Question on EGR

I just bought my second 240sx recently. I was driving it home(about a 4 hours drive) and half way through the "Service Engine Soon" light comes on. So I get home, take it to the shop and they said there was two problems: 1. Something wrong with the EGR and 2. Something wrong with Knock Sensor 1. Only modification on the car is "custom" exhaust. Do you think that could be the problem or will I have to replace the EGR valve? It sometime blow black smoke on start up, but that's after sitting for a while. Also, I have know idea what a knock sensor or, but seeing and there is no indication of whether I'm in O/D or not, I'm guessing it has something to do with that.

Any ideas about these two problems? Thanks

well what a EGR does is that when your exhuast temp hits a certain temp, it would start creating a massive amount of NOx. so what the car does to lower exhuast temp would be to recirculate the exhuast gases back into the intake. hense the name Exhaust Gas Recirculation valve. now what sometimes happens is that they get stuck open so exhuast gas is constantly being dumped into the engine. this would cause mis fires and such becasue your air fuel mixture is all messed up with non combustible gases.

the knock sensor is what picks up detonation are large engine vibrations. when it picks up those signals, it would casue the computer to retard the ignition timing to try to save the engine. generally you can feel power being lost when the timing is being pulled back. when i had a bad knock sensor, the car felt very inconsistent. it would really haul sometimes, but other times, its a dog. and that sensor is a pain in hte freaking ass to change. its right underneth the intake manifold runners between cylinder #2 and #3. it is possible that your faulty EGR could cause your knock sensor to go off.

so its up to you what decide whats wrong with your car from what i told you.

Oh, ok. So is the EGR valve easy to replace or should I take it to a shop to get them to do it. I don't even know where the EGR valve would be, but it seems it might be somewhere close to the intake manifold. Oh, and it's nothing really detrimental to the car, right? I don't want to be driving it to work when I should just leave it alone. Thanks, that was really helpful.

the EGR is a pain in the ass to get to. its right in the back of the intake manifold by the firewall. i don't know how some people can stick their hands back there, but i know i can't. and when its busted, no it won't destroy your engine but it willl make your car run like crap.

Awesome, thanks for everything. I think I'll try and find it and see if I can actually get to it. It might just be worth taking it to someone and letting them see if they can get to it. Thanks again for everything.