A/F in various situations

[PAracer]

What should I be aiming for in different situations?
idle
WOT across the rev band
part throttle cruising
moderate acceleration
closed throttle decell. (could be an ISC adjustment to limit air)

At the current moment, the car idles right around 14.6-14.7. Cruising and part throttle it will run about the same, 14.6. At WOT, it will sit right at 13.5 all the way untill red line. Does this seem alright, or should I richen up a little more at lower MAF voltages.

Also, untill the coolant has a chance to heat up to the point that the fans kick on, I run rich 11.5-12.0 up to redline in WOT. I would like to lean this a bit but I am not sure where to look. The rich situation does keep me from abusing the car untill it heats up, though.

Another issue that I am seeing is that coming off throttle after WOT or moderate/heavy acceleration, the A/F will go lean and often register as 'air'. A little goose will clear it up and have the car decell at stoich. I can't imagine that this will hurt anything since there is a negative load on the engine. Essentially, the engine is firing the plugs in the absence of fuel, right?

My last little issue is that for the first couple minutes of driving with a cold engine, the car will try to stall when I slow to a stop. The ISC just can't seem to react quickly enough. My current programming holds RPMs at 1800, then drops to 1300 untill the car is almost stopped, then drop to my 1100 idle speed. For the first couple minutes, however, the RPMs drop from 1300, but won't catch at idle. Sometimes it will pick back up from 500 or so, but often it will stall. With the car in reverse, it is even more likely to stall (vacuum issue?).

This is on my mtx swap car that uses the D4U1 computer. Spark plugs look fine with a slight whitish dusting.

Thanks for reading and putting up with me,
Mike

I would also love to read a description of how/where to adjust timing.

 

[shomesomesho]

I run my 3.2L MTX (X2J) at 13.1 across the board. Basically the entire stabilized fuel table has 13.1 in every cell except the first column which I left stock.

The car seems more responsive and quicker than with the stock fuel table. I also get slightly better gas mileage, on the order of 1-2 mpg. I don't suffer any drivability issues either and no pinging on 92 octane. Plug tips are light gray.

 

[HotRodKid]

the turbo sho is set for 14.7:1 ate idle, part throttle and cruise

13 something on part throttle and then 12.5 on boost

it was getting 33mph at one point, shortly after we finished the car

it was a safe setup, but didnt do much for turbo spool ...

 

[Mr Anonymous]

Remember that in closed loop the PCM will always be aiming for 14.64:1 regardless of what you tell the base fuel table to do. There are ways to change this, but for part-throttle operation you're really not going to gain anything.

Open loop (such as WOT) is where adjusting commanded fuel values matters.

 

[drivinhard]

going a little fat beyond 6500 may keep CC temps down, easier on everything (pistons/exhaust, oil temps, cats if you have them, etc).

 

[shomesomesho]

Actually, according to the tweecer guru himself:

a. '89-'95 MTX - Command open loop across the board by filling your base and stabilized fuel tables with any safe AFR value below 14:1 - say around 13:1 for N/A setups and at least 12:1-12.5:1 for boosted applications. Commanding a value richer than 14:1 on any '89-'95 MTX calibration will ensure that the EEC stays out of closed loop, where it would otherwise attempt to ramp around a stoichometric AFR of 14:64:1 regardless of what was actually being commanded.

I have verified this by tinkering with various AFR's both below and above 14:1. Whenever the commanded AFR is richer than 14:1, the kamrf's all magically become exactly one, signifying a departure from closed loop strategy.

 

[PAracer]

I just went through Adam's post on the thread that shomesomesho posted. Thanks for the link by the way.

Following his advice, I got the car to run even better in non-wide open cases. I think I might richen up a little at lower MAF voltages, and lean a bit on the high end. Basically, twist the Transfer function counter-clockwise.

I learn stuff every time I read yous guys's posts. Thank you!

Any tips on tweaking my spark tables? I'm totally green to the concept of changing spark timing via a computer.

Thanks and Merry Christmas,
Mike

 

[SHOZ123]

closed throttle decell. (could be an ISC adjustment to limit air)

After a couple of seconds of this the FIs should shut off giving an A/D ratio of +18 as read by a WBO2.

 

[PAracer]

Let's say, for instance, that my car is running as lean as 15.5 during a nice easy cruise, then goes as rich as 12.0 at WOT near redline. Should I just be happy and live with it? Or should I keep working to get closer to the magic 14.6 when I am pumping less air?

I think I will be calling it quits for today's tuning. I'll return on Tuesday if I feel up to the challenge.

 

[PAracer]

After a couple of seconds of this the FIs should shut off giving an A/D ratio of +18 as read by a WBO2.

That's what I expected to hear. I actually remember you saying this a while ago in a different thread, Paul. Is this a function of the D4U1 programming that I can access?The only thing I worry about is running down the backstretch at VIR, then downshifting at the end of the braking zone, only to have te car stall at the top of a nasty downhill run. I've only had to coast a car from the top of the roller coaster once, and the car rolled all the way into the pits and into my parking space without the aid of combustion.

 

[SHOZ123]

It's called coasting fuel shut off (in the SCT software) and you can do quite a bit to it to eliminate or exaggerate it. The car shouldn't stall as you are still getting ignition and as soon as you give it any gas the fuel comes back on. It can easily be turned off too.

Max load to enter
Min coolant temp for fuel shut off
Min N/V to allow fuel shut off (engine speed/vehicles speed)
Min rpm to enter
Min VS to enter
RPM below to turn fuel on
Time at closed throttle to enter
Time at closed throttle to enter extended

Are some of the parameter to adjust this. (again in the SCT software).

Personally with the ATX I have it come in rather dramatically and quickly, this along with the TC lock on will give me the best engine braking.

 

[Axianator]

What should I be aiming for in different situations?
idle
WOT across the rev band
part throttle cruising
moderate acceleration
closed throttle decell. (could be an ISC adjustment to limit air)

While I would recommend the usual stoichometric AFR of 14.64:1 for idle and part throttle cruise and a WOT AFR of 13:1 for a naturally aspirated motor (12:1 - 12.5:1 for boosted applications at WOT), keep in mind that there are several areas of the fueling strategy where you will not be able to make many (if any) adjustments with the existing TwEECer software. Some of these areas include idle, some part throttle cruising, closed throttle decel (DFSO - see below) and almost any area where closed loop is being commanded.

At the current moment, the car idles right around 14.6-14.7. Cruising and part throttle it will run about the same, 14.6. At WOT, it will sit right at 13.5 all the way untill red line. Does this seem alright, or should I richen up a little more at lower MAF voltages.

If you are commanding a WOT AFR of 13.5:1 within your fuel tables, then it sounds as though you have the perfect fueling strategy (where it produces the desired closed loop AFR of 14.64:1 at idle and cruise and the WOT AFR you are commanding via your tables).

Also, untill the coolant has a chance to heat up to the point that the fans kick on, I run rich 11.5-12.0 up to redline in WOT. I would like to lean this a bit but I am not sure where to look. The rich situation does keep me from abusing the car untill it heats up, though.

On the '94-'95 D4U1 calibration, the EEC will utilize the base fuel table ("Fuel - Base") as the basis for it's AFR mixture calculations whenever the reported coolant temperature is below a guestimated 160F. Once the ECT sensor has reported a "stabilized" coolant temperature above this 160F mark for a specified period of time, the EEC will then begin looking to the stabilized fuel table ("Fuel - Stabilized") as the basis for it's AFR determinations, adding the appropriate fueling multipliers into the mix afterwards. Please note that while the precise stabilized temperature for the X2J and D4U1 calibrations has not yet been officially confirmed, we assume that the typically shared corporate value of 160F was also carried over to the V6 SHO calibrations from their other EEC-IV brethren.

Let's say, for instance, that my car is running as lean as 15.5 during a nice easy cruise, then goes as rich as 12.0 at WOT near redline. Should I just be happy and live with it? Or should I keep working to get closer to the magic 14.6 when I am pumping less air?

While it can be beneficial to command and produce a leaner fuel mixture under certain conditions (most of which relate to increased fuel economy and emissions requirements), remember that sustained lean mixtures can lead to preignition and heat-related valvetrain component and piston assembly damage resulting from increased combustion chamber temperatures.

Another issue that I am seeing is that coming off throttle after WOT or moderate/heavy acceleration, the A/F will go lean and often register as 'air'. A little goose will clear it up and have the car decell at stoich. I can't imagine that this will hurt anything since there is a negative load on the engine. Essentially, the engine is firing the plugs in the absence of fuel, right?

Correct, and what you have just described is actually referred to as the Decel Fuel Shut-Off (DFSO) strategy by the factory engineers. As Paul eluded in his reply above, this otherwise normal strategy will only occur under closed throttle decel when a number of specified conditions have been met. Unfortunately, said DFSO parameters will not be available for the '92-'95 MTX X2J or '94-'95 ATX D4U1 calibrations until Josh and I have released our all-inclusive "mega" TwEECer software updates down the road.

My last little issue is that for the first couple minutes of driving with a cold engine, the car will try to stall when I slow to a stop. The ISC just can't seem to react quickly enough. My current programming holds RPMs at 1800, then drops to 1300 untill the car is almost stopped, then drop to my 1100 idle speed. For the first couple minutes, however, the RPMs drop from 1300, but won't catch at idle. Sometimes it will pick back up from 500 or so, but often it will stall. With the car in reverse, it is even more likely to stall (vacuum issue?).

Assuming zero intake and exhaust system leaks, you can narrow most erratic idles down to spark timing or fueling imbalances.

What kind of timing and AFR values are you seeing at idle?

I would also love to read a description of how/where to adjust timing.

Any tips on tweaking my spark tables? I'm totally green to the concept of changing spark timing via a computer.

Without delving too deeply into the D4U1's otherwise-complex spark strategy and duplicating information that will be in the upcoming EEC Technical Manual, I would recommend that you eliminate the redundant base spark tables by filling them with a maximum value of 63 and rely solely instead upon your borderline spark tables to carry you through the night. In the case of the '94-95 D4U1 calibration with the current software release, these tables include the base ("Spark - Base"), base ECT adder ("Spark - Base ECT Adder") and base lambda adder ("Spark - Base Lambda Adder") tables. I should also note that once you have filled these tables with the proper value(s) given above, you should then take the 11x9 base and borderline spark tables and plug the lower value of the two tables into your new 11x9 borderline table. This task is easily accomplished with a quick cut-and-paste into Excel alongside some quick comparison formulas.

I have verified this by tinkering with various AFR's both below and above 14:1. Whenever the commanded AFR is richer than 14:1, the kamrf's all magically become exactly one, signifying a departure from closed loop strategy.

I should note that when it comes to your run-of-the-mill EEC-IV calibration, this unique 14:1 AFR trick is actually a bit of an oddity and, as such, is only applicable to the '89-'95 V6 MTX calibrations (unlike their brethren, the '93-'95 ATX calibrations do not share in this "ability"). Moreover, since adaptive corrections (KAMREFs) can also be applied during open loop operation, I should also note that one should look to the loop state indicator within CalCon and not their KAMREFs when attempting to determine the current loop state.

 

[HotRodKid]

'94-'95 ATX D4U1 calibrations until Josh and I have released our all-inclusive "mega" TwEECer software updates down the road.

oh snap ... what this gonna include ??

and can we test the current stuff on the turbo atx sho ?

 

[Axianator]

oh snap ... what this gonna include ??

Everything ... and yes, I do mean everything.

and can we test the current stuff on the turbo atx sho ?

I'll have to speak to my associate about this.