Background: Playing with the chip in my '85 - still the "OEM" ECM, using Tunercat RT with the moates cables and ALDL adapter. The datastream def. file I have (and it's the Only $1f file I have found...) is suspect - there are Several issues with it that I aleady have had to fix - and others that I am ignoring for now, but it Does work, mostly. Most of the displayed values I can verify with the MT2500 I have, anyhow. I'm Also using a prom emulator, at times. As a comparison method I have a copy of CATS tuner, also, for checking the .bin editing... This is a Vortec head Crate motor with Edelbrock runners, #24 injectors, BBK TB, true duals with no cat, 700R4 car, etc...

I've gone round-and-round with this thing trying to get rid of a "shake" or vibration, feels like an exhaust resonance almost, at about 1300 rpm. Timing won't do anything for it - and I've had it so far advanced, and retarded, in that rpm range, that it's crazy. Fuel doesn't seem to be much help either - although if I have it really, really rich it isn't Quite as bad - maybe. When I first got this thing up and running I feared that it was an engine balance thing - but 1300 is the Only place that it occurs...

Anyhow - in the process of trying to find an answer to That problem, and I've about given up, I figured out that I was always looking at a very rich (BLM's in the 110 -115 range) condition when coasting. When I tried taking fuel out of the table (Pulse width vs. load) at zero and low loads it had no effect. Hmmm.. Seems that the two injector offset tables - Offset vs. battery voltage and Offset vs. low pulse width - both conspire to add more pulse width down there than the main table has in it, and even Zeroing that main table still you end up with a rich condition.

I know - when coasting it probably doesn't matter or mean anything, but Still...

I ended up taking the voltage offset to Zero across the entire table and then playing with the low pulse width offsets a Lot - particularly at the very bottom of the curve. I then had to compensate by adding pulse width back into the main table (particularly at low loads), but now have it where it stays within a couple of counts of the 128 value for BLM pretty well.

All that is fine - does anyone know why GM in their wisdom had such a large low pulse width correction built in? Or Why in God's name there is such a crazy offset for battery voltage - even "normal" voltages? What are those two offsets supposed to Do, anyhow?

 

those bpw corrections will still work reasonably well if the inj. constant and blm is close to begin with. By the sound of things you may be starting w/to low (rcher) of an inj.constant, and need to work the maf tables more.
I have had the best results on maf cars by first working setting inj. constant, airflow vs. rpm, and maf tables first w/out using other tables. Work the off idle to about 1600 first by keeping the car in the 50 lv range first using air vs. rpm and maf table 1, then slowly keep expanding your tuning by more rpm vs. load . When my blm was near or in the 128 range I then work the timing. Stock tables there aren't to bad a little excessive above 2k around 60lv.
Offsets, AE and temps. etc. will work best by being worked backwards, AFTER, all is done at operating temps gives a starting place to work the rest of the tune. I have found the temp. and batt. offsets pretty close and only a little rich with alt. problems. I believe those tables to be built to work in conjuction with all tables, and allow compensations neccesary due to temps. voltage etc. based on the tune being initially done at OT. I believe they might seem excessive if, the inj. constant is intitally set to low (rich) on a modified car.
As to shake or vibration, if no balancer problems etc. the conv. maybe locking there (if auto) and sometimes needs to lock at higher speed in modded cars.
Instead of working decell through load vs rpm try using dfco tables or if in the hack you can also use pulse width decay.

 

Uh, it has to do with electrical science or engineering.

Starting from first principles, an injector needs to be treated as an inductor in terms of
its electrical properties. Generally speaking, the time to saturate a coil is a number like:


[ t = - LN(1 - (IR/V)) * (L/R) ]

where t = time
LN = Natural Log
I = current (pick a max value)
R = coil primary resistance
V = Voltage (can vary, especially during starting)
L = coil primary inductance


Thus the engineering reasons that GM includes a base PW offset, and voltage
compensation when calculating injector PWs (open times). The injector drivers
are current-limited devices, IIRC.

Learning about the electrical properties of inductors on a bulletin board strikes me as
a fairly daunting task. One might start by doing some background reading. A good
general discussion of injector electro-mechanical properties is given here:

http://www.wellsmfgcorp.com/pdf/counterp_v5_i1_2001.pdf
http://www.wellsmfgcorp.com/pdf/counterp_v5_i2_2001.pdf

Some exerimental data and discussion were presented here:

http://www.turbobuicks.com/forums/bu...jector-dc.html

For details of inductance, current, time, and voltage relationships you might be further
ahead by consulting a good EE text, IMHO.

In terms of the injector mechanical properties they are a fixed-volume device, which GM
generally treats as a fixed-weight controller. The offset and compensation tables put some
linearity back into the calculations to account for non-linear behavior vs. time.

See the fuel load calculation example presented here:
http://forums.corvetteforum.com/showthread.php?t=689344

 

Bring it on, I can figure it out. With a BSME and a good EE background I Still don't see why the offset tables by themselves add up to more PW than you want at low or zero load conditions - with the Main PW table set to Zero. It's not reasonable, unless you Wanted the thing to always be rich under those conditions. Why would you?

BTW - I also have a old ('78) Chevy PU with a simple 5.0L v8 in it and an '85 vintage tuned port on it. Same stuff as the 'vette has - deliberatly, so that everything would be interchangeable between the two vehicles. That truck is a standard shift, the car is an automatic. The Truck displays the Same tendency to be very rich while coasting, apparently for the same reason the Car did - the offsets are just too large at the bottom of the tables - mostly the low pulse width correction table.

Being rich while coasting doesn't really seem to Bother anything - in the car with the automatic it Seems fine - although in the Truck with the standard it does cause some surging as it slows down to a stop in gear. I think, I haven't tried to dial it Out of the truck - yet.

I find the battery voltage offset particularly hard to agree with - in reality why would you offset from the main table for "normal" voltage conditions of 12-14 volts? And Why dial the PW up so high as that battery voltage drops - the only effect it has is to Flood the car should you crank it till the battery nearly goes dead (As a mechanic (man of many hats) you see it time and time again on a cold winter day. Weak battery+poor tuneup+zero degree temps=flooded motor). Linearity of responce to correct saturation times of the coils in the injectors is one thing - the extent to which that idea is taken is just silly.

The '85 bin file/PROM program has no provision for editing DFCO or for even changing the injector constant - at least not with any of the mask files I've seen, using either CATS or Tunercat. (These facts alone may kick me into the upgrade to a '165 ECM, someday) I ended up playing with the "main" PW vs. LV8 table instead - line by line.

There is a setting for "Displayed fuel flow rate" in the CATS bin editor mask (not there in the Tunercat one) that doesn't seem to do anything other than change the trip computer displayed value - like the name says. It does Not change anything related to actual PW - at least not that the BLM values show.

Like I said before - after a few hours of playing around (using the emulator and killing a weekend morning driving back and forth on the same hilly route..) I have the Car pretty close to what I would call "right". Within a couple of BLM counts of 128 across the whole spectrum pf RPM and load. With the exception of any real (more than a couple of seconds - we are talking Back roads here..) of WOT, where the narrow band O2 sensor is going to let me down anyhow. It at least goes Into WOT looking good... Seems to to even Drive fine - no issues, so far. I'll give it a couple of weeks to show me any bad behaviour in daily driving before I say that I'm Done playing with it - but I Think so..

 

Mseven may have a point with the torque converter lockup idea - I hadn't considered That one.

I have the lockup points on this set pretty aggressively - in that I have it staying locked up more/slower than the OEM program did. I use this car as a daily driver/commuter and at least Try to avoid stuff that will detract from the MPG average - keeping the rpm's down ought to help - particularly with all of the torque available.

So - I need to pay a bit of attention to what exact conditions will have it shaking and what Doesn't - at and around the "magic" 1300 rpm where it is the biggest problem. I do know that 1300 cruising along at about 43 mph on an open road Will shake - just barely noticeable.

It's a Lot worse when pulling away from a stop under light throttle as it goes through 2nd and then 3rd gears passing 1300 each time. Sort of "floating" along under almost no throttle at about 30 mph (in 2nd I think - I don't believe it will have bumped up into 3rd at that speed - and certainly hasn't energized the lockup..) is the really bad condition - bad enough that it needs a solution.

Maybe I need to add a switch to the wiring so that I can defeat the lockup solenoid - try That and see if preventing the lockup makes any difference... either that or put the emulator back on there and just turn the lockup off in the program. I'm still not really Used to Having that emulator handy - it Does make a neat toy!

I guess I wouldn't be all that annoyed if there turned out to be an issue with the lockup circuit - the transmission now has roughly 130K on it since being rebuilt at about 120K - and it had a "not serious" but certainly noticeable amount of trash/mud in it when I flushed it out last, two years ago (about 45K miles). It Ought to be about used up - knock on wood..

Since dropping the new crate motor in this last April (12K miles on That already..) I've been sort of expecting to see the transmission become a candidate for surgery. So far it hasn't had a problem - but it's only a matter of time. BTW - since the motor swap I have sort of considered the transmission to be the "fuse" in the drivetrain. It's hanging in there so far.

Of course Now, with the snow tires on the car, there isn't enough bite to really strain anything mechanical anyhow. This may be a good thing. And as I sit here typing this I'm looking out across the yard at it Snowing outside...

At this point I do hope that it makes it through the winter and back to warmer weather before I have to take it all apart - the garage isn't heated

 

That's stange, my tunercats does. I have 36lb injectors (supercharged)
and was able to adjust it. Are you running the latest bin file?

With your setup, 350 ci I'm guessing, the stock '85 MAF ecm should do fine metering fuel. 24lbs injectors were stock on our '85's.

 

I thought there were other bins available, I work mostly w/165's, 727/730's so I don't usually look for other options.
Keep in mind also that the more the converter locks and unlocks the more heat is generated. I set my low speed and high above 43-44. I found I was at 40 too often, which if I was just using light throttle caused some vibration as it was always just about to lock, and it tried to give me some SK's.
Look at everything going on at that rpm and mph, to try and determine what is exactly happening. After 2 years I finally took the apu-1 out of my car, and have a couple chips that are probably as good as it gets......until I see something in a scan

 

In TunerCat I have the version W $1F mask. It's showing on the 'site as the current version. There is Nothing in there for deceleration fuel control, and no constant value to edit for Injector constant. There is a "displayed fuel flow" number, which does nothing to change the BLM's and apparently only effects what the trip computer shows.

In TunerPro I don't even get That much. I have a couple of different .xdf files - a 1F.xdf and a 1Fm.xdf, there is no obvious difference in the two.

With what I've seen the -6870 .bin file (or more correctly the Mask files for either Tunercat or TunerPro) has no provision for editing Either any sort of decel fuel Or a single injector constant.

As for the torque converter lockup... What I'm doing with it is trying to keep the thing locked up and holding the rpm down while travelling "in town" streets. I have it locking at 34 mph in 4th, 30 mph in 3rd. The TPS values to unlock are set higher than OEM as well. Unlock mph numbers are 32 in 4th and 27 in 3rd with the unlock TPS values at just above zero%.

While doing this will cause it to "lug" at times - climbing a grade at low speed and not enough throttle to cause an unlock, or pull the TV cable enough for a downshift, the Rest of the time it cruises just fine. Really no different than if it were a standard shift car left in a higher gear, afterall.

It's obvious (to me anyhow) when the lockup happens, and I've played with the TPS and MPH setpoints until it suits the way I Normally drive the car. I Hate the way it'll drive along "floating" the RPM and Not locking up with the OEM chip in there...

Also - the 700R4 (this vintage anyhow) only routes the fluid through the trans cooler loop if the lockup is On. If it's unlocked then the fluid is Not circulating through the cooler. At least that's how I understand the system to work.... It'll stay a lot cooler with the lockup on anyhow - less slippage making heat in the converter.

 

I've adjusted the injector constant for 36lb injectors in the "Injector Pulse Width vs. Load Value". 85 ecms are a bit more mysterious as they haven't been fooled with as much as say the '165 ECM.
If you're chasing a vibration then I would look to other sources other than messing with the ECM. An 85? Take a look if the motor mounts are sound. 22 years is a long time for original mounts. Check for loose C beam bolts....loose motor to transmission bolts. These cars suffer from exhaust vibration as a default....might not be the culprit.

 

The motor mounts are good - they went in new along with the new crate motor this last spring. The c-beam bolts are Tight - I've had the 'diff in and out of this car a couple of times in the last few years - those bolts are good.

I also replaced ALL of the u-joints in the car mid-summer (making certain all was well before setting out on a 1000+ mile trip).

The 1300 rpm shake Only happens in 1st or 2nd gear, and Only with the converter Unlocked. You can feel sort of a slight exhaust resonance (slight compared to what it Can do..) around 1300 in the higher gears with or without the lockup, but not much - you have to be looking for it. Basically it only shakes at that RPM if there is almost zero load on the motor... It'll do it coasting.

I can either Add fuel or remove timing to effect the shaking - neither will cure it completely, either will reduce the magnitude. I should note here and emphasise that the shaking is Not just an exhaust thing - the car really Shakes bad - if it was the motor on a dyno stand doing this it would be walking all across the floor...

If it Was that motor sitting up on a dyno stand I know exactly what I would do about it - I would move the damn cam timing ahead a couple of degrees. Tough to do that (or tougher anyhow) with it in the Car