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Old 09-20-2007, 04:50 AM   #1
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Default Help: LT1 Hard Start, Miss, and backfiring problems.

Hi,
New to the LT1, but not a typical SBC. I bought my second F-body car for $2750 a few days ago (First was an 85 camaro that was junk from the beginning). I bought it knowing it had a miss, but I drove it home anyways. It's a 1995 Pontiac Firebird Formula M6, with a catless exhaust and some cheap looking ebay intake. When I cold start it, usually takes about 10 seconds to start and fluttering of the throttle. Common or unusual? Next when it does finally run, you can definetly tell it has a miss, rev it, it backfires. Now driving it down the road it hiccups and backfires. Even throughout the entire RPM range. The previous owner said he put a new a optispark, new plug wires and new plugs in. Upon closer inspection, everything looks brand new, I also noticed a bad intake elbow, probably caused by the backfiring. I also removed the plugs for inspection. #3 cylinder doesn't seem to be firing, all covered in black from a rich condition. I still have yet to check the passenger side too. Hopefully all is firing there.

The car also had an 02 gauge wired in also. When it hesitated in 6th gear while in cruise, trying to go uphill it would blow out black smoke. I disconnected the gauge, but no luck and didn't help anything. While it was hesitating, the gauge read dead lean, but was blowing out a black smokescreen like a james bond car !

So...ANY HELP IS APPRECIATED!

Thanks,
Ben
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Old 09-21-2007, 12:53 AM   #2
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I would check the intake piping for leaks or maybe a vacuum leak but it sounds like to much air .If all else fails try replacing the o2's not a bad idea anyways
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Old 09-21-2007, 01:00 AM   #3
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Ok, I talked to the previous owner tonight. Seems though he didn't change the opti or cap and rotor. All he changed was the Plugs and the coil. That didn't help obviously. The wires also look in really good shape. So I might be pulling the water pump and checking the cap and rotor. Also, I noticed that my intake elbow is shot to complete Hell. Looks like the backfiring did its number to it.
Thanks,
Ben
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Old 09-21-2007, 01:09 AM   #4
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You might just want to get an opti but that intake needs to be fixed asap or it will screw up your maf.
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Old 09-21-2007, 09:16 AM   #5
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You might just want to get an opti but that intake needs to be fixed asap or it will screw up your maf.
I'll probably just remove my MAF and bring it inside the house so it don't get messed up.
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Old 09-21-2007, 10:52 AM   #6
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If you have a backfire through the INTAKE, then something is horribly wrong with the VALVE timing. The stock elbows have a tendancy to break right at the connection to the T/B, I dont think it would "blow out" from a intake backfire, so if its torn, replace that first.
If you have a EXHAUST backfire, and not just the typical LT1 exhaust "pop" then scan for codes, and look into your complete ignition.
get some o2's as well, with proper extensions, if thats what you need. Obviously, somebody hacked the hell out of the old ones.
BTW, your torn elbow can cause most of these symptoms

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Old 09-21-2007, 11:06 AM   #7
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Originally Posted by DJ_Kovacs View Post
If you have a backfire through the INTAKE, then something is horribly wrong with the VALVE timing. The stock elbows have a tendancy to break right at the connection to the T/B, I dont think it would "blow out" from a intake backfire, so if its torn, replace that first.
If you have a EXHAUST backfire, and not just the typical LT1 exhaust "pop" then scan for codes, and look into your complete ignition.
get some o2's as well, with proper extensions, if thats what you need. Obviously, somebody hacked the hell out of the old ones.
BTW, your torn elbow can cause most of these symptoms
Yea, but would a torn elbow cause just a misfire in only cylinder 3? Thats what I'm wondering because its not firing at all it seems. Plug all black and sooty from a rich condition but does not smell of gas, but all the other plugs have white showing. Also, they didn't hack the hell out of the o2 wire, just spliced into one cleanly with what looks like came with the auto meter 02 gauge kit. Thanks for the help though guys! Also, the torn elbow probably would contribute to my hard starting condition.
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Old 09-21-2007, 11:12 AM   #8
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Quote:
Originally Posted by Halucinator View Post
Hi,
New to the LT1, but not a typical SBC. I bought my second F-body car for $2750 a few days ago (First was an 85 camaro that was junk from the beginning). I bought it knowing it had a miss, but I drove it home anyways. It's a 1995 Pontiac Firebird Formula M6, with a catless exhaust and some cheap looking ebay intake. When I cold start it, usually takes about 10 seconds to start and fluttering of the throttle. Common or unusual? Next when it does finally run, you can definetly tell it has a miss, rev it, it backfires. Now driving it down the road it hiccups and backfires. Even throughout the entire RPM range. The previous owner said he put a new a optispark, new plug wires and new plugs in. Upon closer inspection, everything looks brand new, I also noticed a bad intake elbow, probably caused by the backfiring. I also removed the plugs for inspection. #3 cylinder doesn't seem to be firing, all covered in black from a rich condition. I still have yet to check the passenger side too. Hopefully all is firing there.

The car also had an 02 gauge wired in also. When it hesitated in 6th gear while in cruise, trying to go uphill it would blow out black smoke. I disconnected the gauge, but no luck and didn't help anything. While it was hesitating, the gauge read dead lean, but was blowing out a black smokescreen like a james bond car !

So...ANY HELP IS APPRECIATED!

Thanks,
Ben
My engine did this when I blew a head gasket. I wasn't getting any smoke out of the tail pipes, but it would be very difficult to start, when it did start it would miss like crazy, and it would also backfire like crazy.

I didn't notice any power loss, but just symptoms such as the ones you're describing.
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Old 09-21-2007, 11:27 AM   #9
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Yea, its not a head gasket, I would notice it overheating or at least spewing of some white smoke out the tailpipe, or at least have water in my oil.
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Old 09-21-2007, 01:36 PM   #10
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Originally Posted by Halucinator View Post
Yea, but would a torn elbow cause just a misfire in only cylinder 3? Thats what I'm wondering because its not firing at all it seems. Plug all black and sooty from a rich condition but does not smell of gas, but all the other plugs have white showing. Also, they didn't hack the hell out of the o2 wire, just spliced into one cleanly with what looks like came with the auto meter 02 gauge kit. Thanks for the help though guys! Also, the torn elbow probably would contribute to my hard starting condition.
Did you check to see if it is actually a dead cylinder? or do you just think it is?
Black and sooty could also mean leaky seals/rings, which isnt all that uncommon. put the plug in the boot, fire up the car, and ground the plug to metal, if the arc jumps then your golden, if not, then you check further in. Its actually good if it doesnt smell too much like gas, because if it did, that might indicate a dead plug. (gas is just loading up)
The torn elbow will cause a harder start, because some of the air is not being metered by the MAF. You should get that fixed.
Scan for codes. That will tell you alot
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Old 09-21-2007, 01:49 PM   #11
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I have a elbow brand new if you need it,30.00 plus shipping
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Old 09-21-2007, 02:02 PM   #12
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Yea, its not a head gasket, I would notice it overheating or at least spewing of some white smoke out the tailpipe, or at least have water in my oil.
Here's the funny thing. My car didn't overheat with the blown head gasket.
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Old 09-21-2007, 02:21 PM   #13
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Did you check to see if it is actually a dead cylinder? or do you just think it is?
Black and sooty could also mean leaky seals/rings, which isnt all that uncommon. put the plug in the boot, fire up the car, and ground the plug to metal, if the arc jumps then your golden, if not, then you check further in. Its actually good if it doesnt smell too much like gas, because if it did, that might indicate a dead plug. (gas is just loading up)
The torn elbow will cause a harder start, because some of the air is not being metered by the MAF. You should get that fixed.
Scan for codes. That will tell you alot
Alright, tried taking it out today, I fixed the intake elbow temporarily and its still hard starting. I came back home, its seems pretty hot outside, even with the 160 thermostat (previous owner), it looks like it started to overheat!!! Well I got back home after having it running and bam it dies in the driveway. Stalled completely out, now it won't even start. So what I'm gonna do tonight is drain all the coolant, remove the pump and optispark and do a thorough inspection of the opti, cap and rotor. I'm sure its not that bad of a job to do, people just bitch about it. Any things you guys suggest I should do while I have it apart?
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Old 09-22-2007, 07:06 PM   #14
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Alright, I broke down and tore it apart after it died in the driveway. It was definetly the optispark. Looked like someone was in there before and messed up the Sensor wheel. There are fingerprints all over the disc and its bent to all hell. Doesn't help that the shaft has some play in it, that might of also screwed it up. So I'm in the market now for a new distributor. MSD or OEM? What about the Jegs cheap distributor?
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Old 09-23-2007, 12:04 AM   #15
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Alright, I broke down and tore it apart after it died in the driveway. It was definetly the optispark. Looked like someone was in there before and messed up the Sensor wheel. There are fingerprints all over the disc and its bent to all hell. Doesn't help that the shaft has some play in it, that might of also screwed it up. So I'm in the market now for a new distributor. MSD or OEM? What about the Jegs cheap distributor?
Stay away from cheap distributors. In the case of the optispark, the OEM one is still the best, even though other reputable aftermarket companies such as MSD and Accel are in the business of making them.
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