Ok, this is for the Red Auto Z28 below.

Long story short:
- The car was running like crap, stumbling at idle and under a load.
- less than 10k miles ago replaced wires, spark plugs, fuel filter.
- Scanned the computer, saw a huge split BLM.

I took a look under the hood and moved some spark plugs wires around, one was uncomfortably close to the pass. side exhaust manifold, but the wire was ok. I then bumped the AIR fitting and it cracked in half, so I removed the system. I then cleaned out the intake with carb cleaner, and I put a can of B12 Chemtool in the half empty fuel tank. I cleaned the K&N filter, and cleaned out all the crap in the breather tube (it was pretty oily) and I put the breater filter on there (Note: It is still a closed system, it doesn't "vent" to the atmosphere) Anyway, after doing all of that the car ran tremendously better, feels like I gained 50hp (Seriously) and it sounds much better and is quieter at idle.

My Fiancee drives the car every day and she told me the SES light cam on, so I scanned the car and sure enough the EGR DTC came on. I also noticed the EGR duty cycle stayed at 0% for the entire 20-min scan. AFAIK, I didn't touch the EGR, only the AIR components. I did plug up the 5/8" intake as well.

I do notice still a very slight rough idle, but only at idle. The scan confirms as fuel cell 16 has a somewhat high correction from 128 for the BLM's.

The other thing though is that the computer is detecting knock at WOT and the computer pulls up to 9* of timing....could all of this be from the EGR?

I don't want to block the EGR off, there's really no point to in my book, but did the whole valve fail, or only a solenoid that can be replaced seperately?

BTW the car has 165k miles on it, so I am not expecting it to be perfect, but I'd like to see the knock and DTC code vanish. As shown below the car does have HPP III programming done to it, but it is my understanding that they actually retard the timing a little at WOT, so I cannot see why that would affect the timing or knock at all?

 

maybe I missed it in your post but did you check the egr valve??? was it stuck open that could cause idle prob. if it is

 

I forgot to mention that I did have to put in a new fuel pump about 5k miles ago. I seem to remember checking it and saw 36-44 psi at the schrader valve.

I did a few searches and see that the EGR system is two parts, a solenoid and the valve itself. Is there a way to check the pieces seperately?

Assuming my EGR is bad, could that explain the 9* of retard at WOT, or is that likely something else?

 

your right, sorry I replied late last night I think, at wot the egr woundn't have anything to do w/ it but it could cause iratic idle what kind of fuel pump did u get I recently got the racetronix it's a sweet setup. I don't know the spec's on the egr the way I check it is to push the diaphram in and see if the rpm's surge or not. After you put in the new pump did you check your fuel pressure?? spark related would be my first guess though. Has your opticrap ever been replaced? does it only happen when it's warm, does it hesitated, loss of hp? probably w/ the timeing that off huh?

 

You can push on the diaphram of EGR valve to see if it moves back and forth freely.

Other option... delete EGR from computer and see how it runs then. You dont need to block it off. Just unplug the lines, and delete from computer.

 

Your timing retard at WOT could be the cause of a bad knock sensor! I read an article on this in Chevy High Performance recently!

 

Does that borla y-pipe have cats? EGR DTC could be related to a lack of backpressure in the exhaust.

 

Yeah, the borla y-pipe does have a factory cat. I am somewhat suspect if it is slightly clogged though because it was running a little rich for so long. Right now, yesterday as a matter of fact, I noticed a leak right after the cat, so I am probably going to have a new carsound welded on.

I will have to look at earlier logs I have done, however (unless knock sensors go bad) I don't ever remember seeing any knock before.

I'll check the movement of the EGR diaphram out later today -- that's a good idea.

I got a carter OEM replacement unit -- this car's not my "race car" so to speak, my Fiancee drives it, so for the most part, it's all stock and then, as parts crap out, they get upgraded. As much as I wanted something with better flow, availability was a big concern (Needed the car fixed asap)

I do remember checking the fuel pressure a few times, however also a good point to recheck since I cannot remember if I checked it after I replaced the pump. I'll have to do a search to figure out how to tweak the fuel pressure so I can get a WOT reading (Without going WOT) I seem to remember pulling a vacuum line or something...

The opticrap was replaced almost 110k ago if I remember correctly. Certainly a possibility, but I don't get knock all over the place as far as load goes. As a matter of fact the only knock I get is under high loads (Either WOT or low rpm/high load (Think going up a very steep mountain in 4th gear at 60mph)

I forgot to mention I also replaced the coil as well, so it's probably not that. I haven't scanned the car too ofern to give an accurate description of if it happens cold or hot, however I don't really start screwing around (Going WOT) until my fiancee' lets me know the car's in closed loop.

Spark plugs could also be a possibility, I thought about pulling one or two when I was working on the AIR system, however I decited against it because they are such a PITA to get at. They only have 10k miles on them though so I would hope they are still decent.


I think I'm going to have someone weld up the exhaust first, then I will clear the computer and see if the EGR DTC comes back. I'll also make a few more WOT runs and see if my knock is present. Hopefully, the knock sensor was unhappy with the sound from the exhaust leak.

Thanks for the help guys