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Discussion Starter #1
So my 1994 4.3 TBI sounds like it has a slight miss. The dealership diagnosed it as a clogged fuel filter. The miss is a lot quieter and the truck runs a ton better but the miss is still there. The engine also tries to "diesel" and keep running after being turned off. It makes a hissing noise which sounds like its coming from the right side injector. Do these symptoms sound like a leaky or bad injector?
 

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Age: 15 1/2
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Hissing noises are often vacuum leaks.
Cracked vac line, leakining sensor, or EGR plunger stuck open by carbon balls.
Simple test is to pull the front pass side vac line off of the intake port. The idle rpms should rise.
The best way to test is to coonect a ~$15 vacuum gauge and run a few quick tests.
4.3's are known for a lot of problems but dieselling is not one of them.
I'd recommend doing seafoam, or at least add it to the gas...
 

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Discussion Starter #3
I already replaced the EGR and it didn't help much. I'll try unplugging the vaccum line and see what it does.
 

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Dieseling is a result of residual air and fuel getting into the combustion chambers after the motor has been shut off. The fuel is ignited without spark plugs by glowing, hot deposits in the combustion chambers. It could be caused by a leaky injector and aided by a faulty IAC (idle air control).
 

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I wasn't recommending replacing the EGR valve. The 4.3 is well known for having cabon build up blowing from the exhust port of the EGR and getting stuck between it's intake port and the egr plunger, holding it open. Cleaning the exhust port while the EGR is off is needed if it is sticking open. Replacing the EGR won't fix that problem, since it will just get stuck open again.
You only need to replace EGR's when they are broken (which is very rare on the TBIs).
There are a lot of threads here on cleanning the EGR ports. Try a search.

How does the spray of the injectors Look?
 

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Discussion Starter #6
Spray looks good, I found a huge vacuum leak and now it's running a ton better. It still sounds like it has a cam but it runs a lot smoother.
 
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