V8 DIS revisited

[Shannen Durphey]

Hector wrote:
If there's _any_ way for you to fix the width of your messages, that would be
very helpful.  They currently look like one giant sentence.  The reply is hard
to distinguish from the original post, as you'll see below.

> 
> I have done some searching through the archives that I can find on the list (Feb 99-Jan 00, if a solution has been found after that I wouldn't know so sorry if this has been beaten to death) and have seen some interest and a failed attemp at getting a HEI bin working with a DIS. The signal to the ecm from the module seems to be the culprit and the other problem is what hardware to use.

****
It's a little more complicated than that.
****

> 
> The signal problem was supposedly taken care of by one person using some type of inverter. However, it was never stated what was done. The HEI provides a short high reference pulse to the ecm while the DIS sends a long high pulse. I hope this is correct as I may be saying the opposite of what is true. Tinkering with the bin netted a running engine but not a working ecm spark table. The DIS would stay in base timing. It has something to do with the reference pulse being 60* advanced to the ecm. My thought for a fix is this: build a disc that doesn't trigger the module until later (actually I think earlier; I'm still confused) making the reference signal like that of the HEI. 


***
The problem with this approach may be that there's no way to start the vehicle. 
The DIS module as used in the 2.8/3.1 V6 and the 2.0/2.2/2.3 4 cyls fires at TDC
when there is no voltage on the bypass line, then switches reference pulse
timing after 5V is applied by the ECM to provide a signal that's advanced
relative to piston TDC.  The signal is not 60 deg advanced for every engine, nor
is it 60 deg advanced for every type of DIS system.  
***


This would mean that the disc would have short valleys and long peaks as opposed
to the original crank reluctor that has quick square peaks like were replicated
by welding bolts to a pulley. 
You're speaking of two different issues.  The signal from the ecm to the module
is one area where a problem occurs.  This is the signal that some people
invert.  The signal from the crank sensor is an A/C signal, a completely
different beast.  Again, I'm speaking of the DIS system used on the 2.8/3.1 and
others mentioned above.

****
The difference in wave shapes can be attributed directly to dwell control. 
Since this DIS system handles it's own dwell control, the ecm simply cuts the
time availabe between spark plug firings in half, and provides a low/high
signal.  Single coil distributor signals are calculated to rpovide optimum dwell
times, hence the varying width on/off portions of the signal.
****
> Now, would this work or would this mess up the module's signal so badly that it would render it useless as a > trigger for the coils and as a signal to the ECM?

****
Timing and consistency are the most important parts of the DIS crank sensor
signal.  Any missed pulses from the crank sensor can result in the module
"resetting" #1 cylinder. 
****
> 
> Next is the hardware issue. The only two V8 DIS that I know of are Northstar/Aurora and the LT5. I happen to have a Northstar DIS in front of me that was pirated from an engine swap at work. After looking at the wiring diagram, it shows that it has two crank sensors and a cam sensor. Also from reading the archive, I have noted that 4 or 6 cylinder engines use a  reluctor ring that has 60* reference points with TDC being marked by a second reference only 10* apart for a total of 7 ref. points per rev. The 4 cyl. fires every 3 pulses and the 6 every other pulse. I am *assuming* the Caddy has the same thing except for the 7th signal, and has the two crank sensors spaced 30* from each other going into the same module giving it 12 ref. points for one rev. and the cam sensor for TDC. 

****
Better stop right there.  The reason that little's been mentioned about the
Caddy system is that no one's provided good information about the system.  Do
not
assume that the 30 degree offset sensors proide the needed signals.  At least
one individual who _should_ have Norstar DIS information has claimed the sensors
are part of a redundant system.
***

> The module outputs the same signals to the ecm as a regular DIS would except that it also outputs a 24X   > signal, a 4X signal, and a cam hi signal. This is why I think the reluctor is still spaced at 60* for a V8  > even though 45* would be logical. If this is the case, this may be a little awkard to adapt to a car never  > equipped so. The cam sensor being the key as you would have to do something with the dist.



> 
> The other option was to use two 4 cyl. DIS modules and coils. This might work quite well and I believe Ford uses something like this on their 4.6L cars. You need two crank sensors and one reluctor referenced just like a 4 or 6 cyl. except that the second sensor would be 90* apart. At TDC, one coil pack would fire #1. Then at 90* later, the other coil pack would fire #8, and they fire every three refence pulses. In other words, two DIS units working as 4 cyl units just that one is firing 90* from #1 cyl. TDC and thinks it is #1 cyl. This is just like the Caddy in that it sees 12 pulses per rev (for both modules, each sees 6) but it needs no cam ref. The ecm signal is the one I don't know will work. I don't know if both modules will need to send a signal in order to work or would one signal be enough? If they do, would a diode in the line take care of any interference? Would the ecm freak out with these two pulses.

****
You need to merge the output pulses from the modules, since each would only
provide 1/2 the needed pulses.  You'll need to separate the output pulse from
the ecm to be delivered to the correct module, since each handles 1/2 (and only
1/2) of the spark firing chores.  You'll want to synchronize the pulses from the
ecm to the correct module to prevent firing the wrong plug.  Remember that
startup can cause either module to fire first.  Also, just for reference, the
DIS systems that we're speaking of do not fire #1 cylinder first.  It makes
little difference at this point, but it's somthing to keep in mind.
****

> 
> Someone was working on adapting a system to their V twin bike and they made a reluctor that they have been testing on a bench. They were able to get a spark from the module, although I don't remember if it was ecm timed. Would you care to comment on how the project is coming and what do you think of my rookie findings?


> Let me apologize now for beating a dead horse....again. Please, take into consideration that I am only trying to help as I see there is interest (at least there was a year and a half ago) in accomplishing a V8 DIS with GM equipment as others have shown interest in the past. Yes, Electromotive and others have something already but what's the fun or frugality in that? I also understand that a HEI dist. will work well enough but so does the carb and fully mechanical dist. that's presently on my car. If I'm going to swap to EFI and be silly, I might as well be real silly and try and make the DIS work!

****
Welcome aboard.
Shannen
----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org