I know this isn't a 3rd gen, but I am hoping someone can point me in the right direction...

Quick history: Car is a 1985 Corvette, and has 4+3 transmission...
I just swapped on a set of new, better (than stock) flowing heads, 1.6 rockers, Hedman Elite longtubes, with new 2-1/2" front Y pipe, Ported Edelbrock base, Ported and Siamesed plenum/SLP runners, and an adjustable fuel pressuire regulator. I also deleted AIR pump and it's supporting hardware.

I had a few vacuum leaks, big ones, that have been corrected.
I also checked and reset TPS to .54v. It was at .65v when checked.

After a short drive, I get a CEL lighting up and when I pulled the codes, I have a 13 and a 42.

From what I could find in this little code book,
Code 13 says:
O2 sensor signal stays LOW ("lean") during warm cruise OR sensor cicuit is open.

I'm wondering if this code is from when I first got it running and had all the vacuum leaks? I did not "clear" them from the other day, or as of yet. FWIW, instead of running a non-stock heated O2, I ran the stock O2 and because of the longtubes, I welded an O2 bung 10" from the cylinder head, on cylinder #7...

Code 42 says:
Electronic Spark Timing ("EST") circuit - open or shorted to ground during engine run
OR
Direct Ignition System ("DIS") fault - bypass circuit open or shorted to ground during engine run.
OR
Fuel cutoff relaycircuit - open or shorted to ground.

I'm not sure where to head on the Code 42 issue...

FWIW, car seems to have a dead or weak cylinder at low rpm/higher load times...like when first taking off, or if I try to cruise at low rpm in OD...it'll buck like crazy and acts as if it has a dead cylinder...
Car "feels" pretty strong at WOT. Idle is a little rough, and acts like a bad spark plug or cap/rotor problem, so I plan to change them as well...unless the problem is related to the codes.

Any help or ideas are appreciated...:cheers:

 

If you have a timing light..
make certain you can see the timing advancing with rpm. If it stays at 10 degrees, check the EST wire.

 

You definitely can. In fact when EST wire is connected, the timing mark is almost out of sight, totally off of the timing scale tab. You can also hear the engine rpm's slow slightly when EST is unplugged to check and/or set base timing.

That code wouldn't come up because I have had the EST wire unhooked a few times playing with base timing, would it?

 

clear the codes, where is the o2 sensor now that you have long tubes?

the 42 - is most likely the EST not the others you mentioned.

I had similar codes - but it was coolant temp low and the est
changed the coolant sensor then it jumped codes - it ended up being the ecm

 

That code WILL come up, and stay up , until you reset it by unplugging the battery. Maybe that is all that it is.

 

I welded an O2 bung about 10 inches from the head, in cylinder #7's header tube.

Could this code 13 have been set when I drove it from my garage to my house (about 30 miles) with a bad vacuum leak? I had both runner to plenum gaskets leaking, as well as a leaking PCV hose...bad enough leak that I had to turn idle hard screw up almost a full turn.

After I fixed vacuum leaks, I never reset codes & the CEL never came back on, until today.

but...

I have to double check tomorrow, but the Code 42 may be operator error. I think I forgot to plug the EST wire back together after checking/re-setting timing today...

 

Now I'm confused...EST wire was not unplugged like I thought...

 

the est code needs to be cleared after you set the timing. Disconnect the battery for a few seconds and see if it comes back.

 

Cleared codes today.

I replaced O2 sensor to see if that cured the Code 13...it did not.

I also replaced spark plugs, distributor cap and rotor, and plug wires (did wires a few days ago), to see if "MISS" went away. It didn't.

I'm at a loss now...

I guess I can put a heated O2 sensor in to cure the Code 13, but the miss at low rpm/high load has me baffled.

BTW, Code 42 is gone.

 

UPDATE!!!

I had a brainstorm at work today, so I came home and acted on it.

I know my car hasn't been running on all 8 cylinders since all the mods were done, and I said to myself, "Self, I'll bet the dead cylinder is the one that the O2 sensor is reading off of. That's why it isn't getting hot enough to send a signal to ecm."

I brought home a hand-held infrared digital laser thermometer/pyrometer and after running the engine for just a few minutes, all header primary tubes were in the 300 degree range, except cylinder #7, the one my O2 sensor bung is located in. It was less than 100 degrees...

To make a long story short, the SLP runners force the injector connector on cylinder 7 to be right against them and the injector wasn't getting a good connection. I simply "tweaked" the terminals on the injector itself, so that connection was much more positive, and VOILA!...all 8 cylinders are firing, car runs 100% better, and NO CODES!!!

Thanks for the replies and tips. I appreciate the help!