Ralph:

In response to some of your Q's:

1. WRT the http://www.dynamicefi.com/ product, Rausch(sp?) is a EE of many years experience. I bought a board for his original DIY WB unit way back when. It was a first-class design & a mil-spec board. I installed it in the Vette ~ 10 years ago and it's still running. http://www.corvetteforum.net/c4/doct...bboardc800.jpg

His ECMs start with stock (new) GM boxes to which he adds some minor circuits, chips, and software. The reliability should be the same as a normal Delphi part - which is very good indeed. If I were starting out in programming for the first time today, I'd work off one of his units - it would be WAY easier than the way I had to learn.

2. WRT to your FAST controller difficulties, the HEI distrib has been around for 40 years. I discussed their internal features here: http://www.corvetteforum.net/c4/doctorj/heicoilinfo.htm
and here: http://www.thirdgen.org/techboard/df...technical.html

The problem you describe is usually caused by picking the wrong phase from the HEI DRP (reference pulse). The GM HEI triggers on the FALLING edge of the square wave signal. Most aftermarket computers are user-selectable for rising or falling edge trigger - lots of people pick the opposite one, or get the wrong signal wave entirely. Either could have caused the symptoms you describe. See the reference here: http://www.megamanual.com/ms2/heiest.gif

3. In most GM P4 masks, fuel adders (AE & PE) are SUMMED. I wrote a short discussion of 8D fueling here, the older masks are philosophically similar: http://forums.corvetteforum.com/c4-s...-equation.html

4. WRT enrichment, I had a small discussion of rich tip-in conditions here that speaks to what I think was GM's design spec (starts around post #14): http://forums.corvetteforum.com/c4-s...eleration.html AFR target depends somewhat on whether you still run a cat.

5. Lastly, WRT atmospheric compensation - yeah, air density at sea-level changes by 10-15% between summer & winter conditions. GM (in your ECM) used a MAF sensor to approximate air flow. MAF means MASS Flow, and mass - in engineering terms - is independent of atmospheric conditions such as intake air temp.

That leads to three points to remember:

a. The SD ECMs do not measure mass - hence they NEED Temp and Press compensation. The basic calcs are covered in my 8D fueling memo above.
b. The MAF ECMs don't require such compensation AS LONG AS YOU ARE WITHIN THE DESIGN RANGE of the program. That is, GM took air density, relative humidity, etc into account in the original equipment design. The issue was covered in some way or fashion.
c. ONCE THE MAF SIGNAL IS PEGGED the ECM will no longer compensate for changes in air density. FLOW is not measured, and there are no calc routines in the program to compensate. Thus the fueling and AFR adjustments are only accomplished with CODE changes in the ECM tables.

Since a drag race engine is only oprerting in that regime for a few seconds, I guess it's OK to have the fuel tables approximate real conditions.. For a road racer, that just won't do at all .


Hope that helps. YMMV. And if any of the above info is wrong, the money you paid for it will be cheerfully refunded.

DRJ

 

Hey Doc.......have we met? Did we buy or sell the other a cam or something like that. Thinking i might have sold you my 219 cam or I bought your TPIS cam.....getting old and the memory aint what it used to be

Anyway, thanks for the input. I lot to read and digest. The FAST is setup for a crank trigger, so i used the inductive pick up in the distributor to trigger it. I tried swaping the wires to change the pulse phase, but it didn't seem to help. The problem is the rotor is physically way out of phase with the cap when the inductive pickups are aligned. To make matters worse the FAST needs about 10 degrees of timing to figure out what it wants to do with the timing, so the rotor is even further out of phase when it fires. It's probably about 20 roitor degrees past the pole on the cap (or 40 crank degrees). So the rotor is about 1/3 of the way to the next pole when it fires. I'm guess'n, the spark is jumping ahead to the next cyclinder coming up on the compression stroke....and causing it to kick back. I need to find a way to change the phasing in the distributor (adjustable rotor or reluctor), but i haven't found a solution yet. For now i"m just going to work with the stock computer and see if i can get it close.

 

Hey Ralph -

Yup, I bought that L 219 cam from you some years ago, up at HPN.

Re the FAST, a couple of points:

The HEI distrib is usually set at 6 - 10* base advance at the crank (stock). The engine starts on that base timing, before the ECM takes over. That did three things for GM.

a. The engine could start and fire - sort of - no matter what state the ECM was in.
b. It starts with no kick-back.
c. The 'zero crossing' signal from the HEI pickup triggers the square wave (DRP) going to the ECM at that same base point of 6 - 10*BTDC. That signal from the HEI module is where the ECM measures the RPM for all its control calculations.


Once the engine gets to ~400 rpm(?) the GM ECM closes the 'bypass' and assumes control of spark timing (EST).

The engine normally operates at 20 - 40* BTDC, CALCULATED from the position of the DRP.

So the actual spark event is only related to the position of the trigger signal by ECM time calculations.

The relationship of the 3 events (VR pickup, DRP, spark timing) are shown on the B&G figure here:
http://www.megamanual.com/ms2/heiest.gif
There are more comments on interfacing an HEI with an engine computer in that section of the MegaSquirt manual, for reference.

The details of the HEI module inputs are similar to the circuit description of the Nat Semi 1815 chip shown here: http://www.national.com/ds/LM/LM1815.pdf


I don't have a FAST manual around anymore, but I'm surprised if yours doesn't allow the use of either the DPR signal (5v square wave) OR the variable reluctance (VR) signal for trigger input - but I don't know. The GM VR input was sensitive to signal phase, IIRC. Most of the modules wanted a negative-going wave before the zero cross point. But don't rely on my memory - you can see the relationship on an O-scope, but I haven't looked at one in a few years...

Anyway, your FAST book should tell you if it is phase-specific or not on VR. If it accepts a 5v signal you can also use the DRP with trigger on the FALLING edge, as previously stated. Lots of people get that mixed up.

If it's none of the above there is one other possibility. I knew one guy who was having a kick-gack issue with an after-market ECM way back when. Seems to me that unit took spark control right from engine start. What he had to do was set the timing tables (at 0-400 RPM and 0 vacuum) down to a low number - like GM does - to get the thing to fire up safely. He was running a 427+, and it really smacked the starters around...


ALSO note that the ECM trigger point has little to do with the physical phase of the distrib finger. They are only connected inside the ECM calculations. Setting up an HEI is easy - to review, just find #1 compression stroke. Roll the crank back to whatever base timing you want, eg 10* BTDC. Twist the distrib body to the spot where the 8 lobes of the distrib rotor wheel line up EXACTLY with the 8 points of the stator. Clamp the body and you are done, #1 plug is where the rotor arm points. When the spark fires depends on the ECM, not the position of the VR pickup.

Hope that helps.

Dave

 

I DID remember you.....lol

The FAST system can be setup for the HEI module OR a crank/cam trigger, but it's a change in H/W, not a S/W change. This unit started life as an HEI unit, but was later sent back and changed to a crank trigger setup. There is a setting for timing offset. The instructions say set the crank at 50 deg, and then align the reluctor pickups in the distributor. The method works well, cause the timing was almost dead on. I tried swapping the trigger wires, but it didn't seem to help.....however the starter was about done by then. I just got the starter rebuilt, so I can try again. Meantime it's running pretty well on the old ECM and 30# injectors.

 

OK, that would explain why the HEI was kicking back @ 50* BTDC. I'm not familiar with the old FAST hardware. If it controls spark down to start-up RPMs (say 0 - 200) you could try running it thru the HEI module - maybe by holding the bypass line 'high' all the time, so it won't try to use internal timing to crank. IIRC the bypass line was 5v, but it needs checking; and verify the spark tables downn low. Dunno if that will work though, so I'm glad you're running these tests on your engine, rather than mine....

FWIW I built a crank-trigger out of Vortech truck parts back in the day. It fed the standard HEI module with no problem. Turns out a crank-trigger does smooth some of the 'jitter' out of spark control when racing. For road use on my car it was over-kill (and leaked oil) so I eventually pulled it out.

http://www.thirdgen.org/techboard/at...-0gmpartsa.jpg
http://www.thirdgen.org/techboard/at...timingseta.jpg
http://www.thirdgen.org/techboard/at...mingcovera.jpg

Have fun
D

 

Doc, the FAST system can control the timing down to the 0-500 rpm range. That wasn't the problem......the problem was the physical location of the rotor relative to the cap when the reluctor was lined up. A good 20-25 degrees past the pole (#1 wire) and the more you retard the timing in the FAST s/w, the further away it gets. I'm assuming the spark was jumping ahead to the next cylinder causing the kick back. The reluctor or the rotor needs to moved about 25 degrees or more. The only other possibility would be to offset the spark enough in the FAST to get it to the next cylinder, but i don't know if there are limits in the s/w or if it would even work. btw, the rotor phasing using the stock computer isn't very good either. It's firing about 20 rotor degrees before it reaches the pole.

 

OK, now I see your point. You're saying when the distirb body advances ~50* the distrib posts also advance relative to the distrib finger. Which means the posts are ~25 cam degrees more advanced than GM design. Which is causing cross-fire. Makes sense, sorta. You could see if the FAST s/w will take a 90+* trigger advance (which is how GM runs the HEI/ECM). . . Otherwise:

MSD used to offer a phase-adjustable distrib, IIRC. Doubt it would be in an HEI body however, so you would also need a new coil and ignition box (examples of the ones I use are on my HEI web page). Or you could go back to a crank trigger.

Like I said in the beginning, you could also look to new hardware and get a clean design that solves all the old control problems, and has better data recording as well. Seems to me the newer ECMs can also run the AFR setpoint directly from the WB signal, although I haven't used that feature myself.

Good luck
D

 

I was thinking of trying to trick the system by programing a huge advance, as you suggested, and moving it to the next cylinder, so to speak. Otherwise, i'd like to get an old EFI distributor and do some experiements moving the reluctor or the rotor. I just don't want to mess up my only dist. The MSD unit would work for the FAST, but i need to also trick the old computer into thinking that it's still controlling the engine. And a new ECU is not in the budget.

 

Wow I can't believe someone is actually farting around with a 870 ecm That should have been your first upgrade to a 165 ecm or go sd.