Contour Enthusiasts Group Archives Forums Modifications Forced Induction Misfire Problem....

Originally posted by Swazo:

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I've been getting a misfire here and there. It will happen in either the #1, 3 or 4.

I've done a compression test, and all is still good.

I've got some older Bosch plug wires that replaced the FMS plug wires that crapped out. I am getting the Mangacor 8.5mm wires today.

I'm going to get an additional ground strap for my coil pack to make sure it's grounding well. I'm planning on pulling and double checking the plugs gap (.35") to be on the safe side. I've got the NGK iridiums in a stock heat range. If it still misfires once all of these steps have been taken, I was thiking of trying 1 step colder copper (cheap way to find out...) plugs to see if that cures the problem.

Any other ideas?

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Good god! Why such a tight gap, that can also lead to a misfire. IF you aren't getting a misfire under heavy load and high boost, then gapping the plugs closer is a bad idea. Do a search for an old post I made about plug gap where I expained it to the best of my own understanding.

I run 0.045" to maybe 0.047" and I was able to boost 14psi on a 10:1 compression motor! So how come there were no misfires there...on Autozone Duramag wires to boot?
Well, because the spark generated by our ignition coils is more than strong enough to jump the gap.

The misfire is probably due to plug wires, Gap between 35-55 thousandths seems to have very little effect on misfiring other than the smaller the gap the lower the energy of the spark.
So that means you want the most spark energy which would be the largest gap without a misfire under boost.


EDIT**************

I also forgot to point out that I took out my NGK TR6 plugs and am running autolite double plats. Almost a completely stock setup except a slightly smaller gap.

Sometimes tuning can be at fault too, if it is running a bit too lean or too rich it can misfire. Lean misfire would be more common, especially if secondaries are removed and not been compensated for.

Originally posted by Swazo:

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Cool, thanks for replies guys

Rick, I'll agree a set of plugs are cheaper than a new engine. I'll pick up a set that's one step colder to be on the safe side.

Tom, TH sent me an email saying FI should run .32". I appreciate he'd respond via email, but I'll go with what you advise in this situation seeing that you have more (to my knowledge atleast) hands on tinkering with turbo duratec V6's.
Honestly, everything I've read here on CEG has said to start out at .35, and the people I've asked have said the same. Though since you're able to run upwards of 14 psi, I somehow think my candy assed 3.5psi won't blow out the spark

I'd go cheapy plug wires again, but the Ford Racing turds and now these Bosch wires have got me spooked.

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I hate to cause dissension, but I really should reiterate that unless you are misfiring under boost then gap the plug as close to the factory spec as possible! Why would you want to reduce the power of the spark? It is also an easy thing to test, you can gap the plugs close to stock and see how it runs. If it performs worse tighten up until there are no further improvements. Then keep it a bit under where you last experienced misfiring due to wide plug gaps.

I don't understand why people keep going back to the old school stuff that was figured out back in the day with weak stock ignition systems. As I stated earlier, the shorter the air gap the lower the spark energy. You want a bigger gap for a higher energy spark. This is PHYSICS of electromagnetism is taught in basic course curriculum when going to school for engineering.

Here is some interesting reading from the web though I can't guarantee the accuracy of anything posted on the web, I think it is valid. Just remember, the stock contour ignition is VERY good and is better than the stock 4.6 mustang ignition from back in the day.

From the Dodge Stealth Forums:

Stock plug gap on Dodge Stealth/3000GT turbo V6: The stock gap is 1.0-1.1 mm (0.039-0.043"). The proper spark plugs are platinum NGK PFR6J-11 (or Denso PK20PR-P11 or equivalent) for the DOHC engine
The only reason for reducing spark gap is to eliminate misfires. Misfires are usually occuring because the ignition energy produced by the coils and wires is less than what is needed to produce a good spark. Smaller gaps, or smaller electrode tips (like found on platinum- and iridium-tipped plugs), require less energy to spark. So reducing gap to elminate misfires is OK up to a point. After that either the ignition must be made better (more energy) or the cause for increased spark voltage requirements must be dealt with (lower the boost).

For our engines, too large a gap, say over 0.045", should offer no performance advantage. Medium gaps, say 0.034" to 0.043", should be fairly equivalent powerwise. Use the largest gap that also produces the least amount of misfires for your setup. Small gaps, say less than 0.030", may start to hurt combustion a little and lead to poor idle (popping in the exhaust for example) and poor emissions (the spark kernel may now be too small for good initiation of combustion). Use small gaps only in extreme situations (such as the ignition system is maxed out and boost is very high).
Remember, this is a factory turbo setup going on 15 years ago!!


Chrysler PT Cruiser Turbo forums report 0.045" for Turbo and 0.050" for Naturally aspirated.
Exactly the same as what I decided to run. Factory contour is what, .050-.053". It's nice to be validated over and over again.

More light reading for you.

Sparkplug 101

Wires testing...cool stuff here

Originally posted by Swazo:

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...I have my IMRC turned off in my tune all together. ...

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Originally posted by Rev. Po-Jay:

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Originally posted by Swazo:

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...I have my IMRC turned off in my tune all together. ...

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That damned IMRC. I went 3.0L with oval ports and no IMRC to speak of. I still got a wierd A/F bump where the IMRC would have opened... Damn thing was haunted.

Tom- Good to see that some things do not change. You are still the reference material king!

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Originally posted by MapOfTaziFoShoââ??¢:

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Originally posted by Rev. Po-Jay:

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Originally posted by Swazo:

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...I have my IMRC turned off in my tune all together. ...

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That damned IMRC. I went 3.0L with oval ports and no IMRC to speak of. I still got a wierd A/F bump where the IMRC would have opened... Damn thing was haunted.

Tom- Good to see that some things do not change. You are still the reference material king!

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I am hoping to smooth that bump out with my tuning/

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