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PostPosted: Tue Apr 03, 2018 1:54 pm 
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Turbo EFI

Joined: Wed Sep 17, 2008 6:48 pm
Posts: 2339
Location: Indianapolis
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Just got out of EMI - ECU hell yesterday, and it feels great :D

I had installed a MS3 Pro on the 68 Barracuda, maybe two years ago, had it running the fuel side only, no issues.
This past Feburary, I set the ECU's controls and changed around the wiring to have the MS3 Pro also control the ignition side.

for hardware: Ms3 Pro, Lean Burn Distributor, MSD 6A and a MSD Blaster coil

the car would start, and run, over a couple of days of garage time I was going through the various ignition settings in the MS3 ECU and trying to determine, what the system seemed to like. All seemed well, then I went out to start the car one more time..

I have a lap top in the car that I set up to show a virtual dashboard, The car started, but the AF gauge was red rich, the fuel pulse meter was pegged wide open, the engine was barely running but the tach showed crazy high RPM's,, then the motor died.

Hit the key to re start, with the motor cranking, the analog tach would peg at 9000 RPM's the digital tach would show 35,000 to maybe 55,000 RPM's, the fuel pulse width for the injectors would go wide open, of course, that would immediately flood the motor. After two turns of the motor when starting, remove the sparkplugs and there would be fuel dripping off the sparkplugs.

I checked what I knew to check, went over the wiring, all connections,,,, everything was as it was before the issue started.
I contacted the DIYAuto Tech line, actually once the issue started I talked to them everyday for about three weeks, They recommended installing a new starter, that resulted in no change, PRM and fuel load still very high when cranking. Per their request I made extensive line diagrams of the wiring system. I got some suggestions from them, but nothing I changed per their recommendation made a difference. DIY finally recommended that I return the ECU to them for testing. A week later the report was no trouble found. They returned the ECU to me and said they believed the issue was in the wiring and gave me the name and number of a MS dealer in Southern IN.

So I just started reading about every article and internet forum session that I could find that discussed radio frequency or electro magnetic interference.
found a couple of interesting ideas:
This first one was,,,the shielded crank position sensor wiring (the wire set that seemed to be picking up the EMI/RF) that came with the MS3 Pro has foil wrapped by a bare conductor inside a plastic shroud for its RF shield. An article I found discussed that grounded foil generally is a good RF shield, but there are cases where a grounded woven wire sheath on the outside of the cable is better. So I found 3/8 diameter woven wire sheathing ( pretty cheap on e bay, about 8.00 shipped for 10 feet) and installed that on the crank position sensor wiring. The crank position sensor is the lean burn distributor variable reluctor wiring.

** the second idea was that to combat EMI, have really good grounds at the source of the EMI. The starter seemed to be the source of some of the EMI, but not all as initially the engine was running when the high RPM issue arose. But now all I had to do was engage the starter and the very high RPM / fuel load started. I have the battery relocated to the trunk in the 68 Barracuda and for a ground I had a 1 gauge welding cable running from the alternator mount threaded hole on the passenger side of the cylinder head to the battery negative post. I moved the ground that was on the right front of the cylinder head to one of the starter mounting bolts.

Bingo, the motor started, gauge readings are normal, life is great again.

the fixes were relatively simple, glad that is behind me.

here is an article that discusses foil vs braided shielding
https://www.mouser.com/pdfdocs/alphawir ... -Cable.pdf

and here is an article that discusses sources and fixes for under hood EMI
http://www.powerperformancenews.com/tec ... your-hood/


Last edited by DadTruck on Sat Apr 14, 2018 9:45 am, edited 2 times in total.

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PostPosted: Tue Apr 03, 2018 2:03 pm 
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Joined: Mon Oct 21, 2002 11:08 am
Posts: 12534
Location: Blacksburg, VA
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Wow, thanks for sharing. That sounds like not a lotta fun, but glad you figured it out. I am about to set up crank trigger on MS3X on the turbo car, so we'll see how that whirls...

Cheers,

Lou

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PostPosted: Tue Apr 03, 2018 3:48 pm 
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Joined: Fri Nov 08, 2002 4:48 pm
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Location: Burton BC canada
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Thanks.

You are a patient man.

Grounds are the biggest obstacle in EFI swaps.

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PostPosted: Tue Apr 03, 2018 10:34 pm 
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Joined: Sat Feb 08, 2003 2:37 pm
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Location: CA
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Is there any chance you grounded the original shield on both ends?


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PostPosted: Wed Apr 04, 2018 6:05 am 
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Turbo EFI

Joined: Wed Sep 17, 2008 6:48 pm
Posts: 2339
Location: Indianapolis
Car Model*:
Quote:
grounded the original shield on both ends?


the shielded crank position sensor wire, what Mega Squirt calls the CKP+ and CKP-
the internal aluminum foil simply ends where the connection is made to the lean burn distributor wires
The other end of the foil is grounded through the MS ECU. As part of the trouble shooting I checked the
resistance and continuity from the foil at the terminal end to the braided wire that exits the bundle and is pined into the ECU, that was fine.


Quote:
set up crank trigger on MS3X

and going to a crank trigger was one of the options that DIYAuto offered as a fix. Using a lean burn distributor / variable reluctor is mentioned in the MS3 Pro install manual, and it shows the CPK+ and CKP- connection as an option in the wiring diagrams, but they offer no other 'lean burn' trigger support other than that. I am thinking there are not many installs that use the lean burn distributor so they have little history with it.
Most folks use a crank trigger, as a crank trigger is more accurate, and does not have the voltage shifts like a VR,,,,, but I had already had a lean burn distributor on the shelf,,,


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