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"Miss" When Warms Up

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Old 08-03-2008 | 11:57 AM
  #1  
danziger's Avatar
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From: Chesapeake, VA
Car: 1991 Formula Firebird
Engine: L98 with headers/exhaust
Transmission: 700R4
Axle/Gears: 3.23 10-bolt
"Miss" When Warms Up

Hey...just want to pick your brains for advice.
I just picked up a mint 1991 Formula 350. The car runs great upon start-up, but as it gets progressively hotter, it runs rougher with a pronounced "miss". The previous owner had the distributor replaced and I just changed the plugs and wires, which were in bad shape. I was thinking the coil would be my next move, but I'm open to suggestions. Thanks in advance! Ben
Old 08-03-2008 | 06:49 PM
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BASSETT IROC 85's Avatar
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From: Heart of Dixie
Car: 1987 Camaro Sport Coupe
Engine: 355
Transmission: 700R4
Axle/Gears: 7.5 inch 342
Re: "Miss" When Warms Up

Did any of the plugs look greenish? you may have a blown head gasket or a cracked head.
Old 08-04-2008 | 06:30 AM
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danziger's Avatar
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From: Chesapeake, VA
Car: 1991 Formula Firebird
Engine: L98 with headers/exhaust
Transmission: 700R4
Axle/Gears: 3.23 10-bolt
Re: "Miss" When Warms Up

Well, I've had a head-gasket go before and the Formula has none of the symptoms. The plugs looked/smelled "wet" with fuel, which I thought backed the ignition theory... I replaced the coil last night with no improvement.
Any ideas?
Old 08-04-2008 | 06:14 PM
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Theking's Avatar
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From: Sweden
Car: 1989 IROC-Z
Engine: 350 TPI
Transmission: Th700R4
Axle/Gears: 3.27
Re: "Miss" When Warms Up

Hows your fuelling ? is it getting the right mixture when hot ?
Old 08-04-2008 | 07:16 PM
  #5  
BASSETT IROC 85's Avatar
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From: Heart of Dixie
Car: 1987 Camaro Sport Coupe
Engine: 355
Transmission: 700R4
Axle/Gears: 7.5 inch 342
Re: "Miss" When Warms Up

I would run a cylinder leakdown test. Or pull the plugs and put pressure tester on the radiator. see if you get any water.
Old 08-04-2008 | 07:36 PM
  #6  
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From: oxford n.c.
Car: 1991 transam
Engine: 305 30 over long tubes into 3" y
Transmission: 700r4
Axle/Gears: 4:10
Re: "Miss" When Warms Up

ohm your injectors, should be between 14-17 ohms.mine did the same thing one was at .005 ,later jimmy
Old 08-04-2008 | 08:27 PM
  #7  
danziger's Avatar
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Joined: Aug 2003
Posts: 482
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From: Chesapeake, VA
Car: 1991 Formula Firebird
Engine: L98 with headers/exhaust
Transmission: 700R4
Axle/Gears: 3.23 10-bolt
Re: "Miss" When Warms Up

Thanks for the replies, guys. I think it is the injectors. I'm really pressed for time so (don't laugh) I'm having the Pontiac dealership do a diagnostic on the Formula. It barely made a 7-mile trip...
Old 08-04-2008 | 08:54 PM
  #8  
ultimatefighter's Avatar
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Posts: 144
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From: Topeka, KS
Car: 1992 Z28
Engine: 305 TPI
Transmission: 700r4
Axle/Gears: 10 bolt posi. G80
Re: "Miss" When Warms Up

Maybe ignition control module???
Old 08-05-2008 | 02:17 AM
  #9  
Theking's Avatar
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Posts: 924
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From: Sweden
Car: 1989 IROC-Z
Engine: 350 TPI
Transmission: Th700R4
Axle/Gears: 3.27
Re: "Miss" When Warms Up

Yeah it could be the ignition module and/or pickup coil to.
Had similar problem, runned good cold, but a as soon as the car got running temp and the sun hitting the hood, the dist started to miss, and was really hard to start sometimes when it was hot. Turned out to be a really bad ignition moule and a "on the way" pickup failure..

Got new parts from MSD (warranty) and im on the road again.
Old 08-06-2008 | 06:44 AM
  #10  
danziger's Avatar
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Joined: Aug 2003
Posts: 482
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From: Chesapeake, VA
Car: 1991 Formula Firebird
Engine: L98 with headers/exhaust
Transmission: 700R4
Axle/Gears: 3.23 10-bolt
Re: "Miss" When Warms Up

***Update***

The dealer found 10psi at the fuel-rail, so they replaced the fuel pump and that seems to have fixed it. They are taking it for an extended road test to make sure there are no other issues. I need to get some diagnostic tools for the 3rdGen...
Old 08-06-2008 | 01:58 PM
  #11  
Icarus 402001's Avatar
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Joined: Feb 2008
Posts: 133
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From: SE PA.
Car: 92RS
Engine: 305
Transmission: 700R4
Axle/Gears: 2.73
Re: "Miss" When Warms Up

"Extended Road Test"? Are you going to follow them around?
Old 08-06-2008 | 09:10 PM
  #12  
BASSETT IROC 85's Avatar
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Posts: 465
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From: Heart of Dixie
Car: 1987 Camaro Sport Coupe
Engine: 355
Transmission: 700R4
Axle/Gears: 7.5 inch 342
Re: "Miss" When Warms Up

To the local drag strip fortest and tune .
Old 08-10-2008 | 08:08 AM
  #13  
danziger's Avatar
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Joined: Aug 2003
Posts: 482
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From: Chesapeake, VA
Car: 1991 Formula Firebird
Engine: L98 with headers/exhaust
Transmission: 700R4
Axle/Gears: 3.23 10-bolt
Re: "Miss" When Warms Up

Got the Formula back yesterday and it is running fantastic. Thanks for the input guys!
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