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Question EFI & Ignition Problem

I'm having problem with ignition miss at high RPM/boost and am wondering if anyone has ideas about where to begin?

The problem: when I'm on "extended" boost (i.e. longer than 1-2 sec) on track at 5000 RPM or higher, the car will literally buck & I can hear it misses. If I lift (& lose all the boost) then it will stop. And the bucking will get worst if I turn my boost up from 0.7 bar to 1.0 bar.

Could this be dwell? Spark plug gap? Or ???

thanks.
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Old 10-31-2006, 11:17 AM
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Could be a lean condition. Have you checked your AFR's at higher RPM's?
Old 10-31-2006, 11:28 AM
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Quote:
Originally posted by JimCulp
Could be a lean condition. Have you checked your AFR's at higher RPM's?
I am using the Innovate LM-1 WB02 meter. My datalog shows I'm running about 11.8-12.1 AFR at those RPM/boost level.

In fact, I was leaning her out as I started with 10.9
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Old 10-31-2006, 11:40 AM
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is it possible the fuel pump is not keeping up or the injectors are at to high of duty cycle at that RPM to work properly?? I am interested in know this as I will be switching to MSII and edis with my new setup
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Old 10-31-2006, 11:46 AM
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Quote:
Originally posted by mb911
is it possible the fuel pump is not keeping up or the injectors are at to high of duty cycle at that RPM to work properly?? I am interested in know this as I will be switching to MSII and edis with my new setup
I kinda ruled out fueling issue because my AFR is ok (unless I'm actually running waaaaay lean to a point of "tricking" the LM-1?), and according to datalog, my injector duty cycle max at ~65% so far.

Maybe I need a passenger to look at the real-time gauges for me as datalog still have milliseconds of gaps for what it logs?
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Old 10-31-2006, 11:52 AM
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I recognize the symptoms. If fueling is OK then I advise you to check spark-plug gaps and if needed, change plugs alltoghether.

What happends is that dense mixture effectivly extinguish the spark. It's too dense for spark to jump across. If problem persists, look for more powerful coils.

Cheers.
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Old 10-31-2006, 01:17 PM
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Quote:
Originally posted by beepbeep
I recognize the symptoms. If fueling is OK then I advise you to check spark-plug gaps and if needed, change plugs alltoghether.

What happends is that dense mixture effectivly extinguish the spark. It's too dense for spark to jump across. If problem persists, look for more powerful coils.

Cheers.
Beep is correct. I had a similar issue a while ago and once I installed a Crane HI-6 ignition system, the symptoms went away. The boost was literally blowing out the spark, resulting in the miss under heavy load
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Old 10-31-2006, 02:10 PM
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Thanks for the advice, Merv & Goran.

I can try to close the gap on the plugs and test.

If I do need stronger sparks, do I need to simply change to a different coil - what kind would you suggest? For the beginner, how would an external ignition system help? I'm particularly curious about other EFI system (like SDDS) that also uses wasted spark (like Megasquirt) - how could they produce a stronger spark?

thanks.
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Old 10-31-2006, 02:45 PM
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So what ignition set up do have with your MS? stock, modded, or MS controlled... will help to know in order to diagnose.

Jim
Old 10-31-2006, 04:28 PM
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Oops - my mistake

Here's the set up - I'm using MS to control both fuel & ignition. MS directly controls 6 ignition drivers (dwell & when to fire) directly; driving 6 coils to support my twn plug set up.

MS can only support wasted spark. And I'm using Mitsubishi/Diamond coils. According to spec I got, running dwell should be ~4.0ms.

The RPM trigger is via VR sensor mounted to the crank pulley.
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Old 10-31-2006, 04:33 PM
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Sounds like the dwell time might be wrong. I am not sure of the set up you are using but the if the igniter are not smart and require a dwell chart then you need to find what it is for those igniters and coils. 4ms seems really long. You might want to double check that. Also what is the trigger, rising, falling? This too can make a difference.

I recently had an EFI car that did this to me. It wasn't suppose to since it was a smart igniter but the damn thing was fine on the dyno and 3 days later freaked out. I had to switch to a B&W and throw the MSD to the curb.
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Old 10-31-2006, 05:03 PM
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Hi Stephen,
I scoped the coil & found that 3.5ms seems to be sufficient but have been playing with different dwell to see if it makes any difference.

Wrt trigger - not sure if I understand

The ECU assumes that the coil will take Xms to charge. Then based upon the crank trigger, it "knows" the RPM hence is able to compute the different triggering timing for each of the 3 (6 in my case) wasted spark coils. The coil is connected to +12V all the time and the ECU basically ground/un-ground it based on dwell & when to fire.

So, how would rising/falling edge fall into this?

Thanks!!!
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Old 10-31-2006, 05:10 PM
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Quote:
Originally posted by hobieboy
Oops - my mistake

Here's the set up - I'm using MS to control both fuel & ignition. MS directly controls 6 ignition drivers (dwell & when to fire) directly; driving 6 coils to support my twn plug set up.

MS can only support wasted spark. And I'm using Mitsubishi/Diamond coils. According to spec I got, running dwell should be ~4.0ms.

The RPM trigger is via VR sensor mounted to the crank pulley.

Hmm...I believe I smell the problem here, depending on how you set up your ignition. If understand this correctly, you use six wastespark coils to lighten 12 plugs in total.

Now you migh and might not know this, but I'll write it anyway:

When using wastefire on twin-plugged 911 engine, you don't just connect each wastespark coil to it's own cylinder and call it a day. With other words, having one wastespark coil lighten two plugs in same cylinder is bad way of doing it as those plugs are connected in series and you will have twice the resistance to fire trough. If this is the case in your setup, there is no doubt why you have ignition problems on boost.

Correct way of wiring twin-plug 6-cylinder pancake motor with 6 wastefire coils is by multiplexing the coils so each coil fires one plug on cylinder that should fire and one plug on cylinder that is in exhaust phase.

Resistance across non-pressurized plug in exhaust phase-cylinder will be low, and this way majority of spark energy will be transfered to cylinder that has mixture in it (plugs being connected in series trough the coil). So effectivly, you will be (almost) chanelling energy from two coils into one cylinder, instead of dividing energy from one coil to try to lighten two plugs in pressurized enviroment.

Now....did you or did you not multiplex the wires??

One twin-plug coil trying to lighten the mixture trough two plugs in single boosted cylinder will have helluva time to do so, regardless of dwell. You will need very big coils indeed to do so. It's much smarter just to rearrange the connections and let two coils work for one cylinder instead of having one coil just waste it's energy in non-firing cylinder.
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Last edited by beepbeep; 11-01-2006 at 01:08 AM..
Old 11-01-2006, 01:04 AM
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Seen one like this and it was the spark plug wires.

AFJ
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Old 11-01-2006, 03:57 AM
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Hi Goran,
I have tried it both ways and have also tried using only 1 coil (with the 2nd set of plugs simply not used). All with identical results.

Maybe I can test with a narrower spark plug gap to start? What gap should I run?

thanks.
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Old 11-01-2006, 04:00 AM
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What coils did you use? Twin Ford EDIS-6??

A plan:

1. Start with MUX-ed cable setup (one plug in live and one in dead chamber per coil). Measure ingition wires for equal resistance.

2. Re-gap all plugs to smaller gap.

3. If it doesn't work, change to new plugs (NGK B8EGV or such).

4. If it doesn't work, start fiddling with dwell time.

5. If it doesn't work, purchase bigger coils.
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Old 11-01-2006, 05:02 AM
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Hi Goran,
I'm using Mitsubishi/Diamond F-608 coils and NGK B8ES plugs right now. I'll pull the plugs to make sure they are still ok then re-gap them.

If I do need bigger coils - what are recommended? M&W?
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Old 11-01-2006, 05:44 AM
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Quote:
Originally posted by hobieboy
Hi Goran,

If I do need bigger coils - what are recommended? M&W?
Depends on your ignition drivers in MS box. Are you using MS or MSII?? The stronger the coils the more current they draw trough ignitors.

Are you using two of these?



Check their resistance to begin with according to manual found here:

http://www.stealth316.com/2-ignitioncoils.htm
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Old 11-01-2006, 05:54 AM
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Quote:
Originally posted by beepbeep
Depends on your ignition drivers in MS box. Are you using MS or MSII?? The stronger the coils the more current they draw trough ignitors.

Are you using two of these?



Check their resistance to begin with according to manual found here:

http://www.stealth316.com/2-ignitioncoils.htm
yep - exactly what I'm using. From my research, these are pretty big/effective coils...
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Old 11-01-2006, 07:13 AM
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Where did you source the coils from?

Cheers
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Old 11-01-2006, 03:38 PM
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