KILMERKARZ

Car has horrible spark retard. When I hit the gas it falls on its face. It does ok at part throttle, but still sputters here and there. This all started happening the day my air filter fell off so im not sure if that had anything to do with it. So far this is what if tested.

Unplugged MAF and reset computer "removed PCM fuse for a few mins".....Still runs like crap. I also checked the voltage on the MAF. Everythings normal there. I even switched MAFs with a friend and THAT didnt help either. Reseting the computer before that also.

Unplugged O2 sensors and reset computer again...Seems to run even worse and stalls out when I come to a stop.

Tried my old coil....Still runs like crap
Bypassed the Accel ignition....Still runs like crap

I checked for spark arching at night, I didnt see any
I checked for glowing headers at night, I still didnt see anything

The car is a 95 z28 with...
LT4 Hot Cam
Forged pistons and rods
LT4 intake
Bored 30 over
58mm throttle body
New magnecore wires and NGK iridium plugs .35 gap
Also cover plug wires with taylor heat shields
Eddlebrock Headers
Accel 300+ ignition and coil
and I allways run 93 octane

Also I can hear a ticking coming from the passenger side of the car. Sounds like its under the valve cover, but it could also be an exhaust leak, I dunno but this has allways been there and the car ran normal before with it ticking.

Anyway I need some experts with datamaster to read my .uni file and see if they can notice whats going on, Ive been staring at it for hours and cant pinpoint anything
Heres the link to the file...

http://www.uploading.com/files/LSB86...e_run.uni.html

Please help. this is my daily driver and I dont have much time after work to see whats going on because it gets dark here in FL as soon as I make it back. "I HATE daylight savings"

Shon Herron

several possible things.
Eliminate the exhaust leak theory by tightening it all up.
But normally with 12* of KR it is a bad Knock Sensor.
If you have a way to turn out the KR then do that and see if that helps. I had one go bad and it would barely idle, I happened to have my LT1edit stuff with me so I turned it off to get home. replaced sensor and all was well again.

Injuneer

You are running an LT4 intake...... with LT1 heads??? Was the intake or the heads machined to eliminate the interference between the tops of the manifold runners and the head valve cover rails? Any chance of a vacuum leak at the gasket? See next item.

In cell 16, the passenger side BLM is maxed out at 160 and the INT is elevated most of the time. Drivers side doesn't seem as bad. Low load/rpm cells are similarly elevated. But higher load/RPM cells are often less than 128. Cell 7 starts at 108/108, and stays there until you stall it in the middle of the log, then suddenly starts elevating, reaching 127/127 by the end of the log. Really strange.

In this log, most of the knock retard seems to start when you are decelerating with the throttle closed. In several cases the passenger side O2 volts drop to 0xx levels just before the knock begins. It's normal to have fuel cut on decel, but the left and right banks don't seem to be tracking each other.

MAP seems to be highly variable, with about 54kPa at idle, and then there are other places where you are accelerating lightly and is drops down in the 30-40kPa range. As the throttle opens, MAP should generally increase.

KILMERKARZ

Thanks for researching my data file. Unfortunatly I didnt build up this engine, thats how it was when I bought it a year ago, so I have no clue if the heads were changed or what might have been machined or not. Just wanted to add that this morning I stopped and bought 104 unleaded octane and that didnt help the knock/spark retard either. Its still just as bad as before. So based on your diagnosis what parts should I check or replace? I'll look for an intake gasket leak when I get home from work.

Should I also post my datalogs with the MAF disconnected and then with the o2s unplugged?

Injuneer

I'll have to look at it some more. The low MAP is interesting, because the PCM puts in more timing advance with low MAP. The fact that it happens coming off decel is interesting - is there any possibility that its simple noise as the engine rocks from side to side, or hits something as it changes from decel/coast to accel? The knock sensor is right next to the motor mount, and any mechanical noise can be picked up.

I don't think its a faulty knock sensor, in the sense of an electrical problem - that would show up as a DTC code, and you don't have any. I've seen at least one case where someone had a lot of knock retard for no reason, and found the end of the knock sensor was filled with a chunk of silicon that had fallen in the water jacket. Always possible its a mechanical problem with the sensor. Hate to suggest "replace it and see what happens"..... but that might be something to try.

KILMERKARZ

UPDATE: On my way home from work today I could feel the car falling on its face as always, but when I looked over at the laptop it wasnt showing any spark retard at that exact moment it was happening like I had noticed before. Still getting 12 degrees of knock here and there though. I'll try to replace the sensor this weekend. I cant do it this week because I cant miss work and its too dark here when I get home to change something like that, I'd never be able to see what I was doing.

KILMERKARZ

Still need help guys! Today I fixed the knock I was getting. The last plug on the passenger side was loose. I tightend it back down and took her for a test run. All the spark retard was gone and no more knocking. I'm glad thats out of the way, but the car is still running the same..heres what else I did.

I went around and made sure that ALL the plugs were tight

I tightend the header bolts to eliminate the small leak I had

Here are some other things I noticed when driving......

Regardless of when the car is in open or closed loop it seems to run fine for a few mins before the stumbling occurs. Also when I SLOWLY give it throttle there is no stumbling, only when I press it too fast. Not sure if that helps to pinpoint anything or not.

KILMERKARZ

ttt Help?

Sweetred95ta

Did you replace the plug that was loose? I'm sure that it isn't 'clean' and in proper working condition anymore. You should pull the plugs and see what they look like. If it's stumbling, it could be ignition related, which will show up in blackened plugs (misfires). Is the car an auto or 6 speed? If your MAP is varying as Injuneer said (I can't see the DM file at work), then it is referencing parts of the timing tables it shouldn't be. That will cause the car to act very strange and also explains your 'Also when I SLOWLY give it throttle there is no stumbling, only when I press it too fast.' problem. If you want, you can email me the tune and log and I'll check them out. Start with the plugs though. Sweetred95ta@hotmail.com