To start off, I have a 94 Z28 with a CC306, ported heads, 1.6 RRs and longtube headers with a dumped X-pipe. The car is loud, to say the least. I have been logging my car recently, and it turns out that I have a ton of knock retard, and it is pretty constant. I changed the knock sensor, since the old one had a slightly damaged post. However, that changed absolutely nothing. I am getting 4.85V at the connector with the key on and the engine off. Awhile back, I noticed some insulation missing on the wire to the knock sensor and covered it up with some liquid tape. The wire did not look torn any, so I do not know if that could be causing my troubles. I have the LT4 knock module, but it looks like that is not helping enough.

I took a Freescan log and then a Datamaster log immediately after. They can be found here and here. You can see that it is pulling up to 6 degrees retard randomly. Also, the spark retard increases without knock being registered. I do not know the system 100%, but that seems strange to me. The computer is normally pulling 6 degrees at WOT, too.

My car runs well and pulls hard, so I do not think there is anything mechanically wrong with it. When you look at the Datamaster run, you can see that it's throwing three codes right now: 33, 26 and 77. My MAP sensor seems to be working fine, so I do not know what is wrong with that. Maybe it is being caused by the cam? Regarding 26, I replaced the CCP solenoid, and that did not get rid of the code. I replaced the fan 1 motor, but the fans are not coming on when they are supposed to. I have to use my manual fan switch to engage my fans. I am not asking help right now about those codes, unless someone knows something that it could be. I should be able to track the problem down with the service manual when I have some time. I just thought I would mention anything wrong with my car, just in case it may be related.

Any ideas?

 

Its possible to get knock retard when the knock count is not increasing. And its possible for the knock count to increase without causing knock retard. When the knock count does suddenly increment, there are cases where the 6deg retard shows up. Look around record #836. The knock count starts to increase rapidly, and you have the 6deg constant retard. Look at the MAP in that case..... the throttle is at 0%, but the MAP is pushing upward. Something is screwing with the MAP readings. With the throttle closed, and road speed decreasing, MAP is increasing. Then you open the throttle 8% and then to 16% and the MAP is dropping. When you open the throttle, MAP should increase. There are other cases of this erratic behaviour. Was there any evidence of a misfire or a stumble? ..... valve sticking open?

At idle you seem to get erratic MAP readings. Start at record 1742.... 0% throttle, "0" road speed..... its idling. MAP varies from a high of 80kPa to a low of 60kPa.... that's way too much variation, although the overlap on the cam can contribute to it. Anything over 68kPa at idle/closed throttle sets the MAP code for low vacuum, so it all fits.

All the above was from looking at the Freescan file, since its in .csv format. If you export your DM files as .csv, those of us who don't have DM can look at them in Excel. Otherwise, you need DM to open the .uni file.

 

Hmm, that's interesting. The engine does not appear to be acting any differently than it used to. The heads were redone less than a year ago, and I have not put 3000 miles on it since then, so I don't think it could be a sticking valve. I have an Autometer vacuum gauge in my car, and it varies a bit, but I don't think it varies that much. That would be a 6.5 inHg range. I'll have to watch it more closely today.

 

I think part of the reason for your irregular idle in the first part of the log is your A/C kicked on.

Now for the knock retard its my opinion the computers actions are legit. Reason being if you find record #748 youll notice the knock count starts increasing fairly rapidly and at the same time the O2 readings are in the low 800's... kinda lean.

Then there is a region in the computer called "spark retard recovery rate". Basically this slowly heals the motor if you can think of it that way. It prevents full timing for a certain amount of time after initially retarding the spark. You can have that table modified so it doesnt allow the slow recovery.

 

Yeah, I was playing around with turning the A/C on and off multiple times to see if that affected anything. When I first turn the A/C on, my idle drops a bit, and so does my vacuum. I do not think that you can tell the A/C status from the Freescan logs, so that is why I also took a Datamaster log immediately after.

I see your point about the O2s reading a little lean at that WOT run. However, why am I getting knock retard all over the place? I'm going to scan it some more tonight.

 

Right the reason you are getting KR all over is because of the recovery rate. The computer will continue to pull timing based on RPM for a certain amount of time after originally detecting detonation.

 

I took some logs driving around tonight, and my car tried to die on me twice. The Datamaster log is here, and the Freescan log is here. I took the Datamaster log first, and coming to a stop sign, my car started idling exceedingly low. I killed it and started it back up immediately. Here is a CSV version of that log. On the way back after I ate, I ran Freescan, and it tried to do the same thing at a stop light. The car did this to me last night for the first time right after I filled up at a Racetrac. It had gotten pretty low, so I maybe I picked some stuff up in my gas tank or got some bad gas? I may just post in the LT1 engine section, since this has strayed from my original topic of knock retard, which is, of course, still very present.