspected that a backfire through the intake is to blame.

and
My 1999 Buick Park Avenue GM 3800 Series II ~33K did the same thing, but fortunately did not catch fire. This happened on 13Jun03. After the car was parked for two days, I tried to start the engine. The very loud explosion occurred in the engine compartment, shooting smoke from under the hood on both sides. I immediately turned off the ignition and opened the hood.
The intake manifold was destroyed. It had split longitudinally and thrown large sections of plastic around the engine compartment. The fuel rail was stretched. The open seam at the top of the mainfold was 8 to 12 mm wide. The regulator on the passenger end of the manifold was also blown off.

Even GM has issued a recall because on an intake backfire with a bad fuel pressure regulator leaking excess fuel in the intake, the intake manifold explodes and shatters.
GM RECALL NO. 03054.

Oh look here is another fellow who had problems:
http://www2.abc.net.au/science/k2/stn/may2000/posts/topic64601.shtm
(second post from the bottom of the page)

Backfireing (through the intake ) can still occure in EFI cars. As an example if you pump the throtle of your Ford and then hit the key it will more than likly backfire.This will the blow your MAP sensor (manifold absolute pressure) and this will cost you money to fix

Here is a website that shows that a bad/defective PCV and a backfire could ignite fumes inside the engine block and igniting the engine afire.
http://www.aicautosite.com/garage/subsys/baemmiss.asp

And finally:
http://www.autoforumz.com/-BIG-Problem-HELP-ftopict103909.html

Which was a Honda Civic that had a defective ignition system, It backfired hard thru the intake and damaged the throttle position sensor which is part of the throttle body. (see a dmaged throttle body.)

quote Originally posted by Oreif: Funny I typed in: "engine backfire intake damage" under Yahoo and got this as the 6th result: http://www.cartrackers.com/Forums/live/YourLemon/395.html I hope someone out there can help me out. Last Jan. my '97 Bonneville SE (3800 V-6, ~68k) literaly exploded with fire during start-up. The intake shattered and fire engulfed the engine compartment.

Fieros don't have plastic intakes. Not applicable.

quote Originally posted by Oreif: [i]My 1999 Buick Park Avenue GM 3800 Series II ~33K did the same thing, but fortunately did not catch fire. This happened on 13Jun03. After the car was parked for two days, I tried to start the engine. The very loud explosion occurred in the engine compartment, shooting smoke from under the hood on both sides. I immediately turned off the ignition and opened the hood. The intake manifold was destroyed. It had split longitudinally and thrown large sections of plastic around the engine compartment. The fuel rail was stretched. The open seam at the top of the mainfold was 8 to 12 mm wide. The regulator on the passenger end of the manifold was also blown off.

Fieros don't have superchargers. Not applicable.

quote Originally posted by Oreif: Backfireing (through the intake ) can still occure in EFI cars. As an example if you pump the throtle of your Ford and then hit the key it will more than likly backfire.This will the blow your MAP sensor (manifold absolute pressure) and this will cost you money to fix

Damage to a Fiero MAP sensor is less likely due to the vacuum line that runs to it. Like I mentioned before, it dampens the blow.

quote Originally posted by Oreif: And finally: http://www.autoforumz.com/-BIG-Problem-HELP-ftopict103909.html Which was a Honda Civic that had a defective ignition system, It backfired hard thru the intake and damaged the throttle position sensor which is part of the throttle body. (see a dmaged throttle body.)

I don't know Hondas, so I can't comment on that. You mentioned:

quote Originally posted by Oreif: Bend/warp throttle plates in the TB

Which would never happen in a Fiero.

As much as I like to see to really smart people like ryan and dave argue over something Im gonna say to get back on topic.

The reason your getting a backfire when your ignition module is crapping out is the raw fuel is being dumped into your exhaust, and then being set off by something. This causes a big explosion in your muffler. I recently destroyed mine because I cranked for too long when I was setting my timing.

If I were you, I would replace the module with one under some kind of warranty. A good parts supplier will not sell crap over and over, they care about their customers and if you explain the situation, you should be ok. As well, get some heat sink compound from radio shack and use that rather than the dielectric grease provided with the module. Make sure your ign. module screws are clean and creating a good ground. Also check your muffler seams for breaks, thats most likely where your gonna have damage. The bad ignition module should not create an intake backfire large enough to damage anything.

quote Originally posted by ryan.hess: Fieros don't have superchargers. Not applicable.

Huh?? The 1999 Park Avenue was a 3800 Series II normally aspirated engine not supercharged.
Look at the recall it's for normally aspirated engines not the L67 supercharged engines.

Now wait a minute, I said it could damage items. Which it could possibly do.
Then you wanted proof and said ANY example from the web. So I provided a few examples.
Now that you lost that argument you want to change parameters to say it's "Not Applicable" to a Fiero??????

Obviously, You are going to keep changing the conditions and parameters until your side of the argument actually has a true fact.

As for "Fiero's" that have actually had problems:
https://www.fiero.nl/forum/Archives/Archive-000001/HTML/20060206-2-062995.html (bottom post)

Oh wait, Let me guess, It's "not applicable" because it's a 4-cyl right?

As for the rest of the members reading this, I apologize. If Ryan wishes to continue, I will move it to PM's.