Megajolt or MSD problem on EDIS Corvette

[jcuprisi]

This is a copy of a post that I made to the MSD Forum. Is there any way that the Megajolt running the default MAP could cause this problem? I am waiting for a serial to USB connector to arrive in order to use the Megajolt software.

The MSD Tech Line leaves much to be desired. I spoke to a disinterested tech on the phone and he mumbled something about the signals from the EDIS Module. I was a Ford/LM tech for 15 years and now am an instructor for Ford for the past 20 years. When I say that I have checked everything on this build I mean it. Obviously I have missed one thing. By everything, I mean all the related EDIS related signals on an O'scope. Each circuit has been double checked.

I will be contacting MSD again tomorrow to try to resolve this. I can also post a wiring diagram of the circuit when I complete some details.

Thanks

As Posted to MSD:
1981 Corvette 5.7L. 4 speed.

TPI Conversion:

1981 Corvette 5.7 converted to 1989 TPI specifications. 5speed Tremec TKO. Edelbrock Cylinder Heads, Crane Roller Cam, 4degree advance Cam shaft. TPIS Runners on ACCEL Lingenfelter Intake manifold.

All factory sensors check out OK with GM Tech1 scanner: MAF, TP IAC, etc.

No performance issues with fuel or ignition two years after conversion.

EDIS Conversion:

Converted GM HEI to Ford EDIS-8 Ignition system modified to run as a Coil-Near-Plug: 8 Ford COP coils with MSD Spark Plug wires: Super Conductor Spark Plug Wire Set Corvette 305-350 HEI, Part No. 31769.

Mallory Oil Pump drive in place of HEI distributor.

EDIS Module mounted on aluminum bracket at left fenderwell. Bracket has dedicated 10ga ground wire routed directly to battery negative post.

Custom 36-1 trigger wheel mounted to front pulley bolted to Fluid-Damper. Shielded twisted pair wiring from Crank Sensor to EDIS Module. Ocsciloscope shows clean CKP pattern.

Mega-Jolt Ignition on default setting to provide required SAW/SPOUT advance signal. Stock GM PCM EST signal will not provide advance signal for EDIS module.

PIP and SAW/SPOUT twisted shielded pair to the Mega-Jolt from EDIS Module.

PIP signal is also routed to GM PCM to provide cranking signal. Stock HEI module attached to EDIS mount to control vehicle Check Engine Light. HEI module provided with 12v ignition power, EST signal from PCM, IDM signal from EDIS module. Check Engine Light functions properly. No codes set.

Factory tachometer is plugged into DIS-4 tach output without factory tach filter and works properly as confirmed by GM Tech1.

The 4 coil driver channels from the EDIS module are routed to the Green/White/Violet/Yellow trigger wires on MSD DIS-4 Plus Distributorless 4 Channel Part number: 62152.

The 4 coil driver channels from the EDIS module are a fabricated 2 twisted shielded pair to a firewall WeatherPack connector to the MSD Green/White/Violet/Yellow trigger wires.

The MSD Brown/Green/White/Violet/Yellow Striped wires run to the 8 coils. 4 mounted on each valve cover. The Cylinder pairs of coils are in parallel and fire as a Waste Spark System. Coil power from MSD shares this 6-pin GM style weatherpak connector

I fabricated a wiring harness from the MSD striped coil wires 1-4 to the 8 coils.

The original HEI power source provides the Ignition 12v power to the MSD DIS-4 Plus.

Here is the problem:

The engine starts and idles fine. First test drive a miss was evident at about 4000rpm during 1-2 shift and during 2-3 shift.

PID check with GM Tech1scan tool reveals all signals; MAF, TP, IAC, Loop etc show no problem during miss.

Troubleshooting Steps To Date:

Double checked MSD settings:

Switch 1: pos 3 WS ON Plus 4K
Step Delay: Inactive
Step Retard: Inactive
Max Rev: 9000rpm

Problem is consistent in the shop. If the RPM is gradually brought up to 3500 rpm the engine runs fine. A timing light confirms that the SAW/SPOUT signal is advancing the timing. Continue to raise the RPM and the miss begins at 3800 rpm as read on the GM Tech1 scan tool. The engine will not rev past 3800 rpm and a missfire is obvious out the exhaust.

If the engine is slowly brought to 3500rpm and the the throttle is pushed rapidly to the floor the engine will miss slightly as it revs past the miss at 3800 rpm and will freely run to 5000 rpm with no miss evident.

At 3800 rpm when the miss occurs the LED will flash 3 times. Intermittent input signal.

I installed a second MSD DIS-4 and rewired the coils so that each DIS-4 Module ran only 4 coils. The same problem occurs.

I went back to one DIS-4 Module and installed the 2 Tach Adapters. The same problem occurs.

What should I look for to diagnose a condition of Intermittent input signal. What exactly does that mean? Is it a catch all for a miss in the system?

[brentp]

Hello,

Big post lots of information.

However, it's not clear - if you have Megajolt + EDIS-8, why do you need the MSD device in the mix?

[brentp]

A misfire at a particular RPM could indicate the VR sensor bracket is vibrating, causing the EDIS module to lose sync with the trigger wheel. The losing sync->re-acquiring sync->losing sync manifests as a misfire. You can inspect your sensor bracket design and reinforce it so that it's more rigid.

Also, you can consider removing the MSD device and just have the EDIS module run the ignition coils - it would simplify things and remove one more variable from the mix.

[jcuprisi]

Original build was with two stock coil packs. The engine ran fine but I did not run it at 3800rpm because the wiring was only mocked up. I did not like the way the coils mounted where the distributor had previously been located.

When I changed to 8 stock COP coils the engine would not start. When I installed the MSD DIS-4 I was able to get it started. I assumed the EDIS-8 would not trigger the coils. I have been thinking about that also. I am going to double check tomorrow and confirm whether the EDIS-8 will or will not fire the COP coils.

The CKP was one of the first things I suspected and the Ocsilloscope showed a problem. I reinforced the bracket and verified a good CKP signal with an Ocscilloscope. Now there is no problem with the CKP signal when the miss occurs.

[jcuprisi]

I verified today that the EDIS Module will not fire 8 coils. Hence the need for the MSD DIS-4. I will be returning the car back to HEI because autocross season has begun. I will probably not get around to trying to make the EDIS work until October.

Although my CKP signal looked good on the Ocscilloscope I think I will try to design a different style mount. Since the miss is at a specific narrow rpm I think it may be possible that the CKP vibration may not be obvious.

[jcuprisi]

I spoke with JD at MSD. He seems to think the Megajolt is causing the problem. I am sending him the Megajolt, EDIS Module and a wiring diagram for them to test my setup.

He claims the Megajolt does not have the power to run the coil drivers. My understanding is the Megajolt provides the SAW/SPOUT signal and the EDIS module runs the coil drivers. My scope pattern of the EDIS output shows no problem with the signal even during the miss.

[brentp]

I wouldn't bother sending them the Megajolt, because the Megajolt does not power the coils directly.

The EDIS module powers the coils, and the Megajolt simply tells it what ignition advance to run via the SAW/PIP signal. This is a very important distinction to understand.

To verify the engine runs correctly you should *not even* need the Megajolt connected to the system. Without the Megajolt connected the system will run at the EDIS default 'limp home mode' of 10 degrees BTDC, which is sufficient to prove whether it fundamentally works, or not.

Hope this helps.

[jcuprisi]

Thanks for verifying my understanding of the EDIS system. I could not get JD at MSD to understand that point.

On an ocscilloscope I have four good signals from the EDIS module to the DIS-4 that do not show any problem when I get the miss. The frequency changes when I raise the rpm which confirms that the SAW/SPOUT is functioning. I verified that the EDIS module will not fire 8 coils. It will only fire the coil packs designed for it.

I have heard from another tech at MSD (msdtech1955) who wants to see the wiring diagram of the system. I have three versions that I am completing for him. I can attach them here when completed also if you wish.
He also commented that he had a call into AutosportLabs about this issue.

[cng1]

Fundamentally this has nothing to do with whether Megajolt/MSD-DIS is compatible it is all about whether the DIS-4 is compatible with the Ford EDIS system. I would have like to think that MSD would have a stock answer to that question but clearly not. As Brent suggests you want to factor the Megajolt out of the equation as that is likely to confuse the issue with MSD.

The EDIS module expects to be talking directly to the coil and managing coil charging itself. If you instead connect the EDIS module to something other than a coil and all bets are off.

[jcuprisi]

My original question: "Is there any way that the Megajolt running the default MAP could cause this problem?" was a search for another opinion based upon the lack of response from MSD.

In response to your post, I agree; I don't think the MegaJolt is causing the problem.

I would assume, based upon the MSD instruction booklet, that in fact the EDIS Module IS compatible with DIS-4. And it does beg the question why MSD does not have an answer. It may be that the forum techs are not engineers or familiar with their product.

I have attached a copy of the MSD wiring diagram which clearly shows the DIS-4 being triggered from the EDIS module. To me this shows the DIS-4 merely needing an input from the EDIS module.

Thanks,

John

[cng1]

I'm not sure that diagram does show EDIS triggering the MSD DIS as it doesn't show the source of the coil feeds. Those coils on the diagram could just as easily be triggered direct from an ECU or standalone ignition amp.

[jcuprisi]

Although the resolution of the picture is not clear, the two harnessess coming from the top of the page next to each coil are in fact the factory wiring. You can see the actual instructions here from MSD:

http://www.msdignition.com/WorkArea/Dow ... 5032386155

This is a PDF document: Page 12 Diagram 13.

Whether it is a stand alone EDIS Module or Integral EDIS in a factory ECU or an aftermarket ECU the trigger signal goes to the DIS-4 which then triggers the coil.

[brentp]

have you considered going to a standard dual ford coil pack configuration like you would typically find on an OEM EDIS-8 configuration?

That, with EDIS-8 and Megajolt will certainly work well for your application. It would simplify your wiring and let you sell the MSD box to recoup some costs.

[jcuprisi]

My original build was a mockup of typical EDIS with 2 coil packs. I installed the MegaJolt to handle the timing as the Corvette ECU EST signal would not advance the timing.

I was not satisfied with the mounting of the coil packs because I was not able to fabricate an acceptable mount that I felt would handle the rigors of Autocross. So I built the system with the 8 COP coils.

Although, I don't know how the stock EDIS system would handle to ignition requirements of my modified engine I have considered going back to the original build with some new coil mounting ideas.

That seems to be the reasonable thing to do. It would allow me to establish a baseline. I could later install the MSD system on the 2 coil pack system if needed.

Thanks

[brentp]

Thanks for the details.

While your engine (I think) is not boosted, the EDIS system has been proven in many applications to over 20 PSI of boost in turbocharged applications. If you're normally aspirated but with higher compression ratio, you can translate that to the equivalent boost pressure. It's likely you'll be well within the capabilities of the EDIS system.

Also, the spark energy is directly related to available dwell time. with a wasted spark setup you will have 8ms of dwell up to 7500 RPM, and still 6ms of dwell at 10K RPM. See the chart here: http://www.autosportlabs.org/blog/?p=1318

I'd give the straight EDIS + megajolt system a try and see how it goes. Let us know!