Hi, I'm new here so please bear with me. I recently bought this 94 z28 used so I can only tell you what I can visually see. It is an LT1, headers to 3" single to flowmaster then double out, alum heads not sure by who, had MSD 6A (removed), K&N air intake system, 4L60E, not sure of cam but idle is pretty rumbly (a good rumbly, well... until lately) I am about to replace NGK iridiums with Autolite plugs when I go through each cylinder to check wire etc. Anyway, when the engine reaches normal operating temp ~180-185 that ping starts up and is bad! long and connected pings not short and sparse. I will be looking at the injectors at the same time to make sure they are atomizing and not dribbling or clogged. The ping is most apparent with engine under load (obviously). Then lately during accelleration it displays this "stumbling" behavior (still pinging) like a loss of power. And the Check engine light comes on. The CE light used to not come on hardly at all. Now it comes on consistantly at least once a day. I suspect this could be PCM/ECM related but that's why I am here now, to ask anyone who knows about this. But like I said when cold, it runs *better* but were talking cold here. It should be "***** to the wall" when warmed up. I recently replaced the optispark cap only (the expensive part ...the old one was cracked ) the ping never went away but there was a big improvement in performance. I also recently replaced the water pump and radiator during the summer months when the water pump failed. I use exclusively 91 octane and this motor is not a "cheap date" cheap gas gets horrible performance so I stick to 91 or better if available. Whew! There are other issues but these is my main unresolved gripes. Sorry if this was long and verbose, but describing these situations takes a little effort and detail. Any suggestions would be greatly welcomed. I love this car and want to see and feel it running right. Thanks, JC

 

How is your fuel pressure? Test pressure with key on but not cranked and also cranked at idle. Also Pull the vacuum hose off the fuel pressure regulator on passengers side rear of intake and see if there is any fuel dribbling out of the pressure regulator vacuum port. Reconnect vacuum hose of course after checking it. The stumbling may be a fuel delivery issue. I recently had similar problem and it was a fuel pressure problem on my LT1.

 

Get the SES code read, that will provide a starting place to correct your issue(s). I'd also invest in a set of new wires when you replace the plugs. Inspect the color of the plugs when you pull the old ones to see if it's been running rich or lean. New O2 sensors would be a good idea. See if you can find out what cam was installed and what size injectors you have; you may need to have the computer programmed to get the car running optimum.

 

Get it scanned and go from there