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I recently had a problem with my truck. This is not directly related to our motorcycles but I post this in the hopes that what I’ve learned may help someone someday.
The truck is a 1985 GMC Vandura with a 350 cubic inch motor. It has a 4-barrel Quadra Jet Carburetor.
The problem:
After the engine sat overnight it would start up just fine. However, after about two to three minutes it would run like crap. I’m talking like at least three cylinders had dropped out. The engine would continue to run like this up until the point when the temperature gauge indicated that it was at operating temperature. After that point it ran perfectly. I could shut the engine off, let it cool for a couple of hours until it was cold to the touch, restart the engine and it would run just fine from cold all the way up to normal operating temperature. The problem only occurred after the engine and the truck had sat overnight. This started happening less than two weeks ago.
Working Theories:
Some component which was time or temperature sensitive was malfunctioning.
Possible that at startup moisture was somewhere in the ignition system and the heat from the motor eventually dried it out.
Initial Corrective/Investigative Actions:
The spark plugs: All were good.
The inside of the distributor cap: Clean and no indications of moisture.
The electric choke: the coil inside had never worked so I had hard wired the choke butterfly in the fully open position. (I ruled this out as a potential problem.)
All vacuum lines to the carburetor and emission systems were connected and I verified proper operation of all vacuum diaphragms/switches with a vacuum gauge and a vacuum source.
Since I didn’t find the “smoking gun” on this first pass I decided to make small changes like disconnecting/plugging various vacuum lines one at a time. (Have you seen the emissions layout for today’s modern vehicles?) The next day I would start the truck and look for any improvement/ worsening of the symptoms. If no improvement then I would reconnect the vacuum line and try another one. This led to a week long process of “change-test-reset” where every day I would try something new.
At the end of the week I tried disconnecting and plugging every single vacuum line/port from the carburetor: still no improvement. In my line of reasoning this ruled out everything except the carburetor itself: the Quadra jet. I had the choice of buying a rebuild kit and doing it myself or buying a remanufactured Quadra jet online for about $300.00.
The Answer:
While I was in the parts store pricing a rebuild kit (So very much looking forward to doing that here in the Pacific Northwest on a cold/wet/miserable day….), I spoke with the young lady at the parts counter and told her what my trucks symptoms were. She listened patiently and then came out from behind the counter, walked through the store and led me to the aisle where the fuel additives were. She picked up a can of “Sea-Foam” and handed it to me.
“All the stations around here have water in the fuel.” she said.
“Use this right now and put a bottle of this”, she handed me a container of HEET, “every time you fuel up.”
With nothing left to lose I followed the young ladies advice. That was the only “change” that I did to the truck that very day. The next day of course the engine started and ran properly through the entire heat range from cold all the way to normal temperature. One week later the truck is still symptom free.
Conclusion:
I never used any type of fuel additive whatsoever in the time that I have owned my truck. All this time the moisture that was in the fuel was collecting at the bottom of my fuel tank and had finally reached the point where it was being siphoned in by the fuel pickup during the initial start/warm up. The truck/tank sitting overnight allowed all the water to settle enough to be a problem.
Final Thoughts:
I had spent considerable time trying to figure out what was wrong with my truck and was about to by a new $300.00 carburetor which in the end would not have solved the problem. As part of the troubleshooting process I should have started by ensuring that the fuel itself was not the problem.
“When you hear the sound of hooves, look for horses….not zebras.”
The truck is a 1985 GMC Vandura with a 350 cubic inch motor. It has a 4-barrel Quadra Jet Carburetor.
The problem:
After the engine sat overnight it would start up just fine. However, after about two to three minutes it would run like crap. I’m talking like at least three cylinders had dropped out. The engine would continue to run like this up until the point when the temperature gauge indicated that it was at operating temperature. After that point it ran perfectly. I could shut the engine off, let it cool for a couple of hours until it was cold to the touch, restart the engine and it would run just fine from cold all the way up to normal operating temperature. The problem only occurred after the engine and the truck had sat overnight. This started happening less than two weeks ago.
Working Theories:
Some component which was time or temperature sensitive was malfunctioning.
Possible that at startup moisture was somewhere in the ignition system and the heat from the motor eventually dried it out.
Initial Corrective/Investigative Actions:
The spark plugs: All were good.
The inside of the distributor cap: Clean and no indications of moisture.
The electric choke: the coil inside had never worked so I had hard wired the choke butterfly in the fully open position. (I ruled this out as a potential problem.)
All vacuum lines to the carburetor and emission systems were connected and I verified proper operation of all vacuum diaphragms/switches with a vacuum gauge and a vacuum source.
Since I didn’t find the “smoking gun” on this first pass I decided to make small changes like disconnecting/plugging various vacuum lines one at a time. (Have you seen the emissions layout for today’s modern vehicles?) The next day I would start the truck and look for any improvement/ worsening of the symptoms. If no improvement then I would reconnect the vacuum line and try another one. This led to a week long process of “change-test-reset” where every day I would try something new.
At the end of the week I tried disconnecting and plugging every single vacuum line/port from the carburetor: still no improvement. In my line of reasoning this ruled out everything except the carburetor itself: the Quadra jet. I had the choice of buying a rebuild kit and doing it myself or buying a remanufactured Quadra jet online for about $300.00.
The Answer:
While I was in the parts store pricing a rebuild kit (So very much looking forward to doing that here in the Pacific Northwest on a cold/wet/miserable day….), I spoke with the young lady at the parts counter and told her what my trucks symptoms were. She listened patiently and then came out from behind the counter, walked through the store and led me to the aisle where the fuel additives were. She picked up a can of “Sea-Foam” and handed it to me.
“All the stations around here have water in the fuel.” she said.
“Use this right now and put a bottle of this”, she handed me a container of HEET, “every time you fuel up.”
With nothing left to lose I followed the young ladies advice. That was the only “change” that I did to the truck that very day. The next day of course the engine started and ran properly through the entire heat range from cold all the way to normal temperature. One week later the truck is still symptom free.
Conclusion:
I never used any type of fuel additive whatsoever in the time that I have owned my truck. All this time the moisture that was in the fuel was collecting at the bottom of my fuel tank and had finally reached the point where it was being siphoned in by the fuel pickup during the initial start/warm up. The truck/tank sitting overnight allowed all the water to settle enough to be a problem.
Final Thoughts:
I had spent considerable time trying to figure out what was wrong with my truck and was about to by a new $300.00 carburetor which in the end would not have solved the problem. As part of the troubleshooting process I should have started by ensuring that the fuel itself was not the problem.
“When you hear the sound of hooves, look for horses….not zebras.”
)
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