rlf07

In the past tense, igniton timing in wot was dropping to zero and to the minuses… I changed my motor ears on that didn't fix. I dare and bypass the knock sensor. now wot'ds is not falling to zero, and the worst is 5-6 degrees. i solved some of this problem. The second problem is when driving, especially in the 1st gear, when I take my foot off the gas and slow down, igition timing falls down to -3 and it jumps to 18-20 degrees after a few bursts from the exhaust. The timing in my foot without stepping on the gas goes up and down between 8 and 24 degrees very quickly. I tried and unplugged the map. Timing stopped falling to negative values and blasting went away. but in slow driving without pressing the gas pedal, the timing still goes around 8-24 even though I never press the accelerator pedal. Could this up and down fast play optispark made in China especially loose rotor screws ?? Thank you.

Injuneer

Just for the background of anyone reading this thread and trying to help:

- "rlf07" is located in Turkey, I mention this only so that readers are aware of the limitations of access to technology and parts. And to make you aware of possible issues due to a language barrier. For example, "engine ears" are "motor mounts". I asked many months ago, after his first post that he add this to the "Location" field in his profile, so it shows up in posts, but he has not chosen to do this.

- This ignition timing problem appears to have been going on since he first posted it on 11/28/20. I have been trying to help with the issue without success. Appears he has now followed my suggestion and started a new thread, rather than tacking it on to old threads, with dissimilar problems..

- Earlier thread:

https://www.camaroz28.com/forums/lt1...g-zero-177457/

When I last responded, it appeared he had found a local person (member "SerdarD")who was able to retrieve PCM data and do tuning. In response to a question from that individual, I provided a copy of the stock timing table. That was the last contact, and there was no follow up. It would be interesting to know what actions were taken since that contact on 12/6/20. Appears that he may have changed the motor mounts in response to my suggestion that his erratic knock retard might be due to mechanical noise from something like a worn or loose motor mount.

My questions/comments are:

- How did you "bypass the knock sensor"? If done incorrectly, this should produce an SES light/code, and there will be continuous ignition timing retard based on other sensor inputs like MAP, RPM, TPS, etc.

- Did you reconnect the MAP sensor? That input is used for the timing table lookup, along with RPM. Forces the PCM to use other (unknown to me) methods to set igntion timing. That is not "curing" the problem. That is covering it up. MAP is used for controlling other engine functions, and should have set a code.

- When you take your foot off the throttle, the PCM cuts fuel and reduces ignition advance, until the engine RPM drops to a specific value (maybe ~1,300 RPM ??) . Then it turns the injectors back on. Is this when you experience "a few bursts from the exhaust"?

- Ignition timing that you see on a scanner is the timing the PCM is using to fire the spark plugs. It is a number picked off a table in the PCM program, based on RPM and MAP (and a few other factors that will only add confusion) There is no feedback from the Opti as to where the timing actually is. If the Opti is indexed incorrectly to the camshaft, the actual spark timing will be "off", the PCM has no way of knowing that. The lookup in the table will not be affected by the Opti, unless the Opti is giving erratic RPM signals. The PCM sets the timing primarily based on RPM and MAP (a measure of engine load).

rlf07

hi ) and thank you
location change ok.

-yes motor mounth changed
-104k resistor installed between knock sensor and cable (no code)
-yes,
When I unplugged the map, it became a code

-When I connect the map, when I take my foot off the pedal, the ignition starts to drop very quickly and eventually negative values ​​are written and a lot of exhaust burst. (and the car forces itself to slow down). but when I remove the map, the problems I wrote are decreasing by half violence. less problematic driving.

-In general, there are exhaust bursts when I take my foot off the pedal. but 1300rpms is the most severe time. but 1300rpms doesn't do that when the map is removed.

-What I see in the obd2 reader is that the inconsistent jumps up and down are very fast and continuous. and it is very noticeable in driving time with my foot off the pedal. (mostly downhill and in gear). Those firing jumps, loose optispark rotor screw? or loose timing gear?


thanks for your interest and patience

Injuneer

Are you saying the ignition timing no longer drops to "0"? And it now drops TO 5-6 degrees, or it drops BY (subtracts) 5-6 degrees? But ignition timing still drops WITHOUT the knock sensor working? Ignition timing is not a constant. It varies with RPM and MAP. When you go to WOT, you increase the MAP and the RPM. The PCM is picking the numbers off a table that uses RPM and MAP as the axes (baselines).

By eliminating the knock sensor, you are risking damage to the engine. If using the knock sensor was resulting in knock retard at WOT, it was either TRUE knock, or FALSE knock caused by some mechanical noise.

Did your tuner friend check the timing table to see if it matched the one I provided?

Quite logical that disconnecting the MAP sensor changes the timing and changes the way the timing varies. The PCM has been deprived of one of the main inputs it uses to set timing. It has to use some sort of algorithm based on other sensor values, and not the programmed timing tables.

At this point, the only way I could possible help determine the cause of your problems with timing is for you to provide a PCM data log showing at a minimum, simultaneous values for:
- RPM
- MAP (kPa)
- Throttle %
- Spark Advance
- Knock Retard
- Knock count
- Coolant temperature
- Inlet air temperature

The log should include cold start, about 4 minutes of warmup without being driven and without using the throttle, a few minutes of moderate driving and a WOT pull. The knock sensor and MAP sensors should be functioning, not bypassed.

rlf07

-

-After wot, the ignition no longer goes to zero or negative values. gone. now sees positive 5, 6 degrees. And yeah still drop in wot but I recovered about 12 degrees.

+ 3, + 5 degrees more than the standard ignition table. He said you can load the standard table.
-

-The hard part is getting logs. because it's a simple cellphone program. There is a bluetooth obd2 reader. Logging is bad and simply. but I try. I connect the map but the knock sensor unfortunately ... I don't do the mechanical work myself. mechanics are very busy and opposite people.
getting work done is difficult and boring

Injuneer

Don’t bother logging it until the knock sensor is reconnected.

SerdarD

Hi Injuneer,

- Did your tuner friend check the timing table to see if it matched the one I provided?

I have compared the provided timing table against the currently loaded one on the pcm and the other few 96-97 stock bins in my database. It's almost same but little different than all 96-97 timing tables. Probably its because of little different cam profile of the 96-97 cars. For being 100% sure, i asked a friend who is well known 96-97 LT1 tuner Stevie Devillier for another stock 97 M6 car bin file. Long story short current bin on the car is completely correct for 97 car. I have no doubt about it.

Meanwhile rlf07 changed the motor mounts. I suggested him to also check the headers and exhaust pipes for leak and cracks which might cause a false knock. Result all good no leakage nor crack. My another suggestion was to check flywheel and clutch related parts may cause vibration/mechanial noise and false knock. They have found a broken part and replaced it.


- By eliminating the knock sensor, you are risking damage to the engine. If using the knock sensor was resulting in knock retard at WOT, it was either TRUE knock, or FALSE knock caused by some mechanical noise. EXACTLY

He keep asked me to cancel knook sensor with tune and i decline each time, at the end he used a resistor to deactived it. I still insist to remove the resistor and activate the kncok sensor.

He still drives a car MAP sensor disconnected also. As you say : " That is not "curing" the problem. That is covering it up."


- When you take your foot off the throttle, the PCM cuts fuel and reduces ignition advance, until the engine RPM drops to a specific value (maybe ~1,300 RPM ??) . Then it turns the injectors back on. Is this when you experience "a few bursts from the exhaust"?

DFCO should be enabled at 10mph and at 0.8% TPS between 1200 -2000 rpm. as factory setting

- Ignition timing that you see on a scanner is the timing the PCM is using to fire the spark plugs. It is a number picked off a table in the PCM program, based on RPM and MAP (and a few other factors that will only add confusion) There is no feedback from the Opti as to where the timing actually is. If the Opti is indexed incorrectly to the camshaft, the actual spark timing will be "off", the PCM has no way of knowing that. The lookup in the table will not be affected by the Opti, unless the Opti is giving erratic RPM signals. The PCM sets the timing primarily based on RPM and MAP (a measure of engine load).[/QUOTE]

Also there are other tables to correct the timing related to IAT, Coolant temp. He changed the aluminum intake elbow to factory one and IAT readings are lower now which is good. EGR spark adder is not the issue because already deleted. And also there is famous LT1 unknown spark adder, probably it's not related to his problem.

According to your explanation i assume that wrong RPM reading by opti might cause the wrong timing advance by PCM. As an example, opti sends 2400rpm signal to PCM while actual engine rpm is 2300 or 2500 , and the PCM checks MAP reading and the wrong RPM signal and will uses wrong part of the timing table? This is what i was told to rfl07 and thats why he asked the opti question.


Best Regards.

Injuneer

His statement of the problem as I understand is the advance is jumping around rapidly, in an irrational manner. I have diagnosed a problem with a specific production run of the MSD Opti which was producing random, erratic RPM signals. An idling engine would start surging, jumping up as high as 2,500-2,800 RPM. The engine RPM didn’t increase directly based on the erratic Opti RPM signals (as high as 7,000 RPM for one or two frames of data in a data log), but increased because the PCM reacts to high RPM by opening up the IAC valve to prevent the engine from stalling if the throttle blades suddenly close.

I had to send marked up data logs to MSD to get them to acknowledge the problem. All I could get out of them was they fixed a problem with the cap, nd rebuilt owners faulty Opti’s with the revised parts. I suspect the dielectric compound on that batch was breaking down, and allowing sparking that was inducing RFI in the cam position signal.

Point is, the PCM reacts to the pulses received from the Opti. If you have RFI inducing spurious pulses, the RPM (pulses interpreted by the PCM) could be causing the advance lookup to be jumping all over the timing table. You could also have the same effect if the MAP sensor was producing erratic signals. Very common for the factory harness connector for the MAP sensor to dry out and start to crumble, loosening the pin contact. I saw that happen with my engine running a huge shot of nitrous, tuned to run speed-density with a MoTeC M48Pro ECU.

Just stories, but trying to point to possible problems. But you can’t evaluate those problem causes without a data log, where you can look at multiple sensors and parameters simultaneously..... at least that’s the only way I am able to do it. And a data log would also allow me to see the exact way the indicated timing advance is jumping around, which I can't derive from the words being used to describe it.

If the knock sensor and MAP sensor aren’t being used I won’t even waste my time looking at the log, if able to produce one.