Hi folks.

I have a 5.7 Iroc that has been ported, cammed and has high compression heads. I have no idea what brand the parts are, or whats been done since it was done before I bought the car.

When I fire up the engine everything works just fine, but when the engine is warm, the service engine soon light lights up. I have noticed that there is a knocking sound from the engine, its not much, but its there. I have a guy working for me on the car, and he told me that the knock sensor wire has been cut. I am sure that this is the reason for the light to light up, but my question is as following: Why would you cut the wire for the sensor? Could there be some kind of problem that I should be aware of? It usually light up when I change speed from ie 45 to 65 or the other way. What kind of engine problems should I be aware of since its been modified?

I am a little scared of the car. Nothing has been as I thought that it would be and I hope that I didnt buy myself a big problem. I would be happy to get any feedback considering potential engine problems that could occur so that I can check it out so that I dont blow the engine.


I should also say that I filled her up with 87 gas. I dont know what kind of gas it had when I got her, but I dont think I had the light going off before I filled her up with 87. It only took a couple of minutes for the SES light to turn on after I did. The tank was less then a half way when I got the car, and I have no idea how long its been sitting.

 

I would first contact the person you bought it from and ask them how old the gas has been sitting in the tank and ask them what exactly is done to the motor. Then ask them about the knock sensor. Also, SES lights on our cars do not turn on until approx. 55 mph so that is why that occurs on the freeway. Get a scanner and check out what codes it is throwing out, then troubleshoot your way to the problem. As of now i would put some heet in the tank and fill it up with premium (at least 91)

 

I have talked to the guy that sold me the car, but he claims that he doesnt know anything about the car. He says that he bought the car to help out somebody he knew. He screwed me over, but its hard to do anything about it since he is living about 1000 miles from here.

The SES light turns on when I have a change in speed of over 10 mph regardless if I am doing 35 to 45 or if its 65 to 55.

The fuel might be part of the problem. I will fill her up with premium next time and see if there is any changes. I dont like driving the car right now, because I dont know if she is going to blow up on me.

 

Is the noise you hear detonation or a metal-to-metal knock like a rod? If the knock sensor wire is cut it is probably detonation. Splice the wire back together. That needs to be fixed no matter what the cause of the SES light is. Check the timing and set it properly after you put good gas in it. I wouldn't take a chance with old gas. If it were me I'd drain any questionable fuel out of the system and start from scratch. Then use the paper clip trick to pull the codes and see what's tripping the SES light.

 

I think I have found the main problem to the knock. The gasoline. I filled her up with 87.. After using that tank I filled her up with Premium, and she is running better now. The SES light is on because the speedo isnt working. The engine runs no codes.

The engine is still more noisy than I am used to with the 2000 S4 I used to have, but Ive been told that its supposed to sound something like that because its been cammed.