TBI 7747 Idle Fueling Issue while Cold - Too lean, AFRs not responding to bin changes

[JMcD]

Been lurking here for a while as I've been doing TBI tuning on/off over the years. Searched a bunch on this forum, but haven't seen other treads with the same or similar issue.

Basic problem: Not running as rich as I'd like at idle when cold. Results in a stall if driver or reverse are engaged shortly after startup. Also the crank time is extended, but one problem at a time. Changes to the target AFR in the tune don't seem to have the expected effect. Idles fine warm, at the desired AFR (13:1). Cold it also tries to idle at 13.5-14:1 and does so poorly. I'd like to get that down into the 11:1 range when warming up, but changing the Open Loop AFR vs Temp table doesn't impact Actual AFR. I've tried lowering that table by 2 across the board and AFR doesn't appreciably change. This is after the choke tables should be out of the picture (idling for more than a couple minutes). Has this issue until about 70C coolant temp where the engine is warm enough it'll idle okay at 13:1.

Engine info: 355 w/ vortec heads, 9.5:1 CR, performer RPM intake manifold, carb to tbi adaper, headers, dual exhaust, 212/222 hydraulic flat tappet cam. GM 80 lb/hr injectors, stock fuel pressure.

I'm using a stand alone WB02 (LM-1) and watching it as I'm connected with an Ostrich 2.0 and ALDL using TunerProRT. I've used the WB02 recently on a carbed vehicle and it seems accurate (I free air calibrate when I move it between vehicles, engine behavior matches expectations when AFR is too rich/lean).

Latest bin and log file from cool idle (14C) where it is running leaner than desired attached. I'm thinking there must be something overriding the target AFR tables, but haven't found anything obvious yet. If I heavily skew the main VE map in the idle region, it will richen up some and idle better. However, that produces an overly rich idle when warm. Running exclusively in open loop (255 deg C enable value for closed loop).

Any suggestions would be appreciated!

[Fast355]

Been lurking here for a while as I've been doing TBI tuning on/off over the years. Searched a bunch on this forum, but haven't seen other treads with the same or similar issue.

Basic problem: Not running as rich as I'd like at idle when cold. Results in a stall if driver or reverse are engaged shortly after startup. Also the crank time is extended, but one problem at a time. Changes to the target AFR in the tune don't seem to have the expected effect. Idles fine warm, at the desired AFR (13:1). Cold it also tries to idle at 13.5-14:1 and does so poorly. I'd like to get that down into the 11:1 range when warming up, but changing the Open Loop AFR vs Temp table doesn't impact Actual AFR. I've tried lowering that table by 2 across the board and AFR doesn't appreciably change. This is after the choke tables should be out of the picture (idling for more than a couple minutes). Has this issue until about 70C coolant temp where the engine is warm enough it'll idle okay at 13:1.

Engine info: 355 w/ vortec heads, 9.5:1 CR, performer RPM intake manifold, carb to tbi adaper, headers, dual exhaust, 212/222 hydraulic flat tappet cam. GM 80 lb/hr injectors, stock fuel pressure.

I'm using a stand alone WB02 (LM-1) and watching it as I'm connected with an Ostrich 2.0 and ALDL using TunerProRT. I've used the WB02 recently on a carbed vehicle and it seems accurate (I free air calibrate when I move it between vehicles, engine behavior matches expectations when AFR is too rich/lean).

Latest bin and log file from cool idle (14C) where it is running leaner than desired attached. I'm thinking there must be something overriding the target AFR tables, but haven't found anything obvious yet. If I heavily skew the main VE map in the idle region, it will richen up some and idle better. However, that produces an overly rich idle when warm. Running exclusively in open loop (255 deg C enable value for closed loop).

Any suggestions would be appreciated!

Did not look at the mask or the bin file you are running but more often than not their are constants to limit the minimum and maximum afr in open loop and at idle.

If you are running $42 remember that the Open loop AFR has two tables. One is vacuum and the other is temperature. You add the two together to get the commanded. Most are over 16:1 in stock form and limited to 15:1 at idle by the limiting constant.

[JMcD]

Re: the two tables for target AFR, did a spot checked that to make sure:

At 16deg C Coolant, 40 kPa MAP: AFR vs Temp = 9, AFR vs Vac = 2.5 = 11.5:1 target. Admittedly, up at 67C and 40kPa, that goes up to 15.5:1 (should lower that).

When I tuned the idle via main VE table during the summer, I zero'd out the AFR vs Vac table and set AFR vs temp to 14.2 across the board. My thinking was that if I was able to get target AFR across the board, VE table would be good and subsequent changes in target AFR should produce the desired fueling. Actual AFR at idle could have been controlled by the Idle limit cals, but VE adjustment had the desired effect on AFR.

Currently: Open Loop Idle Lean Limit set to 11.70 (stock is 13.5). Open Loop Idle Rich Limit set to 13.0 (stock is 13.7). Those names are somewhat misleading(?), but the description makes it appear the Open Loop Idle Lean Limit is the lower AFR (rich limit).

Open Loop Max AFR is set to 14.1 in the current cal.

To simplify things, I think going back to a zero'd out AFR vs Vac table and tapering AFR vs Temp to a desired curve will take out one variable. I'll experiment some with the idle limit cals to to see if I can get them out of the way of the target AFR calc.

[JMcD]

A couple updates -

Latest bin is a little better.

1. Seems like there could be a slight exhaust leak skewing the WBO2 readings leaner than actual. No matter how rich I skew fueling (large BPW increases), WBO2 only dips to 11:1 or so.

2. IAC is too high when warm (80+ counts in drive). Some reading here and at thirdgen.org says that might be part of the reason the idle is rough. Too much air through the IAC valve vs throttle blades. The counts are at ~130 cold and in Park.

Plan is to adjust the throttle stop to open it a bit more and reduce the IAC counts (at all times). And look for an exhaust leak.

One question about the "BPW Hack" - what are the units? Values I'm seeing are between 100 and 200. XDF notes on the hack say miliseconds, but that doesn't make sense.

[Fast355]

A couple updates -

Latest bin is a little better.

1. Seems like there could be a slight exhaust leak skewing the WBO2 readings leaner than actual. No matter how rich I skew fueling (large BPW increases), WBO2 only dips to 11:1 or so.

2. IAC is too high when warm (80+ counts in drive). Some reading here and at thirdgen.org says that might be part of the reason the idle is rough. Too much air through the IAC valve vs throttle blades. The counts are at ~130 cold and in Park.

Plan is to adjust the throttle stop to open it a bit more and reduce the IAC counts (at all times). And look for an exhaust leak.

One question about the "BPW Hack" - what are the units? Values I'm seeing are between 100 and 200. XDF notes on the hack say miliseconds, but that doesn't make sense.

Hex decimal....0-255..You have to setup a conversion to read that number as Miliseconds.

[JMcD]

Thanks Fast! - that makes sense.

Here's my formula (compared to Inj Duty Cycle value to confirm):

"BPW Hack Value"/65535*1000 = Pulse Width *Before* Pulse Width Adder.

Warmer here today (43F), so I fiddled with the warm idle and throttle adjustment. Turned the idle set screw in to open the throttle to the point where I'm 38-42 IAC counts warm in Drive. This pushed TPS voltage up to 0.82v, so I drilled out the holes slightly on the sensor (1/4" bit), and remounted. TPS voltage is now at 0.55v with no pedal input.

I also had to re-tune idle fueling some warm since one of the changes I made in the last rev was to increase the Pulse Width Offset from 0.274ms (AZFT 7.4L bin) to 0.396ms (ASDU 5.7 bin). I also pulled some timing from the idle area. It was in the 28-30deg range, so I dropped it about 3 deg and blended that out some. Warm idle is back in the 12.5-13.0 range on the WB. Seems a bit smoother now with the throttle open more vs more air through the IAC.