Both Mufflers Exploded.......What's wrong?

ram360

Founding Member
Oct 19, 2002
2,162
1
57
Pennsylvania
My friend picked up his 87 GT yesterday. It's a pretty nice car, but I'm somewhat concerned. We were aware the mufflers were blown out before purchasing the car. I just assumed it was from age, rust, etc.... However the previous owner told him something along the lines of when he went to start the car one day both muffs exploded, and it was because the car was getting too much fuel because the FP wasn't adjusted. (I wasn't there to hear the guy explain all this to him) When I had my chance to look at the car. I looked under the hood and it still has the stock FPR. I've never saw anything like this before. Both muffs look like someone put some explosives inside each one and set them off. Motor is 100% bone stock, stock headers, stock h-pipe, just an exploded cat back, and gears? Any ideas? :shrug:
 
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Dont drive or ride in that thing till the gas pedal is fixed. I have heard of mufflers blowing up, but have never seen it happen, got any pics? Raw gas in the muffs and a little spark is all it takes. You can cause a carbed car to backfire in the exhaust by turning off the key while you are driving and leaving the tranny in gear. This will dump fuel into the exhaust. After a couple of secs, turn the key back on and boom! I dont think this should work on an EFI setup unless something is wrong with it. Pull the codes for starters, and I would be checking the FP, maybe the FPR went south and its dumping tons of fuel.
 
When mufflers explode like that its from fuel pooling up in them (mostly on chambered mufflers like Flowmaster) and eventually the gas ignites and blows a hole in the muffler........so yeah the guy is right, it's definitly not burning all the gas in the combustion chamber. Try checking the spark plugs, timing, etc...
 
Ok, Thanks guys. I have an extra FPR laying around so we'll put that in for starters. I don't have any pics but I'll try to get some. That's scary. BTW any ideas on how to free up the sticky gas pedal?
 
Fox Saleen 163 said:
First thing you may want to check is the Vac line going to the FPR. Does it have Vac? Pull the Vac line off at idle, if you put it on your finger it should stick to it like a house Vac would.


Some AFPR's look like the stock one, once you pull the vacuum line you will see a screw on the part the hose was connected to, the stock one does not have this....
 
yeah, I've seen this happen. Normally it happens when there is an intermittant ignition problem, like a wet TFI module or something, where spark is beign killed and raw fuel is being dumped into the exhaust, if you get enough of it far enough back and it ignites, those restrictive rusted stock mufflers will explode, and it is LOUD.
 
We replaced the FPR last night. I figured that was a good place to start. The gas pedal on the car is very weird. When the car isn't running you can push the pedal and it works just fine. Opens the throttle very smooth and works fine applying the normal amount of pressure to the pedal so the cable is fine (not kinked, or binding on anything). Once the car is running the gas pedal is difficult to push down (feels as stiff as the clutch pedal) I'm totally confused on this one.
 
Fox Saleen 163 said:
First thing you may want to check is the Vac line going to the FPR. Does it have Vac? Pull the Vac line off at idle, if you put it on your finger it should stick to it like a house Vac would.

All the vacuum lines seem to be fine.

Some AFPR's look like the stock one, once you pull the vacuum line you will see a screw on the part the hose was connected to, the stock one does not have this....

The reg on the car non adjustable but was bigger than those found on stock 5.0's. We replaced it w/ an oem part.

Check to make sure the idle adjustment screw is not sticking by the throttle body.

This also apprears to be functioning as normal. :shrug:
 
JadeFalcon said:
yeah, I've seen this happen. Normally it happens when there is an intermittant ignition problem, like a wet TFI module or something, where spark is beign killed and raw fuel is being dumped into the exhaust, if you get enough of it far enough back and it ignites, those restrictive rusted stock mufflers will explode, and it is LOUD.

So it's possible it's an ignition problem? Like I said other than the gas pedal being siffer than normal, everything else if functioning as normal. The cap and rotor look good, however the previous owner said it has Bosch platinum +4's in it. I'm wondering if they are causing the problem w/ a misfiring cylinder or something. I never understood how you get the gap correct on a 4 prong plug? :shrug: