Runs Bad When Hot
Thread Starter
Instructor
Joined: Aug 2005
Posts: 112
Likes: 0
From: Lone Tree CO
Runs Bad When Hot
My LT-1 runs super when cold.
When it warns up it is like is leaning out and the car almost stalls out off the line. once it is rollin it runs strong Also it won't pass emissions, too high HC's.
I have recenly replaced optispark, coil, distributor, wires, plugs, fuel injectors. O2 senors working and system isn't throwing any codes. Tried exchanging Mass Air Sensor to no avail.
The only thing I can thing of I computer?
Any ideas or tests?
Thanks
Ken
When it warns up it is like is leaning out and the car almost stalls out off the line. once it is rollin it runs strong Also it won't pass emissions, too high HC's.
I have recenly replaced optispark, coil, distributor, wires, plugs, fuel injectors. O2 senors working and system isn't throwing any codes. Tried exchanging Mass Air Sensor to no avail.
The only thing I can thing of I computer?
Any ideas or tests?
Thanks
Ken
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Air pump may be continuing to pump air to the headers and the O2's will sense that extra air as a lean condition and dump in a bunch of fuel. HC's skyrocket. Pinch off the air hoses at the headers to see if it goes away. Also make sure that the header checkvalves are in good shape. You should only be able to blow air through them in the direction of the header.
Burning Brakes
Joined: Nov 2001
Posts: 920
Likes: 0
From: Cherry Hill NJ
Originally Posted by ken93vette
My LT-1 runs super when cold.
When it warns up it is like is leaning out and the car almost stalls out off the line. once it is rollin it runs strong Also it won't pass emissions, too high HC's.
I have recenly replaced optispark, coil, distributor, wires, plugs, fuel injectors. O2 senors working and system isn't throwing any codes. Tried exchanging Mass Air Sensor to no avail.
The only thing I can thing of I computer?
Any ideas or tests?
Thanks
Ken
When it warns up it is like is leaning out and the car almost stalls out off the line. once it is rollin it runs strong Also it won't pass emissions, too high HC's.
I have recenly replaced optispark, coil, distributor, wires, plugs, fuel injectors. O2 senors working and system isn't throwing any codes. Tried exchanging Mass Air Sensor to no avail.
The only thing I can thing of I computer?
Any ideas or tests?
Thanks
Ken
I've been working the last couple of days and couldn't see if it would repeat.
Mine sat for a bit ( maybe a month or so) and I'm hoping for some bad gas.
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Thread Starter
Instructor
Joined: Aug 2005
Posts: 112
Likes: 0
From: Lone Tree CO
Originally Posted by REDC4CORVETTE
Do you have any mods to the engine?
You need to fill out your sig.
See if the seal is good on the map sensor at the front of the intake.
You need to fill out your sig.
See if the seal is good on the map sensor at the front of the intake.
Thanks
Thread Starter
Instructor
Joined: Aug 2005
Posts: 112
Likes: 0
From: Lone Tree CO
Originally Posted by Alvin
Does the car just feel less peppy or is there actually a driveablity problem with the car?
Thanks
Race Director
Joined: Jan 2000
Posts: 16,488
Likes: 25
From: USA. Northern Virginia
Try looking at the EGR valve, your promlems sound like what I went through last summer.
Hook a vacuum gauge up to the old EGR, if it holds a vacumm you're OK, if not put on a new EGR valve
Hook a vacuum gauge up to the old EGR, if it holds a vacumm you're OK, if not put on a new EGR valve
Pro
Joined: Oct 2005
Posts: 721
Likes: 1
From: Charlotte NC, behind someone going 10 under the speed limit
Sounds to me like the throttle stop isn't set right, like it's closed too much and the IAC is dialed out to fix the idle. Then when you crack the throttle the burst of airflow causes a lean burp. It needs to be open a certain amount at idle so that air is already flowing past it when you hit the gas pedal. Could also be a leaking fuel pressure regulator sucking gas into the vacuum line, it sometimes won't throw a fuel trim code.
Thread Starter
Instructor
Joined: Aug 2005
Posts: 112
Likes: 0
From: Lone Tree CO
Thanks for al your suggestions. Trottle position OK, air pump & EGR OK. Checking the voltage from he coil it is Ok and it is getting to the spark plugs when cold, when the engine heats up the voltage to the spark plug DROPS by 70% yet the voltage output from the coil remains good. When you shut the enngine off and restart it the voltage to the plugs is OK for about 30 seconds then drops again and the engine has problems again. Any ideas on where this power drain could be, as mentioned earlier replaced coil and opti-spark.
Thanks again for everyones input.
ken
Thanks again for everyones input.
ken
Team Owner
Joined: Feb 2006
Posts: 24,460
Likes: 7
From: sw Ohio
i'm having a similar problem on my '85 L98. It runs fine until engine temps get up to about 180 degrees or higher, then the rpms will drop to about 350-500 and it sounds like it wants to stall. Could a broken vacuum hose from the intake manifold to the evaporative canister cause this?
