Wierd Prom Issue - HELP

[corvairnut]

I almost dont know where to start, so I will from the beginning.

I bought 6 ea 16196395 ECMs. I remove each prom, cut out the existing chip and solder in a terminal to later install allow a removable 27C512 chip.. I use the OD$ mask and all is well with 4 of the 6. Each terminal and pinout was checked and passed. The Prom work in all ECMs and all ECMs were checked with other proms/chips and later with a romulator that I use. I have also tried the prom in a 16197427 ECM, but with the same results.

THE PROBLEM: The 2 proms will run my engine, but not well, both give have strange/low readings in turnerpro and dont run well....almost like I have the wrong mask. Timing is low and skips at lower RPMs. I have verified chips and plugs my romulator into the prom and still the same problem. It appears there is something up with these proms. Both proms have knock chips with 119**** numbers printed, but I dont know if that means anything.

Any ideas will be appreaciated as I dont know where to start.

Thanks,

Ted

[EagleMark]

4 out of 6 ain't bad? Were they all V8 and are they all going in V8? I think there's cylinder select issue with mis matched memcals... not in chip, in memcal...

[corvairnut]

Unknown, but the 16196395 is a V8 only ECM if all I read is correct. I change the Cly to 6 in a custom chip for the Chev Corvair and all runs fine. Correct me if im wrong, but the mem cal will only come into play in "limp home" mode.... correct? I have always discounted the "limp home" mode anyway since I run DIS and had to set the initial timing to a 60 degree offset to make the DIS work and will not work in limp home ever since I made the change.

I bought a 7427 today and will pay attention and document as I never thought this would be an issue. this issue first came up about a year ago with another prom, and I thought it was just a bad prom..... so there ya go.

Ted

[Six_Shooter]

Spark advance during LHM will not be affected by any changes that are made to the BIN. The ignitions system will run in a base timing mode, which for most GM DIS systems seems to be 10* BTDC.

I'm not sure how the hardware side of the CYL select issue is handled with TBI calibrations. If what I suspect to be true, actually is, then in TBI modes it is in a none issue and only affects MPFI applications.

[corvairnut]

EagleMark... you may have hit something. These are V8 TBI that I changing the Chip and making a 6 Cyl Corvair Engine Chip and A couple of the ECMs may have had unknown origin. I was looking at a writeup by Bill Hamilton on Bender and he was talking about netres (network of resistors) and the V6 has a 7.5k and the V8 had 15k between pins 12&13 on end memcal chip. I have found that the ones that work have the 15K between the pins (v8) and the 7.5k (v6) are the ones Im having trouble with. If nothing else, I have found a difference that makes one work and the other dont.... and sometimes thats half the battle

Ted

[EagleMark]

He's just wonderful at claiming everything that was figured out elsewhere...
http://www.thirdgen.org/techboard/di...-starting.html

And the instructions for how to do it...
http://www.thirdgen.org/techboard/di...es-values.html

[1project2many]

This relates to infor in a couple of threads. The latest is here:
http://www.gearhead-efi.com/Fuel-Inj...st-your-Memcal...

The 2nd and 3rd digits on the knock board will tell you what engine the memcal came from. 19 is from a 4.3 V6 engine so there's no need to make a change in terms of the number of cylinders. But there are two versions of the 4.3 V6. One is TBI and one is CPFI. While the cyl select / memcal connections for a TBI are likely known, I have never seen the same info for the CPI version. The starting point imo would be to properly identify which engine the memcal is from. If you have the original chips you can us BCCFind to identify the application and fuel system. If not then you may want to do some looking around through the 7427 related threads and on other boards about the fuel mode select.

[EagleMark]

That's a sweet system you build for the Corvair!
www.Corvair-efi.com

How do you wire the DIS? We've been talking about one from NorthStar V8 but always seems to come down to a crank sensor... looks like your using a crank sensor... very cook system! Now we know where all the one barrel TBIs are going.

[1project2many]

I've always loved those kits.
http://www.corvairnut.com/GMDis.htm

[corvairnut]

Thanks. The 6395 ECM did not use DIS, but a dizzy as you all know. The trick was setting the initial timing to 60 degrees and setting max timing at about 75. You loose you LHM, but you loose the dissy too (which is worth it....right). The wiring and signaling for the DIS and the dizzy is the about the same. I have the wiring documented if you need it. I know using the saw blade as a crank signal generator at the same time using my dizzy (which was a GM 4.3 mated to a Corvair base), was a little crude, but that was the only way I could work it out in my head. My crank wheel is provided by drilling holes in the HB and setting and the first holes are at 10 and 20 degrees and every 60 there after.

My stuff is mostly on www.corvair-efi.com. Corvairnut.com was my start and keep for mostly personal stuff.

Yes... I am always shopping for TBI-700s w/ left Pull (long metal bell crank) and buy about 10 a month for the conversions. I modify and rebuild them for that setup. See the site. I will say though, corvairnut.com does have the hovercraft on it.

Ted

[Six_Shooter]

Spark Advance is not affected by LHM.

If LHM is not working it is due to fueling, not spark.

I'm very familiar with the GM DIS systems. ;)

[corvairnut]

SS-Im sure your an expert, but when it goes in LHM (Tan disconnected), timing light shows from +25 to -10 (approx of course) and bearly runs... so you tell me. I figured the offset I had to install the make DIS work with a dizzy ECM caused all that.

Please enlighten me... I come here to learn

Ted

[Six_Shooter]

That's not "LHM," LHM would be running off the redundant fuel chips on the MEMCAL, you can force this by removing the EPROM from the MEMCAL, or G1 (style) adapter. In LHM, the ECM does not send the ESC/Bypass 5V trigger to take over timing, which is where the base timing of the ignition system itself comes into play.

That being said, the base timing of the DIS system, should be 10* BTDC, with the ESC/Bypass (tan/black) disconnected. So by the sounds of it, your base timing is not correct.

[corvairnut]

OK.. Im cool with all that. Bill Hamilton worked with me on that and that is why base is set at 60 degrees. It will not run on 10...Ive tried...hard. If you have a better idea... Im all ears. My bin is attached if you would look at it.

[Six_Shooter]

What do you mean by "it will not run on 10"?

Do you mean that when you set the base timing to 10* in the bin it will not run?

Wait a tick, is that what you're doing setting the base timing to 60* in the bin? If that's the case, then I think what you're doing is actually firing the wrong cylinder. The base timing setting will remove that much timing from overall calculation.

What you need to do is add 60* of total timing to the EST output.

The method I use, is to change a few of the offsets, I'm using $59 to do this so far, I haven't looked at $0D to see what will be needed to do that, even though it is planned, since I have a truck running on $0D currently that I would like to add DIS to.

1project2many has a different method that I couldn't get to work, that involves negative numbers.

I'll have a look at your bin.