Lo rpm coil control problem

Joffrey · Post by **Joffrey** » Sun Apr 30, 2006 3:18 pm

I'm trying to use a MS II, V3, ini 2.3 to drive my coil directly. The output to the coil is not steady under 1100 rpm. It intermittently skips ignition pulses. it's worse at lower rpm. It takes more cranking to start it than it should. Sometimes it will stop while cranking as if it fired at the wrong time. I have the timing set the same on MS as I do on the stock ignition and I can switch between the two.
I've had help on this before and it was suggested that the input trigger or the predictor algorithms might be the cause. However, if I run it on the stock ignition it idles with MS fuel at a very steady 800 rpm. Could it do this if the input resistors need to be adjusted? Logs show no jumping around of the rpm. I guess that doesn't prove it's not the predictor algorhythems, but how could it track very fast rpm changes over 2000rpm but can't follow a steady 900 rpm? Same for the loose conection theory- why would it work at hi rpm but not low? I don't have an oscilloscope to view the MS coil output, but I can listen to it on a speaker (while the car runs on stock ignition) and hear that it is missing pulses here and there. The speaker heaves out for the missed beats which seems to indicate negitive volts rather than a open. Logs show no resets. When I listen to the stock coil input wire, it vibrates steady, though not as loud. So the coil signal comming out of MSII is not right but I can't see the problem in megatune or on data logs. What should I be checking?
Thanks for any help Jeff

Timmerklits · Post by **Timmerklits** » Mon May 01, 2006 12:12 am

Hello,

I have just the same problem.

On my datalogs the rpm is steady at 1500, but I can't get it lower, because then the skip of ignition pulses will cause the engine to stop.

Nick

Joffrey · Post by **Joffrey** » Mon May 01, 2006 5:59 am

Yup, it's annoying when it stalls out when it reaches the condition you a re trying to check. Sometimes mine would miss a few times which would lower the rpm to a range where it would miss even more and then stall out. I think it gets worse as it warms up. I have a very light flywheel and hi compression, so the rpm was jumping around too much for me to know for sure that the tach signal going into MS was right. That's why I set mine up to run on the stock ignition while I check MSII output. Just to be clear, when I said it sometimes "stops" during cranking, I meant the engine stops turning for a split second while cranking. I see there is another post (MSII coil output) after this one that seems like the same problem with the same set up. Is there a way to check the coil driver circuitry in MS?

Post by **grippo** » Mon May 01, 2006 6:26 am

If the problem is caused by missed tach inputs, it should show up as jumps in rpm. There are 3 pulse tolerance settings to handle this: one for cranking, one for after start and a third for normal running. You can try adjusting these - generally you want them larger at cranking and less at idle and above, but I have seen people use the opposite. Try adjusting the normal pulse tolerance during idle and see if it helps, then you can worry about cranking.

If your rpm at idle is rock steady then you may need to play with your coil driver circuit. But its hard to tell if your rpm drops because there is no output or because there was a missed input which would cause a missed output. That's where adjusting the Pulse Tolerance comes in - if there is a missing pulse it will put one in for you - but only for a few times.

Joffrey · Post by **Joffrey** » Mon May 01, 2006 11:35 am

Thus spake Grippo: "If your rpm at idle is rock steady then you may need to play with your coil driver circuit. But its hard to tell if your rpm drops because there is no output or because there was a missed input which would cause a missed output."

By running the car on the stock ignition system (not megasquirt's) while using MS for fuel, and getting a smooth idle, while seeing missed outputs from the coil driver, I thought I was ruling out the posibility of a missed input. Is this true?
Wouldn't a missed input cause a stumble due to missing a fueling pulse or at least show up as a glitch in rpm?

Do we have it narrowed down to the coil driver circuit? how do I play with it?
Thanks so much Jeff

Timmerklits · Post by **Timmerklits** » Mon May 01, 2006 12:48 pm

I haven't tried with the stock ignition system.

But if there are missed input signals, then you must see them also in megatune I think?

I will give it a try with adjusting the pulse tolerances.
I hope this will help.

Thanks for the advice.

Nick

Post by **grippo** » Mon May 01, 2006 12:56 pm

Joffrey wrote:T
By running the car on the stock ignition system (not megasquirt's) while using MS for fuel, and getting a smooth idle, while seeing missed outputs from the coil driver, I thought I was ruling out the posibility of a missed input. Is this true?
Wouldn't a missed input cause a stumble due to missing a fueling pulse or at least show up as a glitch in rpm?

Do we have it narrowed down to the coil driver circuit? how do I play with it?
Thanks so much Jeff

You are probably right that it is the coil driver circuit - unless the insertion of the stock ecu into the system is changing things. The only other thing I can think of is if your trigger offset is in a bad place. If its easy you might try moving it a few deg and changing the offset in MT to correspond. I assume the timing with a timing light matches the MT timing. Another thing to try is tio increase the dwell a bit.

bleoh · Post by **bleoh** » Mon May 01, 2006 5:46 pm

"The only other thing I can think of is if your trigger offset is in a bad place. If its easy you might try moving it a few deg and changing the offset in MT to correspond. "

I was wondering what would cause the trigger offset to be in a bad place. The reason I ask is my MS2 PCB3 2.34 code running my coil seems to like little or negative trigger offset.

Post by **grippo** » Mon May 01, 2006 7:38 pm

bleoh wrote: I was wondering what would cause the trigger offset to be in a bad place. The reason I ask is my MS2 PCB3 2.34 code running my coil seems to like little or negative trigger offset.

If the offset corresponds to a table advance value so it needs to fire right away, then what could happen is that the logic could switch from this cylinder to next cylinder. That means if the predicted moment for firing has passed when the tach input arrives, it has to wait for the next one. This is fine if it is consistent, but if, because of normal variation in tach input and in prediction it switches back and forth around the table advance point, this might cause timing jitter and possibly a miss, although I think I have fixed the logic enough to avoid this. But its worth a try to see if moving it helps.

Joffrey · Post by **Joffrey** » Tue May 02, 2006 3:30 am

I was tempted to say- Yes I tried all the algorithms! It turns out the default predictor algorithm "1st hi rpm 2nd lo" returned by accident. I had previously determined that it ran better with "last interval" though I didn't know how important it was because I improved the grounds and replaced a coil at the same time and figured that's why it was better at that time. Putting it back to "last interval" fixed the prob, I have a steady stream o pulses out of MS at all rpm. I thought the predictor algorithms only affected the timing of the output pulses I had no idea having the wrong one could cause output drop outs. Thus I didn't recheck it. Thanks for the help!