HEI 8 pin hot-start problem

[hytekauto]

HEI 8 problems

Here's the setup:

1968 Dodge Super Bee, 426 Hemi, Cross Ram intake w/ 2 Holley 670 cfm throttle bodies, MegaSquirt 2/3 firmware v 2.35 with Relay Module, GM HEI 8 pin ignition module, input to HEI module from locked stock Chrysler magnetic pickup distributor. The wiring to MS is per the book: Terminal R to "tach in", terminal E from pin 36 (via Fast idle terminal) from JS10, start control via mod using Knock Enable (RPM > 300 goes high), then to proto area using a 2n2222 to provide +5 when above 300 RPM, this is wired to the HEI module B via DB37 pin 5 properly ungrounded and wired. The Tach In is the typical Opto with diodes jumped out, 560 ohm R12, C30 removed, and XG1 to XG2. This all works as advertised.

Here's the problem:

The engine fires right up, idles decently at <1000 rpm, timing is handed off to MS (as verified with a timing light). All is well for about 2-3 minutes, then little by little the timing control cuts out intermittantly, as indicated by the tachometer and the ignition LED on MS. This gets progressively worse with the cutouts getting longer and more frequent until the engine dies. Let it sit for a minute or so and the process can be duplicated. However, if you hold the throttle a bit open to keep the rpms >1500 or so, this problem doesn't occur?????? Nothing gets hot, just nicely warm. The injectors are following the ignition and cut out when the ignition does, the engine usually catches when the RPMs drop below the 300 rpm level indicating that the internal startup part of the HEI mod is working properly. I've switched HEI modules, replaced the coil and reluctor in the distributor, tried two different Mega 2 modules, tried several different combinations of parts in the Opto area, all with no change. The next step is to pull the startup control get it running without ECU ignition control and see what happens. If the reluctor/coil in the distributor is flakey, the problem should continue, if not, then there is something going on in MS. Anybody have any further ideas? Thanks!

[hytekauto]

Thanks for the reply Lance.  It's nice to know that I'm not the only one seeing this problem.  I have a nice dual trace scope, and can easily verify that the trigger, return, and control lines are correct.  I do believe that the gain of the 8 pin HEI module varies whether or not it is in the startup mode or run mode.  This was also verified via scope, which explains why the engine will "catch" and continue to run a few times before the "problem" gets to the "kill" the engine point.  Also the Chrysler VR system is much smaller and only looks at one point of the 8 point reluctor as it passes the pickup coil, unlike the GM designed eight points in an HEI distributor.  This probably explains the lack of sensitivity at low distributor speeds.  To add more fuel this line of thought, my brother has a MSD dist in his big Chevy, which has a much larger Ford style reluctor and he has had zero problems with the same HEI 8 pin module.  My intent is to time the engine statically with the control disconnected, via the same connector used in the original GM installation, then run it to see if the gremlins return.  If they do, then I'll try the transistor amp as outlined in #93343.  That sure sounds like exactly what I'm seeing.  If not, then the means that the timing control in the MS has a problem, and I'm in deep trouble....Eventually, I'll probably just go to EDIS.  I've planned that mod for the future, as I have the machined adapter to connect the Escort wheel to the center of the pulley mount on the Hemi. 
 
If this transistor mod fixes all of the hassles I've been having, I sure believe that that mod should be documented in the HEI portion of the Ignition Control Documentation.  Thanks again for your input!
 
Posted by email.

[jsmcortina]

There is an alternate simpler way of doing this that Joethemechanic has been trying out with improved results.

viewtopic.php?p=117643

James

[hytekauto]

Lance,
 
The addition of the switching transistor in the opto input did the trick!  That and discovering that the polarity of the input as documented is wrong.  The documentation for the HEI says that the orange lead for the Chrysler VR is positive, however, when used with a HEI 8 module that's reversed.  Wired so the orange lead goes to the "P" input and black to the "N" input, the timing is all over the place, and way out of phase with the cap.  By wiring the black to "P" and orange to "N" the timing is rock solid and the cap phasing is correct.  This is verified by scope.  The engine will now runs very well and I can get this thing tuned.  The Hot Rod Power Tour is only three weeks away........I would be the first to suggest that this mod for anyone using the HEI 8 ignition interface, as it works solidly.  It also has no negative effect on using the stimulator for testing either.  Thanks again for your outstanding help!
 
Tom Westcott
Hytek Automotive
Portage, WI
  Posted by email.

[hytekauto]

Thanks for your comments James.  I chose to use the transistor switch mod, because in testing I also felt that the output of the HEI 8 module was marginal.  The additional gain with the transistor totally fixed the issues I was having.  Keep up the GREAT work, as I follow your work closely.
 
 
Tom Westcott
Hytek Automotive
Portage, WI
 
'68 Hemi Dodge Super Bee
Posted by email.

[clint78z]

I am a bit confused by this GM HEI diagram given at megamanual



It looks like the VR signal should be -ve first??

Then at PICOTECH they have the +VE voltage first on the VR Sensor I need to confirn how too hook it up to the module.


http://www.picotech.com/auto/tutorials/ ... er-1_1.png
I have a scope so it's no problem to check, but need to get them right.

[clint78z]

bump!! Nobody knows if the positive voltage of the VR sensor is supposed to go first?? Reading the Megamanual it describes it as going first, but the diagram doesn't jive !!

[The Witzl]

bump!! Nobody knows if the positive voltage of the VR sensor is supposed to go first?? Reading the Megamanual it describes it as going first, but the diagram doesn't jive !!

I've wondered the same thing myself, but I am yet to actually run my MS-2 (will be trying it tonight), so I will post up what I find later.
My MS-2 is on a Toyota 18R-GEU using the stock VR dissy, locked, and a GM HEI-8 ignitor. The cranking override pin of the HEI-8 is sorted out via a relay.

The Toyota VR signals are normally wired such that they go negative first, but i dont know which way to wire it as the GM HEI ignition page here is confusing:

GM and most other electronic spark driven reluctor electronics trigger on the negative going zero transition after a positive voltage. While they could trigger on the rise that is not how they were designed. Thus polarity of the reluctor signal is critical to proper function.

This sentence above sounds contradictory and non-definitive to me, and it definitely doesnt match the diagram - what signal does the GM HEI-8 module want??

[The Witzl]

Thanks for the reply Lance!

Yeah I understand all that the VR signal is arbitrary based on which wire you consider the signal - I've done a lot of work with aftermarket ECUs on Toyota engines with factory VR sensors. In particular Autronic and Wolf3D ECUs tend to want a (+to-) VR signal, but the normal Toyota signal is (-to+).

In any case, the engine started up fine last night, with a (+to-) signal to the P-pin on the HEI-8, so I'm happy


For reference, Toyota VR sensors are always 2-wire, and in factory configuration have a positive going (rising edge) zero cross (- to +)

• Pink/Brown/Yellow wire = signal
• White wire = earth

Thus to get a falling edge zero cross (+ to -), the white wire is your signal, and the coloured wire is your earth

I've written a fair bit about toyota ignition systems on the Toymods forums, see here - http://www.toymods.net/forums/showthread.php?t=10002

[The Witzl]

also worth noting is that most Toyota engines POST 1986 that have factory ECU controlled ignition timing have two or more VR sensors inside the distributor.

Both VR sensors have their white wires (signal earth in factory config) wired together to a common signal earth wire.

No worries with the help Lance, Toyota tech info is what im good at.

[Black_Angel]

GUYS, this has nothing to do with MS2. It could be a vacume leak. I had the same problem with my blazer when I had the stock TBI computer.

To see if it is a vacume leak spray around the top of the engine and spray around the intake with carb cleaner. You will notice if it is a vacume leak the engine will drop RPM dramaticly when the leak is hit with the carb cleaner.

[Toehead]

http://megasquirt.sourceforge.net/extra/setup-hei7.html


do you have to do the output mod as well?

My car is acting the same way... RPM dropping to zero and progressively getting worse until the car stalls. If i keep moving it seems to be fine, but red lights are a strictly fingers-crossed occasion.

It also doesnt do it all the time... It seems to be tied to how sunny and hot it is out.


Please advise!

[Toehead]

In addition... The problem is very hard to pin down. Today it was doing it the entire way home and I had to wrestle with it to make it home. When I got home I was planning to run some tests, but when I arrived It refused to do anything and was running great. What a PITA.

Chime in guys, does this sound like the same problem?

[Toehead]

For any new users with HEI problems:
viewtopic.php?t=27509&postdays=0&postorder=asc&start=0

That should keep you from falling into the same trap I did.

[Sprig]

AhHA!

...
That should keep you from falling into the same trap I did.

Just a snippet here. I've been working on this from time to time. Problem is I have a dozen other projects with higher priority.

So far, I recommend the MSnE mod (for negative switching) and changing R12 to 220 Ohm.

I have yet to do testing on the output side of the circuit. When I get that done I'll then spend the time to finish the HTML for the MegaManual so that all the information can simply be uploaded.

Hope to have this done in within the next month or so.

[Toehead]

I have yet to have ANY problems since that thread, so the methods described are correct. It has also been running for 6 months, so reliability of the mods should not be an issue.



-Brendan


Ps. Nice to see you around Sprig. I havn't been all that active on the forums because the camaro is hibernating. That will change come spring!

[Sprig]

Read.

I have yet to have ANY problems since that thread, so the methods described are correct. It has also been running for 6 months, so reliability of the mods should not be an issue.

Adding the transistor only adds an extra part; a part that should last nearly forever.

I don't have any issue with doing what it takes to get the job done.

However, from an engineering geek standpoint, I want to know "why" and make things simple as possible.

I'm glad you have a solution that works! I hope I have a more simple solution that works as good, or better!

(I reserve the right to be horribly wrong, and all my parts may go up in smoke!)

Thanks!