Is this normal???
Thread Starter
Safety Car
Joined: Jun 2006
Posts: 3,605
Likes: 2
From: Latrobe PA
Is this normal???
--------------------------------------------------------------------------------I have a 91 L98 with no mods. In the morning when I start up it runs rough and sputters until the engine is warm then it runs normal.
It only does this after sitting overnight. I just changed the plugs and air filter.
Any suggestions on what to look for next or is this just normal. I have 49,000 miles on it.
Thanks.
Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 15
From: backwoods upstate ny
cold engine runs in ''open loop'' based on ecm memory, warm engine runs ''closed loop'' based on actual o2 sensor input to ecm
sounds like your problem is lean fuel mixture during open loop....could be a restricted (dirty) fuel filter, weak fuel pump (first stage of failure), or dirty injectors.
fuel pressure reading at start-up might help.
fuel filter should be changed annually...$20 item (D.I.Y.)
in-tank fuel pumps have a 10 yr / 100,000 mile life expectancy...its a $70 item (D.I.Y.) and even if its not a problem now, you're due.
injectors can be cleaned, i replace em...wrong cleaner will kill em...others here know more than i on this
sounds like your problem is lean fuel mixture during open loop....could be a restricted (dirty) fuel filter, weak fuel pump (first stage of failure), or dirty injectors.
fuel pressure reading at start-up might help.
fuel filter should be changed annually...$20 item (D.I.Y.)
in-tank fuel pumps have a 10 yr / 100,000 mile life expectancy...its a $70 item (D.I.Y.) and even if its not a problem now, you're due.
injectors can be cleaned, i replace em...wrong cleaner will kill em...others here know more than i on this
Safety Car
Joined: Oct 2005
Posts: 3,545
Likes: 17
From: Bartlett Tennessee
Photoguy
Fuel filter on 91 is located in back of passenger side front wheel well(next to the frame)Mine had a cover plate hiding it from view.BEWARE I put fuel injector cleaner in my gas tank and RUINED MY FUEL PUMP ,strainer and ALL 8 FUEL INJECTORS !!!
Melting Slicks
Joined: Mar 2003
Posts: 2,898
Likes: 0
From: Oklahoma City Oklahoma
Originally Posted by LIGHTMAN
Fuel filter on 91 is located in back of passenger side front wheel well(next to the frame)Mine had a cover plate hiding it from view.BEWARE I put fuel injector cleaner in my gas tank and RUINED MY FUEL PUMP ,strainer and ALL 8 FUEL INJECTORS !!!
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Le Mans Master
Joined: May 2006
Posts: 5,383
Likes: 2
From: The real question is; When you turn your car on, does it return the favor..
Cruise-In VIII & IX Veteran
St. Jude Donor '07-'08
My 84 had sort of the same condition. It spitted and sputtered until she got going. Then it ran fine. I went through the whole ball of wax changing plugs, plug wires, coil, dist cap, rotor and fuel filter. It finnally turned out to be the fuel pump. Now she runs great... 
Safety Car
Joined: Oct 2005
Posts: 3,545
Likes: 17
From: Bartlett Tennessee
Fuel Injector Cleane4r
CMYC4GO LUCAS FUEL INJECTOR CLEANER !!!!! BTW check the Chevrolet service bulletins on the 91 VETTE and you will find acording to THE GENERAL they tell you not to put any kind of fuel injector cleaner in because in their opinion due to the way their are made the don't need any !!! I FOUND THIS INFORMATION here on this FOURM !!!!!
Pro
Joined: Apr 2000
Posts: 696
Likes: 18
From: Jenkintown PA
Try, this and it will not cost you much $.
Start car cold and let idle for about 10 secs to build up oil pressure. Then still in park, get rpms up to 2000 and hold it there for about 4 minutes. You could have some carbon build up on the O2 sensor.
It won't harm anything and could help solve the problem. Particularly if you do not run the car a highway speed for any amount of time.
SAVE THE WAVE!
Start car cold and let idle for about 10 secs to build up oil pressure. Then still in park, get rpms up to 2000 and hold it there for about 4 minutes. You could have some carbon build up on the O2 sensor.
It won't harm anything and could help solve the problem. Particularly if you do not run the car a highway speed for any amount of time.
SAVE THE WAVE!
Le Mans Master
Joined: Oct 2003
Posts: 7,625
Likes: 4
From: Director of Bands
St. Jude Donor '08
Originally Posted by EvanD
Sounds like your opti is going bad.... hehehehe
If it were me, I'd try vetteman42's advice first... sometimes it's the simple cheap things. After that, put a test your fuel pressure.
