I need advice. I've got a 95Z28 with a 96LT1 motor in it. Doing some datalogging and the car is retarding the timing as much as 12* sometimes. I disconnected the knock sensor and it still does it. Put on shortie hooker headers recently. One spark plug boot has a tiny hole in it in number 7 cylinder. Also, at closed loop the O2 readings are in the 900's. Is this normal or is it running too rich. Thanks...

 

I am using Datamaster for logging. Found out from watching the replay that it appears that when the MAF readings increase over 20 that the spark retard kicks in. Does this make sense? I am new to this so I am having trouble understanding what I am seeing in the program. There is also a box at the top of the screen that says DTC ERR and its red. My understanding is that there is a code but the check engine light is not on. I really need to get a handle on this because I cant take the car back to the track since last time it was supposed to run mid 13's and all we could get was 15's cuz of the spark retarding.

 

Pulling the wire off the knock sensor will put you into a set of retard values computed by the PCM, and reaching as high as 15deg. Since you get the same results with and without the wire connected, maybe the "code" is for the knock sensor.

 

If your are using the PCM from your 95Z28, did you put the KNOCK SENSOR from your 95 motor in the block or leave the Knock Sensor that was on hte 96 engine on the block ?

OBD1 and OBD2 knock sensors work on DIFFERENT ohms and will cause problems like you are explaining if you are using an obd1 KS with an OBD2 PCM and vice versa.


NOTE: you can have the PCM programmed to accept the different knock sensors.

 

Ok guys...thanks for the replys. I am narrowing things down. Apparently the knock sensor is throwing a code in the datamaster. It was doing it before we disconnected it. Just didnt know it at the time. As far as the correct KS goes, I will have to ask the guy we bought it from. He took out the original 95 LT1 and put in a 383 stroker. Removed that and put in the 96 LT1. However, how can the comp work off a set of values that are preprogrammed if the sensor is disconnected? I dont understand that. I will find out about the correct KS and also buy the LT4 knock module. I am using an OBDI PCM in the car but I have to use an OBDII cable for the ALDL box. Does that make sense? Is there anything else that would retard timing besides a knock sensor? MAF? Charcoal canister purge? EGR? My O2 sensors are reading high in closed loop in the 900's. In open loop they are in the 500-700 range.

 

How do I do that? It would be easier than changing out the wrong one for the right one.

 

Ion @ MADZ28 can do it.

as far as O2 sensor voltage.....I use a wideband and Open Loop tuning so I can offer any real experience in this area.

 

If the PCM can't get a signal from the knock sensor, it starts to retard timing to protect the engine. It appears to calculate the amount of retard based on things like load and rpm. A very conservative strategy, to avoid engine damage when the KS fails.

I don't run a KS (PCM shows DTC 43), and I can watch the knock retard vary in proportion to various inputs on my ScanMaster. (I also don't run the ignition off the stock PCM, so retard doesn't concern me ). Knock sensors don't like solid roller camshafts.

 

Fred when I data log my car I never see any spark retard being pulled. But I see occasional knock sensor activity. I have a solid roller cam and have sometimes wondered if the knock activity is hurting my power. But I see ZERO timing being pulled from the datalogs. I have most of the timing retard tables disabled in my PCM, do you think the car could pull timing without showing it on the scan tool as actual ignition retard?

Im toying with the idea of disabling my knock sensor for the solid cam.

 

Thanks again for the responses. I found out that everything on the motor is 96LT1 except the PCM and the wiring harness. Figured out that I have the 96 knock sensor instead of a 95 and I was using a 95PCM. I now know why the first time we went to the track we ran a 14.0. Its because I bought the car with an OBDII PCM in it and the guy gave me an OBDI on the side. The OBDII had the wrong gear ratio for my car (4.10's). So after I took it to the track we replaced the PCM so I could have the right speedo etc. Then when we went back to the track after installing the headers it ran a 15.7 to 15.3. Very upsetting. Couldnt figure out why except we thought the spark was retarding somehow. Now I know why. So my next question is this: With me having a 95LT1 harness and 96LT1 sensors, is there anything else that should be changed besides the KS? I know the LT4 knock module will work with the OBDI PCM but will it work in the OBDII if I decide to use that one again?

 

Ok thanks....
I checked the rich/lean tables in the datamaster on our last datalogging run and they showed the car was running in the middle. Not too lean and not too rich. But the O2 sensors show them running in the 900's when in closed loop. Someday I'll get this all figured out.

 

you can use an LT4 KM with an OBD1 or an OBD2 PCM.