87 GN at idle

[gnjones231]

Let's see if I can peel back this onion. Only one question for Earl. Tell me exactly when the injector fires.

 

[gnjones231]

I think Earl may have missed my response. No matter. Here are two scope waveforms showing what happens to the injector firing point as a function of changing
the cam sensor timing. So, in a nutshell, you can't change when the injectors fires. It always fires on the negative edge of the crank signal.

The top dark blue trace is the cam signal. the middle aqua trace is the crank signal, and the bottom purple trace is the injector signal. Note the falling edge of the cam
signal in relation to the rising edge of the crank signal. It has changed, but also note that the injector signal is still starting on the negative edge of the crank signal.

 

[1952ray]

I think Earl may have missed my response. No matter. Here are two scope waveforms showing what happens to the injector firing point as a function of changing
the cam sensor timing. So, in a nutshell, you can't change when the injectors fires. It always fires on the negative edge of the crank signal.

The top dark blue trace is the cam signal. the middle aqua trace is the crank signal, and the bottom purple trace is the injector signal. Note the falling edge of the cam
signal in relation to the rising edge of the crank signal. It has changed, but also note that the injector signal is still starting on the negative edge of the crank signal.

Hmm, interesting

 

[we4Mateo]

I think Earl may have missed my response. No matter. Here are two scope waveforms showing what happens to the injector firing point as a function of changing
the cam sensor timing. So, in a nutshell, you can't change when the injectors fires. It always fires on the negative edge of the crank signal.

The top dark blue trace is the cam signal. the middle aqua trace is the crank signal, and the bottom purple trace is the injector signal. Note the falling edge of the cam
signal in relation to the rising edge of the crank signal. It has changed, but also note that the injector signal is still starting on the negative edge of the crank signal.

This def makes me wonder why tweaking the cam sensor has any affect at all on the starting of the engine. I've seen it numerous times on a 1/2 dozen cars now though.

 

[RmvBfrFlght]

During cranking, the only item that uses the cam signal is the ICM. The ECM is in batch fire mode until the engine is running.

As for needing to tweak the cam sensor for better start up, it is due to the slop in the timing chain.

RemoveBeforeFlight

 

[gnjones231]

Could you please describe what batch mode is for the people who may not know. One thing that adds to confusion is using terms that may not be fully descriptive. Batch mode
could mean different things to different people.

 

[RmvBfrFlght]

Not a problem, batch fire is when all injectors are fired together at the same time. In the case of our engines it is all 6 being fired at the same time.

RemoveBeforeFlight

 

[gnjones231]

Thanks.

Also, if you find the need to adjust the cam sensor to make an engine run smoother, please don't think that your moving the injector timing around. As stated before, the timing
chain may be suspect, or possibly there is too much up and down play in the cam sensor. And I hope nobody thinks that once you set the cam sensor to 25 degrees that it
stays there, it doesn't. It does move a few degrees with a running engine, and no doubt as the miles and wear and tear mount over time, the cam sensor timing will move around
a bunch more. And for the BIG ONE! If you have a big cam you need to advance the cam sensor! From what I hope people have learned from this so far, that seems to be incorrect.
If anybody swears up and down that advancing is needed for a big cam, please post some waveforms so I can learn something too.

Here's a little trivia question for everybody. There are only two instances where batch mode is used (as far as I know). One is for starting the motor, what or when is the other
one?

 

[we4Mateo]

...Here's a little trivia question for everybody. There are only two instances where batch mode is used (as far as I know). One is for starting the motor, what or when is the other
one?

When no chip is present in the ECM? I know they do still run then but on very basic parameters.

 

[gnjones231]

HA! Here I am ready to talk more about using more descriptive terms and I think I stepped in it myself. What I meant to say was "One is for starting the motor, what or when is the other one on a normal running engine". I really don't know how the engine will run with no chip, I've never tested that scenario.

 

[RmvBfrFlght]

Here's a little trivia question for everybody. There are only two instances where batch mode is used (as far as I know). One is for starting the motor, what or when is the other one?

At least three: during cranking, during delta-TPS AE, and during an active cam sensor malfunction.

RemoveBeforeFlight

 

[gnjones231]

I edited this message.

 

[RmvBfrFlght]

Once the ECM recognizes the fact that the cam sensor signal is gone, it reverts back to batch mode firing (all 6). This can easily be seen in the code and on a test bench. The ECM firmware (code), will halve the calculated injector PW and switch the ECM hardware into batch fire mode. The reason for halving the injector PW is that it is in double fire mode.

Double fire being that the injectors are fired twice per cylinder system (2 engine revolutions).

I also got batch mode during cranking correct. IOW, my post #71 is fully correct.

RemoveBeforeFlight

 

[RmvBfrFlght]

When no chip is present in the ECM? I know they do still run then but on very basic parameters.

Have to give you credit for this one. Just tested it by removing the chip and it does stay in batch fire mode. And if the chip is OK and running SFI, it will revert to batch fire if the chip becomes intermittent as the ECM goes into limp mode.

Seat the chip back down and the ECM will also go back to SFI mode.

RemoveBeforeFlight

 

[gnjones231]

WOW! I can't believe how bad my memory is. I had to edit post #68 and delete some bad info. Sorry about that folks! I either need to get back into my Buick, or sell the damn thing!
Carry on!