CBR Crazy

Ok here it is. I have a 96 Z that was just rebuilt(everything in the sig) now it is having this stumbling issue and it bucks with a lite load on th ecar and is really bad when like trying to park. I have noticed in the last few months that the plug wires were arcing through and I have replaced them three times. They are not touching the headers it is like it is easier for them to pop off to the valve covers than the plugs, but the plugs look like the car is a little on the lean side. So I took it to a friends house and put it on his scanner and it was saying that the spark advance was -35 at idle and -45 at 1/2 throtle. At idle it would not show any KR but while driving it would show 1-3 at cusing speeds and 3-8 at 1/2 throttle.but when I start to decel it would all go away and the spark adv would go to like -8. I don,t know much about this part of the car still trying to learn but this is not right. I asked the dyno guy about it the secound time I went and he said there was no Knock and everything seamed ok. I am worried that I am hurting my engine if I am getting that much knock. I looked at the o2 and they seemed to be about the same they were both bouncing up and down between the same values,and the fuel trims were very close to the same. Any hepl would be great I don't really know much about this stuff and could really use some help with getting this car up to par.

BUBBA

Don't listen to me, cause I don't know squat, but what I do know is that since I don't know squat, I would never own a scanner. Having said this about that----did you actually get a dyno tune, i.e. did someone who tunes lt1s actually tune the pcm while it was on a dyno?

Just curious.

CBR Crazy

Yeah I do have a dyno tune but the guy was not very helpful in getting the car right. It makes about the power it should with the cam and mods I have but I can't seem to get these plug wires to stop arcing and I can't get the car to drive good. And now with looking at it on the scanner last night I obviously have some problems else were to.
Were is a good place to get Datamaster program? It would probably help if I could data log the car to get help on the web. Thanks for any info.

bringBackCamaro

A scanner is the best place to start especially if you have no idea what your doing. Its much easier to see what certain sensors like (IAC, MAF, TPS, etc) are reading and determine where the problem is than to just throw parts at the car until it gets better.

I highly recommend Autotap with the extra GM parameters. It is enormously more useful than a datamaster, plus it works on all OBDII vehicles.

Your IAC should be around 30, MAF depends on cam, but 18 is ok, tps, .6-.7 at idle, 4.0+ volts at WOT

Injuneer

Your timing number look fine at cruise, but 35deg advance at idle is excessive. What numbers are you seeing for various RPM at WOT? But you do not want any knock retard. You need to find out if its "real" knock that's causing the knock retard, or "false" knock caused by extraneous engine and other mechanical noise. Running high octane fuel to see if the knock retard goes away is one way to check.

You won't hurt your engine. When the knock sensor "hears" knock begin, the PCM retards the timing to prevent the knock. As long as your knock retard isn't max'd out, you'll be OK. Just recognize that you are losing HP as long as there is knock.

I have an online guide to scanner data:

http://members.aol.com/InjuneerZZ/ScanMast.htm

If you have a data log that you can post to a server, or e-mail to me, I'll take a look at it for you.

CBR Crazy

Thanks Injuneer, man I wish that I had a way to log some but the scanner that I was using is on a lap top that does not even allow me to monitor all the sensors at the same time, my friend needs more horses in his lap top. Thanks again for the web site it has cleared up a lot of question but I am still confused a bit. When I was giving the car 1/2 throttle and started to go up in RPM's the KR would start to go up and the spark advance was also going up, I would think that the spark advance would go down with the KR going up? Do you have any idea what would cause the plug wires to arc other than the normal reason(burnt wire,ect). Thank you very much for all the info.

Injuneer

As RPM increases, the programmed advance increase. Look at the stock timing table in my writeup. The value for spark advance you read with a scanner is the number picked off the timing chart (with some hidden offsets totalling ~ +3*) MINUS the indicated knock retard.