1994 LT1 Sputtering - Stalling
Thread Starter
Cruising
Joined: Nov 2007
Posts: 12
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1994 LT1 Sputtering - Stalling
I got my triple black 1994 LT1 about 1 1/2 years ago. It has 133k miles. The previous owner indicated a complete? tuneup was performed prior to my purchase. It has flowmaster exhaust and runs and sounds like a real beast. But.....about a year ago on rare occasion it would start running rough a couple of minutes after starting while still as slow speeds. Hitting the accellerator would cause the roughness to go away. About a month ago, it got worse and on my way home it stalled twice at stop signs while still cold. Now, it will do the rough running routine almost every time while still warming up. Or rare occasion, it will hit a dead zone for just an instant at slow running speeds. This morning, for the first time it died when I was almost to work so it was all warmed up. At first it would not start, not even hit at all. I cranked for a bit. Scratched my head, did the key on, key off, key on, key off, key on, key off, cranked a little more and it started.
Does this sound like a fuel or electrical problem? Any suggestions?
Does this sound like a fuel or electrical problem? Any suggestions?
Le Mans Master
Joined: Feb 2003
Posts: 9,087
Likes: 0
From: Chicago IL
I would replace the fuel pump relay first. That seems to be the most common place to start.
Get a good fuel pressure guage and check pressure when engine is stone cold at the first key turn. It should spike to 38-42psi. Start the engine and let it idle and watch the pressure after the engine warms up. Then, remove the vacuum tube from the FP regulator and see if the pressur goes up.
Replace the fuel filter also. If it is plugged up, that will cause a fuel pressure issue.
Next would be the fuel pump itself.
Get a good fuel pressure guage and check pressure when engine is stone cold at the first key turn. It should spike to 38-42psi. Start the engine and let it idle and watch the pressure after the engine warms up. Then, remove the vacuum tube from the FP regulator and see if the pressur goes up.
Replace the fuel filter also. If it is plugged up, that will cause a fuel pressure issue.
Next would be the fuel pump itself.
Thread Starter
Cruising
Joined: Nov 2007
Posts: 12
Likes: 0
I would replace the fuel pump relay first. That seems to be the most common place to start.
Get a good fuel pressure guage and check pressure when engine is stone cold at the first key turn. It should spike to 38-42psi. Start the engine and let it idle and watch the pressure after the engine warms up. Then, remove the vacuum tube from the FP regulator and see if the pressur goes up.
Replace the fuel filter also. If it is plugged up, that will cause a fuel pressure issue.
Next would be the fuel pump itself.
Get a good fuel pressure guage and check pressure when engine is stone cold at the first key turn. It should spike to 38-42psi. Start the engine and let it idle and watch the pressure after the engine warms up. Then, remove the vacuum tube from the FP regulator and see if the pressur goes up.
Replace the fuel filter also. If it is plugged up, that will cause a fuel pressure issue.
Next would be the fuel pump itself.
Team Owner
Joined: Oct 2000
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From: Fort Knox, KY
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Could be a bad plug wire(s) or a coil wire, too. Open the hood at night or in a darkened garage, then pull the underhood lamp fuse. Look for telltale electrical arcing along the wires.
Melting Slicks
Joined: Feb 2008
Posts: 3,286
Likes: 6
From: Palm Beach
Le Mans Master
Joined: Feb 2003
Posts: 9,087
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From: Chicago IL
Don't be cheap.
Oh, and try replacing the courtesy light bulb in the door. That might work too.
Last edited by formul89; Sep 16, 2008 at 05:20 PM.
Drifting
Joined: Sep 2003
Posts: 1,363
Likes: 7
From: 1994 LT1 Coupe 6-speed with FX3 & 2000 LS1 Vert 6-Speed with F45 Hunterdon County, NJ
In addition to the above suggestions,
check/clean MAF (only use MAF cleaner, other products may damage), especially if you have a oil-soaked air filter (e.g. K&N).
check the O2 sensors.
check ground points (e.g. driver side bell-housing).
check/clean MAF (only use MAF cleaner, other products may damage), especially if you have a oil-soaked air filter (e.g. K&N).
check the O2 sensors.
check ground points (e.g. driver side bell-housing).
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Race Director
Joined: Dec 1999
Posts: 11,813
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From: Work
St. Jude Donor '09
I had similar issues with both plug wires and a cracked plug in the past.
Thread Starter
Cruising
Joined: Nov 2007
Posts: 12
Likes: 0
Throttle position sensor
I picked up a few parts and the man behind the counter said my problem could possible be the throttle position sensor. Symptoms have usually shown up when my foot was off the pedal or at very slow speed. I've looked at other threads and it appears to be very straight forward. Is the TPS a possibility and are there any tricks to changing one on a 94 LT1?
Thread Starter
Cruising
Joined: Nov 2007
Posts: 12
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Le Mans Master
Joined: Feb 2003
Posts: 9,087
Likes: 0
From: Chicago IL
I picked up a few parts and the man behind the counter said my problem could possible be the throttle position sensor. Symptoms have usually shown up when my foot was off the pedal or at very slow speed. I've looked at other threads and it appears to be very straight forward. Is the TPS a possibility and are there any tricks to changing one on a 94 LT1?
Try unplugging the Mass Air Flow sensor and drive it around the block. IF it runs better unplugged, that might be your problem. Clean it first and replace if that doesn't work.
Thread Starter
Cruising
Joined: Nov 2007
Posts: 12
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1994 lt1 sputtering-stalling "solved"
I bought the fuel pump relay and fuel filter. I had to take the relay back once I got the old one out, wrong fit. Installed relay, looked at filter and said "oh my gosh" and decided to have that done by a mechanic. Anyway, after installing the relay I have now driven it 4 times, not a sputter. The simle $9 relay seems to have solved the problem. Kudos to "formul89" who nailed the problem on the first reply. I didn't mess with anything else, so thanks to formul89 for solving my problem! I guess i was fortunate as the list of potential problems continued to grow. Thanks to all who responded, I'll keep the list in case the problem comes back.
Le Mans Master
Joined: Feb 2003
Posts: 9,087
Likes: 0
From: Chicago IL
I bought the fuel pump relay and fuel filter. I had to take the relay back once I got the old one out, wrong fit. Installed relay, looked at filter and said "oh my gosh" and decided to have that done by a mechanic. Anyway, after installing the relay I have now driven it 4 times, not a sputter. The simle $9 relay seems to have solved the problem. Kudos to "formul89" who nailed the problem on the first reply. I didn't mess with anything else, so thanks to formul89 for solving my problem! I guess i was fortunate as the list of potential problems continued to grow. Thanks to all who responded, I'll keep the list in case the problem comes back.
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
But.....about a year ago on rare occasion it would start running rough a couple of minutes after starting while still as slow speeds. Hitting the accellerator would cause the roughness to go away. About a month ago, it got worse and on my way home it stalled twice at stop signs while still cold. Now, it will do the rough running routine almost every time while still warming up. Or rare occasion, it will hit a dead zone for just an instant at slow running speeds. This morning, for the first time it died when I was almost to work so it was all warmed up. At first it would not start, not even hit at all. I cranked for a bit. Scratched my head, did the key on, key off, key on, key off, key on, key off, cranked a little more and it started.
I can’t see how the relay could cause a runability problem or relate to these symptoms when it is not even necessary for normal engine operation provided all other systems are operating properly. It seems like the original problem could be still hiding in the dark. Just my opinion to keep an open mind about the situation.
Last edited by pcolt94; Sep 23, 2008 at 07:22 AM.
Le Mans Master
Joined: Feb 2003
Posts: 9,087
Likes: 0
From: Chicago IL
Good that your fixed and can’t argue with success. But I am troubled by the facts and events as I understand them. One of the main functions in life of the fuel pump relay is to pressurize the fuel system before cranking. But once it starts and oil pressure comes up, the pressure switch for the fuel pump closes and puts 12 volts to the fuel pump. The relay them becomes secondary to engine run. Even with no relay installed in car, the engine will still start with additional cranking.
I can’t see how the relay could cause a runability problem or relate to these symptoms when it is not even necessary for normal engine operation provided all other systems are operating properly. It seems like the original problem could be still hiding in the dark. Just my opinion to keep an open mind about the situation.
I can’t see how the relay could cause a runability problem or relate to these symptoms when it is not even necessary for normal engine operation provided all other systems are operating properly. It seems like the original problem could be still hiding in the dark. Just my opinion to keep an open mind about the situation.
In this case though, I am leaning towards the fuel filter as being the culprit because the OP replaced that also and the car had driveability problems.
Melting Slicks
Joined: Feb 2008
Posts: 3,286
Likes: 6
From: Palm Beach
Don't confuse him with facts. Of course it was the relay. He fixed his window motor by changing the courtesy light bulb.
Good that your fixed and can’t argue with success. But I am troubled by the facts and events as I understand them. One of the main functions in life of the fuel pump relay is to pressurize the fuel system before cranking. But once it starts and oil pressure comes up, the pressure switch for the fuel pump closes and puts 12 volts to the fuel pump. The relay them becomes secondary to engine run. Even with no relay installed in car, the engine will still start with additional cranking.
I can’t see how the relay could cause a runability problem or relate to these symptoms when it is not even necessary for normal engine operation provided all other systems are operating properly. It seems like the original problem could be still hiding in the dark. Just my opinion to keep an open mind about the situation.
I can’t see how the relay could cause a runability problem or relate to these symptoms when it is not even necessary for normal engine operation provided all other systems are operating properly. It seems like the original problem could be still hiding in the dark. Just my opinion to keep an open mind about the situation.
Thread Starter
Cruising
Joined: Nov 2007
Posts: 12
Likes: 0
I started it all
Ok, so maybe the relay is not the final answer, but I've driven the baby every day since I replaced the relay and not a single sputter or shutdown. Prior to that, it had acted up every day for a week. The guy I know at Autozone said he couldn't believe it was the relay either. He thought it might be the throttle position sensor. At any rate, it it comes up again, I have many ideas to search out.
Since there is some humor involved, my left rear turn signal light burned out yesterday. Maybe that was the problem.
I had to take the courtesy light bulb back.
Since there is some humor involved, my left rear turn signal light burned out yesterday. Maybe that was the problem.
I had to take the courtesy light bulb back.