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

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!

Quote:

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Originally Posted by 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!

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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.

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.

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.

Quote:

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Originally Posted by 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.

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

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.

A few things that have seemed to have improved cold idle and general performance:

1. Didn't find an exhaust leak, so I ruled that out.

2. Did remember that the gas in the tank was at least 6 months old and likely bought during the winter...not much volatility left. Tank was low, so I put nearly a full tank of fresh in and that really helped. Can hit 10:1 on command now.

3. AE needed major increases. Thanks to this site, found that 5000+usec (5+ms) values are often needed on aftermarket intakes. Huge help with cold and warm tip-in and upshift at steady throttle performance. Was always going lean temporarily, especially on upshifts.

4. Went back to a stock non-async bin and applied changes from there (again, this forum was a big help finding that). Saw Async briefly on one of my earlier bins, then a major lean spike and nearly stalled during coastdown. Do. Not. Want.

5. I'm in Open loop all the time (WB02 tuning), so I set the idle target AFR to the same as non-idle open loop AFR target (14.1:1) to prevent step changes in pulse width when dropping into "open loop idle" mode.

6. Adjusted VE table significantly in a few places. (high map, low RPM)

7. Several other changes (PE target AFR, AE CTS multiplier, choke AFR at low temp, idle air tolerance, etc)


Slightly different problem now. Cold start seem better (at -3C), but I do get a stall if I drop it in gear (drive or reverse) without letting it idle for a couple minutes. Made some changes in the latest cal that I haven't tested on a cold start, so we'll see if they help (AE CTS multiplier, MAP AE PW).

Now for a rant. Context - I work on automotive embedded controls as my day job. This includes writing software and doing calibration work. When you write the software and know exactly what the calibrations you added do, there's no guessing involved (well, not much anyway). If you need an extra variable to log, you add it in the software and log it (whether internal RAM or over CAN). Trying to do the same type of work but on a 7747 ECU is maddening. I give major props you those of you who have more patience than I on the guess and check work needed to make these ECUs work on modified engines, especially without a WB02. Between the lack of variables (what all parts of the equation are doing what to determine the total PW?, what threshold am at I for AE?), the slow rate of data (1 second/sample when the ECU is calculating at ~12.5ms per loop), not knowing how all of the different calibrations are actually used or what they even are, and on and on, this work many of you are doing is much more difficult than doing it at an OEM or wherever the code and cal are being developed. Ostrich and EEPROM chips help, but still, ugh.

FWIW, this problem isn't limited to OBD1 GM stuff...EFILive/HPTuners and the like all suffer from many of the same issues. Lack of full control over spark and fueling, limited data logging, can't actually change the software, etc. There's just a bunch of stuff running in the background, not well understood or even known, that is impacting engine behavior. These tools are almost always working from a limited set of parameters, many with limited descriptions/understanding of their actual function.

Thankfully the next vehicle I'm doing aftermarket EFI work on has a megasquirt. Open source code, fast data logging, built in WB02 closed loop control, all calibrations defined, etc. Sure, host of other issues when you start from scratch, but at least there won't be a bunch of stuff lurking in the background, changing things without me knowing about it. It'll be a nice change from the ole 7747.

bin and latest log attached if anyone made it this far :)

Another handful of changes and what seems to be more progress (at least around 9 deg C).

Painting with a bit of a broad brush, I decided to disable most temp based corrections an allow the Open Loop AFR vs Temp to handle most of the work.

This seemed to help with cold startup behavior, specifically the act of putting the vehicle in gear very quickly after startup. No stall this time.

A bit more driving found another hole in my AE tables. I had flatlined all of the AE correction vs CTS to the highest value in the table (0.398). Now at 85C, the upshifts went a bit leaner than before, not initially, but at the end/slightly after the shift. I dropped the MAP - Filter vs Coolant table down to .2 across the board, which seemed to help.

One more AE finding was on low RPM tip-in. It sputtered and bogged here some when warm. This was on small tip in events that were enough to trigger the AE, but not so much that a downshift would happen. I'm guessing here this is a small TPS AE (if any) coupled with a large MAP AE and it resulted in too much fuel. So, I dropped the MAP AE some, especially in the 0,20,49 cells. Tested this by holding the brake in drive/reverse then doing light throttle tip in events. With the prior cals, the WBO2 would peg rich. New cals go just slightly leaner (12:1 at idle), but not so much that is misfires. A little over-correction on the way back down (MAP AE possibly a bit high still for this condition), but live-able. Would be nice if these parameters had an RPM component to them to keep large AE PW adders from bogging the engine at low airflow conditions.

Data log and latest bin attached (log is from a couple bins before changing the AE).

One more update and a PSA on MAP AE -

Made a few more tweaks in March. Ran well, but the spark advance was a bit more aggressive than I really wanted. Dialed it back some.

Now for the PSA on MAP AE. I had been tuning MAP AE based on upshift AFR performance. Adding MAP AE during steady throttle upshifts to prevent lean transients as the engine speed is pulled down and MAP drops quickly. I had to run really high values to get most, but not all of the lean dip resolved. On the order of 5000+ uSec at 80% (max value in the table). Stock values look to be in the 500 range. This had an unintended side effect - causing stalls on shifts from Park/Neutral to Reverse or Drive. The quick drop in MAP at low RPM + large dose of fuel from MAP AE was causing the engine to flood and stall very quickly. Datalogs would go from 1200rpm to 0rpm in 1second. No data between those two points. I can see how on a manual trans vehicle, you could get away with more AE since you aren't loading the engine in quite the same manner. You modulate the clutch out to prevent the quick dip in MAP. Transmissions with a higher stall converter may also not have as much of an issue either since the MAP may not change as suddenly during Reverse/Drive engagement. Oddly enough, it wouldn't occur until the engine was nearly or fully warm. Same .bin at 11-70C ECT didn't stall, however, up at 80+C it would do it very consistently. I'm not entirely sure why, but it may be due to the fact that when warm, the MAP in Park/Neutral while idling is lower (more vacuum), so when the engine is pulled down the delta MAP is higher (35kPa -> ??kPa) vs (45kPa -> ??kPa). Could also be the fact that the transmission will engage gear more quickly when the transmission fluid is warm, causing the engine speed to drop more quickly and the MAP to change more rapidly as a result. All this is also compounded when running higher flow injectors (since this parameter appears to be PW adder). Anyway, I went back to a stock MAP AE table and no more stalls on garage shifts.