sorry if this is in the wrong forum mods, dont want to make your job harder but ive looked everywhere trying to find some answers.....

i understand that the LT-4 engine does not have an egr because of the design of the cam. i also know that the LT-4 "hotcam" is not really the same cam that came in the factory LT-4 motor. but could this cause an LT-1 motor with the hotcam kit to have trouble with the EGR?

im trying to get answers from you performance knowledge guys and also from GM factory mechanics (my father-in-law & Brother-in-law). they have no answers and i cant seem to find anyone who has had my problem.

the problem is that the EGR valve and the solenoid all are working when checkout by my brother in law. but its coding for the EGR!

Being a negative pressure EGR i was thinking that the supercharger has changed the manifold pressure thus causing the EGR to not work properly. or the map sensor isnt reading correctly because of the forced induction making the pcm think that it isnt working.

please help. ive tried the LT-1 forum, the forced induction forum, searched the web and cant find any kind of help.

i know this is a trivial problem to most people and im sure guys are getting sick of seeing me post this question but i live in california and i need to smog the car and its very frustrating to have a problem that no one has ever encountered!?

thank you for taking the time to read this,
jeremy

 

Can we assume you are getting P0400?

The diagnostic for that code is run once per trip (unless the PCM has just been reset, in which case it is run 4 times per trip). The PCM closes the EGR valve for 1.5 seconds, and records the peak change in MAP. It then compares the recorded peak change in MAP to a table of filtered value of expected vs. actual. Anything that upsets the MAP reading has the potential to cause the system to fail the test. Even the stock OBD-II LT1's have a problem with EGR when the exhaust back-pressure is reduced. Increasing the MAP has the same effect on the EGR flow ar reducing the exhaust back-pressure.

What kind of boost level/MAP readings are you seeing at moderate load/low rpm/increasing throttle (e.g "lugging") cruise condtions under which the EGR would most likely be operating?

Have you checked the EGR valve, and the port on the manifold for carbon buildup, that would reduce EGR flow? What does your exhaust look like? Cats? What else beside a "Flowmaster"?

 

thank you so much for helping me out, i really appreciate it.

i dont remeber the code but it was the EGR performace code if that helps any.

sorry i cant tell you about the boost levels. i dont have a boost gauge yet (i feel stupid having to admit that). i have the stock pulleys and it is the 6psi kit.

i dont know about the map reading because i dont have scanning capabilities, id have to go for a ride with my brother-in-law and have him scan it if he can. im surprised at the limitations of the factory mechanic's equipment.

my exhaust is stock manifolds, stock cats, 3" in/out flowmaster race muffler. its 6.5" long and i dont think it has nearly the back pressure of my SLP 2-on-the-left. but it never caused problems before the SC. actually the problem didnt occur immediately after i put the SC on either so thats kinda weird. it actually started soon after i got my pcm back from madz28 but ive talked to him and he assured me that he didnt change anything that would be causing the problem.

we did check the egr and it was holding vacuum, and the solenoid was receiving the signal from the pcm to operate. should i check the port that the metal flex tube goes into? how should i check it and how would i clean it if its dirty?

im wonering if i could find out if back pressure is the problem by removing the SC belt and driving NA after resetting the code. i know it wont drive well with the restriction of the SC and the aftercooler but it would restore the backpressure right?????

if back pressure is the problem could i solve the issue by switching to a positive-pressure EGR valve? or is it not that simple????

thanks again injuneer, very much appreciated!!!
jeremy

 

also, would a 2 bar map sensor be any help in any of this? ive been told yes and no.

i know they are for SC applications and come standard on factory FI GM cars.

thanks!