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My husband is a great back yard mechanic and tries to fix anything that goes wrong with my 2002 Ford Mustang V/6 with 190,000 miles on it. So far he has done a great job, until now! I have a check engine light on and the local part store read the codes for me. They told me I have a misfire code on cylinder #4 and an EGR code of insufficient flow. They want to sell me an EGR valve and new plugs and wires to fix this problem. Of course they can’t guarantee this will fix the problem. Of course it already has new plugs and wires in it and it still misses when I give it gas at 45 MPH. How can I get this fixed and what will it do to my engine if I leave it alone?

Please don’t be too hard on your husband about this problem. A lot of good technicians have pulled their hair out on this same problem you are describing. In most cases this is all about the EGR Low Flow code and the engine miss code is just a symptom of this problem. Let me explain how this happens: When you’re driving down the highway at 45 to 60 MPH you don’t need so much fuel to keep the car moving. So the EGR Valve (Exhaust Gas Recirculation) redirects hot exhaust gases into the engines combustion chamber. It does this for a several reasons: 1) The hot exhaust gases “cool down” the combustion chamber by displacing the amount of fresh air and fuel. 2) These hot exhaust gases keep the engine from “pinging” when you go to pass someone. 3) They lower the amount of (NOX) Oxides of Nitrogen (smog) coming out the tailpipe 4) Assist the catalytic converter in by lowering the (NOX) 5) Give you better gas mileage! Now to the engine miss on Cylinder 4: I suspect that the EGR passageways are clogged on every cylinder but Cylinder #4. When the EGR does work like it should, all the exhaust gases go to Cylinder #4. When it does this all of the fresh air and fuel has been displaced with hot exhaust gases. (since this is the only cylinder that is not restricted) This will cause the “check engine light” and code and make the car miss when you step on the gas. If this is the problem then the intake manifold will need to be removed and the EGR passageways will need to be cleaned. This needs to be done carefully to avoid breaking pieces of hard carbon off. That MAY cause engine “knocking” or noise if the hard carbon gets between the piston and cylinder head. Chemically cleaning the passageways and using a vacuum cleaner is the best way to avoid this potential problem!

 

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