Four port vacuum switch
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Mountain Pass
Joined: Nov 2016
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Four port vacuum switch
My 83 4.9L is acting up. I believe the vacuum switch is causing unwanted surging to the EGR. When I disconnect the vacuum line to the EGR and block it with a screw the surging stops. However, after doing this the engine now pings. So I'm in search for a (blue) 4 port switch to replace the failed part. I've had a look online but don't find any replacements. Wondering if the good folks here have a source, or an answer to the pinging. Tweak the timing? I'd rather replace the switch.
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Joined: Jan 2001
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From: Virginia
People love to block the EGR off and claim it doesn't hurt anything, but I have had pinging problems doing it just like you have. Have you modified the exhaust system? That will cause the EGR not to work correctly. It uses backpressure to regulate the amount of EGR.
If you can't find the ported switch, one thing I found that helped with the pinging was to put a 180 thermostat in the engine. I was messing around with the stock 351w, and all engines are different. I messed with the jets in the carb and the timing also. The timing helped but made it doggy with no power. The 180 thermostat had the most beneficial affect and actually stopped the pinging on that engine.
If you can't find the ported switch, one thing I found that helped with the pinging was to put a 180 thermostat in the engine. I was messing around with the stock 351w, and all engines are different. I messed with the jets in the carb and the timing also. The timing helped but made it doggy with no power. The 180 thermostat had the most beneficial affect and actually stopped the pinging on that engine.
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Joined: Jan 2001
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From: Virginia
That is very true. Sometimes you really have to dig to find some of this emissions stuff. It's almost like they do not want you to fix it and keep it smogged. They want you to buy a new truck.
Post Fiend
Joined: Feb 2008
Posts: 5,831
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From: St Albert, Alberta
My 83 4.9L is acting up. I believe the vacuum switch is causing unwanted surging to the EGR. When I disconnect the vacuum line to the EGR and block it with a screw the surging stops. However, after doing this the engine now pings. So I'm in search for a (blue) 4 port switch to replace the failed part. I've had a look online but don't find any replacements. Wondering if the good folks here have a source, or an answer to the pinging. Tweak the timing? I'd rather replace the switch.
Short of finding a NOS one you are pretty much boned. The only thing you can do is back step to a non-emissions setup and will likely need to get a new carb. The pinging is a result of modern fuels. These trucks run lean on modern fuels as it is so, remove the EGR and you just walk past the edge of too lean.
You may be able to simplify the system to use available parts.
Cant determine that without seeing the vacuum diagram though.
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