Help me figure out what's wrong in this CSV engine log...

[ryan.hess]

I'm hoping that someone with the knowledge of what a good running engine should look like can tell me what's wrong with mine... I highlighted the portions which are "out of whack", mainly when the rpms drop to 525rpm about 600 seconds into the engine log. My spark timing seems to jump wildly while this is happening, and my MAP jumps to .54 (although it could be rising because the rpm's are so low, but on the other hand, it could be rising and stalling the engine.) Pay particular attention to the Integrator and airflow... they both do some *crazy* things! (When rpms drop, shouldn't airflow drop? and vice versa!?) I await your opinions......

[brian89gp]

Auto or Getrag transmission? And are you running an auto or manual chip?

The Spark jumping wildly is the under/over idle control and stall saver routines doing their job, though it looks like yours is to the excess.

The MAP looks normal for what the engine is doing. I don't se any airflow variables in there...

What it looks like is that you have a super rich idle, too rich to idle correctly. I bet this is worse when the engine is warm? If you look at the INT and BLM where you bolded, the INT is pegged at 103 and BLM is at 120. If you go down towards the end of the log you will notice you have a more consistant idle (I have NEVER gotten a 3.4 DOHC to idle perfectly) and is only jumping between 775 and 825, which isn't bad, but look at the INT and BLM, INT is at 128 and BLM is at 107. This means you have a really rich idle.

FYI, INT and BLM are the self tuning in the fuel portion, the INT is fast reacting and tends to bounce around, the BLM will follow the INT. Below 128 means its cutting fuel (ie VE is set to rich) and above 128 means its adding fuel (ie VE is tuned too lean).

[brian89gp]

Have you done anything to your fuel system, injectors, fuel pressure, etc? Anything at all?

[ryan.hess]

Auto or Getrag transmission? And are you running an auto or manual chip?

Auto, running an auto chip.

The Spark jumping wildly is the under/over idle control and stall saver routines doing their job, though it looks like yours is to the excess.

So this is normal considering my engine is crapping out you're saying

What it looks like is that you have a super rich idle, too rich to idle correctly. I bet this is worse when the engine is warm? If you look at the INT and BLM where you bolded, the INT is pegged at 103 and BLM is at 120. If you go down towards the end of the log you will notice you have a more consistant idle (I have NEVER gotten a 3.4 DOHC to idle perfectly) and is only jumping between 775 and 825, which isn't bad, but look at the INT and BLM, INT is at 128 and BLM is at 107. This means you have a really rich idle.

It only stalls when the engine *is* warm, and I have driven it around for a long distance... It should be noted that the output above is after it idled for 10 minutes in the driveway, then it started randomly dipping in RPM's.

FYI, INT and BLM are the self tuning in the fuel portion, the INT is fast reacting and tends to bounce around, the BLM will follow the INT. Below 128 means its cutting fuel (ie VE is set to rich) and above 128 means its adding fuel (ie VE is tuned too lean).

I figured as much, I just didn't know how much was "too much"... I suppose those "gm update" injectors that flow richer at idle probably won't help me then I should note that I did replace the injectors with those from a 94, although it was doing this before then as well... Could it be my fuel regulator is shot? I got the fuel rail with the injectors from that '94 if I need to replace it........

*edit: I'm gonna get/rent a fuel pressure gauge to check this out first... I HATE taking off the plenum. God, this is like the 41st time (literally!!)

[ryan.hess]

Okay, key on, pressure rises steady to 41psi, then slowly drops back down to 39psi, and stays there. Engine running (idling), pressure remains at 39psi. I checked this at a shop, and forgot to ask them to hookup a vacuum pump to check the regulator, but assuming the hose isn't disconnected, it's bad. Am I on base here? I'll post this in maintenance.

[brian89gp]

Looking at the log, it went into closed loop around 2887, which the bad idle soon follows. Before the engine warms up, how does it idle?

Something just doesn't make sense. How old is the O2 sensor and what type of gas milage are you getting? I've never used freescan, but your O2 voltages should be jumping all over the damn place.

[ryan.hess]

Looking at the log, it went into closed loop around 2887, which the bad idle soon follows. Before the engine warms up, how does it idle?

Something just doesn't make sense. How old is the O2 sensor and what type of gas milage are you getting? I've never used freescan, but your O2 voltages should be jumping all over the damn place.

Before it warms up, it idles like a champ! My O2 sensor is brand spanking new, and I usually get ~14mpg. I should also mention, that the fuel pressure seems to be "leaking", almost 10PSI in 5 minutes (on it's way towards 0). Probably 50 problems compounding on themselves

Oh, and, at idle, pressure raises to 43 when I disconnect the FPR.

[SappySE107]

I havent looked at the file yet, but I can tell you that the O2 sensor has an issue warming up at just idle. If you don't drive the car around, it will start cutting fuel whent he car warms up and stall out. Tapping the throttle or driving around and then letting it idle will show you the true idle fuel needed. Ill look at the file and see what it says though.

[SappySE107]

Just as I thought:P Look at your O2 values. They don't really move much.

[SappySE107]

Here is an example of mine. I also redid the file so you can see how I set it up for tuning. Remove the first 4 columns.

That is what the O2 shoud look like before you bother trying to figure out how your idle fuel should be.

[ryan.hess]

As per your request... I ran the engine a couple minutes at 2000-2500rpm... dropped it down, and took some readings. Here's the log, judge for yourselves:

[SappySE107]

Cool, so BLM of 110. Typical for the DOHC to be programmed for too much fuel at idle.

[ryan.hess]

Cool, so BLM of 110. Typical for the DOHC to be programmed for too much fuel at idle.

So that's normal? By chance can it cause the stalling? As mentioned above, it only stalls when in closed loop... Why in the world would GM want to richen it up w/new injectors if most of them are already rich? Doesn't make sense...

[SappySE107]

Where did you get the info on these new injectors with higher flow rate at low ms open time? Its not really "rich' since the ECM is adjusting fuel. However it is rich till the computer has learned idle fuel.

[ryan.hess]

Where did you get the info on these new injectors with higher flow rate at low ms open time? Its not really "rich' since the ECM is adjusting fuel. However it is rich till the computer has learned idle fuel.

See! That's EXACTLY why it doesn't make sense to me... Unless they put in some huge injectors, the computer can compensate! The info on the injectors is in my post phantom stalling in DOHC maintenance... somebody posted the whole TSB.

*edit: so my car is running perfectly right now, according to the log? (Computer has taken into account whatever causing the rich condition, and "fixed" that.) Maybe they do put in some honking 26lb injectors... The ecm can only go down to 1ms (I believe?), so you're stuck at a fixed AFR at idle/deceleration conditions... Maybe I should try that?