What sensor is used to determine actual timing in a log?

[LosLS2]

I have this problem and it's only the second time that I have seen it. The other guy switched to an aftermarket PCM so it was never resolved. The problem is that we are getting 2* less timing in the logs than what we are commanding in the tune. The car does not have knock sensors and is tuned in open loop speed density. All the modifier tables are zeroed out. I'm thinking that perhaps it's a mechanical problem. Just trying to understand how it is that the scanner determines how much timing is actually being run. Guessing cam and/or crank but would like to know exactly before I start switching stuff around.

[LosLS2]

tqm can and will pull timing, log all timing pids and tq pids.

The car has a th350 transmission.

[LosLS2]

Anyone?

[LosLS2]

Is the cam sensor really used or just the crank?

[MNR-0]

You will have to post up your tune for others to verify if what you are saying is actually true

There are so many corrections in these ECUs its hard to know and get at all of them first up

Also post up a log showing whats happening and be sure to log IAT, ECT, dynamic cylinder/air, Advance, MAP, commanded AFR/equivalence ratio, Engine RPM, TPS, Calcualted Engine Torque

[Frost]

Last week I had a swap to tune. It was a truck (05ish Regency custom 1500 shortbed) and had an LSX and M6 swap. Before rescaling the trans pulses per, the calibration showed 'error' in HPTuners. The PCM would display a speed while logging, but because of that issue with the VSS input in the calibration, the truck was running off of idle spark tables. As soon as that was straightened out, it was back to the hi/lo octane table. A quick way to verify if you are stuck in idle tables is to set them to a flat value such as 22 everywhere and see what you get when the car is moving. If you have no VSS signal at all back to the PCM, this could be the issue as well.

[LosLS2]

You will have to post up your tune for others to verify if what you are saying is actually true

There are so many corrections in these ECUs its hard to know and get at all of them first up

Also post up a log showing whats happening and be sure to log IAT, ECT, dynamic cylinder/air, Advance, MAP, commanded AFR/equivalence ratio, Engine RPM, TPS, Calcualted Engine Torque

The tune and logs are on my buddy's laptop as he bought his own copy of HPtuners. I will have him send them to me and post them ASAP. I am extremely competent when it comes to tuning the fbodies. I actually have several tunes that work flawlessly in other cars that I have compared against just to make sure that I am not missing a modifier table. Also, I have tuned this vehicle before and this problem only popped up after this most recent rebuild. The setup is and has been on the aggresive side. We aren't talking about a stock tune file here. It is a 416ci LS3 setup with a th350 and a 9" rear. The car has been bottom 10's on motor with a varition of this same tune.

The tune is pretty stripped down. The car is tuned in OLSD and the transmission has no outputs to the PCM. IAT sensor is locked out at 77*F. Timing is locked out at 24* from .55 up and 3400+ RPM.

Last week I had a swap to tune. It was a truck (05ish Regency custom 1500 shortbed) and had an LSX and M6 swap. Before rescaling the trans pulses per, the calibration showed 'error' in HPTuners. The PCM would display a speed while logging, but because of that issue with the VSS input in the calibration, the truck was running off of idle spark tables. As soon as that was straightened out, it was back to the hi/lo octane table. A quick way to verify if you are stuck in idle tables is to set them to a flat value such as 22 everywhere and see what you get when the car is moving. If you have no VSS signal at all back to the PCM, this could be the issue as well.

We are currently getting the VSS signal off the front ABS sensor and it's pretty close +/- 2 MPH. I'll check to make sure that we aren't dropping a signal that would cause it to jump into the idle tables.

The intent of this post apparently wasn't clear though because people are trying to help me with troubleshooting and that isn't really what I am after. I am more after an understanding of how it is that the scanner comes to the timing displayed in the table and the histogram. I read somewhere else that what the scanner shows is what the PCM is commanding and not what is actually going on based on sensors. Is this true? If I am not getting the timing that I am commanding in the high/low octane tables and all the modifiers are correct (zeroed), then is the PCM just screwing up or can a bad cam or crank sensor or any other mechanical ignition problem cause this issue?

[Hunter02ss]

If the scanner is saying one thing and the ECU is showing you what you want, then your timing on the motor itself is off as long as no other tables are automatically adjusting for you. The scanner shows what the engine is actually doing. Have you put a timing light on the motor to make sure the timing on the motor is the same as what you are commanding?
Is this what you are asking?

[LosLS2]

If the scanner is saying one thing and the ECU is showing you what you want, then your timing on the motor itself is off as long as no other tables are automatically adjusting for you. The scanner shows what the engine is actually doing. Have you put a timing light on the motor to make sure the timing on the motor is the same as what you are commanding?
Is this what you are asking?

Not really. The car is running commanded timing (according to the scanner) at everything but WOT. At WOT, it's dropping about 2* for most of the pass. Even if I were to put a balancer on with timing marks and setup a pointer, I still can't check it under a load while making a pass.

You mentioned that what the scanner logs is ACTUAL timing and not the COMMANDED timing (+/- any modifiers). That is not what I saw elsewhere so I would like for someone like Chris@HPtuners or anyone else with knowledge of how the scanner software works to explain to me how the scanner comes to the number that it displays. Basicly, assuming that the tune is correct and no modifiers are pulling timing, what MECHANICAL problem (if any) could cause the scanner to read 2* less than commanded.

[WS6FirebirdTA00]

There are several things that play into the final value of the timing. One of the biggest issues is the rounding done by the computer. Chris explained it one time and there isn't much you can do about it.

[LosLS2]

There are several things that play into the final value of the timing. One of the biggest issues is the rounding done by the computer. Chris explained it one time and there isn't much you can do about it.

Got a link to this explanation? Can you verify that the number displayed is actual and not commanded?

[LosLS2]

He is using a new Windows 7 mini laptop to log. He is going to log a pull with his old laptop that runs windows xp and see if it reads right or if it's something else.

[MNR-0]

There is no sensor controlling ingition timing. The PCM commands an instant during the 4-cycle process using the crank signal as a reference. If your crank is not phased correctly, then yes, your ECU can infact command timing that is out of sync with actual TDC

Have you disabled AC and M6 torque smoothing? What about burst knock? Sorry if we are not answering your questions, but without somethign to go off, we are only guessing here...

[majorpayne317641]

One suggestion you may want to look at, there are timing modifiers that are based on IAT and ECT, therefore if you check these and you happen to be in certain ranges while waiting at the track for a run or on the street, the PCM will add or subtract from your desired timing. Look around and you will run into these tables, simple zero out the areas you might be runing in during a run or test on the street and you will get the timing you command.

[WS6FirebirdTA00]

One suggestion you may want to look at, there are timing modifiers that are based on IAT and ECT, therefore if you check these and you happen to be in certain ranges while waiting at the track for a run or on the street, the PCM will add or subtract from your desired timing. Look around and you will run into these tables, simple zero out the areas you might be runing in during a run or test on the street and you will get the timing you command.

All the modifier tables are zeroed out.

[Hunter02ss]

When you are logging, your log is created by what the engine is actually doing. Not what it is commanded to do. You should always verify with a timing light, the old fashion way and make sure the engine's timing is the same as the timing commanded in the ecu. Without proof of this your timing can and will be off.
I learned the hard way.