Ok, I have a 93 LT1 that has been rebuilt as a LT4 383. Heads and intake are from a 96 corvette LT4 ported and polished as well as intake ports matched. Has the Eagle specialties B13054L030 balanced rotating assembly, bbk 58mm throttle body and shorty headers. Converted the stock single wire O2's to the 94 four wire heated O2's and added a wideband after the "y" pipe. The cam is a crane cams 230/238 duration @.050, .575/.595 lift with 1.6 fully roller rockers and 112 degrees seperation and +5 advance built in. Running a MSD 6AL with MSD blaster coil and MSD billit opti. Have MSD 8.5 Super Conductor wires and was using the ACDelco 14 platinum plugs. I have switched the injectors to 36lb EV1 injectors and the fuel pressure at the rail is between 40psi and 43psi.

I have been playing around with the tuning and gotten the VE tables close using VEMaster. I know it is running rich from the raw fuel smell and the 9 mpg I am getting. The integrators are staying between 128 and 130 and the AFR according to the stock O2's is between 12.4 and 13 and the wideband O2 see's the AFR as 11.8 to 11.9.

Hopefully that is all the pertinent information. Now on to the plugs. I am getting nice clean plugs at the front then they quickly turn dark and dirty towards the back on both sides of the engine.
Drivers side:

Passenger side:


As my car is a 93 and does not have the table in the programming to adjust individual cylinders I am kinda at a loss. Any help is appreciated and there are more photos of the plugs both individually and the groups of 4 showinf clean to dirty at:
http://s2.photobucket.com/albums/y9/...0Camaro%20Z28/
and if there is any information I missed or you might need let me know I will do my best to get it quickly.

 

And you pulled these plugs after what? Did you try an all out pass and then pull them and look?

Is your PCM staying in closed loop at idle? I'm asking because my O2 sensors quit after idling a while. Come right back if I rev the engine a tad. I'm wondering if the header wrap helps.

Al

 

Well I changed the plugs because it has about 2k miles on it since the rebuild and when I pulled the O2's just recently to convert to the four wire O2's the brand new single wire ones I had put in there about 1k miles ago (after the first 1k miles break in and dyno) were already black and sooty. I knew the car was running rich so I wasn't surprised to see the O2's so fouled out. Mainly I wanted to put some of the E3 plugs in and if I was going to pull the plugs even just to clean them, it was as good an excuse as any to put in the E3's. I was interested in what if any difference I saw with them over the ACDelco's.

Now as for the open / closed loop thing:

SEE! this is why I LOVE people asking me questions and making me go back over my data. I mainly used Tunerpro RT to do my real time emulating, tuning and datalogging but either it doesn't show open or closed loop operation or I just haven't found it yet. But I went back and looked at my data logs (log 7 and 8) from Datamaster which I used along with VEMaster to get my VE tables close, I noticed it is staying in closed loop full time. I went back and looked at earlier logs and it was switching between open and closed. In those logs it did look like it was in closed loop alot while at idle (hope that helps some).

I think it might have registered a high voltage reading at the map sensor at some point in the last two runs as it started doing that at idle after I had adjusted the tables a couple of times. I am thinking that may have caused it to stay in closed loop and I somehow missed it.

Anyone who knows whether or not that would cause it to stay in closed loop or have any other idea why it did that please feel free to tell me how stupid I am. This is my first attempt at tuning by the way so don't be too harsh.

Last as for the wrap on the headers, yes for me it has made a huge difference. I went from reading of 700-900 degrees on the bare headers down to 500-750 degrees. Depending of course on where on the headers I took readings. I also wrapped the "y" pipe all the way down to where the cat would have started if were still there. My alternator isn't getting as hot now either, obviously from lower under hood temps.

 

E3's aren't worth a damn. They just add more area to have a hot spot. I've had good luck with NGK's, champions, and autolite's. Had a bunch of delco's foul out if running too ruch.

 

Well that sucks to find out now. Wait they can't be bad plugs because they said on the TV that they are great and the TV doesn't lie.......right?


aww man

 

absolutely no vacum leaks correct? You sprayed carb cleaner or an equivalent around the intake to check?

 

Mine looked the same way and I had an intake leak but it was under the intake. It was pulling crank case gases in the lifter valley. Mine were fould at the rear cylinders and clean up from back to front on both banks. You may try pulling the pcvvalve out and seeing if it has any vacume to it.

 

also make sure your iac is working correctly. if it idles by use of the blade and not the iac the back 4 will not get the air due to the front ones taking all of it. then the back ones will be rich. to me that looks like what is happening , due to the different color of 5/7 and 6/8.

 

I didn't find any vacuum leaks around the intake (or anywhere) but the idle thing sounds likely. Since I started tuning the VE tables (the tune is incomplete, long story) it has a problem idling, when cold it wanted to die and when hot it idled too high. I have the idle tables adjusted in the tune, I could see the IAC steps moving, not sitting maxed out one way or the other, and adjusted the stop until my steps were at about 25-30 and it still idled too low when cold and too high when hot. I pulled the IAC valve because I know the car was running extremely rich before I adjusted the VE tables and it was rather dirty so I cleaned the valve, the seat and all the ports and put it back together. I tested the reference voltage going to the IAC valve and that was good and I checked the resistance across the pins on the valve and that too checked out fine. Still had the same problem but was much better, it wasn't trying to die but still not hitting target idle.

I have a BBK 58mm throttle body and I have seen topics saying you need to drill a port in the after market tb's to allow IAC to operate properly. I had been sent a link for an article explaining the why and how of it all in my e-mail but somehow lost it. I asked in the forum here if anyone knew what the link was for the article or knew of any good articles on it, but last time I checked that thread I hadn't gotten any responses. If anyone knows about a good step by step with photos on how to drill the port in an after market tb to help the IAC valve function properly, I would greatly appreciate the info. I knew the problem with the IAC and after market tb's would affect the idle but wasn't aware it would cause that specific pattern on the spark plugs, thank you for the help and information.

 

http://members.***.net/chipsbyal/page/idle/index.html

i never saw your post asking for that, sorry. just hope this resolves your issue. good luck

 

I ran the 58 BBK with a bigger cam and had no problems..

 

Thanks for the link I greatly appreciate the help.


Did you run yours mainly for street or track? Right now I am mainly using mine for short trips around town to different local shows or the parts store etc. and I get stuck in traffic alot so I think the idleing problem may be magnified in my case. I also do not have the tuning finished yet (main reason she has never been to the track yet) so that is a big issue for me as well.

I haven't pulled my tb back off to see if it even has the bleed hole yet as I heard about this after I had pulled out the IAC valve, cleaned everything and put it all back together. It may be that the BBK 58mm tb does just fine and it is my tune that is to blame for the idle issue. I was just trying to figure out why my plugs look so bad from the back of the engine and fine from the front.

What kind of mpg did you see with your set up? I am only getting around 10 mpg and again I am sure that is mostly due to the tune being incomplete. I have heard alot of people saying they get 15+ with a big cam 383 and some get alot more. The car was initially tuned by a shop but it ran terrible and only got 7 mpg. After some research, getting the equipment I needed and starting to learn to tune it myself it runs 100% better and is up to 10mpg but it has a long way to go.

Once my car warms up the idle is fine unless I sit for a LONG time and it gets a little hot then it tends to idle a bit high. I am thinking this is because the IAC valve cannot function 100% with the aftermarket tb and the plugs seem to be telling the same story. I think if I were just using mine for track and the occasional short trip I wouldn't bother with it.

 

Mine was a DD, road trips, in town ect. Built 383 getting in the 20's mpg on the highway with a 6 speed and 3.73's, I did no mods to the T/B..

 

Neither of my aftermarket TBs would idle properly on my 93 without drilling the hole and isolating it.

The Engineers who developed the cars knew that the factory manifold has air distribution issues, so it has internal passageways to deliver air at idle to each runner from the IAC. On some cars they don't care, but on others if you try to get it to idle using the blades on the TB, you may only be feeding the front runners and it will make it more difficult to idle.

After drilling and isolating the IAC passage my idle went back to normal, and my plugs readings became similar for all cylinders. The variance wasn't as bad as yours, and I did the mod because of my idle, but its still something I would do.

 

I had to drill my iac and adjust the blades also on my 58mm bbk. It wouldnt idle for **** until I got the volts back to. .67 or whatever it was supposed to be