I'm trying to get this TPI setup going, large cam, idle vacuum in park around 80 KPA.

The issue is as soon as its put in gear, the pulse width drops within a second or so, and engine dies.

It seems to happen as soon as things switch from fuel trim cell 12 to cell 4?? I've got it setup for open loop under 1500 rpm using Super AUJP.

The fuel table is pretty close to spot on in the idle ranges in park or neutral. If I give ever so little throttle when shifting into gear, I can maintain idle, however, I can slowly release the throttle, and there will be a point that the BPW just drops from 3.xxx to 1, and engine will stall and die. The only thing I can see changing is the trim cell from12 to 4.

any ideas?


throttle blade is adjusted so IAC counts just drops to 0 at desired idle speed, giving a large authority for cold startup.

fuel trim cell boundry's. 1500 2000 3500, 30, 50, 70

 

What RPM is it idling at?

Mine idles at 1200 rpm and between 80 and 85 kpa with no trouble dropping it into gear. I do have the IAC eliminated and locked into open loop though.

 

idle anywhere from 800 to 1000 just fine. When you drop it in gear, the BPW starts to increase taking on the load, then just drops in just one frame of the datalog, from 3.xxx BPW in gear to 1.xxx It always seems to happen when the RPM drops below 800 it does this.


attached is another log, midway though log, I put it in gear and apply a little throttle, this keeps it going fine, and then I slowly start to let off the throttle, letting the IAC maintain idle speed. There seems to be a point or throttle % that all of sudden the BPW again just drops like a rock.

I have no clue at this point why BPW is dropping like it is, I'm sure it has somthing to do with the changing fuel trim cell. I made a few changes on this datalog from the last, including setting DE multipliers to 0.0 and adjusting the trim cell MAP boundary hysteresis from 20 to 5. Doesn't seem to make a difference.

is there a chart someplace that lay's out the number identification of the different fuel trim cells? which ones are used in what conditions? accel? decel? idle? and so on???

 

I hooked up my Tech 2 scan tool and selected 1992 L98 5.7L, and it shows updata stream and full output controls to my surprise.

I went into IAC test, Engine RPM Control, I can adjust desired engine speed with the tech 2.

I selected a few data items to view when controling the engine speed, I looked at MAP, RPM, Inj PW, Fuel Trim Cell

Same thing as I was seeing in TTS Datamaster, as I lower the RPM (IN PARK) below 800 or so, the fuel trim cell will switch to 4, and Inj PW drops from 2.9 at steady idle to around 1.2. I was able to get engine to stay running, bet every few frames it would show cell 4 and pw of 1.2, then bounce back to cell 12, 2.9 - 3.2 pw. this was right about 775 rpm or so (original default fuel trim cell boundary)

I have defined fuel trim cell boundaries as 1500-2000-3500 and 30-50-70 kpa. The RPM or MAP never goes out of what I would think should be cell 12. Cell 4 as its showing would be under 1500 rpm, 30-50 kpa...

I even went into my fuel table in the 20-60 kpa 400 to 1000 rpm range and increased the values to something crazy high, still no dice, I was thinking maybe the PCM was seeing some incorrect MAP value for a split second, but I don't see it on scan tool.

I had this issue on the original AUJP, and I switched to the S AUJP to try to resolve some issues.

 

Whats your kPa in gear?
Whats your VE look like?
(cant open any files here at work )

My engine needs a shitload of more fuel in (D) than in (P)........so my VE is very steep in Idle area....

 

Yes the ve values do go up steeply in the 90 kpa column. The issue will also present its self in idle and commanding idle speed with tech 2. It dies like someone shut off the key almost.

 

video on youtube of engine running, and shot of tech 2 showing fuel trim cell and inj pw

 

I had this exact problem in a different mask, i had to adjust the threshold for high MAP trouble code trigger.

I forget if it was 33 or 34 but once i changed the value from 60kpa to 90kpa i had no problems. Not sure how well your mask is mapped in Tunerpro, i had to go digging in a disassembly for mine ( $A1).


Mine would go from 70kpa no load to 80kpa or so once i put it in gear. it would stall every time.


good luck!

 

I think I have access to that using the Super AUJP in tunerpro. However it never sets a code for high map. I wonder what the strategy is when the code sets? Does it use backup mode resistors, or go to a value in the fuel table it would expect the stock engine to idle at?

 

The ECM goes N-Alpha to create a default MAP value. It will do this prior to setting the SES light or setting a code. And continue to do this until it thinks that the actual MAP value is OK.

RBob.

 

so would changing the fail parameters of the MAP sensor high code prevent this from happening, or do you have any insight to preventing the alpha-n mode? i'm going outside to work on this shortly so I will post my findings.

thanks for the help so far all.

 

well I set the value for ERROR QUAL 33, Min RPM to Increment Timer to its maximum value of about 3100 rpm. My understanding is that the dtc 33 will only set if conditions are met for a certain amount of time. The timer is not aloud to increase unless its now over 3100 rpm. Now my idle conditions won't occur over 3100 rpm, so I should never see this issue again.

I loaded these settings up on my emulator, fired up the engine and it goes into gear perfectly now every time.

If ANYONE has any inputs to the way I've disabled this, or a better way I'm all ears, thanks for the help so far..

 

I'm not a fan of disabling malfunction codes. It would be better to set the RPM, timer, and/or MAP/BARO thresholds to values that work with your engine.

In AXCN, the MAP/Baro thresholds are at 84%. If I understand this correctly, if baro is at 100KPa, the malf 33 MAP threshold is at or above 84 KPa, above that for 1 second (cal parameter), with the RPM above 650 it will go N-Alpha.

Note that once the malfunction code parameters are set correctly, you should also adjust the tables that create the defaulted MAP value when code 33 is present. Just unplug the MAP sensor to simulate a failed MAP.

RBob.