MC4 plug gap

lecroy · #1 07-16-2007, 09:35 AM

I am using an MC-4 on a turbocharged 4-stroke. I use the MSD red coils and your plug wires. I bought the ignition new a few years ago to replace my MC-2 and it has been working fine.

I am finding that the engine starts to miss once the boost gets to a certain level. Seems to be regardless of gear selection. Valve seat pressure seems fine. It is no where near the upper limiter. Does not appear to be a lean problem. Also does not appear to be a battery or wiring problem. The MC-4 is getting 12.46V running RPMs much higher than where the miss happens. Battery is charged between runs. I don't see any signs of arc near the boots or coils.

Getting down to plug gap. I am using NGK D9EA plugs, one step colder than stock gapped at 0.028". This is the high side of stock. I wonder if the MC-4 just can't bridge this with the boost I am trying to run. Do you have any data on plug gaps for turbo applications?

Thanks

msdpowersports1 · #2 07-19-2007, 11:39 AM

I know that on some of the Funny bikes that run turbos with about 40 lbs of boost they run the gab at about .018. If these doses not clear up the problem you can send the unit in for testing.

Sorry for the problem

Thank you

lecroy · #3 07-27-2007, 08:02 PM

Thanks. I think we found the problem. After putting the motor back together again, went to start it and it fired right up then died. Hit the starter, it fired back up and died. Third time I hit the starter, it never fired. Checked the spark, nothing. Did all the simple tests, nothing. Hooked up the tester, and the laptop. Ignition seems to read the RPM just fine, but will not put out anything. Called an spoke with Ray. Nice guy. Very helpful, but it seems the ignition is dead and can not be repaired. Ray seems to think that this could have very well been the problem with the studder. Unit was purchased new in Sept of 05, and is out of service.

So here is my question. The unit is being used on a drag bike with no charging system. I charge the batteries between runs. Should the MC-4 be disconnected from the batteries before charging them?

During motor break-ins, the engine can be running up to an hour. During this time I plug in the charger to keep the battery up. I have fans blowing across the motors during this time, but the ignition has to fend for itself. Does it have thermal protection if it were to get too hot?

Because I was told the unit could not be repaired, I did a few more checks on it. It appears that the large red wire that would normally hook direct to the battery does not draw any current. The unit seems to work the same, with or without it. So with the small red hooked to power, I can talk to the unit with the laptop and run the pickup tester without problems even with the larger red wire disconnected. It's like the internal switch that turns this main power on died. I assume this wire only feeds the high voltage supply that drives the coils which make sence why there would be no spark.

Also, I had been using an MC-1 that was later upgraded to an MC-2. This unit was on this bike when I purchased it, and the previous owner claims that it was put on when the bike was built. My point is that at least this unit seemed very solid. I never unhooked it during charging and it sounds like no one else did. Is the MC-4 some how a poorer design in reguards to this internal switch?

If you have ANY ideas how to prevent this failure, or any possible causes I would VERY much like to know them. Would hate to damage the new one once it gets here because of something I am doing wrong.

Thanks again for your help!

lecroy · #4 08-01-2007, 02:48 PM

I decided to go ahead and dig into this a little deeper (literally). I downloaded all the patents, read them and then took a mill and sliced up the case of my dead ignition and removed enough of the potting to start probing it. It appears that the switching regulator has failed. I was able to bring the high voltage supply up but have not yet replaced this part to see if anything else has failed.

Looking at the data sheet for the UCC3800 devices, they have an absolute maximum input voltage of 12.0 Volts. I have not verified the schematics in the patent are correct yet and I know that they are not 100% but it appears at least around this converter that they are very close. The patent shows the part UCC3800 device being protected with a P6KE12A. The maximum breakdown voltage for this part is 12.6, which is already outside the absolute maximum rating of the UCC3800 device. Looking at the pulsed clamp voltage, it is up at 16.7, way outside what the UCC3800 part can handle. Once I remove the potting in this area I will have a better feel if this is really what my MC-4 has in it.

I believe what may have happened now that I am thinking about it, I had removed the trigger input to the MC-4 and was doing some compression tests after putting the motor together. I normally disconnect the charger, run the test, then hook the charger back up. This time I think I left the charger on while I ran the test. These chargers have a switching supply built into them. It is very possible that it may have not liked the load change and put out some sort of deadly transient. None of the other electronics failed but it does not mean that this was not the cause.

So I will assume it was a $700 mistake on my part. You may want to look into finding a better way to protect that Unitrode part. Ray did mention that my MC-4 was very old (<2 years) so I wonder if this is part of what was changed in the design.

lecroy · #5 08-02-2007, 11:23 AM

The new ignition arrived last night. Ray had said that the ignition I had damaged was old. He said that the labels were changed from the unit I had and that he personally had changed what they look like. The problem is the new ignition has all the same markings as the damaged one. When I hooked up the PC, it also IDs the same. Is there really a newer version of the MC-4 and if so, how do I know if this new one is the latest?

I did some tests on the transorb that was used in the damaged ignition and it does appear that its break down voltage is higher than 12.0.

lecroy · #6 08-07-2007, 06:37 PM

I received the new UCC3803N today from DigiKey. $3.00 part, so I bought a few to test. I was able to change out the part and checked the suspect part out side of the circuit and it is defective. I instered the new part and the ignition now seems to work just fine when compared to the new one.

Looking at the power to the UCC3803N, again having an ABSOLUTE WORST case of 12.0V, I measured over 12 Volts with as low as 16 Volts feeding the battery input. It seems very marginal.

Looking at the patents, it seems this same circuit was used in your automotive ignitions as well. You may want to look into this also.

msdpowersports1 · #7 08-08-2007, 10:55 AM

Thank you for your information. I am going to past it along and see what they tell me about it. Feel free to call me any time at 188-285-3835 if you need anything.

Thank you
Ray
MSD Powersports 1

lecroy · #8 08-08-2007, 02:16 PM

Hey Ray. I am all for ACC making a better product. Maybe we both can learn something from this little snafu.

I assume your the same Ray I spoke with on the phone who told me my dead ignition was old. Could you tell me how I would know if this new one that I just bought is the latest? It has all of the same markings as the last one and I thought you had said that the labels were changed on the newer ones and that they did not use the 15-00-2530 part number on them.