Help with Spark outputs

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smalcol
Helpful MS/Extra'er
Posts: 42
Joined: Mon Dec 23, 2013 10:58 am

Help with Spark outputs

Post by smalcol »

Hi All,
Could really use some help. I have a BMW m62B44 V8 running MS3X, semi-sequential. (Running well for about two years) Was on my way to Laguna Seca today, hoping to watch some races this weekend and my car started running very rough. I've made two changes to the car recently, added LS "truck coils" to replace the BMW COP's fired with quad spark drivers and installed an external circuit to finally drive my old analog tach. The tachout signal goes through a Dakota SG-8 and then to the relay coil and transistor to boost the signal before connecting to the analog tach. The coils were installed using a prebuilt harness connected to a pigtail and the signal wired directly to the 8 MS3x outputs, both grounds are on the engine heads for each bank. The coils are switched by the fuel pump relay and fused on their own circuit.

It was running amazing yesterday and this morning, did some minor VE table tweaks. About an hour into the 2+ hour drive it felt like it was low on power and picked up a minor misfire. this increased over the next few miles and was badly misfiring, no sync loss. Stopped to troubleshoot and checked all connections, nothing was loose or out of place. Verified correct fuel pressure, spark plugs look normal, I disconnected the tach circuit completely as I thought it may be introducing noise. I went to test the coils and they all seem to be firing constantly with the ignition on, engine stationary. I happened to have a spare extra board and replaced it. I was able to test the coils successfully then, but the same issue returned after restarting the car, firing all coils at a rapid pace when the ignition is on. It idles rough and will rev somewhat, but misfires very badly under any load.

Any thoughts? things to check? Was going to start unplugging coils individually to see if one is failed and somehow introducing interference. Also reload the firmware, as I did scope the signal and see a square wave pattern, but didn't note the voltage. I thought it was low, not logic level, but will verify in the morning.

Anyone attending the races at Laguna this weekend?
Bavaria-august-2017.msq
2017-08-18_15.52.35.zip





Thanks,
Seth
jsmcortina
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Re: Help with Spark outputs

Post by jsmcortina »

Possibly a ground offset issue? Eg. Coils grounded to head and ECU to battery perhaps?

James
I can repair or upgrade Megasquirts in UK. http://www.jamesmurrayengineering.co.uk

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smalcol
Helpful MS/Extra'er
Posts: 42
Joined: Mon Dec 23, 2013 10:58 am

Re: Help with Spark outputs

Post by smalcol »

The ECU is grounded to the head, not at the same point as the coils. I will check the difference and try jumperimg it to troubleshoot.
smalcol
Helpful MS/Extra'er
Posts: 42
Joined: Mon Dec 23, 2013 10:58 am

Re: Help with Spark outputs

Post by smalcol »

So, problem was the main ground for the MS3. (Fingers crossed, it's been running great for a few days) I had them all crimped together and bolted to an aluminum coolant pipe on the head. Checked resistance to another point on the head and saw ~5 ohms. I moved the ground connection and the issue has not reappeared since. It's been running like that for years, so never second guessed it.

Check your grounds!...
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